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TC88 description by Donny Petersen
Reprinted with permission of Donny Petersen, Heavy Duty Cycles, Toronto, Ontario.
DONNY PETERSENS
SPECIAL ENGINE FEATURE
FATHEAD TWINCAM88
Twin Cam 88 + 88B "Fathead"
Where should I start? Well how about first describing this engine, 4 ½ years in the making, as a bulletproof platform for the future. Designed with durability and reliability in mind, the engineers are expecting a minimum 100,000 miles before rebuild. I’m writing this in March and as of this date they already have a Fathead with this magic mileage and it doesn’t need a rebuild.
Yeah I know of all the mythical Evos that have supposedly logged on the magic 100 grand but lemme tell you that for every rider that’s actually done that there are many more exaggerating their motorcycles prowess.
The Fathead is gonna consistently do 100 grand without blinking. In fact there are parts in that baby that will not need replacing for a few hundred thousand miles like the pinion bearing that rivals those used in top fuel dragsters. This engine is overengineered. It is a superlative effort in engine design that I’ve never seen or hope to have seen in my 30 years of working on the V-Twin.It’s a platform for many modifications that are going to be extremely reliable. It is obvious to me that screaming Eagle is going to attempt to take charge and control this engines' destiny in the hiperformance arena.
Again, by March 98, the Factory has logged 2 million miles in testing with 12,600 hours on the Dyno.
You see! This engine has been developed to run stock forever and almost forever with Harley Davidson designed Hi-performance components. This is why it’s called a platform. If your heart desires this staging area for more power it will be available, reliable, fast and durable. For more info on this aspect see "Hopping up the Fathead" elsewhere in this issue.
Skeptical as all get out, I entered the room, which was full of engineers, product marketing people and William Davidson himself. The raw emotion emanating from Bill Davidson was readily apparent as Dr. Marty Rosenblum the Factory historian watched Harley history in the making.
I had my list of Evo deficiencies such as cracking cases, leaking base gaskets, oily venting, pulling case studs…need I go on. What had they done to fix these inadequacies in the greatest engine produced by the Factory up until 1999?
Wow!
Approximately 460 component parts of the new Fathead engine were laid out in front of me on a large table for my perusal. To my right, sat a fully assembled engine in its entire splendor. To my left was a 1999 Dyna twin cam 88 cubic inch Fathead motorcycle. Talk about Harley heaven. Only about 15 of the parts are the same as those used in the Evo. It took me three minutes to throw every criticism I was about to launch out the window. For this story see "Ya’ll ain’t Gitting in der boy. Dats were de secret stuff is." elsewhere in this issue.
What followed was three days of intensive training from 6:30 am to 11 p.m. at night on the new motor. The teachers were Bill Davidson, engineers"Skip" Metz, and"Koby" Kobylarz with "Spike" Kieffer giving the overview. Steve, "who bleeds Harley oil when cut" Piehl ran shotgun. "Mr. Clean", Kenny Sutton, the VP in charge of building the Fathead showed us late at night how he was going to actually build the engines in the Pilgrim Rd. 400,000 sq. ft. plant demonstrating all the quality control features. Jerry "Mr. Smooth" Wilke VP of HD and President and CEO of Buell ably demonstrated through his every action why Harley is successful and is going to remain so. Not a big Buell fan because of its departure from traditional Harley styling, Jerry’s enthusiasm and instruction soon converted me to being a big fan. And I’ll tell ya somethin’. For anyone to do that ya gotta be smooth.
Then the Factory Race Team head honchos Steve Scheibe and Art Gomper taught us about the VR1000 in a secret facility in a small town outside of Milwaukee. Three race bikes, three fresh motors on the floor and ten more in various stages of testing and construction allowed for a thorough examination. Again, like many of the hardcore, I never paid much attention to racing. These guys converted me again. Now I can hardly wait to see the VR kick serious ass and along with the Buell rack up the championships. Who would ever think Harley could beat the Japanese, the almighty Ducati and Bimota. It’s gonna happen.
Why mention racing when we’re talking about new bikes for the street? Well, unlike a lot of racing teams that are just used for marketing purposes to sell the manufacturers bikes Harley also uses their highly competent team to develop new product for you and me.
Then we met the guy that everybody thinks screwed up the VR 1000 wheel change in the pits at Daytona. Well the truth is, he didn’t screw anything up. In fact he risked serious injury in a real bad situation. Ever try to take a wheel off a bike that’s doing some real serious spinning because there is no clutch? That’s what he tried to do in a 12-second pit stop.
Never mind that, but the VR held second place for quite awhile with a blown clutch. When the Gods smile Harley’s way, the VR is going to take Harley to the top in what many including myself thought impossible.
