Line boring for the crank?
Thread Starter
Melting Slicks
Joined: Mar 2003
Posts: 2,512
Likes: 49
From: Franklin IN
Line boring for the crank?
Soon I plan on building up a small block. I have no reason to suspect that the block I plan to use will need to have line boring done for the crank. I do plan to have it checked. My question is if it needs boring to true it up that will result in the mains being over sized how do you compensate for that? I know that you can get crank bearings undersized for a crank that has been ground say .010 under. Does the same hold true for the crank bearings outside diameter? Do they come in standard oversize diameters? Also will they hold the dimension between the centerline of the cam and crank through the use of oversize bearings?
Thanks in advance.
Bob James
Thanks in advance.
Bob James
Tech Contributor
Joined: Aug 1999
Posts: 14,379
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
Align boring does not change the bearing size requirement. They will machine a small amount off the main cap mating surface to decrease the journal size, then se-size. Finished size is the same as before.
Yes, the align bore will change crank to cam centerline, but only by about .001. Not enough to cause a problem with timing chain tension.
Yes, the align bore will change crank to cam centerline, but only by about .001. Not enough to cause a problem with timing chain tension.
Pro
Joined: Mar 2002
Posts: 511
Likes: 0
From: St. Louis MO
The machining process for line boring/honing is done by cutting the main caps down so they are a few thousandths shorter. Then they are bolted back on the block. THe machinist will then setup the line hone to the correct cetnerline and will create a new hole that is the exact size required for the standard bearings. More material is taken off of the main caps than the block to make sure that both are aligned to each other and to the other mains.
Long story short, no you shouldn't need any special oversized bearings. But to be on the safe side you should double check with your machinist on their process and they should be able to tell you for sure if the block will require any special bearings or a shorter timing chain. If they are good at their job and do it correctly, you shouldn't need either of these special parts.
Long story short, no you shouldn't need any special oversized bearings. But to be on the safe side you should double check with your machinist on their process and they should be able to tell you for sure if the block will require any special bearings or a shorter timing chain. If they are good at their job and do it correctly, you shouldn't need either of these special parts.
Le Mans Master
Joined: Apr 1999
Posts: 6,134
Likes: 46
From: Raleigh North Carolina
Align-Bore Blues
The practice of align-boring the main bearing saddles and main caps is helpful in that it guarantees minimal drag on the crankshaft. On the other hand, it moves the crank closer to the cam by a small amount, which has the net effect of lengthening the timing chain, directly affecting cam and ignition timing. The process of align-honing removes far less material, and is unlikely to cause timing problems. If you suspect that a potential block has been align-bored, be certain to have a qualified machine shop measure the distance from the crank to the cam to see if (or how much) it differs from stock specs.
http://www.hotrod.com/techarticles/41838/
The practice of align-boring the main bearing saddles and main caps is helpful in that it guarantees minimal drag on the crankshaft. On the other hand, it moves the crank closer to the cam by a small amount, which has the net effect of lengthening the timing chain, directly affecting cam and ignition timing. The process of align-honing removes far less material, and is unlikely to cause timing problems. If you suspect that a potential block has been align-bored, be certain to have a qualified machine shop measure the distance from the crank to the cam to see if (or how much) it differs from stock specs.
http://www.hotrod.com/techarticles/41838/
