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Posted by David Sherman [24.32.202.83] on Wednesday, October 07, 2009 at 10:45:49 :
In Reply to: Re: Rod bearing posted by Chriscase [76.212.168.144] on Wednesday, October 07, 2009 at 09:15:44 :
Just a quick note that I have one of those old in-place crankshaft grinders. I only used it once, but it's pretty neat. It's made by Sunnen and has a deal to slowly rotate the crank while the grinder which sort of hooks over the journal rides up and down as the crank goes around and grinds it. It's very solid and runs smoothly. But it's also large and hangs way down below the engine. Any cross-member or axle below the bad journal would get in the way of it. It uses special cupped stones with thin rims and a threaded arbor that aren't available any more. The thin rims wear fairly fast, but I expect the stones that came with it have enough life left in them for my lifetime usage of it. You're supposed to use a stone whose diameter is exactly the same as the journal, but I've been told you can get by using a smaller stone if that's all you have, and running it back and forth. The manual shows an adapter to mount it on a lathe and use it for grinding both the rod and main bearing journals on a crank that's been removed from the engine, but I don't have that adapter. These days, if I had the crank out of the engine, I'd probably rather just take it to a good machine shop anyway.
This kind of grinder grinds in a circular pattern which you're supposed to polish out by using fine emery cloth wrapped around the rotating shaft and held in place with a leather shoelace looped around it a few times which use use to pull the emery cloth back and forth. I couldn't really get it shiny that way, so I just quit when it felt smooth to the touch, even though I could see fine circular scratches. The engine has other issues and has never run tolerably well, even after that (it had spun a rod bearing badly), so I don't know how the bearing would hold up with the imperfect polishing job. Hopefully your motor just needs a new bearing and the journal is still good.
If the journal has never been ground before, but the plastigage says it's worn down slightly, you probably get a bearing that's .003 under size. Those are made for tightening up a slightly worn assembly without having to grind the crank. Just make sure that you still have .002-.003 or so left for oil clearance after putting on the tighter bearing.
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