Last but not least we could hardly wait for our meetings with Pete Amenda, Manager of Performance Products because it was obvious to us that the Fathead platform just begged for performance upgrades. This Pete, he’s a smart guy who knows his hop-up stuff and he’s got his finger on the pulse of what you and I want. These are the main people we met with but we also talked to machinists on the Factory floor and a myriad of other workers who gushed with anticipation about teaching us when the brass told them we had security clearance. No one was gushing more than we were when it came to learning the "new" knowledge.
‘Cause, make no mistake, the Fathead is where it’s at.
Skip who turns a good phrase said it best "Pain in the early phase of development is better than pain in the end." Explaining further, he said "When I’m at an event, I want people to come up and shake my hand, not give me a blast for some problem in their engine."
Overview of the Twin Cam 88 Fathead.
Let’s get some of the juicy pertinent facts out of the way which will give an overview of more detailed information about to come. The engine weighs in at 165 lbs. which is heavier than previous models but you will soon understand where the excess weight is coming from….out and out quality.
The bore is 3 ¾" a hefty increase over the Evo’s 3 ½" while the stroke decreases to 4" from the Evo 4 ¼". This is good news. The lower stroke means more reliability through slower piston speed and allowing for the potential of slightly higher revs. Big bore doesn’t affect reliability but allows for more cubic inches. Sort of a reverse stroker with the same horsepower increases. This combines to allow a sustained engine speed of 5500 rpm, which is higher than any stock Harley that has gone before. Compression is also increased for more oomph up to between 8.8 and 9.0 to one. Previous engines go as low as 7.5 to 1 and as high as 8.5 to 1. So we got ourselves a fast machine here but as I have already stated; it is going to be the most reliable engine ever used by the Factory.
88 cubes translate into 1450cc.
Horsepower is in the low sixties hovering around 62 H.P.at the rear wheel. Not much, you say! False and exaggerated claims by the horsepower brokers trying to sell their superduper drag pipes etc. make real horsepower figures seem tame but consider this. Your stock Evo probably has around 45 ponies at the rear wheel. Let’s see now. An extra 17 ponies where it counts where the tire contacts the asphalt is about a 33% real increase.
Torque is 86 ft. lbs. For the FLHT models while 82 ft. lbs. For the Dyna. Why the difference? The Bagger mufflers are bigger and can handle more volume. The ability to breathe more is the first principle of hi-performance. Comparative figures for the Evo FLHT are78 ft.lbs. at 100rpm more. Of greater importance, the torque curve has been repositioned into the lower rpm area producing more useable power where you want it. Transient torque is addressed off the line in order not to be soft so the rider is going to feel power sooner than with previous models. The heads even have an AR or anti-reversion, (tork or torque valves), step built into the exhaust port to create more low-end power. Neat stuff, man!
Hey! Check this out. Single fire ignition on all Fatheads.
The carburetors are basically the same but with jetting to accommodate the extra cubes while the fuel injection systems have bigger injectors. Both systems have spark maps instead of the on/off advance/retard curves of an ignition, (brain), control module. The old brain ain’t so smart no more.
What else to tease you with?
Well, as it name denotes, there are two cams connected by a "silent" cam chain, the pushrods are straighter, the barrels are shorter, covers are non-load bearing unlike every other Harley engine, ignition timing is operated also by a timing chain and the oil pump, Sportster style, is inside the engine where you can’t see it.
There are NO too tight whining or too loose clattering timing gears. These are big changes with many more described in detail below.
So you’re a mechanic and wanna go inside one of these babies….go back to school first.
How could I forget. Wanna hear something real nifty? How about jets of oil squirting up from the crankcase to the pistons for cooling. Too much, man.
Last but certainly not least, an external change you’ll see right away. The ultimate torque arm. The engine and trannie have been moved closer together so they almost appear to be uni-construction. No more wigglin’ around. Rigidity is another theme that pervades the Fathead. This translates into better handling, reliability, durability and one tough machine.
In 1999, the Evo will still be in all the Softail models while the Fathead will be in the FLHT and Dyna series. The Evo is not going to be forgotten by the Factory for it’s loyal followers. Me, I can’t even remember what it looks like.
Dissecting the Fathead dual cam 88
The Heads
Bathtub combustion chambers are the first thing you notice when the engine is apart. When assembled the "fat" finning for more cooling is most striking. There is a 60%increase in finning. The more observant will notice the reduction to a 12mm spark plug from the traditional Big Twin 14mm.
Why this reduction in plug threads dimension? Well, with the bathtubbing there is less room between the valve seat insert and the plug hole. If left at 14mm, the engineers felt that it might cause a weakness. More high-grade features will be an ongoing theme in this engine.
The 242 alloy is the same used in the Evo heads.
The bathtubbing is more a rounded rectangular shape than the bathtub or kidney shaped configuration that we are all used to.
