427 crank and rear main bearing

[rcamacho]

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My K5 is down for the count.
Apparantly the previous owner assembled the crank and rear cap incorrectly. The thrust bearing will not clear the thrust surface of the crank. Any tips on measuring the crank to thrust surface?
Perhaps theire is a bearing/crank mismatch?

 

[nvrenuf]

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The thrust bearing will not clear the thrust surface of the crank.

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So the thrust surface (lip) on the bearing itself is too thick to allow the crank to lay in the journals? If so, it sounds like wrong bearings.

 

[diesel4me]

There is a procedure in the "How To Rebuild Your Big Block Chevy" book on how to lap the thrust bearing surface on a peice of glass using 320 grit sandpaper to get the end play within specs,says to put the two shells together like they are installed in the engine and lap them both--it does say its rare to have LESS than the required end play--I agree,after working in parts stores with machine shops,I cant recall ever seeing a motor that was too tight as far as end play--usually its just the opposite,I'd check the bearings real close,make sure the numbers on them jive with the application. /forums/images/graemlins/crazy.gif

 

[rcamacho]

Hmm, are there differences in the main bearing set across the big block engines? Particularly with the two-piece main seal blocks?

 

[4X4HIGH]

You can buy a main bearing set with the rear thrust bearing having a larger than normal width. This is incase you had a rear thrust failure and don't want to weld the thrust back to the proper size the crank grinder can just enlarge the thrust width of the crank and use the larger width bearings. Also the thrust may have been welded back up but not been ground back to the proper width for a standard width thrust bearing.

 

[rcamacho]

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I went down to the shop yesterday and inspected the crank, old bearings and fit with new bearings. The rear crank journal was not machined correctly and will not clear standard size (thrust surface) bearings.

So, net-net the entire engine is going back to the machine shop so the crank can be fixed. I'm out another K in shop labor and parts. !@#!@#@!