Need some expertise...main bearings

Rocketdog1

Rocketdog1

Member
Hey all-

Dropped the pan today to check the main bearing clearances, in hopes of quieting the deep thump that presents at higher RPMs.

Started with the center, which was a little out, and removed one shim. Got that one just about money (.0015-.002)

Rear was a different story, which I'll get to in a minute....

Front was about the same as the center. Pulled one shim from one side and called it pretty darn close.

Now back to the rear. Existing was one shim on only one side - so not a lot a room for adjustment. Plasti-gage didn't even squash toward the front of the bearing, and was roughly .003 at the rear. Removed the one shim that I could and re-assembled. What else could I do???:confused:

A few questions came up. What is the proper torque for these? I went to about 65-70 pounds, and that seems pretty damn tight. The pics show the rear - you can see that all is not well. Are these babbit or inserts?? I'm thinking they're babbit, but I wanted to be sure.

My guess is that this engine is looking at having some work done in the not-to-distant future. Fortunately we don't drive her much, so I may be able to put off the inevitable for a while. If money grew on trees I'd just buy a new touring engine and do the swap. But I can't seem to get one of those trees to bloom.:(

What are your thoughts/suggestions?

As always, thanks for the input.
 

Attachments

  • orca-image-1500157414165.jpg_1500157414479.jpg
    orca-image-1500157414165.jpg_1500157414479.jpg
    34.2 KB · Views: 229
  • orca-image-1500157425294.jpg_1500157425620.jpg
    orca-image-1500157425294.jpg_1500157425620.jpg
    35.2 KB · Views: 224
  • orca-image-1500157441934.jpg_1500157442112.jpg
    orca-image-1500157441934.jpg_1500157442112.jpg
    31.7 KB · Views: 216
since there are no other replys i will give it a try---- from what I can see it looks like a high spot that was "burnished" down in use ----but looking at a picture online isn't the same as being able to turn it in the light to look for a crack around the border --does that spot wiggle? it is babbitt, the oil groove and oil wells look to be ok ---I think cast in
if you can get proper clearance put it together, it'll go a long time
 
Definitely babbitt, and looks very usable. You can decrease the clearance by sanding the cap surfaces where they contact the cap. It is best if you have a surface-plate but I doubt that you do? You can also hold the cap in a vice (gently) and sand the surfaces using a block of wood (hard wood is best) wrapped in emery paper. Work carefully to keep both sides of the cap square against the block of wood. 120 grit works well but 240 or even 320 is better but slower. Do not use a file, they bend under pressure and the surfaces will not be flat. Using plasti-gauge as a guide, sand a little, then check clearances. If the clearance is tapered, use more pressure on the bigger side, keeping some pressure all around. If clearances get too tight you can always add shims. Good luck!
 
Thanks guys for the thoughts on this.

Kurt - the darker "spot" is actually a low point, kind of a divit that you can feel very easily by hand. Nothing "wiggles", all seems to be pretty tight. I thought babbit, but being a rookie when it comes to bearings I wanted to be sure. The oil groove is intact, but notably worn (shallow) near the center.

Tom- that's what I'm thinking as well. Run it til it completely gives up, then worry about it.

Jim - I thought about trying something along those lines, but frankly it kind of scared me a bit. Though you make a good point - if I went too far I could always add a shim. Thanks for the tips.

Art - Wife and I are out and about all day today, and back to work tomorrow. Appreciate the offer, and I'll keep it in my back pocket if this all goes sideways on me at some point. I've ordered some gaskets and so forth, so this may sit for a week or two before I can get back to it. Stay tuned, I may be screaming for assistance at some point!

Thanks guys!
 
Jim Brierley said:
Definitely babbitt, and looks very usable. You can decrease the clearance by sanding the cap surfaces where they contact the cap. It is best if you have a surface-plate but I doubt that you do? You can also hold the cap in a vice (gently) and sand the surfaces using a block of wood (hard wood is best) wrapped in emery paper. Work carefully to keep both sides of the cap square against the block of wood. 120 grit works well but 240 or even 320 is better but slower. Do not use a file, they bend under pressure and the surfaces will not be flat. Using plasti-gauge as a guide, sand a little, then check clearances. If the clearance is tapered, use more pressure on the bigger side, keeping some pressure all around. If clearances get too tight you can always add shims. Good luck!
Click to expand...



