Tonight I finally got the ambition to start reassembling my 55 265. Started with the bare block on the stand, got the new standard size bearings and got the five block side ones snapped in. Cleaned up the main caps, and started at the rear one at a time, torqued to 10ft/lbs jst to make sure nothing was binding.Everything was fine till i got to the very front bearing, I snugged the cap and the crank locked up! Loosened the front and with the other four torqued to spec, no binding.I thought there was something under the shell on the block side, so removed EVERYTHING and cleaned it again, same issue. So I switched out the bearing shells from the next bearing over and had the same problem. So I have ruled out the shells. I started switching main caps and the problem follows the cap. A different cap with the same bearings works fine on that front journal. The offending cap was fine when I took the engine apart, Any ideas?
Chevy main bearing cap ODDITY!
coral55
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Tonight I finally got the ambition to start reassembling my 55 265. Started with the bare block on the stand, got the new standard size bearings and got the five block side ones snapped in. Cleaned up the main caps, and started at the rear one at a time, torqued to 10ft/lbs jst to make sure nothing was binding.Everything was fine till i got to the very front bearing, I snugged the cap and the crank locked up! Loosened the front and with the other four torqued to spec, no binding.I thought there was something under the shell on the block side, so removed EVERYTHING and cleaned it again, same issue. So I switched out the bearing shells from the next bearing over and had the same problem. So I have ruled out the shells. I started switching main caps and the problem follows the cap. A different cap with the same bearings works fine on that front journal. The offending cap was fine when I took the engine apart, Any ideas?
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I took the bare block to the machine shop, the caps stayed home with me.
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1,388 Posts
Std bearings? You didn't grind a used crank? What was done at the machine shop to the block?
The original crank was in very good shape and did not need to be ground. It was polished and I got new standard size bearings. The block was bored .030 and new cam bearings installed. It was not align-bored.
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Inspect the cap for any burrs or dings , Also compare the tangs in the new bearings to the old bearings if you still have them and the cuts in the cap and block that the tangs rest in to make sure they deep enough for the bearing shell to seat properly.
You sound like your familiar with rebuilding engines but i'll mention this for completeness...
Confirm the cap isnt turned around backwards, there should be a arrow mark pointing to the front of the engine.
( and who knows it may have been put on backwards from the factory and machined that way so you can try putting in on backwards and see what happens just don't force anything)
After measuring the bores as mentioned before you can use plasti-gauge and see how tight the fit is . you may have to get some .001-.002 oversize bearings on that 1st cap. If you have the old bearings you may still be able to read the markings on the shells of the old bearings to see if thats what it had in it originally.
otherwise its take the block,caps,bearings and the crank to a competent machine shop and have them correct it.
Regards, Robert
You sound like your familiar with rebuilding engines but i'll mention this for completeness...
Confirm the cap isnt turned around backwards, there should be a arrow mark pointing to the front of the engine.
( and who knows it may have been put on backwards from the factory and machined that way so you can try putting in on backwards and see what happens just don't force anything)
After measuring the bores as mentioned before you can use plasti-gauge and see how tight the fit is . you may have to get some .001-.002 oversize bearings on that 1st cap. If you have the old bearings you may still be able to read the markings on the shells of the old bearings to see if thats what it had in it originally.
otherwise its take the block,caps,bearings and the crank to a competent machine shop and have them correct it.
Regards, Robert
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581 Posts
haveing the cap lock the crank when put in any location other than where it belongs isnt unusual and doesnt mean anything other that it doesnt belong there. the caps arent interchangable. what does mean something is if locks up the crank when its in the right place, like you said. just double check that it isnt backwards and like has been said, make sure the bearing tang slots in the block and cap have enough room so as not to deform the bearing. if all seems well you are going to have to get the main bores measured.
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11,079 Posts
If you have a bearing micrometer, remove all of the shells from their respective areas, keeping them in pairs and regardless if the shells are marked "Std.", measure the thickness of each. If you don't have a set of mics for this porpose, then get a set if dial calipers. Also, you may have a plus shell or, possibly a bent crank. As stated, measure the bores for the correct size in at least 3 places - up and down and close to the parting line and compare what those reading to what a std block is. If you have, or can borrow a machineshop straight edge, lay it in the block to see if there is an alignment issue.
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272 Posts
Believe or not you answered your onw question in the first post
"I started switching main caps and the problem follows the cap. A different cap with the same bearings works fine on that front journal."
A different cap with bearings works fine on the front and the offending cap binds everywher.
The offending cap got dropped/hit or misshape, after it was removed from the engine.
Later
Mig
"I started switching main caps and the problem follows the cap. A different cap with the same bearings works fine on that front journal."
A different cap with bearings works fine on the front and the offending cap binds everywher.
The offending cap got dropped/hit or misshape, after it was removed from the engine.
Later
Mig
You will problably find that the bore where you use that cap is too small in the vertical direction, or perhaps it's offset laterally.
The cure is to have the block line bored. Usually when that is done, the caps are machined to remove some material from the mating surface. With that cap they probably won't even have to do that, but they will have to on the rest. If the cap is offset laterally, one side would have to be machined, and the other side built up with weld or braze, then machined.
While align boring is expensive, I doubt that you can find a ready to run block any cheaper.
The cure is to have the block line bored. Usually when that is done, the caps are machined to remove some material from the mating surface. With that cap they probably won't even have to do that, but they will have to on the rest. If the cap is offset laterally, one side would have to be machined, and the other side built up with weld or braze, then machined.
While align boring is expensive, I doubt that you can find a ready to run block any cheaper.
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