Oops! There I go again. Sorry. For the uninitiated the hemi-heads like the Shovel, Ironhead XL. Pans and Knucks have rounded hemispherical combustion chambers. The piston top or dome is also round and fits into the hemi-head. This system isn’t very good for flame travel or a high percentage of burn.
The Evos have a "D" shaped combustion chamber which is shaped like the letter D. Inside the D is a rounded chamber that is suddenly cut off. The rest of the circle is flat and even with the surrounding gasket surface. A flat top piston squeezes up against this flat "squish band", squishing the air/gas mixture turbulently into the smaller D chamber promoting better flame travel and a much higher percentage of burn.
The Fathead’s bathtub chamber is small having only 85cc volume which is why the compression ratio is higher at between 8.8 and 9 to 1 compared with the Evo 7.5 to 1. With bathtubbing there is a flat squish band all around the chamber so that the big 3 ¾" bore flat topped piston squishes the air/gas even more turbulently into the chamber promoting the best flame travel and highest percentage of burn of the different head configurations described.
The permanent mold head has the same size intake valve as the Evo but the exhaust is about .030" smaller in diameter but a little thicker. It is marked with an indent in its center face for easy recognition. The two length pushrods are also different colored for the same reason.
Combined with this smaller exhaust valve is a smaller diameter, reworked exhaust port that takes advantage of Bernoulli’s principle to get the exhaust gasses exiting faster and more efficiently to help with cooling and emissions considerations. You know…when a wide lazy river narrows, the water rushes to get the same volume through a smaller space in the same time…it’s like the new exhaust port.
Now how about a built in torque, (tork), valve more correctly called anti-reversion or AR. It’s not really a valve but a step in the exhaust port to help confused gases go the way we want out the pipe. The same exhaust pipes will fit the Fathead since the ports and the mounting studs are in the same locations as the Evo.
The head height hasn’t changed although it is fatter with the 60% increase in fin surface area with extra holes to allow air direct access to the exhaust port area. Valve springs are the same although there is a new passage from the rocker cover contained breather to allow internal gases to exit the heads. Notice I said gases…this breather works well, quite unlike it’s predecessor that allows oil, whenever the urge hits, to exit with the gasses all over the external motor.
Pushrod angle holes are almost parallel straight up and down. Evo and earlier motor angularity with its resultant problems have largely been eliminated by the dual cams, which we will be getting to later on.
Engine Covers
All engine covers like the nosecone or timing chest, the split two piece rocker wafers and the guide block covers are just that…covers. No more having covers act as load bearing supports for other engine parts. This helps dampen noise, which is real important to the emissions people. You know…in the Evo, the nosecone supports the pinion shaft and the cam, the lower rocker wafer supports the rocker arm shafts and the guideblock holds the tappet assemblies.
No more. A cover is a cover. Period.
This is one of many major reasons that this baby ain’t gonna leak.
Inside the internally noise dampening webbed and finned rockers is a separate support plate for the rocker arms. This plate bolts directly to the head through the lower wafer. It also holds the breather apparatus, which consists of the oil separator, the flapper valve and the scrub sponge, which we will be discussing in the oil section.
Incidentally, the rocker shafts and rocker arms in the Fathead are the same as those used in the Evo.
Inside the larger nosecone cover is a cam support plate that also directs the oil through the engine from the internal geroter, (similar to the XL’s) oil pump.
Yeah, you got it; the engine case holds the tappets instead of having removable guide or tappet blocks. Over this fit the chrome covers.
I haven’t been a big fan of eliminating things like tappet blocks since they are rebuildable and replaceable. With this engine block, once worn out, the case must be replaced. However it looks to me as if there is enough room to accommodate an oversize. The quality of the aluminum is very much superior to that used in the Evo which will stave off problems as will the cleaner oil that this engine utilizes. More on this later.
The Barrels (Cylinders)
They are shorter due to the smaller stroke of 4" and a higher deck height on the engine crankcases. This is where the barrels mount to on the cases and this area is higher than on previous motors.
They are fatter due to the massive 3 ¾" bore and the increased fin area. The sleeves are thick, (.247" compared to the Evo at .173"), and if I were a guessing man, I would say, able to be bored out to 3 7/8" for about 94 reliable cubes or 1545cc. Screaming Eagle will be offering a conservative 1550 cc upgrade.
The Factory reasoning for this 1/4" thick sleeve liner which runs counter to some thought is that it provides stability for the piston which is shorter, by the way, as it changes thrust axis particularly at the bottom of the stroke.
Huh? Relax. Time for plain talk.
