Side loading crank bearings and belt drives?

[TedV]

Had a conversation with a friend and the question of accelerated wear on crank bearings of an automotive based engine came up.

The 2 basic choices of transmission is the automatic CVT/Harley style geared separate trans, or an inline trans like on a BMW. The belt or chain drive to the Harley style Ultima trans would put some extra side loading to the crank. I thought it was covered in a post on here, but searching did not bring it up. The ability to change final drive chain sprockets makes the Ultima trans a simpler less costly to gear choice than the BMW driveline.

The Hatz, Lombardini, Diahatsu, Briggs, yanclone engines are all industrial and meant to be hooked up to some kind of belt drive side force, automotive and BMW motorcycle has the trans input shaft in line with the crank. Although the power pulse of the piston pushing down on the crank should be some serious pressures, the oil feed to crank bearings are tuned for the downward thrust.

what size belt drive would take 80-120 hp and up to 220 plus ft-lbs of torque??

Can anyone help with this debate?

yes, beer was heavily involved during the discussion.

[Crazymanneil]

Ted,

You are right. Automotive engines in particular are setup to drive a rotary load like a gearbox rather than a radial pull like the belt drive. Put your figures into mitcalc -

http://www.mitcalc.com/en/download.htm

The program figures out the radial pull force generated by a particular setup and tells you rated belts for your application. In general belts like to have higher linear speed and therefore less tension. This is also good for the gearbox though leaves you with a big step down in the final drive.

The lombardini datasheet already has all the calculations resolved down to a simple formula which you can use to figure out min pulley size which is nice.

N