Help with a 302

JohnSunliner

JohnSunliner

Member
I am rebuilding a 1979 302 to go into my 1954. today when I tried to set the crank in to the main bearings I found the center thrust bearing is too wide for the journal in the crank by about 0.010. It is the right bearing for the engine with a 20 under crank grind. I have done motorcycles and outboard motors but this is my first v8. Can some one tell if I should lap that bearing down (looks like copper) or do I have the wrong bearing? Is there a trick to getting that thrust bearing to fit? Thanks for any help.
 
First thing is you should have this book http://www.mre-books.com/smallblockfrd/index.html next if you have the old bearings they should have a number stamped in them to compare to your new bearings, take the bearing you presently have problems with and compare it to another set and check with a micrometer and caliper to see if there is a difference,you may want to verify the block code to see if you actually have a '79 302 http://www.mre-books.com/interchange/interchange2.html will show you how to verify codes.
 
Thanks Jeff, the Book is on order! I have not verified it yet but I bet I have to lap that bearing down to get the proper end play specs.
 
I'd say check the bearing part # with whoever sold you the bearings. All 302's (and 289's) use the same bearing sizes. There are special bearings available with oversized thrusts so a crank with worn thrust surfaces can have the thrust surfaces ground wider and still have proper end clearance. You were likely sold a bearing with oversized thrusts. Crank thrust surfaces and not ground wider unless needed.
 
.010 is a long ways to have to lap. I would try to find a dfferent bearing. That being said, wet or dry on some glass will give the desired results.
 
I got the book and there are many good tips in there. They said to lap the thrust bearing with 320 grit which I did. It was easy. The target is 0.004 to 0.008 inch end play on the crank. Thanks guys, this is a great web site!
 
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