When the piston is descending in the cylinder, it has to turn around at the bottom and start heading up the bore again. Because the barrels are at a 45-degree angle, the piston pushes against one side of the barrel going down but when it changes direction it suddenly thrusts against the opposite side. Again the common theme of rigidity in this platform engine comes into play to provide stability for component parts. This is achieved by the thickness of the liner but also the new spiny lock iron sleeve is cast into the high-pressure die cast cylinder. Earlier models have a pressed in sleeve or liner.
When I first viewed the engine all apart in the Factory archives, it just blew me away to see the base gasket solution and made me a convert to the Fathead.
Why didn’t the Factory o-ring the barrels to prevent oil weepage from the base, I was about to demand. Furthermore why not use the barrel locating dowel pin as a hollow oil passage for returning top end oil which would correct another Evo bugaboo. In this way, no oil could make it to the outside world.
Well guess what! That’s what they did. Right on. No more leaks! Good thing I kept my big yap shut. These guys weren’t fooling around.
The bottom barrel o-ring sits snugly in a groove cut into the inner engine case right where it meets the cylinder. There is a second o-ring around the dowl locator-oil passage and other than that there is metal to metal contact between the former barrel base gasket surface and the crankcase gasket area!
And yes to your next question. The machining is superior to what you’ve seen before and yes the case gasket surfaces are machined with the two case halves together to provide a uniform fit.
The Pistons
The standard 3 ring set up is featured with the hypereutectic, which means "real good", aluminum. The same piston is used, front and rear, with a directional arrow on the crown to tell even the most dotley to point the piston to the front. The wrist pin hole is offset slightly. Speaking of which, the wrist pin is big and I mean big with a corresponding big wrist pin bushing in the corresponding connecting rod that is meaty enough for the biggest engine. An Evo wrist pin is .792" thick while the Fathead one is a whopping .927" in diameter. Like I said this engine is a platform for bigger things to come.
Oh yeah! And besides them piston oil cooling jets we’re going to talk about later is the black Teflon coating on the pistons from the oil ring down. Oh…that’s just another little ditty to ensure correct break in amongst a hundred other little ditties in this engine designed to last a lot longer than any Harley rider has ever been used to.
More on Gaskets
I can’t help myself. I get excited just thinking about them. Of course the problem is that service departments are going to lose a major source of income in replacing defective or weeping gaskets.
Take the rocker gaskets for example. Rubber coated with an embossed steel core provides unipressure throughout. The embossing is a ridge, if you will, something like the silicone beads now found on high quality aftermarket gaskets except its a coated metal. This metal embossing goes around the bolt holes as well as the gasket surface to provide a uniform pressure seal on quality machined surfaces. Now I feel better. I got it out.
You have to understand that like you I have been suffering from Harley oilitus for thirty years now. The cure is here. No longer does Harley mark it’s spot.
The Motor Cases:
High-pressure die cast aluminum that split down the middle like always, these beauties promote rigidity, strength and durability as the framework for what is inside and on top. The 360 special formulated proprietary alloy was designed especially for these cases and the quality is evident as soon as you look at them. Cast into the inner case is the word Mercury that is known for it’s high tech quality castings. No more leaks. No more cracks. We fit a set together for a photo and we couldn’t get them apart. Skip, the engineer was apologizing. Why apologize. They fit like a glove. The deck height is higher. This is the area the barrels sit on and allows a much shorter barrel than you are used to.
A major problem when manufacturing these babies is how many times you have to clamp them for a machining process. You see, everytime, this is done the alloy is distorted which can cause machining distortions as the alloy bounces back to it’s former shape before clamping. Less clamping means a superior product.
The Evo cases require clamping 32 times before they are fully machined. The Fathead cases need only 5. Kenny Sutton the VP in charge of making these engines is real proud of this and so should he be with the guys that did the designing. Why he even offered me a job if I could figure out how to reduce this further. I think I’ll go on other merits. With present technology Kenny and Harley are at the edge already.
Another nifty thing, Kenny is doing is powdercoating the pieces wrinkle black after casting or molding but before machining. Think about it. This powdercoating is tough. This will also tell you that it is much more durable than what you are used to.
There’s that word again….durable.
The scavenging plate or collection center for the oil in the case has been moved from the top, rear portion of the Evo cases near the oil pump to the bottom of the Fathead cases. I mean, why not let gravity do the walking for you and prevent that oil from sloshing around on the flywheels causing drag. The oil pressure-sending switch is now on the front of the right pinion side case near a new location for the oil filter.
The rear looks, sorta, different. Because the engine cases hug and bolt to the trannie case providing enough rigidity that the engine could run without the traditional support provided by primary casings. What you don’t notice right away because of this "hugging" is that the oil pump is nowhere to be found. Yep. Nowhere till you look inside the engine on the pinion shaft. Don’t worry we’ll cover this as we go on.
