Engine: F/M V8 crank main bearings different thickness?

[M-Webb]

As most of you guys know, I'm rebuilding my 289 full flow V8. I had everything ready to put the crank back in today, which I did. I decided to go ahead and put new crank main bearings in it just to be as fresh as possible since the previous ones looked to have some questionable wear on them despite supposedly being "new" as well. I got a set of F/M STD bearings to match what was in the motor before, and which previously mic'd out to be within spec. when I was checking things originally. Because I've learned to not assume anything at this point, I thought it best to re-check the clearance on not just one of the bearings, but all of them. Good thing I did as I found that on every single one of them, the green plastigauge barely even deformed if at all, let alone was anywhere near spec. When I saw that I thought to myself, WTH, how can that be? So I cleaned and redid the #3 bearing one more time and still the same result. So back out comes the crank and bearings.

First thing I did was just check the thickness of a couple of the bearings from each set. I found that the old, very slightly worn set came in at about .0990" thickness on average. The fresh set came in at only about .0940". That was checking a couple from each set and a couple spots on each. So I guess that is the problem right there. How can this be? That is .005" off and mind you that is per 1/2. Again, WTH? The main bearings are suppose to have a clearance of just .0005" - .0025" total. The old set gave me clearances within spec, although on the higher end of that range. With these newer bearings being .005" thinner each 1/2, that is way, way off. No wonder the plastigauge didn't seem to have deformed at all, I don't think it did with that unexpectedly excessive gap.

I double checked the stampings on the bearings and they both do say STD on them and appear to have the same part #'s 1787CP, although it looks like the older set was made in 04/2013 and the fresh set in 06/2020 if I'm interpreting the info correctly.

With that, I checked the crank main journals and looks like they are at about 2.4885" and are suppose to be 2.4995"/2.5". I guess they are not STD to begin with. They are .0110" - .0115" under. So I guess getting correct -.0100" bearings is what I really need? And the older bearings are just stamped wrong somehow? Hard to believe, but unless I'm wrong, that seems to be the case.

Or I guess I can just stick the old bearings back in and call it good enough.

Remember what I said about not being able to assume anything with this motor? I mean not 1 single thing.

Anybody have any thoughts on this? Maybe I'm doing something wrong, what is going on here?

As Lucy says, "Good grief Charlie Brown!"


Fresh one on the right, older one on the left, both 1st 2 photos:













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[christophe]

Congratulations for finding about this before any harm could occur. I would report this to your bearing supplier and ask for undersize bearings in exchange with no charge. And double check again with the new ones, of course!

[swvalcon]

Best way to check your bearing clearance is install bearings with out crank and torque the main caps. Now use a inside mic and compare what you have to the crank and use a little math. What you end up with is your bearing clearance.

[bezhawk]

According to your crank measurements, you should get .010 oversize bearings. The first set must be stamped wrong. Even my old eyes see that they're thicker in cross section.

[M-Webb]

I think you are correct. That photo is a little deceiving. I thought the same thing when looking at it. But then I noticed that the new bearings have a slight bevel to the edge and the old ones don't. So optically up that close it appears a lot more obvious in the photo than it really is. .005" is a pretty small difference at visual scale.

[M-Webb]

New day and I'm still trying to wrap my head around this situation.

But best I can figure is the old bearings are really -.010" bearings and are just stamped wrong. I guess 1 of the 1st (2) shops that worked on this motor got those bearings and put them in and luckily they were the correct size needed, but they were just stamped wrong. Maybe they ordered -.010" bearings and got them and they were in the right box so just installed them and they were what was needed and maybe they never noticed that they were stamped STD or maybe did notice it and didn't care because they actually fit properly as needed. Or given how things have gone with this motor so far, more likely is they didn't notice, didn't check AND didn't care.

I recall thinking when I went to check the size of those to order the replacement set that it seemed a bit oddly fortunate that the crank was still at STD even though it was a used crank. I thought I just got lucky and the crank was good, hadn't needed to be cut down yet on the mains. Especially since the rod bearings were at -.010" and I ordered those to match that. I should have thought to question the mains being standard since the rods were at -.010". But this being my 1st motor rebuild, didn't think to question that any further than just a thought in my head. Now I know better. Question and check everything.

How those bearings got made to one size, then stamped another and then actually made it out the door and got sold and then installed and luckily were the right size as needed despite all of that is surprising to say the least. But the best I can figure is that is exactly what happened somehow as crazy as it seems.

Yes, luckily I checked this now and have already learned my lesson to not assume much of anything with this motor, not even factory stampings on bearings apparently.

I got those new bearings from Phil Harris, which are correct and exactly what I ordered, so none of this is his fault of course. I'll just have to get a new -.010" set and hopefully when I go to check those they are correct and that solves my problem. Seems like that is the solution to the problem based on my #'s at the moment.

