I am working on an old diesel engine. Can anyone see problems fitting roller bearings to the crank shaft instead of plain metal bearings to release a few extra hp. At the moment the engine produces 60hp at
1500rpm and enough torque to pull a house down.Thanks
Smokeyone
snipped-for-privacy@btopenworld.com (Smokeyone) wrote in news: snipped-for-privacy@posting.google.com:
Probably last about 2 minutes. The pounding from combustion, will quickly fail them. I do not feel you have an understanding of how plain bearings work. These are 'Hydrodynamic' bearings, in that there is a film of oil between the crank and the bearing. There is no contact between the surfaces when running. Adding roller bearings would probably produce more friction, in that you have rolling, contacting components.
I believe that the air cooled multi-fuel diesel engines used in some Tatra military vehicles use roller bearings on the crankshaft. This would seem to indicate that roller bearings can survive in this application.
W.P.
"Jerry J. Wass" wrote:
Forget it. Many years ago the late Smokey Yunick ( a famous race engine designer/mechanic circa 1950's-'70's) went to a lot of trouble to convert one his engines to anti-friction bearings. He was very disappointed to discover that they made no appreciable difference on the dyno.
Randy
most 2 stroke engines (at least them without oil sumps + a pressurzed oil supply) use roller bearings.
Better inform Saurer, Mercededs-Benz and all the others that have made high speed diesel engines with roller bearings...
Tom
My Saab 850 GT had such. ...lew...
Thanks everyone for the advice. If it's not going to make a great deal of difference I will not investigate further.
Smokeyone
I would suggest that a greater reason for not doing it would be the requirement to remove enough metal from the big ends or main bearing housings to take up the greater outer diameter that the roller bearings would have.
Regards Mark Rand RTFM
I don't see that making much differance. 1/8" more or less will not make much differancein a main bearing diameter. A roller bearing would take up just a little more space than a shell bearing does. Think rod bearing on a Lawn boy, only bigger. The rollers ride right on the crank, add a thin outer shell to protect the block. Maybe 1/8" more diameter than with shell bearings. The crank probably would need some sort of surface harding for longevity. I believe it is not worth the hassle, the extra work with little or no HP gains, otherwise top fuel dragters would have gone to roller bearings years ago. Those boys do all they can to squeak out a few more ponies! For simplicity, and durability, with a pressure lube system, shell bearings are hard to beat. Greg
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