The stator hole is near the same spot but is round to provide easier more effective sealing. Finally, there is a magnetic sensor hole, which picks up off the sprocket side flywheel to determine flywheel speed and timing location.
The Flywheel Assembly, (the Crank)
The first thing I noticed on the table where all the parts were displayed was the humungous pinion shaft bearing. It’s a huge roller bearing about 3 ½"in diameter about double that of the relatively skinny needle roller bearing in the Evo that sits on a beefy pinion shaft forged as part of the right side flywheel. The Fathead pinion shaft is just shy of a ½" thicker, (.400"), than the corresponding Evo one at the pinion bearing location. Now, you gotta remember that a few thousandths of an inch can be a real long way inside an engine so this is big stuff. This pinion shaft isn’t going to break. It supports the dry sump geroter oil pump and the small silent chain gear that drives the timing plate mechanism. Total flywheel weight is 36 lbs., (we weighed a set), up from the Evo’s 32 lb. and S&S’s 25 lbs. although they look lighter. A lot of the extra weight is from the massive components like the pinion shaft, crank pin assembly and con rods but the rotational mass is close to the Evo. The quality appears to be on a level with S&S wheels except everything is obviously stronger which is a mouthful to spit out as those of you familiar with S&S probably regard their components as being the best in the industry. S&S stroker con rods are big but these are bigger making the Evo ones look puny.
The sprocket shaft is also at one with its flywheel and it appears to be the same dimensions as the Evo. The sprocket shaft bearing setup hasn’t changed as it was always very reliable. This side has slots machined into the flywheel outer rim in order for a sensor to read the crank speed and position for both the carb and fuel injection spark 10 by 16matrix maps. And no, I didn’t make a mistake, they use this on the carbureted model also.
Wait til you see the size of the straight, .007 interference press fit, and 3 hole oiling crank pin. Mama mia. It’s so fat, (muscular), that it’s about a ½" thicker, (.420"), than the diameter of that skinny old single oiling hole crank pin used in the Evo.
The connecting rods look the same, just bigger with more muscle everywhere. Ditto with the "captured" 3 sets of 18 needle rollers in copper coated cages which help break-in procedures, durability and offer easy wear spot identification. There are 3 more bearings than the Evo and they are thicker in diameter and longer in length.
There is still the traditional configuration of the single fork, front, male con rod and the dual fork, rear, female rod. I’ve already mentioned the xtra-large wrist pin, bushing and hole size.
Bottom end inertia is only about 70% that of the Evo due to repositioning of the weight in the flywheels. What this means for the rider is less lag time when the throttle is cranked. There will be a more instant response than with the Evo.
The rigidity produced by these superlative parts produces less noise and vibration and is an excellent base for performance upgrades.
Cams…where did all the timing gears go?
I know, I know. This is the section you’ve been waiting for…and it’ll be worth it.
Yep. 2 cams. 2 big beefy cams supported in the crankcase by oversize Ina bearings and in the cam support plate by roller ball bearings like the 5 speed trannie trap door main and countershaft bearings which are plenty strong especially when compared to the Evo nosecone bushing. Less inertia for those spinning cam journals also.
I suggest that you refer to the cam support plate diagram and the picture in order to familiarize yourself with this part since it is alien to anything Harley has used in the past. We’ll be referring to it a lot especially in the Oil Pump section.
Speaking of alien. How about the 6 plate silent cam chain connecting the two cams but first the rationale for this system.
Mechanical noise reduction in the engine meant changing from the traditional "spur" gear mesh to sprockets and silent plate chain. This produces a consistency in sound as well as the desired reduction in noise. The Evo and earlier model gears whined when tight and clattered when loose and with metal expansion from heat and contraction when cool this became an insurmountable problem.
So, I’ll list the sequence of events in order of priority;
Noise reduction necessitated the move away from the gears to the silent chain method
If the chain went straight up from the drive gear to a one-cam location it would mean that the case deck height would be too high and engine shape would change too much. We all know that this would be a big no-no.
Therefore the chain had to be offset from perpendicular about 22 ½ degrees to allow for the desired deck height of the engine cases.
This meant 2 cams instead of 1
An added benefit became straighter angle pushrods, which gives mechanical efficiencies plus gets rid of that annoying front exhaust lifter tick on the Evo Big Twins.
The dual cams are silent chain driven behind the cam support plate while the second silent chain connects with the Hall effect timing gear plate on the outside of the cam support plate. Both chains have spring-loaded tensions for constant and consistent adjustment. The chains have 6 parallel plates per link and are unlike any chain you are used to on the Evo.
The cams have a .490 lift at the valve and .290 at the tappet with the same rocker arm ratio as the Evo. In fact the rocker arms and shafts as well as the valve springs are the same as those used in its predecessor the V2.