Yes, I bought a cheap dial bore gauge to check the cylinders, which sort of worked out, kind of. To be honest, having to use that and then remeasure the measurement with a caliper micrometer is a PIA and didn't end up accurate enough so had to have a pro measure it for me with a better tool. Would be a lot easier to use a better more expensive one that just gives you the direct read out on the size like he had. But those seem to cost a lot more money. On the flip side, it was actually pretty hard to find the plastigauge at local parts suppliers and now I am almost out. This may be my 1 and only motor I ever rebuild, so a bit hesitant to keep spending $100's++ on more new tools, just trying to get this motor rebuilt properly and done. So will probably just stick with the plastigauge for now. At least it worked good enough to catch this obvious problem, luckily.

[JoeHall]

Agree, plasti-guage is cheap, simple, and very accurate. No need to spend extra $, and make a simple task complicated.

[M-Webb]

I spoke to Phil Harris, new set of -.010" main bearings on the way. Hopefully that will solve the problem.

Well, if anyone wants a set of now very lightly used STD ones for a reasonable price, let me know. Verified to actually be standard.

[StudeRich]

You see that hand marked Marker Pen Check mark on the new MB Box?
If I recall correctly a few years ago there WAS a problem with exactly that, the Mfg. was sending our Studebaker Parts Wholesaler Fm bearings marked wrong !

So, they are all checked now or at least the current stock soon after that occurred was, and the box Check
Marked as OK.

[M-Webb]

I thought that check was just part of the box graphics. But makes sense.

[64Avanti]

The standard bearing should be .095/.0953 except the last part number used was .0946 / .0951 so slightly more clearance.

[64Avanti]

By the way your numbers make it look like you are measuring at the end of the bearing. The place to measure is some distance from the end but you need a micrometer with a special rounded end instead a flat end. It is hard to imagine the problems you have had with this engine. It is hard to believe the engine builder didn't check clearances.

[M-Webb]

I measured at a couple spots on the bearings and a couple of each set, got sort of an average # for each. I did use my standard caliper type micrometer and I tried to be gentle with it to not dig into the bearing surface too much. But in general, there seemed to about a .005" difference for each bearing 1/2 between the 2 sets. The old set checked out to fit OK, but surfaces were a bit marred up. The new set was way off. So I'm hoping this replacement -.010" set is the right size and will check out good once I get that them in and checked.

[DieselJim]

By the way your numbers make it look like you are measuring at the end of the bearing. The place to measure is some distance from the end but you need a micrometer with a special rounded end instead a flat end. It is hard to imagine the problems you have had with this engine. It is hard to believe the engine builder didn't check clearances.

I have used a small ball bearing with my micrometer checking rod bearings.

[M-Webb]

I got the crank installed back in my 289 yesterday with the now correct new .010" bearings I got from Phil Harris, which are also stamped correctly thankfully. They also check out good for clearance @ .001" on the #3 bearing and slightly less on the front and rear main bearings. So now all good on that! Turns nicely by hand, feels good.

But while doing a final thorough cleaning on the crank before I put it in, I noticed what looks like "10" stamped on one of the crank counter weights. Possibly assuming that means that the crank has been turned to .010" which I now know is of course, is that correct? If I had known what I was doing, I guess I could have checked for that to begin with before ordering anything! Live and learn maybe.

And also the fact that the rods are for sure at .010" too might have keyed me into that? Do crank mains and rod journals always get turned the same or do they sometimes get turned differently, as little as possible, whatever is minimally needed?

[StudeRich]

Yes, the machinist did mark them the amount they were turned to.

The Rods and Mains often get turned the same, but it is up to the Machinist and Owner and mostly the Crank, whether that happens or not.
So they are whatever is needed for a good smooth and round Journal surface and proper fit.

[M-Webb]

I'll look more closely and see if I see any other similar marks for rods vs mains, or maybe it is just this one for the whole thing if not. More of a curiosity personal FYI learning thing for myself more than anything at this point so I'll know better for next time I guess, if there ever is a next time.

[M-Webb]

Looking at the crank again, I could not find any other "10" stamped on the crank anywhere else. So guess that is the only one and implies the whole crank is at .010", which it is.

Now that I have the crank back in and the main caps on, I re-did the rear main seal of course with a new seal while at it. In the shop manual it says to lubricate the "sealing edge". I re-read that after I put mine back on of course, dry, did not lubricate the sealing edge. I did put some Right Stuff sealant on the outer sealing edge to the block and cap mounting lip, but not the oil sealing edge to the crank. Is that good or should the crank edge get a little lubrication as well for some reason? I assumed it was better to stay dry, not oil it and encourage more oil to possibly want to come out. But if needed, I can try to get a little oil on it still while I can still move the crank IN/OUT a little before I put the timing gears back on next step.

[enjenjo]

Oil the seal. running it dry on start-up can damage the seal.