The Stovebolt Site Forums The Shop Area Engine Shop Ready to give up and put in a sbc

Can't seem to find the answer to rear main seal leak. Have a 1959 235 that has gotten the works. New cam, lifters, timing gears, pistons, rings, reconditioned rods, reconditioned (.020/.020) crank, all reconditioned 848 head, all new gaskets and seals. All machine work was preformed on the block by a reputable shop I have used for many previous builds. The only thing not done was to line bore the block, something I have never done on previous street motor builds. Running Fenton 2x1 with Rochesters and Fenton split headers, late model GM hei distributor and all backed up by a the stock cast iron powerglide in a 52 Chevy hard top.
OK so thats all the information, now to the problem.
Cannot seem to keep a rear main seal in this thing.
We are on the the 3rd seal and its leaking again. Rubber not rope.
In the car the pan can be removed and the seal changed but this is getting very frustrating. We have only been able to get between 300 and 700 miles on a seal before it leaks, and not just a drip, a major puddle and leaving a trail behind!
Have checked all the clearances every time it has been apart and found nothing out of spec. The last go round the rear main bearing did show some unexpected wear toward the rear edge of the bearing and was replaced with a new bearing shell along with the seal. Once again checked with plastigauge and buttoned it up only to have it leaking again after only 300 miles!
The engine starts right up, has great power, is smooth running and sounds great. Gets expected mileage and is in every other way a fantastic success.
This car belongs to a very good friend and as such I cannot vouch for the way it is being driven (he tends to have a bit of a lead foot) but I would think that this motor could handle cruising the highway at 70 which would put it at approximately 3500 rpm without this type of failure.
I am looking for any thoughts on how to fix this thing before it gets pulled and replaced with yet another belly button sbc. They are a great engine but not as cool as a stovebolt.
Sorry for the long post, I just don't know where else to turn for help at this point.

Chuck

I forgot to mention, this thing carries 45 psi of oil pressure cold and 30-35 warm at idle. I can't believe that could be excessive and contributing to the problem.
Anyways I just thought some might ask.

Help

Chuck

Is the engine vented correctly?
Is the road draft tube clear?
Is the valve cover vented?
Can you see anything wrong with the old seals when removed?

Yes
Yes
Yes
On one it looked as if I may have nicked it on the block side of the top 1/2 of the seal while pushing it in but the seal lip on the crank side looked to be in good shape.

Could the crank seal surface be undersize enough to make it not seal due to being turned? Why would it hold for as long as it does if that were the problem?

Should I go to a rope?

That was my suggestion, maybe try a rope seal instead.... They can be a little tricky in installing but have a wider seal surface than a regular seal.....

John

I can give you the stock crank seal diameter if you want.
The other thing I have seen a number of times is that the seal groove is not concentric with the bearing bore. In that case only a rope seal will work.

So are all rope seals created equal or is there a preferred manufacturer/type?

Biggest thing with a rope seal is getting it installed right. A lot of people pull it in, cut it off. Then in time it relaxes and leaves a small gap between the 2 halves and leaks.....

John

So is it possible to do it right with the engine still in the car and what is the right way?

Best Gasket

I just checked and I did save one of the rope seals out of the last Felpro gasket set I got for one of the many fix attempts. Good or not good? I can order the Best Gasket one if that is the best option.
Best install suggestions with the engine in the car?

The Fel-Pro rope seals are near impossible to cut the ends without fraying.
I would highly recommend Best Gasket brand.

Go with the Best Gasket seal. Follow the direction just as stated in the paper work that comes with it. Do not stretch, or pack the seal, you will have to drop the crank down enough to get the seal in place, don't try to pull it in with a seal puller
( cable puller ), it won't work with this type of material. Do it right, and this will be the last time.

Joe

Two things I have not seen mentioned here:
First, check the crank flange where the flywheel is mounted. The crank flange on these cranks has three pins in the flange to correctly align the flywheel. On occassion, those pins can be left out, maybe not all of them, but it takes just one. If so, it will fool you into thinking you have a rear main seal leak. The holes for the pins go straight through into the bottom of the engine. The oil, under pressure, will come out much like you describe.
Second, if you have to replace the seal, the neoprene seal has never been recommended for these engines. Rope is best. Drop the crank, turn the crank as you feed the rope through trying not to pull too much. Cut each end of a little long and apply a small of gasket sealer on the ends when you put the cap back on. I use a paper hanger's seam roller to roll the rope tightly into the bottom cap. You can't roll it too much. Cut it a little long for the sealant to go into the top rope and the bottom rope.
This happened to me and it took awhile to figure it out. Just my opinion, I think Fel-Pro makes the best gaskets out there.
Good luck with with solving your problem.

Well I was told from Tom at Stovebolt Engine Co that the best seal is a NOS type that has Asbestos in it. I took his advice and bought on from a Patrick J. Harris in Minden, NV. The rest of my seals and gaskets are from a kit by Best Gasket. I have not started the motor so I do not know how its going to hold but crossing my fingers. That's my 2 cents

Felpro does make excellent gaskets, but the seals are worthless since they removed the asbestos. The new ones are hard to cut and come apart pretty easy, nothing like the old seals they used to sell.

Joe

Did you apply a small amount of sealant to the bearing cap and ends of the seal? That's in the shop manual also.

