Main Cap Crank Bearing Crush

[Stewart A.]

How many people measure bearing crush. If the bearing crush is slightly tight can you relieve it by scrubbing the rear of the bearing shell. Stewy

[Michael M.]

Re: Main Cap Crank Bearing Crush

Hi Stew, Thats interesting as I have just tore down my 65 327 with two to three hours run time (in the chassis with no body yet). I was picking up aluminum dust in the oil and found the number 4 main to be wiping too much as to polish the bearing in excess. Just been line bored and professionally assembled by a leading race engine builder here in Eastern North Carolina. I think I am going to do it my self this time. I am installing a brand new Eagle crank and of course rechecking everything involved. It will be interesting what others have to say with their experiences. Thanks, Mike

[Stewart A.]

Re: Main Cap Crank Bearing Crush

I'm not sure how many people measure crush and clearance. I'm trying to save $600 on not getting it line bored. All my caps are good except one mongrel is a little tight on the crush side. The problem is when you scrub the rear of the bearing you change the clearance size. It's a bit of a give and take. I can see what will end up happening ($600) will be added if I cant get close to the correct tolerances.
Michael your lucky you checked it that could of been a costly exercise. Sounds like the old chuck the bearings in and hope for the best. What pees you off is you have paid people to do the job correctly to start with.
The last 3 motors I have rebuilt have had good crush but the bearing size measured slightly bigger than ideal. So I lived with them at those levels and all is good so far.
I just had a 454 line honed and it made no difference. I guess it wasn't aggressive enough to fix the problem I should have just line bored it. I really think it's an antiquated method using oval bearings and crushing them to stop rotation and maintaining circular circumference. Stewy

[William C.]

Re: Main Cap Crank Bearing Crush

Many years ago, the local federal mogul dealer had a setup that could remove a few tenths from the bearing surface on an individual bearing (or set) to give an extra half thou or so of clearance. Might check it out in your area. The guys I was working with had a problem after the crank was chromed and the special bearings made it work.

[Michael M.]

Re: Main Cap Crank Bearing Crush

Hi Stew, The worst of all that was the 3 sets of mains I paid for to get the best fit . The guy has a great reputation and is a nice guy but I also had other problems (rear main drip and some foreign contaminaion) Both of which i may be to blame for. I supplied a "blueprinted oil pump" which had the high pressure spring installed but came with both and I forgot to change before sending to him (80 to 90 psi cold start) which possibly caused the main leak. He ask me to return and he would go through the engine again but I didn`t want to wait another year to get it back. So I will use the oid plastigage and do the best I can. Thanks again, Mike

[Michael M.]

Re: Main Cap Crank Bearing Crush

Bill. You use to be able to order the mains with a half a thousands extra clearance even the standards but they were usually the race sets which had the hard bearings. I always used the soft as they would help embed small particles and not damage the crank.

[Timothy B.]

Re: Main Cap Crank Bearing Crush

Help me with this,

When you talk about bearing crush are you talking about the clearance between crank and bearing or when the main cap is tightened. I thought with line bore the hole diameter is re-established and the only issue is with the crank and camshaft relationship..

[Stewart A.]

Re: Main Cap Crank Bearing Crush

Michael the caps when put together are oval in shape and when placed in the caps and tensioned the cap is crushed into a circle the pressure it creates on the walls stops it from spinning the bearings when the crank swings. If the crush is to severe it can distort the circular shape and wear the bearings and eventually spin and cause oil failure and massive heat build up with eventually rod failure and destruction to the motor. It is just as important as clearance.

Plasti gauge has worked for years and I'm not sure if a dial bore gauge is that much more of a benefit. I suppose if it's for all out race application then yeah it's got to be spot on for all day high revs. Lets face it these cars don't see 7500 rpm to much. Stewy

[Michael H.]

Re: Main Cap Crank Bearing Crush

Help me with this,

When you talk about bearing crush are you talking about the clearance between crank and bearing or when the main cap is tightened. I thought with line bore the hole diameter is re-established and the only issue is with the crank and camshaft relationship..

I'm a little confused too. I don't think I understand what the problem is.

Why would "bearing crush" have anything to do with bearing clearance?

[Stewart A.]

Re: Main Cap Crank Bearing Crush

Ok to much crush effects clearance (distortion) and to little crush you get a spun bearing. Stewy