I could use some help from someone that has rebuilt a 6.2. I'm trying to rebuild the engine from my M1008 and the main bearing diameter are all different sizes. I put the main caps on without the bearings installed and the hole the bearing goes in ranges from 3.1389 (#5) to 3.1424 (#1). The GM rebuild manual and the TM are no help since they talk about "Select fit" main bearings that nobody has ever heard of. When I look for bearings I can only find standard and oversize, not random sizes. I can't believe the crank bore at the block are all different sizes from the factory. How have you guys solved this in the past? It's nearly impossible to find someone that will line bore the crank bore near me and I can't find "select fit" main bearings.
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6.2 rebuild help
- Thread starter Tongloong
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- 10,466
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- Camp Wood/LC, TX
That’s only 0.0035” difference. We are talking GM here. There is some crush when you torque down the caps. If you are worried about the final bearing clearance, do a Plastigage check.
nyoffroad
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I think the "select fit" is a way of saying measure and buy the undersize bearings that fit THAT particular journal.
Unless the crank has been turned or will be turned I buy the standard size and then plasti-gage them, I can't remember when that didn't work.
Unless the crank has been turned or will be turned I buy the standard size and then plasti-gage them, I can't remember when that didn't work.
Thanks for the help. The problem is that the bores in the block are too small, not too large. #4 is negative and will not even allow the crank to turn if torqued. I have seen std, and undersize bearings but those refer to cranks that have been ground and are actually thicker bearings to make up the difference. The measurements I'm getting with caps torqued, both with and without bearings suggest that the bore is too small and all of my tolerances are too tight except for #1 that is too loose. Does anyone know where to source "oversize" bearings vs. undersize? It's confusing since undersize and oversize refers to the crank journal but I need thinner bearings, not thicker ones. I have the Std size and they are the thinnest I have seen.
- 10,466
- 6,544
- 113
- Location
- Camp Wood/LC, TX
Suggest you take careful inside micrometer measurements 360 around the inside of the bearing with the cap torqued. Might need a tiny bit shaved off where the halves meet.
I gotta ask an extremely basic question...are you sure you are getting parts for a 6.2 and not something else? Possibly boxed wrong parts or looked up wrong, shipped wrong? There's really only one size since they are all so close in standard size.
You're not wrong to ask. They are for a 6.2. With a variance of .0035 between bores getting. 0018 tolerance across the board (1-4) just isn't happening. Crazy because the stamp in the oil pan face says #2 across the board but they are all different sizes. The gm manual says they were select fit and has a chart of random bearings to put in place. I just can't find the random bearings. They are all sold in sets
I had a good conversation about this with my local Yamaha dealer. The Japanese motorcycle manufacturers use select fit pistons and cylinders. Cylinders are A-D with A being largest and D being smallest cylinder The dealers stocks D pistons as they are the smallest and fit all bores.
The point is that the mass production tolerances were much tighter than they really needed to be.
The point is that the mass production tolerances were much tighter than they really needed to be.
Can you read anything on the old bearings if there's anything left on them? Sometimes they have some mark on them. IDK I think I'd try another standard set. There's several online military surplus guys that list them for sale pretty cheap. 01-152-4239 I think is the NSN for the set but I'd have to look them up in the TM to be 100% sure. There were a few NSN since they changed the number with the hmmv but had the same 6.2 in it. Here is a screen shot of the TM of the crank and bearings....maybe you can find the correct stuff this way. Looks like 3 of each bearing with a NSN on each...not sure if this helps or not since I remember you posting about 3 sizes before. I hit google on all the NSN numbers for crank bearings and only the #5 standard size didn't come up somewhere for sale. They are out there still NOS.
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nyoffroad
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- Rochester NY
That just doesn't make sense, I'm not doubting that your having this problem just something that we don't see is wrong. Did you disassemble this engine or did someone else?
Could the main caps have gotten switched around?
Is the crankshaft the original one to that engine or is it a replacement?
How sure are you that you received the CORRECT bearings?
Assuming the caps are in correct order and the original crank then that leaves just the bearings (just ruling out the obvious) I also think you somehow got the wrong bearing set, perhaps they are over sized and not marked?
ezgn
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I will look into that. Thank you. I ordered from summit and haven't looked it up from the nsn
DIVE DIVE
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Her is a set of “standard” bearings. If you look very closely, you can see that they all say .013 with the exception of the number 5 rear bearing which says .026. Not sure if this helps; maybe just a data point.
I’ve never mic’d out an engine bearing to the ten thousands position, but that’s just me. Good luck
I think he's using those as an example of what the backs look like.
Well gosh darn, I'm full of manure. I just popped the inserts out of my original 1986 block and it has dates ranging from 1981 to 1986. Never seen that before. My 6.5 engine was all 2004.
The factory service manual is available online and describes the markings on the block in relation to the select fit process.
The factory service manual is available online and describes the markings on the block in relation to the select fit process.
Well, I cracked open another block and it turns out that nobody's crazy. I just have an anomaly block. The bore with mains torqued on the 2nd block came out at 3.142" and a Std. set of main bearings will work perfectly. I understand the "select fit" but that was to mix and match Std, .013, and .026 to achieve the best oil clearance. At no point was it to fit a smaller main line (bore) housing that would take a thinner, and not a thicker bearing for clearance.. The first block is some kind of freak with a main bore smaller in diameter than anyone has ever heard of. Now I just have to figure out how to bore the main line with the 2 piece oil seal. Everyone around here seems to have the pass through bore that would destroy the rear main seal housing.
Thanks again for all of your guys help.
Thanks again for all of your guys help.
The local machine shops only have the line hone machine that goes through all of the main bearing caps. They require that the centerline is both aligned and the same size. The machine they have would delete the rear main seal. I do wonder if it can be done with a lapping bar much like you would hone scope rings since it's only .003" I need to remove.
0.003 is a lot to remove by hone. That would typically require boring first.
It is also imperative that the bore centerlines are matched which is why the honing bar is used. The amount removed from the caps for bearing bore resizing is trivial in your case. The effect on the roundness of the seal bore is insignificant. This is more of a spun bearing problem where a lot of material needs to be removed from the cap.
It is also imperative that the bore centerlines are matched which is why the honing bar is used. The amount removed from the caps for bearing bore resizing is trivial in your case. The effect on the roundness of the seal bore is insignificant. This is more of a spun bearing problem where a lot of material needs to be removed from the cap.