Question about Bearings

debauchee · Post by **debauchee** » August 22, 2010, 10:20 pm

I'm trying to replace my main bearings and was able to get one pair replaced but now I cant turn the engine over at all by hand. Before, I was able to turn it by hand pretty easily. Could this be caused by anything other than the bearings being the wrong size?

R Pope · Post by **R Pope** » August 23, 2010, 12:54 pm

Did you put the cap on the right way? Locks together? Check the backs of the old shells, any undersize will be written there. Loosen the bolts on the one you changed and try turning it like that.

debauchee · Post by **debauchee** » August 23, 2010, 3:19 pm

I put the cap back in the same way it came out but I'll double check tonight that the locks are in the same spot. I was thinking about it just now ans wondering if having only one new bearing in it might be slightly binding the crank since it would be just a bit wider than the old worn out ones.

On another related note, the three front bearing caps are a bit of a pain to get off but doable. The rear cap that holds the rear gasket wont budge at all. Any tricks to getting this thing off? I'm trying to do it while the block is in the truck which is making everything more difficult. My back is starting to wish I had pulled the engine rather then spending the weekend rolling around in rocks and dirt under the truck.

R Pope · Post by **R Pope** » August 23, 2010, 7:12 pm

Put the bolts in the cap just past the ends of the threads and rock the cap back and forth, or use a long punch the same way. Some need a tap sideways with a small hammer.

debauchee · Post by **debauchee** » August 24, 2010, 2:45 am

This is exactly what is stamped on the bearing

DAB 84
6831 CAP
6-20 B
6-20 DA-49

I'm assuming that means 20 under but its not exactly clear.

R Pope · Post by **R Pope** » August 24, 2010, 7:09 am

Those numbers are confusing, all right. Usually, the part #'s are on one end of the shell, and any size info is on the other end, written "020" or whatever. You'll have to get a micrometer and compare thickness with the old shells to be sure. Or plastigage it. You can't mike the main journals with the crank in the engine.

debauchee · Post by **debauchee** » August 25, 2010, 11:50 am

I measured the old and new bearings last night. The old ones are .100" and the new ones are .107". I'm assuming that .007 difference would account for wear in the old ones but these are the first engine bearings I've dealt with so I could be wrong about that. I think this weekend I'm going to try a plastigage and see what I come up with.

6166 Junkyard Dog · Post by **6166 Junkyard Dog** » August 25, 2010, 7:25 pm

what should be done is the crank miked exactly and then bearings matched to fit,, don't go by markings on bearing caps,, if not sure take the crank out and have it proffesionally miked on mains and rods

R Pope · Post by **R Pope** » August 25, 2010, 7:45 pm

.007 thicker bearings means .014 smaller than the old ones, that's a lot to be just wear! Are you sure your new bearings aren't .010 under?

34rdztr · Post by **34rdztr** » August 25, 2010, 8:40 pm

my thoughts exactly

debauchee · Post by **debauchee** » August 26, 2010, 1:24 pm

So this leads to a possible flaw in the way I'm thinking about these measurements. When you say .007 is actually .014, I'm assuming you mean both sides add up to .014 in relation to the crank diameter. For some reason, I was thinking that .020 under meant you need bearings .020 thicker but that obviously doesn't make much sense does it. That does make me think these bearings are too big. May be getting close to the point where I just need to pull the crank out.

R Pope · Post by **R Pope** » August 26, 2010, 8:09 pm

A crank .020 under requires bearings .010 thicker, you're on the right track there. I would suggest that you pull the crank and get it checked, it will probably need turning anyway. Your bearings are quite worn if they are .007 different compared to new ones. The crank must be worn down too.

debauchee · Post by **debauchee** » August 27, 2010, 11:53 am

Well at least I learned something.

Thanks for all the replies R Pope. Can the crank be pulled with the engine still in the truck or is this the point where I finally pull the block out?

R Pope · Post by **R Pope** » August 27, 2010, 6:08 pm

Ya gotta bite the bullet and pull the engine out. Then take the crank to a good shop and have them mike it. It will likely need grinding down.

R Pope · Post by **R Pope** » September 4, 2010, 9:04 am

So, what's happnin? Any updates on the crankshaft?