Can a 55 crank be ran in a 51 set of Harley cases? If so, with what conversion?

Question

I have a set of 51 cases with roller bearings, and a 55 complete crank. can the crank be converted to work in the 51 cases? I have been told it can't be done. Are there any gurus out there with the answer? Can the 51 cases be modified to accept the timken bearing? Thanks...

Answer 1

They are right, It cant be done. The old caged bearing set up works just fine when properly installed. They are not as strong but the old pan cases are too weak these days to seriously hot rod. I had a 51 Pan with a heal/ toe clutch and tank shifter I rode from Maine to Kansas when it was below zero. Best ride I ever built. There are replacement cases made if you want to go real fast, Otherwise use what you have and treat it with moderation. Panheads and Knuckles rule!

Answer 2

Straight rollers were used up to 1952, in 1953 the tapered roller main bearing setup was used. Might be a year off on change. 55 crank would need conversion back to 'old' straight crank pin- but need stepped shoulder to use the straigh bearings. Case modification? Probably, but the machining would be costly, wouldn't advise it. If you have a 51 case maybe you could find a set of UL/ULH wheels- the would fit and give you a 80inch displacement with standard 74 bore, use a FL piston and extra thick or double cylinder base gaskets. Old chopper technique.

Answer 3

Even though there are a lot of smug individuals on Yahoo answers that hate Harleys, here is the perfect example of their interchangeability, versus their "perfect" Jap bikes, that change everything year to year so NOTHING is interchangeable!
Yes, it will work.
To show another example, back in the day before there were so many aftermarket companies making parts, to up the cubic inches from 74 ci to 86 ci, we'd use the flywheels from an 80 ci Flathead (UL model). The crankpin was a "stepped design, prone to allow the flywheels (remember, there are 2 [two] flywheel halves) to shift, throwing the engine out of balance. To cure this, we'd install the newer "tapered" crank pin. For this, the crankpin hole in the flywheels had to be drilled out larger. BUT, we'd drill the as far outboard (towards the outer edge) as possible. This would actually add 3 ci per cylinder, for a total of 6 added inches, bringing the total engine size to 86 ci.
Now, for the cleavet! The way the older Harley oiling system works (the part where the oil gets from the engine back to the oil tank) is once the engine ran throughout the engine, it collects in the bottom of the crankcase. the flywheels picks up the oil, and as it spins, it is "scrapped" off and allowed to ooze through a port to go back to the scavage side of the oil pump, to send it back to the oil tank.
The 80 ci (UL) flywheel, though larger displacement, are actually SMALLER in diameter, allowing the oil to fling off the flywheel to soak the forward wall of the rear cylinder, causing the rear piston oil rings to fight more oil than they can. It'll smoke out the rear cylinder like a WWII battleship lying down a smoke screen.
To cure this, you'd TIG weld a small block of aluminum to the cases, to act as "scraper plates". Even though they're call "scrapers", they DO NOT actually scrape the flywheel, but are machined to allow about .020 clearance.