The Stovebolt Site Forums The Shop Area Engine Shop What Rear Main Seal to use???

Background: Bought a rebuilt engine from a guy in the Vegas area, It sat for several years before he sold it to me. SInce then I have installed and done the necessary break in to get it going, but now It's leaking at the Main Bearing seal. I have done research via stovebolt and it seems that when an engine sits for a while ( even if rebuilt ), that seal tends to dry up and leak. I have also done some searching around and there seems to be two style of seals, one " rope " and the other neoprene. There also seems to be a grey area for what year block uses what seal?
My Block code is : 3738307 which puts it in the 58-62 range. I have pulled the Main Bearing Cap off and I have the neoprene seal, but there are two metal shims on either side. With the research I have done it seems, if the shims are there I need to use a rope style, but I have the neoprene installed. Do I have the wrong seal installed, if so, is that the reason for the leak? Please help

If you study closely you will see that the shims hold the inner ends of the neoprene seal apart causing a leak.
It is unusual for a 1956-62 engine to have shims. I would Plastic-Gauge the bearing to see if the clearance is correct. To much clearance will make it hard for any seal to work.

What is Plastic Gauging? Can you further explain this and how to do it, what tools etc.....?

Plasti-gauge is bascially a piece of wax. You lay it on between the main bearing and the crank journal, then torque the main bearing down. Then remove the main bearing and use the gauge that comes with the plasti-gauge to see how much the wax expands. That will tell you the clearance. I'm thinking you should have between .001 and .003 but check the books.

Here's a pic.

plasti gauge

The good part is that you can pick up a plasti-gauge at any parts store for about $3.. or less!

Hope this helps

So if I do have between .001 and .003 clearance, what type seal do I need? I'll pick up one of those plastic gauge kits.

All the Bearing Caps have these " Shims ". Did the shop ( unknown to me ) that put the engine together not know what the heck they were doing???

It is possible the crank was turned a slight oversize making it necessary to use shims for bearing clearance.

So can I assume that since I have the shims on all bearing caps that I need a rope style seal instead of the neoprene??

Not necessarily. If the shim fits properly, going all the way under the bearing shells, the lip seal will work OK. Do the clearance check with Plastigauge, and see if the shims are necessary. You might be able to remove them and not tighten up the oil clearance excessively. Remove one set of shims at a time, check the clearance as you go, and see what the oil clearance is without them installed. Don't go below .001" clearance. Green Plastigauge will be the right color for .001"-.003" checking. The red or blue will be too thick.
Jerry

Jerry

If the engine is still in the rig, make sure that you hold a slight upward pressure on the crankshaft. This is needed because the shaft hangs down slightly away from the upper bearing and will not give a correct reading using plastiguage. A small jack will work, with only slight pressure on the crankshaft.

So here is a picture of what I have. You can clearly see that the shim is blocking the two halves of the seal from meeting. Can I trim the shim to ( that rhymes LOL ) enough so the two halves of the rear main seal meet??

http://i1236.photobucket.com/albums/ff441/AZ59apacheguy/IMG_1530.jpg

http://i1236.photobucket.com/albums/ff441/AZ59apacheguy/IMG_1528.jpg

Unfortunately the oil will find its way between the shim and the OD of the seal then. Some sealer in the right place may stop this.
BTW try the pic again.

Huh, I don't know why the links went away. I reposted them.

Pre '68 Dave. Can you please look at the bearing surface and tell me what you think? Thanks

just put a rope seal in it and forget about it, fit it with tight ends.

It sure looks like some grit has gone through that bearing. Have you checked bearing clearance?

Thanks for the reply. I have not yet, I was looking for your opinion to see if it was too far gone to even do check for clearance.

There are so many ways to build an engine, depending on how picky one is and how much money they have. It is always tempting to make everything perfect. Some of the engines I threw together just to get by seem to run the best, and the ones where everything was done right seem to give the most problems.
If the bearing clearance is .002-.003" I would not scrap it and start over, it could out last you.

It would be interesting to see how that seal sits in the groove. If you remove the shims on one side, it would show. Also, it might be helpful to pop the bearing shell out and see what is stamped on the back.

Here's a suggestion- - - -how about adding a thin piece of shim stock between the lip seal and the block and cap after trimming the shim so the seal ends can meet? For instance, if the shim between the block and cap is .002", cut a piece of .001" stock the width of the seal, and lay it in the groove in the block and the cap before installing the seal. The ends of the seal will meet, and the pressure on the crank hub will be the same as if the shim was not there. When adjusting clearance on stovebolt rods and mains, I never use pre-made shims, I just cut my own from a big roll of shim stock I've had for years. The same stuff could be used for shimming the fit on a lip seal.
Jerry

I feel that I have better answers to your question as I went through the exact same thing on a '62 235.

The old rope seals are very old technology. The reason your engine likely has a neoprene seals is that they are much less likely to seep and leak than the rope style, and will hold up better. You can get a neoprene seal meant to reaplce the original rope seal for exactly this reason.

While I know all the books show that you need 0.001" to 0.003" clearance on the rear main, but I had 0.003" clearance and siezed the rear main 2 times. I took it to an old engine builder and we looked it over, and he told me to get a shim kit, and I did. We shimmed out the rear main further and it worked well. If it's just the rear main that's leaking, focuse on that, but don't take shims out as you could be causing issues with the bearing.

So I got some plasti gauge and here are the results for the rear main. I left the shims in, I think I'm ok, can you concur?

http://i1236.photobucket.com/albums/ff441/AZ59apacheguy/IMG_1543.jpg

http://i1236.photobucket.com/albums/ff441/AZ59apacheguy/IMG_1541.jpg

Well your photos appear to show a bearing with the babbit worn down to the copper, right near the parting line. That might happen if you had a .002 undersize bearing fitted on a standard journal. That is why I asked what was stamped on the back of the bearing. Have you determined why the seal leaked?

Definitely do not remove the shims! If you choose to stay with the lip seal, you'll need to trim the shims to let the ends of the seals butt together, and maybe add a strip of shim stock behind the seal pieces in the block and the cap. A little brush-on sealer like Permatex Super 300 on the back side of the seal halves might be a good idea, also.

Or, you can use the rope seal. It's not uncommon to get a slight amount of seepage with the rope seal, so if a few drips on the garage floor upsets you, better make the lip seal work some way or another!
Jerry

I would say the bearings were set up to tight to start with. With .001" now it must have been tighter to start with, .001' is the minimum you want, and that is with a align bored engine. I like .002" clearance.
I would also Plastigauge the rest of the bearings.

0.001" is still too tight, these engines like to be more like 0.004" or so.

That much clearance will guarantee a rear main seal leak, no matter what kind of seal is used- - - -the seal can't maintain contact with the crankshaft as it bounces around like a BB in a boxcar.
Jerry

I can testify to what Jerry just said!

MIne didn't leak with that much clearance. As long as it lasted, at least.

Requiring that much clearance on a rear main means:

1. The crankshaft is bent.

2. The bearing journals are misaligned.

Nowhere in this thread was mention made of the alternative method of machining the back of the block/cap for a modern lip seal as I intend and is described here.

You don't need to machine the block/cap for the neoprene seal, just if you want the style he's talking about, to be clear.

The experienced engine builder I took my motor to checked everything, and the crank had been machined on a lathe and was straight. He had rebuilt numerous 235's over the years and said they alway like more than the 0.003" max clearance in the books.