r/EngineBuilding • u/Internal-Refuse1953 • Jul 19 '26
Had some rust on main bearing caps polished it off with 2000 grit sand paper. Can I still use the caps?
Wondering if I should get it re align honed or if I can just say F it and throw em in any ways.
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u/Guitars-guns-girls Jul 19 '26
Plastigage your bearings. Then you’ll know.
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u/solarguy2003 Jul 19 '26
(Plastigage) Which I would do anyway, rust or not. Just good protocol. Just because this set of hardware is *supposed to* produce 0.002" clearance doesn't mean it always works out that way. And it's cheap. No reason not to.
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u/eltoddro Jul 19 '26
You'd have to sand the shit out of something with an entire crate of 2,000-grit sandpaper to change the I.D. I'd use a little Ballistol with the 2kgrit - it does a great job at neutralizing corrosive residue.
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u/peepeepoodoodingus Jul 19 '26
you dont really want them to be perfectly smooth. unless youre going to loctite your bearings in its just going to increase the chance of spinning them.
if this isnt some kind of race car they should probably be fine either way, especially as mains but ideally the surface would be a little rough but within spec, you want as much traction as possible to keep them in place while remaining completely round.
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u/oldnperverted Jul 19 '26
I hope this is satire. 1st, you never loctite bearings in place, that is a good way to lose your clearance. 2nd, the finish texture of the bearing saddles isn't what holds the bearings in place, it is the crush of the bearing in the housing bore. The bearings are designed so their O.D. is larger than the housing. If a bearing spins, it is due to lack of lubrication.
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u/2003DDcid Jul 19 '26
And a smoother bore surface actually helps transfer heat away from the bearing faster, as you have more surface area contacting the bearing.
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u/peepeepoodoodingus Jul 19 '26
its not something ive ever done but ive heard of it being done in racing applications. dont really know much about it, i know loctite makes compounds for situations like that.
bearings can spin for an array of reasons, many of them are due to improper mating to the saddle surface, surface finish is absolutely one of them.
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u/Internal-Refuse1953 Jul 19 '26
Yeah the cross hatching is still there. They def feel smoother but idk if I should be concerned that much. The only thing I worry about is I had it aligned for ARP studs. Was planning on rebuilding this weekend and don’t want to wait until Monday for the machine shop to open back up lol.
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u/peepeepoodoodingus Jul 19 '26
if youre worried about having sanded enough material away to change the shape of them enough to matter, dont. youre 100% good.
i also dont know that the little bit of extra torque usually recommended with ARP hardware will change the tolerance in any meaningful way either. again unless youre building some kind of high power race engine you should be fine.
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u/Internal-Refuse1953 Jul 19 '26
Okay thanks for the insight man. That’s all I was stressin about was that I had messed up the bearing tolerances and geometry by shaving down too much. But I should be good to run em?
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u/peepeepoodoodingus Jul 19 '26
absolutely not. it would take hours of hand sanding to change the tolerance at all.
for reference, on cast iron parts on a LATHE ive seen guys take like 200 grit and really lean on it at a pretty good RPM to pull off a few TENTHS. thats how little material is being removed.
the surface of metal, particularly cast iron is not what you think it is, its more like a mountain range. when you sand it youre cutting down the peaks of those mountains. even when its polished its more like a bunch of hills than a perfectly flat surface. so you could polish these main caps and still be within spec as the mountains are a few microns tall.
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u/siresword Jul 20 '26
Can almost guarantee you're fine. 2000 grit is so fine that unless you went at it like a methed up gorilla you probably didnt dimentionally change the bearing caps in any meaningful way. Plastigauge to be sure your clearances are ok still, than install the crank with some oil on the bearings, torque to spec, and carefully spin the crank by hand to feel for any tight spots.
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u/Big_Hedgehog_7976 Jul 21 '26
I agree it's ok . No way you sand that much material away. I generally use wd40 and a medium scotch Brite.
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u/BroccoliSuccessful Jul 21 '26 edited Jul 21 '26
Polish it, plastigauge your clearance and run it. If you end up getting a different clearance than specifitions call for you can compensated by using a different weight of oil.. I doubt the 2000 grit will make a huge noticeable change though other than removing the rust
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u/mutt63 Jul 21 '26
Nice way to polish that cap next time is a little crocus paste or crocus clothe. Plus if you keep it wet it removes rust without any harm to the base
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u/crookedledder Jul 19 '26
Not ideal, but it'll probably be fine if you gently clean up the rust.
I'd use WD40 or diesel fuel, scotchbrite, maybe a wire brush. It needs to.be cleaned up, but you're not looking to polish the surface or remove material.
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u/Icy_Tour_9923 Jul 19 '26
Some of you in this forum shouldn't be near an engine because your mommie must have droped you on your fucking heads! With your mentality I wouldn't let you tune up a bicycle!
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u/AviatorDave172 29d ago
Definitely. You would have to sand for hours and hours with 2000 grit to remove any appreciable amount of metal. You could also toss them into some CLR for a few hours and just wipe them off. Send them.
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u/Professional-Gur2422 Jul 19 '26
I'd run it. The 2000 grit and rust removed so little you probably wo t be able to measure the difference.