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MGB Talk to me about bottom end bearings

drooartz

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So I was out in the shop today working on the trans crossmember for my MGB project and contemplating Doc's question as to if I had checked the bearing shells while I was replacing the oil pan gasket. (I hadn't.) So I contemplated false economy and flipped the engine back over so I could get to the bottom end.

My goal is not to rebuild this engine, but if there are things I can do that are close at hand I'll do them. Good chance to learn a bit as well and maybe extend the life of this engine a few more years.

So I've not got any experience with engine innards, so I need some guidance. What to check, what to replace?
 

DrEntropy

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If you've the desire, take the pan back off and pull the main cap off the rear main. If you see copper, you would do well to replace the main bearings. No complete tear-down, just put new same size bearings in. As for rod big-ends, if the main shows wear to copper you'll have to remove them anyway to replace the mains, a set of rod bearings don't cost much compared to a spun bearing and the damage that can do.

I know this goes deeper than your plan but if the engine's out and on a stand, it's my opinion you'd do well to check, and if that rear main is through the babbit you'll save that engine so it will be a viable "second" by pulling the crank and refreshing the main and rod bearings.

Somewhen in the past I posted a photo of a piece of cast iron block, the "MOWOG" on the side of a block snapped apart from a spun rod bearing:

mowog.jpg
 
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drooartz

drooartz

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Do I need to remove the rear plate/flywheel to pull that rear main cap?

I'm going to dig in, the engine is right there and it seems silly not to at least check.
 

Grantura_MKI

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Yes.
you want to make sure the caps are replaced in the same orientation that they where remove.
be sure to line up the oil feed holes on the bearings.
bad thing is you are going to need to leave the cam bearings alone with out a total tear down.
make sure you have a quality torque wrench on hand.
will need to remove the timing chain cover, chain and gears, etc.
there a lot more to it, but giving you a start.
 
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drooartz

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Thanks for the tips. I'm trying to avoid going full on with a rebuild. Not really in the budget to do any machine work right now.

Would it make sense to pull one of the center bearings, figure out their size, get things ordered, and then swap them all at once? I'm trying to be strategic with my disassembly and parts ordering, so I don't have the block apart for too long (and thus forget how it goes together. Hard not to go whole hog on a rebuild, but I'm saving those funds for redoing my original engine. Just need a couple years from this one.
 

JPSmit

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Didn’t mention machine work?
would put it in and cross your fingers then... INHO.

+1 - reinstall it and enough with this paranoia!

 
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drooartz

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Didn’t mention machine work?
would put it in and cross your fingers then... INHO.

That's pretty much the plan with this one. Do the minimums and get it going. Machine work was my mention, and something I'm working to avoid. :D

I will tend to want to do it all right and go through the whole thing -- not productive for me right now. So I'll take a look at the bearings this week and see how bad they look. In the mean time I'll get the trans cleaned up a bit and ready to go back in.
 

Bob Claffie

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I would do it differently. Rod bearings are more likely to wear than main bearings. I would take one of the rods bearings caps off and inspect. If no copper showing and no scoring visible put it back together and leave it alone.
 

DrEntropy

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Only reason I suggested the rear main is it's the one to seemingly get the most stress/wear. If you just pull the fourth from the front and have a look at that, it would also give you a good idea about whether to go after the rest. And #3 rod bearing to check those. Good idea to pull one of each and see if the crank has been ground undersize and have the bearings to hand if needed.

Though I HAVE seen cranks with TWO different sized rod bearings, that was an anomaly, likely some cheap-arse rebuild(er). Some folks are idiots.
 
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drooartz

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Thanks for the continued ideas. Hope to get in and take a peek this weekend if I can carve out an hour or two.
 
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drooartz

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New bearings it is.

I finally had a chance to check the bottom end bearings, and at first things looked good. First 2 I checked were still nice and silver. Checked a 3rd and saw some copper, so it's replacement time.

Rod and crank bearings are .010.

Now to order new bits from Moss. Other than the bearings (any recommendations on type?) what else will I need on hand to be able to replace all of the bottom end bearings?

Pics to follow when I get a minute.
 

DrEntropy

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Some Lucas slime for assembly lube and a torque wrench.
 

DrEntropy

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Lucas "Heavy Duty Oil Stabilizer" is what I'm referring to as assembly lube. RTV for gasket sealant, a THIN film on the gasket surfaces. May as well replace the crank seals as they're right there now.
 
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drooartz

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Here are some pics from my bearing investigations, in the order I pulled them from the car. Pulled that first main bearing and it looks great. Pulled a piston bearing and it was a little scored but still silver. Pulled another piston bearing and saw more wear.

bearings3.jpg


bearings2.jpg


bearings1.jpg
 
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drooartz

drooartz

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So Moss has bi-metal and tri-metal bearings. Other than cost, what am I looking at here?

Hoping to put together a shopping list in the next couple days, will post it here first to make sure I've got the things I need.
 

Bob Claffie

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I'd run a little crocus cloth around the journals to make sure there are no "surprises". The first two pictures wouldn't cause me any concern but the last picture is worrisome. Might have lasted 10000 miles could have started rapping next week. I always used Vendervell brand bearings in the past, they were the gold standard for British cars. Stay with the tri-metal bearings.
 
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drooartz

drooartz

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Thanks, Bob. Advice noted about the tri-metal bearings.

What, may I ask, is "crocus cloth" -- not a term I've heard before.
 

PAUL161

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Drew, as I remember, crocus cloth is a stiff fabric impregnated with jewelers rouge. Been quite a while since I've used it and memory isn't as good as before. PJ

Thanks, Bob. Advice noted about the tri-metal bearings.

What, may I ask, is "crocus cloth" -- not a term I've heard before.
 

DrEntropy

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I'll concur with Bob: Vandervell here for decades of building Brit mills. Mine and customers'. Agree also about that third photo. No sense in chancing REAL damage for the price of the bearings. And appropriate "crocus cloth" comes on a spool, varying grits, 1000 should be fine for what you need. Use the narrow strips, cut about 18" long to "see-saw" around the journals EVENLY and that should take off any irregularities. Time consuming but nowhere near machine shop costs. :wink:

FYI: The tips of your fingers can detect irregularities as small as 0.002"!!!


EDIT: These guys have about ANYTHING for metalworking at a fine level.
 
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