Need information on roller crank!

[asagodowns]

What is a roller crank and can anyone provide info. about them?

[toyjunk]

this one is like new dont know anything about them would like to know myself thanks

[55samba]

I'll try not to make it too long, there are SPG roller cranks for VW's and Hearth for Porsches.
Sticking to the Spg cranks, they were made in the 60-70's, multi piece pressed together at the rod journals because the rods are one piece with roller bearings. The SPG cranks had no keys or splines so they could be twisted out of alighnment from hard starts ect. Detonation could also damage the rod bearings, there were no oil holes so you would have to cut groves in your main bearings to spray an oil mist for the lube slots in the rod bearings to catch as they rotate. The piston should be special with a correct inner spcing to guide the rods because they had no real guide on the crankshaft.
This type of crankshaft is worthles today, dont waste one moment on one, there are very few who can work on these and have the right tools to do so. Renn Sport was the only person I new of in the US who had the correct tools to align one up. Back in the day people would weld the joints on these so they would not twist them, you could not service them after that.

[sixfootdan]

I could not agree more with 55samba, They are not worth the time/money.
_________________
Schrodinger's cat walked into a bar and it didn't.


GO SEAHAWKS!!!

[george4888]

I agree that you should forget about the roller bearing crank. Porsche is the only one I know of that tried them and had lots of problems with them. If the Porsche factory stops using something, you know it has problems.
If you can find one, they probably cost in the thousands. Forget it--it is a bad idea. They were only good for limited low rpm road racing. They blew apart with higher rpms, so if you think the roller design would allow for higher rpm's , you are wrong. The way they were put together, they would twist at higher rpms. See the books, written by Harry Pellow, the POrsche 356 genius. He has pictures of the cranks twisted and broken. Being a Porsche expert, Harry agreed that it was not one of the factory's best ideas.----George

[toyjunk]

looks new was given to me

[gears]

The Porsche 356 roller cranks were physically small, and thus weaker than the VW ones. In the '60s & early '70s, the SPG roller was the only option for stroking the VW engine. So long as you didn't dump the clutch, and so long as the oil was changed with regularity, these cranks lasted a very long time.

[keifernet]

The thing about the cranks getting " twisted" is that it took alot of horsepower and a real hard launch/ bite to do it. So assuming every one of these cranks you run across is tweaked is probably not likely.
ANd possibly more likely to happen to the 82 stroke and not the 69 for obvious reasons.

the best info I've read on these old school cranks is in Bill Fisher's "How to Hot Rod Volkswagen Engines" by H. P. Books...

I think Pauter Machine or Rimco may be able to answer some questions on the modification needed to the mains.

I also heard ( although I have not tried it) that by assembling the crank . bearings and case... no cam or lifters needed) ( even on un modified bearings) and test fitting the cylinders, by careful measurement of the deck height you could check and see if the height was all the same, thus showing if one of the sections was indeed "twisted"

Has anyone else heard that ?...or think it is a feasable way to get some indication of if the crank is twisted?

[ekimthemad]

[E-boyz67]

Like 55 samba said not worth it. Back in the early 70s I had spent a grand to have Brian Croford of Prototypes Plus do the work to make that crank as strong as possible.He did a beautiful job,welded steel pins through and around the areas where the crank is pressed together. The stroke was 78.4, pistons/cylinders were 90.5,cam was engle K-8 with 1.4 rockers,heads was 40/37 D port and polished,cced and 1 5/8 merge/dual mufflers and webers. Its also a very heavy crank and I don't recall the weight. One thing is that the motor would rev and accelerate quickly and decelerate as well. It lasted for a while due to the fact that I never would do a full on drag start, it was always a rolling start. Sold the motor to a friend and told him the rules about drag starts and few month later he told the motor blew to pieces. I asked what happened and his reply, I broke rule # 1 never do a drag start.
_________________
2-67
1-67vert

[yetibone]

Funny thing about roller cranks is that they actually have MORE friction than plain bearing cranks, but LESS rolling resistance.

Since the needle bearings at the rod journals have less surface area than lead-babbet bearings, the bearings tend to push oil out of the way, instead of riding on a film of oil.

Plain bearings, however, have a much greater surface area that can be supported by oil, and thus the friction is reduced.

[Juanito84]

[Boolean]

Plain bearings are waaay better at supporting heavy loads than roller bearings - as compared when weight and bulk is an issue. At the wheel bearings, this is not much of an issue but at the crank it is.
Roller bearings are also bad when the engine detonates - they may desintegrate not so gracefully...
Plain bearings have less friction, but higher starting friction - which is only of interest when the engine is started.

[raygreenwood]

[Boolean]

So - why did every engine maker in the world stop using them? Except some small engines like mopeds and such?
There is no problem making split rollerbearing shells, so pretty ordinary cranks can still be used.
I would suggest because they are unsuitable for internal combustion engines of our kind.
If they had better efficiency, they would be used in F1 for example, but they are not.