Re: Houston, we're going in (was 656 spark plugs) PICS

Posted by ScottyHOMEy on February 24, 2009 at 04:54:46 from (70.105.240.166):

In Reply to: Houston, we're going in (was 656 spark plugs) PICS posted by TX656 on February 23, 2009 at 22:20:57:

Nice pics of good project! I keep promisin' my self to take pictures like that of one of mne one of these days . . .

One observation, and it's JMHO, but I don't think a crank is a place to skimp. Plastigauge is useful for a general evaluation of clearances at the outset and a final check when reassembling, but it's of very limited use in practical terms for finding out of round pins and the like. If you're going to have it out anyway, I'd suggest you get it to a shop and have them mic it to see just what shape it's in.

You might get away with just popping new bearings in. (I'll admit to having done it, but only after the shop cleared my crank -- basically the motor was badly stuck on the top end from neglect not long after an overhaul, and the bottom end was surprisingly clean. The shop measured up my crank and said it looked like it had been turned jst the week before. I only put the new bearings in bacuase it didn't make any sense givent he minimal cost to clap the old ones in as long as I had it apart.

I don't have the specs for your motor at hand but, by way of example, assume your good clearance on the rods and mains is in the range of 1.5 to 3.5 thousandths, and your initial evaluation with plastigauge is showing 7 with the existing bearings. You might be able to make up 2 or a little more, with new bearings, which would still leave you with too much clearance. If the bearings were wearing hard, so was the crank, and you wind up with the crank dimensions out in that no-man's land between multiples of .010 under and it will need to be turned down.

This is gettin' longer than I intended but there is one slim chance of popping in new bearings if they're still available. A shop, in evaluating the crank will measure it. The measurements will be what they will be, but lathe shops usually stamp a mark in the crank to show that it's been turned down and how far, and your guys will look for that, too. If the crank has never been turned and your clearance is a little excessive with standard bearings, IH used to sell a bearing that was .003 under (or over, as you wish -- another discussion!). Some folks have said that they used them at the factory to take care of cranks that were ground a little undersize in the manufacturing process. They were also used in maintenance to make up for light wear, so if that's what they find and everything is round, those bearings might work but, after that, you'll need a crank ground to .010, .020., or .030 under.

If you're doing that much work anyway, I'd have the pros evaluate the crank and make my decision from there.

Keep us posted.

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