Duration is increased anywhere from 40 to 180 depending on the model and whether it is the intake or exhaust valve.
Good news. The cams have been designed to increase bottom end torque below 4000 rpm which is where the power is need. This will make you feel good blasting away from a stoplight.
Lifters
The engine crankcases have holes machined in them to accept the hydraulic lifters similar to those now used in the XL and based on Chrysler parts. They are installed from the top as opposed to their Big Twin predecessors, which were done from the bottom. Evo lifters are cast while the Fathead ones has a steel body for better wear characteristics. The pushrods are of two lengths; intakes are equal in length, as are the exhausts. The whole pushrod is a different color for easy identification. Intakes are a silver color while the exhausts are black. They look to be of better material quality but are made from the same steel as the Evo rods.
Oil Filtration
Two biggies here.
The oil is filtered before it goes into the engine not afterwards as in all previous models
There is a new filter. It still looks the same. It’s still chrome. But it filters the oil much better. How much better? Well the old camel hair filters from Shovel and Pan days were basically designed to filter out small rocks….if debris laden oil didn’t flow around the outside of the filter canister. With the Evos Harley got serious about filtering out impurities as small as 30 microns, (30 millions of an inch). Well check this out! The Fathead filter lowers this to 10 microns.
This and other changes have allowed the Factory to extend service life between oil changes up from 500 miles initially to 1000 miles and then every 5000 miles thereafter.
The Oil Pump
Calm down with the next sentence. I’ll explain.
The pump is a twin geroter, dual scavenge, crank mounted and driven internal dry sump oil pump.
You know, the words dry sump always used to confuse me and everyone assumed that I knew what it meant. I won’t do the same to you. First a wet sump, which is not used in any modern Harley,
stores it’s oil inside the crankcase while a dry sump stores oil in an external oil tank. Wet sump does not have a return side since it is bathed in the oil while a dry sump must have a return to get the oil back to the tank.
Now, I’m going to explain the old gear style pump used on all previous modern Big Twins versus the geroter style on the Fathead. This geroter or trochoid, (I don’t have a clue how the name trochoid came about), pump has been used on Sportsters since 1977. Sometimes it takes the Big Twin awhile to catch up. The gear pump like that used on the Evo Big Twin is OK but not the best. It produces moderate volume and moderate pressure which like I said is OK.
The geroter pump, which uses rotors instead of gears, produces high volume and high pressure. Twin geroter is a little misleading since there are four rotors. Two for feed and two for return. It actually means that there is both a feed and a return, which is necessary for a dry sump system. The thicker geroters are for the feed side while the skinnier ones are for the return and fit right over the pinion shaft being driven by it with the oil pump housing over them.
Dual scavenge means that oil is picked up for return to the oil tank from two places, the crankcase and the timing chest, and this will be explained further in the oil return section.
Crank mounted means that the oil pump is mounted on the pinion shaft. Internal means that the pump is inside the engine not outside like every Harley you are used to. Driven means that the rotors fit over the pinion shaft and the rotating crankshaft drives the oil pump rotors. One last thing. Evo oil pump gears mesh with each other side by side but on the Fathead an inner rotor sits inside an outer rotor squeezing oil between the two to produce pressure and flow.
Recommended oil is HD 360 20W50.
Oil Feed into the Engine
Here’s how it goes;
The oil pump pulls oil from the oil tank into the cam support plate.
The oil is then routed through the crankcase to the filter mounted on the front of the right side of the engine.
A 10-micron filter cleanses the oil.
Then the clean oil is routed back into the crankcase and the cam support plate for distribution to;
The crank shaft through a feed bushing in the support plate
The two silent drive chains via squirting through two small oiler holes
Fills a main galley in the cam support plate to supply oil to the lifters and the top end
When oil pressure reaches 15 psi, oil is routed to the piston cooling jets, which squirt a stream of oil from their location at the base of the engine cylinder deck. Engine oil pressure is 35 psi at 230° F. at 2000 rpm. This cooling action relieves about 50° F. from piston head temperature.
The Breather System
This is all about separating gaseous materials from the oil to allow the engine to breath without puking all over it’s exterior which I’m sure all of you have experienced more than once. Well, apparently it’s not gonna happen no more. And from examining the new system, it sure doesn’t look like it’s gonna happen.
The dual scavenging allowed for this new generation breathing system in the top end by separating the functions of getting the oil in and out. The engine becomes compartmentalized in the Fathead while the two lower compartments intermingle in the Evo. A little confusing, I know, but read on. The engine is divided into 3 sections for oil related purposes. They are the crank, the timing chest and the heads. In the Evo, this separation doesn’t exist as oil sloshes around wherever the will takes it. Because of the Fathead dual scavenging pump action there is less oil mist going to the top end for separation.
