Main Bearing Crush vs. Clearance

[Ramberghini]

On an automotive type main bearing, how much does the housing diameter effect the bearing clearance. Can I open up clearances by enlargine the bearing housing slightly? Does increasing the housing diameter .001 increase bearing clearance by the same amount? Any info on this would be of great help. I'm in the middle of my first engine rebuild.

 

[SMOKEY44211]

Most engine and bearing manufacturers recomend that the main bearings be held in place by the crush of the housing id be smaller then the assembled bearing od between .0005"-.0015". If you increase the amount of crush it will buckle the bearing and enlarging the housing will eliminate the ability of the housing to keep the bearing from spinning. The tangs you see on most bearing inserts are there as a lateral locating device. To answer your original question yes the clearance between the crank and bearing will change by the amount you enlarge or reduce the housing id as long as some interfearance exits but it is not the recomended procedure.--------Phil

 

[Azmio]

how about using thinner bearing shell for greater clearance?

 

[BCjohnny]

Reducing the crush to increase bearing clearance is NOT the way to do it. In fact depending on the intended use, accepted wisdom leans towards setting the housing dia at the lower end of the manufacturers specs, especially for a perf build.

Most manufacturers have "graded" bearings available, at least at their assembly plants, and some (Honda, Toyota etc) make these available for aftermarket builds, as do some manufs (aftermarket) for certain V8's, Chevy etc. If available, you can often "juggle" these to get the clearance you want.

Talking of which you should be shooting for 1.5-2 thou for a cooking build, and a little more for perf work, depending on your engine.

Other than that, get the crank resized, after you've mock assembled the bearings you have and established the dimension you actually require. Go to the trouble of giving your grinder YOUR micrometer as well, to make sure you're singing from the same songsheet.

Increasing the housing diameter is just asking for trouble in most cases, and make sure you have a spare block & crank............

John.

"It's not always a case of learning more, but often of forgetting less"