Adjusting main bearings question

[700rpm]

Can someone direct me to a site that describes step-by-step how to adjust main bearings with the engine in the car. I've done rods, but never mains. I tried my center main a couple years ago and securing the top of the bolts so I could loosen the nuts was dang near impossible; I don't see how I'd get a good purchase on the rear main.

Thanks.

[Tom Wesenberg]

The rear main bolts are self locking, so they are easy to remove the nuts on the bottom. To check clearance I'd use a piece of aluminum foil folded in half to form a strip the length of the bearing and about 5/8" wide. Mic it to see how thick it is, then install it in the center of the bearing cap and bolt it to the torque specs, or about 50 ft. lbs. If you can still turn the crank freely, then use a razor to peel off just one thin shim and try it again. If you need to remove another shim, then remove it from the other side, so you try to keep the sides even. Once you can't turn the crank by hand then remove the aluminum foil and try again. If it turns now, then you should be at a good clearance. Repeat for the other two main bearings.

[700rpm]

Thanks Tom!

[pat in Santa Cruz]

indeed, the center main bolts are tough to work on. I remove the manifold. Its not necessary, but being able to see the cotter pin helps remove it. Once its out, I hold it with a box wrench I have that fits right in there and rests low against a valve guide. I then use a 9/16ths square socket and unscrew the bolts from the bottom. The other side can usually be done the same way, resting the box wrench against a cylinder . Looking at the square head of the bolt, you will notice a raised dot in one corner. That allows you to align the cotter hole when you reinstall it. Face the dot in the direction you want the hole. I use stainless cotters, and do not spread then very much, so the next poor soul who has to dig them out has an easier job of it. The removal of the front cotters can be a horrible experience too. Be patient and you will get them out. The preferred method is to straighten the pin, and pull it out by the head. A pair of wire dykes works very well to grip the pin and pull it out by prying against the nut.. Sometimes I cut the head off and drive the pieces through with a drift punch.

[160B]

I recall doing the mains on my 1931S/W.
Since the rear main bolts are inside the flywheel housing, you have to remove the cover plate on the flywheel housing and work through the cover plate opening. It is a tight fit to get through the opening and get a wrench or socket on the main bearing nut. I purchased a proto 3/8 drive universal 3/4 socket pn Proto 5279. This universal socket is short in length and was the only one that would allow me to get through the opening in the flywheel and get the socket on the main bolt. It made the work go a lot smoother.

[1930artdeco]

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Originally Posted by Tom Wesenberg

If you need to remove another shim, then remove it from the other side, so you try to keep the sides even. .

O.k. I now need to ask. why would you take one shim out of just one side and not both to keep everything even? Or is taking out just one shim such a small amount thatcocking the cap won't matter? Dad did this on the rods of my engine when we rebuilt it so that the rod was even all of the way around.

Thanks,

Mike

[700rpm]

I'm beginning to ask myself why I ever thought about taking up the mains.

[Tom Wesenberg]

Originally Posted by 1930artdeco

O.k. I now need to ask. why would you take one shim out of just one side and not both to keep everything even? Or is taking out just one shim such a small amount thatcocking the cap won't matter? Dad did this on the rods of my engine when we rebuilt it so that the rod was even all of the way around.

Thanks,

Mike

Those shim packs are glued or soldered on the edge and can be tricky to peel off just one thin shim. If the shim is .0015", then removing one from just one side will change the clearance by .00075", and the the cap balance will be fine. Just remember to try to keep both sides as even as possible.

[glenn in camino]

Get some plastiguage, a torque wrench and Les Andrew's book. It's not difficult, but It's much easier, upside down, on an engine stand.

[700rpm]

Originally Posted by glenn in camino

Get some plastiguage, a torque wrench and Les Andrew's book. It's not difficult, but It's much easier, upside down, on an engine stand.

I didn't find anything in Les's book about doing this with the engine still in the car. Maybe I just missed it. I've got all the stuff and some experience; I have always done mains with the engine out. My puzzlement is with the engine in.

[glenn in camino]

If you're going to do it in the car, it will be much easier if you can have a helper. Especially on the mains. One person under the car holding the bolt heads and one on top loosening and tightening the castle nuts.

[pat in Santa Cruz]

Another thing to think about if adjusting shims under the car is to remove the pan and let the engine drip for a couple of days until the valve chamber has drained. Wipe off all oil drops you can see. Still, the odds of a drop in the eye are still pretty good. If you just jump into the job immediately after having driven the car within a day, you are guaranteed to get oily hair, face and eyelids.

I jack the car up on stands a few inches to get more comfortable clearance. Get something comfortable to lie on, relax and take your time. The job can be tedious. I agree with Glen about a helper. It often seems as if two persons will triple the speed of the job. All that up and down, out and under required to do it solo can be very tiring. The advantage to plastigage is that you can calculate the approximate number of shims to remove once you get a reading, which eliminates a few repetitions of removing and installing the caps trying to lock it up if you use the foil method.

[Tom Wesenberg]

If you try plastiguage with the engine not upside down, you will have to jack up the crankshaft to get the weight of the crank and flywheel off the plastiguage, otherwise all the weight will be down on the plastiguage and no matter what the clearance is the plastiguage will be flattened and give a false reading.