Blow by gases from piston movement can escape through the heads.
After the oil is separated and the gases flow out of the heads, they are sucked back into the venturi and into the combustion chamber and burned.
With the previous models a breather gear in the timing chest brought oil from the crank into the timing area
to be picked up by the return, (scavenge). The breather gear has been eliminated as oil flows from the top end into the timing chest rather than the crank. Dual scavenging eliminates further need for the former breather gear.
The whole system is moved up into the rocker boxes. The obvious first advantage is that gravity will assist in separating the heavier oil from the gases but the process needs more help than that.
So here is what happens with the 3-stage system.
The oil separator takes the oil out of the air and lets it return to the timing chest. It does this by making the oil follow a "tortuous" or "strenuous" path allowing the gases to separate and escape. This is new.
The flapper valve is a rubber, umbrella shaped one way valve that lets air out of the engine but will not allow it back in. This part also exists in the Evo ’92 and up engine but if overwhelmed will let the dreaded oil out along with the air.
An "open cell" foam shaped like a 1" long barrel, scrubs oil from the air. It is very porous and air can easily be blown through the foam. This is also new.
All three components fit together and are bolted to the head through the lower rocker box in between the rocker arm assemblies.
Once the gas is separated, it flows out a channel machined in the heads to the outside world only to be sucked back in and burned for emissions purposes.
Oil return from the Engine
Finally, I can explain dual scavenge. Scavenge basically means "return" or "pick up and return". Evos have to scavenge oil from the crankcase via a breather gear and return the oil to the timing chest. The return side of the oil pump scavenges this and other oil in the timing chest to return it to the oil tank. Two separate steps.
On the Fathead this is one step as the oil pump scavenges oil from the crank and the timing chest at the same time thus dual scavenging. There is less oil to scavenge in the crank and more in the timing area because returning oil from the top end is directed right into the timing chest. In the Evo this returning oil goes into the crank to slosh around on the flywheels causing inertial drag. See we get a minor speed advantage with the new system also.
Top end returning oil comes down through a passage in the barrel as usual but when it gets to the barrel deck it is prevented from any untoward wayward wandering through a weeping base gasket. On the Fathead, in one of each cylinders dowel locating pins, the pin doubles as an oil router. The pin extends up into the cylinder and down into the barrel deck with an oil ring around it for good measures. The oil is then transferred over to the timing chest. Any oil in the crankcase has been delivered there specifically to lubricate the crank bearings and the sprocket shaft bearing assembly.
Ignition
First of all. It’s single fire with no wasted spark on the exhaust stroke. This has been a hi-performance upgrade for years now by the aftermarket and now in 1999 it will be stock on all Fatheads whether they be carbureted or fuel injected.
Instead of a "brain" more properly called an ignition control module with advance and retard timing curves to tell the spark plug when to go off according to load and rpm, the new system has a 10 by 16 matrix spark map. What, you say?
The main difference is that with the Evo "brain" set up is that the curves are basically on or off like a light switch. The new system is gradated as in gradual shifting by small increments.
There are six main sensors to instruct the spark matrix on timing when the spark plug should ignite on either the carbureted or injected models. Using this with a carburetor is a first for Harley.
The sensors are;
The crank or flywheel speed and position.
Cam speed and position.
Throttle position.
Cylinder head temperature.
Intake charge temperature.
Barometric pressure.
After this information is computed the spark plug will ignite the incoming charge in order to produce the best efficiency in terms of power and emissions controls.
Of course the single fire aspect requires a different coil or put more precisely 2 coils in 1 and better quality spark plug wires. The carbureted models have an additional sensor called MAP to measure intake manifold pressure. The pickup unit located by the cam support plate is Hall effect.
This system is very similar to the one used on the 1998 XL1200S hot rod Sportster. You know the fastest street Harley ever produced. Yeah, similar to that one. Right on!
Fuel Delivery
Two choices on the Fathead;
The 38.5-mm CV carburetor is pretty much the same as the ones used on the Evo’s except internal jetting is bigger to accommodate the 8 extra cubic inches.
The EFI is similar to the Evo set up but the injectors are the former over-ride hop up ones. They are larger to accommodate the extra cubes.
There are minor differences in throttle levers for manufacturing efficiencies and air breather clearances.
Idle is 1000rpm +/- 50rpm.
Air Breather
The air cleaner looks custom and for once, Harley riders might not change it but of course that would be a hard habit to break. It has rounded points on both front and rear and produces more volume of air both for performance reasons and noise emissions. More air equals less intake noise.
The air intake hole has been moved to the front like the XL’s to get cooler as opposed to heated air.
Another main feature is a flattened backing plate instead of the Evo wrap around one in order to allow more cooling air to go past the fat cylinder fins.
