main and rod bearings - why not ball bearing?

[Koreth]

The title pretty much sums up the whole of my question.

It ocurred to me earlier this week when talking with another fellow about crankshafts, why not use a ball bearing setup, kind of like those seen in in a transmission or roller skates (for example of course, crank bearings would have to be made to MUCH tighter tollerances). I recall it being stated by someone in a thread about turbochargers that his turbo had a ball bearing, and it spooled sooner as a result. I came up with the idea of rather than have a crank journal on a one peice crank, you would have a multi-piece crank, and where your rods connected to the crank, you have a place where a reverse-thread bolt (or normal thread bolt, depending on direction of crankshaft rotation) which screws through your ball bearing and to the next piece of the crank and then a nut holds it all together. Your bearing bolt could be as big as a crankshaft journal, and if bolts can be made to hold the mains and crank in place for those mega powerful diesels, I think a bolt can be had/found/made for this application. As far as lubricating your bearings goes, unlike roller skate bearings, which have plates on the side of the bearing to prevent anything from getting inside, the balls in the bearing itself would be exposed, and the your oil passeges could be on the sides of the bearing.

Kind of like my titanium crankshaft I idea which I put forth in the thread that was initially about titanium rods (which has been shelved for feasability/cost reasons amongst others). Does anyone else have any data or experience which would help me determine if this is a workable idea or not?

[iniviate]

i know they make roller cam bearings for the small block chevy...

supposedly it's worth a very little bit of HP.... however, they're also prone to coming apart, and putting little needle bearings all over. it's been awhile since i've read about them though, so maybe things have changed.

either way.... i dont think they can take the abuse a rod or main bearing takes, which is why you dont see them. however, i have no edivence to back that up. it's just my opinion.

[Aries_Turbo]

most roller cranks are pressed together. 70's kawasaki kz motors were roller and so are some snowmobile engines. they still have oil passages like normal but lower oil pressure. the problem is with a roller crank it can twist, messing up the angles and break stuff. a pressed splined crank would be cool though... i wonder if anyone makes something like that.

Brian

[Mike Radowski]

jet skis and motorcycles all over have pressed cranks/roller bearings. i was curious myself, but always figured it was a cost and durability thing.

[Garret]

I believe it's because a crankshaft does not go in a perfect circle while it is inside the bearing, it is slightly oblonged, and if it were pressed in roller bearings it would wear them down getting shavings in and then you'd have excessive crankplay

[Bad Vibe]

Quote:

Originally Posted by Garret I believe it's because a crankshaft does not go in a perfect circle while it is inside the bearing, it is slightly oblonged, and if it were pressed in roller bearings it would wear them down getting shavings in and then you'd have excessive crankplay

Bingo!

[Koreth]

well darn. It sounded like a cool idea. A man can always dream.

[ToiboTonaZee]

Ive heard that F1 cars use them and they make them for SBCs

[Garret]

F1 car = incredably short stroke and not very much torque... compared to HP that is

and I'm sure they even make like plastic cranks for SBCs... they make everything for those motors, just if you need one you'll know exactly what you'd need to know to be running it properly if they do make them

[Koreth]

Please pardon my ignorance; what is an SBC?

[Garret]

SBC = Small Block Chevy

[Koreth]

With that now known...

WHY would you want a PLASTIC crank? I know of no plastic that is more durable than metal, save those fiberide wheels for the CSX. Hmm.

Quote:

Originally Posted by Garret and I'm sure they even make like plastic cranks for SBCs... they make everything for those motors, just if you need one you'll know exactly what you'd need to know to be running it properly if they do make them