Donny’s Unauthorized Technical Guide to Harley-Davidson, 1936 to Present

The Evolution Platform for Performance
There were with many Evolution deficiencies. From the deficiencies, a platform of success will emerge.
Let’s view the Evolution historically, in terms of reliability, longevity, speed, and technical design developments. It is simply the best engine to date on every front. Surely, many innovations and improvements were tested in later Shovelhead years while the Evolution was secretly developed. Superior chassis, braking, and handling aspects also followed step to create a safer bike.
Some advancements were also borrowed from the ultra secret Nova project like the FXRT faring and the first H-D 5-speed transmission. Shovelhead to Evolution Advancements
The late-Shovelhead successfully guinea pig experimented with many ideas put forth for the Evolution. Most occur after 1980. Some are:Vibration reduction in 1980 with the rubbermount 5-speed models probably benefitted Harley-Davidson more than any other single item. Rigid mount models survived on sheer cool, riding on the back of chopper design and traditionalism. The rubbermount touring FLT and sport FXR’s made high speed and putting on the miles a joy. Rider comfort appealed to the mainstream bringing new riders into the fold. Vibration reduction also meant a more reliable bike. Parts did not break as often and the life span of bearings and related components increased.
The fabulously successful rear belt drive worked out its 4-speed pulley problems before introduction in the Evolution.
Piston technology refined from eutectic to hypereutectic design increasing piston life and reducing piston tolerances.
Piston ring improvements kept in step with the 3-piece oil ring. Compression and middle ring metallurgy also improved.
Improved electrical switches and connectors replaced predecessor deficient systems.
The offset front connecting rod reduced piston thrust on the cylinder wall increasing wear life and reducing frictional loss of horsepower.Initial Evolution AdvancementsSome designs were too advanced or complicated for Shovelhead testing:
Heavy, inflexible cast iron engine barrels replaced with lighter aluminum cylinders.
Matching metallurgy allows each top end head and cylinder to tie to the bottom casings with 4-equidistant long cylinder studs. Compare to Shovelhead 5-bolts and 4-studs/nuts piling the head on top of the cylinder, and both to the bottom end cases.Tolerances again, become closer because top end flexing controls but certainly does not eliminate.
The D-shaped combustion chamber with its built in squish area combining with a flat topped piston increased the percentage of burn of existing fuel in the combustion chamber. Flame travel efficiently crossed the chamber without hindrance from a domed piston top. This resulted in fuel efficiency married with increased motorcycle speed. I first learned that fuel economy could make a faster bike.Brake master cylinders, calipers, and disc rotors improved exponentially in 1984.The efficient power transfer, wet, multi-plate clutch began replacing the inefficient dry clutch in 1984.Ongoing Evolution ImprovementsThe Evolution kept improving the product, albeit slowly and only when necessary as time progressed:The Nippodenso starter motor with an incorporated solenoid augmented quality control and instituted a more efficient, long lasting design in 1989.Electrical switches and connectors improved again in 1995.
Harley-Davidson began using a new technology on transmission gears. H-D changed the shape of gear teeth so they rolled into the mating gear teeth. Tooth slap noise reduced. The next noise problem was high spots on the gear teeth caused by the hardening process. H-D began using a new grinding technology to make the gear teeth smooth and consistent after hardening. A thick transmission casing with gears immersed in oil also assisted in noise reduction.
The introduction 5-speed rubbermount model pan oil reservoirs underneath the transmission case further assisted in noise dampening.Evolution Engine Deficiencies
I am going to list some Evolution deficiencies. The purpose is not to disparage the engine although some are inexcusable and downright embarrassing. My goal is to educate the reader, which components are exemplary, merely adequate, and those that are inadequate for a stock Evolution engine, never mind a performanced one.The reader will probably infer my frustrations with some of the deficiencies because I lived through them. I had to constantly fix them, sometimes with innovative aftermarket cures.Worst of all, I had to explain to customers why new engine cases were required or why some gaskets could not control design shortfall leaking.The Deficiency Has Probably Been Fixed
I am sure that the majority, if not all inadequacies, imperfections, faults, and weaknesses have been fixed or dealt with since they first became known. The biggest problem especially from a performancing perspective will be the engine cases. The many debilitating flaws like cracking, breaking, porosity, leaking, loose case inserts, pulling top end studs, oversized seal holes, and base gasketing were a nightmare for owners in the day. Adding the stress of some extra compression or increased rpms will speed along and exacerbate problems.This exercise is not intended to make the reader afraid of touching their engines as pioneers of the era tried every performancing option known. The groundwork has been laid. We now know what works for speed, longevity, and problem free riding.Chances are that any Evolution on the road today will already have had corrective surgery from the original defects.The Gasketing NightmareThe nightmare is the weeping cylinder base gasket syndrome that the Evolution suffered from its inception to its demise. Harley-Davidson began attracting a less forgiving clientele with the Evolution. Oil leaks were becoming a big problem with both the consumer and the EPA. The weeping base gaskets were not a gasketing problem at all but one of engine design. In my opinion this could have been easily fixed. The oil flowing down the return oil passage from the top end will often weep through the connecting base gasket as the oil transverses from the cylinder into the engine casing. On some year base gaskets:The weeping oil saturates the base gasket near the return oil hole.Engine heat then bakes the gasket until it becomes brittle.The gasket then breaks and a chunk may work its way out between the gasket surfaces.This leaves a wide open path for returning top end oil to escape the engine.The weeping now becomes a flowing leak. Compare with the Twin Cam where weeping or leaking oil from any gasket surface is a rarity. My opinion is that H-D did not put much effort into fixing Evolution gasketing foibles but they sure paid attention and showed their expertise when designing the Twin Cam.
Aftermarket Base Gaskets
The aftermarket came out with Silicone-bead base gaskets, as well as copper and aluminum gaskets that all worked far better than Harley’s successive feeble attempts.
However, the cure involves a redesign because oil weepage is a design symptom. The oil comes from the return oil passage from the top end, which must transfer from the cylinder into the engine block via a hole in the base gasket. It is easy to correct but the Factory never got around to it in 16-years of production.
Improved gasketing as welcome as it is, is nothing but a Band-Aid for a symptom.
It is not a cure for the cause.
The O’ring Solution
O’ringing the oil passage where the cylinder meets the engine case works well and requires a mating gasket with an oil-hole circumference that fits around the O’ring.
This necessitates machining an O’ring groove into the engine case around the oil return hole...