This is the same thing i was thinking
Good advice Jim


Sent from my iPhone using Tapatalk
 
Hey Dog, if you are going to remove a bit by sanding the cap surface and you don't have a surface plate, I know somewhere around the house you have an extra window pane, or mirror. That piece of glass is just as straight and flat as a surface plate and I would use that as a base for the sand paper before I would take a chance on using a vice, which if done wrong can be catastrophic.

I would start with 600 or so wet/dry and use a bit of oil on the paper to keep whatever metal you remove from gumming up the paper. And yes, any oil you have layin around will work, from 3-in-1 to that 20/50 you use in the motor, even ****** fluid. After you are done, just squirt a bit of brake clean on it to remove any sandings.
 
Last edited:
Kid-

Thanks for the tip - I may go ahead and give the "shave" concept a whirl and see what happens.

Does anyone have any thoughts on these bearing clearances being the cause of my deep thump at higher RPMs?? I understand that it could be a contributing factor, but I guess I won't really know until I get all of the clearances spot on and actually run the engine again - yes?

Has anyone else noticed that when you were 25 you could lay under your car all day long, wrenching away, then get cleaned up and go dance and party all night with no issues?? 25 years later, I lay under there for an hour or two, then feel like taking a nap - under the car is just as good a place as any - then maybe another hour wrenching. Then I get cleaned up and go to bed, only to spend the first 2 hours of the next morning trying to work out all of the aches and pains. This getting older stuff really sucks, but I suppose it beats the hell out of the alternative.
 
You can buy a 9X12 imported surface plate for about $35. I would think it's good enough for what Jim is recommending as a repair method.
Dirk
 
Rocketdog1 Wait until you are 80 and then slide under the A. You can dream of the days when you went dancing after, but you will need to spend the next 20 minutes trying to figure out how to get up again. In the early 50's I fit the mains and rod bearings with a file and by using or removing shims. I was just a kid but it worked and I drove the A like a kid would with no mercy for the machine. Jack
 
Loose mains will generally thump on first startup, then quite down when oil gets to them. As Chuck says, now is the time to check the rods too. Thumping at high RPM could be spark knock, retard the spark lever a bit to see if the thump goes away. jhowes, I'm 80 and the hard part now is getting down (worse getting up) to get under the A, never could dance!
 
Rocketdog1 said:
Kid-

Thanks for the tip - I may go ahead and give the "shave" concept a whirl and see what happens.

Does anyone have any thoughts on these bearing clearances being the cause of my deep thump at higher RPMs?? I understand that it could be a contributing factor, but I guess I won't really know until I get all of the clearances spot on and actually run the engine again - yes?

Has anyone else noticed that when you were 25 you could lay under your car all day long, wrenching away, then get cleaned up and go dance and party all night with no issues?? 25 years later, I lay under there for an hour or two, then feel like taking a nap - under the car is just as good a place as any - then maybe another hour wrenching. Then I get cleaned up and go to bed, only to spend the first 2 hours of the next morning trying to work out all of the aches and pains. This getting older stuff really sucks, but I suppose it beats the hell out of the alternative.
Click to expand...





A loose or bad rod bearing won't last very long, but, a main will go quite awhile.

I had a similar issue. The old 1961 engine would not make any noise at any time, but, I could 'feel' what seemed like a loose main. When I finally got around to checking it. The front was fine [.0015"], I took .0045" from the center[ I could not believe it was not rattling or beat up] and .0025" from the rear main. All 3 are/were set at .0015". Well, actually I tightened the rear a bit more than that just making sure I could turn it with my hand. What 'felt' like the loose main is now gone. I find it easier to sand the shims, but, always get flack about that procedure. I sand the shims on the piece of glass and then measure along 3 places to make sure they are even.

I don't find much problems with the rod bearings, the dippers give them a lot of oil and pressure. But, I set them also at .0015".

I still don't have much of a problem lying under something as long as everything is within fairly easy reach. I may nod off for a few minutes until too many drips end up in the wrong places.:rolleyes:

Even though your problem is a bit different and you want to stretch this out for awhile longer, I wouldn't have a problem sanding the cap as you want to.

Oh, I don't think you mentioned what the clearance was after the shim removal. As long as its no more than .002" I wouldn't worry much about it.
 
You must log in or register to reply here.
Back
Top