Manifold
The manifold looks like the Evo one except it is a little longer to take up part of any gap previously left to the manifold rubber to seal. The seals have been upgraded to Viton, which remains pliant and resists cracking. The Evo rubber seals crack and become brittle with the hot temperatures. There is also a MAP sensor hole for the ignition.
Noise
The non-load bearing, ribbed inside, covers help dampen noise. The elimination of timing gears and the use of silent timing chains is the biggest noise reducer. Again, the higher volume intake manifold also makes a big difference in power and noise dampening.
Why the concern?
Traditional throaty Harley exhaust noise that we all love is why.
Here’s how it works. The bike has to be ridden through a decibel noise reading trap at a certain rpm.
Eighty, (80), decibels is the magic maximum number.
There are three sources of noise ;
exhaust…that we like;
intake manifold …we’re neutral on;
mechanical, ( like from the timing chest)…we don’t like.
The ride by noise test is a measurement of all three.
So, do you get it, yet. Sure you do.
Lowering the intake manifold and mechanical noises will allow the throaty sound of the exhaust to remain and even become more apparent.
Right on!
The Transmission
The trans box or housing is definitely different as it is manufactured to hug the engine cases to produce rigidity, which is another recurrent theme with the Fathead. And rigid it is. The primary system is depended on with previous models to provide structural strength and rigidity: but as we found out with previous Dynas…not enough. This new system is so strong that the primaries, while an added benefit, are not necessary for this function anymore not that you want to throw this additional support away.
This rigidity throughout the Fathead combined with a new rubber mounting system for the Dyna has produced the first Harley hotrod since the FXR. Harley engineer, Skip Metz’s eyes lit up with pride when telling me this.
The trannie gears are the same as before as is the 9-plate clutch introduced on 1998 models.
But the oiling is different.
You can see why I’m getting high off the Fathead. I’ve been a Harley wrench going on 30 years now. I’ve fondled the Fatheads component parts over four long days and the commitment to quality and longevity of service just marches on.
The oil in the Evo pan under the transmission has a feed and return at the front which means that the same oil gets used over and over again while fresh oil is allowed to hang around at the back. This promotes oil breakdown because of oxidation, doesn’t disperse pollutants evenly throughout therefore diluting them and allows for higher temperatures that are not necessary.
The Fathead eliminates this situation by having a baffle plate in the oil pan that ensures the returning oil follows a "tortuous" path throughout making sure it is totally circulated. This allows more efficient cooling and the use of all the oil all the time.
Kenny Sutton, the guy in charge of making all this stuff showed us thousands of gears being heat treated in the traditional oven-quench format as well as cams being heat treated by modern wave technology where in a mere 20 seconds a cam becomes red hot and then quenched to produce a .040 thickness of the desired hardness.
But what got Kenny excited was new technology to make the gears quieter that didn’t even exist ten years ago. Remember that the elimination of noise is very important as we discussed in the Noise section above.
The gears used to be straight cut and they clattered away as they interacted. Then came the full contact ratio gears that you may have read about. The gears are machined to roll into each other utilizing the whole contact area available. This disperses pressure and produces less noise. So far, so good. Then the gears have to be heat-treated which causes some distortion to the machined surfaces causing high points that result in noise. The new technology allows the gears to be machined again after the heat treating process with out damage. The result expresses a beaming Kenny is a quieter gear. If you were in charge of this Factory you would be proud too.
The primary derby now has a quad seal, which is a definite upgrade as are the 5-derby hold down screws that differ from the round rubber seal and 3 screws on the Evo.
In 1998 all Dyna and FLHT models used a 25 tooth motor sprocket and a 36 tooth clutch sprocket. The Fathead carbureted models still use this ratio while the fuel-injected models have changed to a 24 and 37 tooth configuration primarily to ease up on the starter motor.
Conclusion
I would like to quote Skip Metz:
"Success in the End makes failures in the beginning worthwhile"
And succeed the Factory has through defeating early failures 4 ½ years ago when the Fathead was first conceptualized. My last comment is that this is the most exceptional motor ever to be developed by Harley Davidson. Congratulations on a superb effort.
The articles express the opinions and views solely of Donny Petersen. They are not intended in place of or to diagnose or resolve any issue not assessed by a qualified technician. Donny Petersen and Heavy Duty Cycles Limited does not assume and expressly disclaims any liability with respect to the use of, or for damages resulting from the use of any information, advice or recommendations within. Reference to any product, process, publication, service, or offering of any third party by trade name, manufacturer or otherwise does not constitute or imply the endorsement or recommendation of such by Donny Petersen, Harley-Davidson or Heavy Duty Cycles Limited. E. & O. E.
As submitted to American Iron Magazine.
Donny Petersen
Heavy Duty Cycles Toronto
Writing for American Iron Magazine
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