And these may seem dumb, but not out of the real of possibility:

Is the drain hole in the cap clogged?

Are you putting the seal in the proper place. There are two slots and the seal will fit both.

I think that if an engine is designed to have a rope seal, you cannot use a rubber seal as the block/cap are not machined true enough for the rubber seal to seal perfectly when the cap is shimmed properly and torqued down.

Also, Best Gasket rope seals come with a pin (to keep seal from rotating with crank) that you drill into the cap (and maybe the block, cant remember). So, maybe someone installed a pin in the block and that is why you cannot push/pull the new seal into place.

Are you wetting the rope seal prior to installation? The manual does not specifically mention it... but in all the old motors that I (GMC/Ford) have that use leather / natural seals (even asbestos) its is common practice to soak 24+ hours in oil to soften them. At one point a TB was put out that all local spares should be kept in clean motor oil while on the shelf to allow for instant installation.

Its not enough to simply place oil on the surface... gotta let it stew in oil to fully penetrate.

What this does is allows the seal to self lubricate until the motors natural flow of oil would reach it.

What do the seals look like when you remove them? Are the charred? Have uneven wear? If the seals still look new, then its not the seal.

I'd say post pics...

The Neoprene seal will work on most late 1955-62 engines as they do not use shims and the seal groove is more accurately machined.
Chevrolet even sold Neoprene seals as a replacement for these engines. There is the rare occasion where the seat groove is not concentric to the crank but that is rare.
I know Best Gasket includes a pin to keep the seal from spinning but I would take my chances on that. I do not use the pin.

So to update. I ordered the Best seal and as soon as it arrives will be putting her back on the lift one more time. I really appreciate all the input and I guess we'll just have to wait an see how it goes this time.

Chuck

I do not pin the best gasket either, and have really good success with them.

Joe

If I remember correctly, Best specifically says to NOT soak the seal before installation. I do believe that you are to oil the surface before installing crank and cap (I think). Regardless, rear the instruction that come with the seal and follow them to the letter and it should work. If not, you have other issues that need to be addressed. I will say that once the new seal is installed, the engine becomes very difficult to rotate. Certainly not by hand.

OK so to update.
I received the Best seal from Egge Machine.
I have the car on the rack and the oil draining.
Plan is to pull the pan tomorrow after work and remove the old
seal. Clean everything up and check all our clearances one more time and then install the new seal per the (brief) instructions that came with the seal. The instructions say to oil the seal surfaces after installation but make no mention of soaking it.
Plan is to not use the sneaky pete tool, so as not stretch the seal at all. After loosening all the mains and removing the spark plugs I will try to feed/push the top seal in while rotating the crank. If successful I plan to pack it a bit and trim per the instructions and install the other 1/2 in the cap per usual and trim accordingly. Apply Permatex aviation sealer to the cap mating surfaces and re-torque the whole thing again. Instructions say not to use any sealer on the mating surfaces of the seal. I think it best to let it sit for a spell, maybe overnite, before filling with oil and firing her up again.
So, that's the plan. I guess we'll have to wait and see if the plan comes together in a couple of days.
I have also given my buddy the "though shalt not over-rev" speach more than once in hopes that this as a possible cause will be taken out of the equation on the next round!

If any of you guy have any last words of wisdom or see any flaws in the plan, don't hold back now.

Chuck

The only thing that comes to mind is...
If you do pull shims and have the bearing clearance at a minimum I would feel the main cap after the engine starts to make sure it does not get to hot. Rope seals can generate a fair amount of heat until they wear in. I have had the rear main seize from heat expansion. Be careful to keep your fingers out of the flywheel though.

Good tip Dave. Thanks and I'll make sure to keep all my tips, finger tips that is!

Chuck

Update #2.

So we opened it up and found the rear main bearing wasted. So, got online and ordered another set of .020 under mains. Looked at all of the others and they are perfect. The good news is the crank isn't scored and just had a bit of bearing material stuck to it which polished of easily.

Flash back for more history on this motor.
The owner (my buddy) took this car out and ran it down the interstate at 70 mph, which might have been OK had it had time to get broken in properly however, the motor only had 4 miles on it when he took this joyride! Overheated badly and took out the bearings and original crank.
For the second rebuild we bought a re-ground crank, reconditioned rods and all the other new bits necessary to get it back together. Now is where the seal problems seemed to really start to occur. After about 600 miles it started to leak, badly. Pulled the pan and found the rear main bearing was warn enough to warrant replacement, but is was worn more on the rear (toward flywheel) than front and the crank was undamaged. Back together with a new bearing and new seal. 350 miles and we are back to it again.
Each time the pan was off we checked the thrust with the dial indicator, checked the crank diameter, and plasti-gaged the rear main. Always checks fine although the rear of the bearing does seem very slightly tighter than the front edge.
This engine did not use shims and I believe left the factory with the neoprene seal as it came out of a 59 Biscayne.

Back to the present.
Tomorrow I plan to get out the dial indicator and micrometer and once again check all the clearances I can while we wait for the new bearings. I plan on checking with the dial the roundness of the rear main of the crank this time also as well as trying to check more accurately to see if it might have been ground tapered.
I am truly at my whits end with this haunted machine.

Question: Could the trans be causing a problem? 1952 cast iron power glide. Does the torque converter have to be indexed a certain way for balance on these engines?

I feel like maybe I'm missing something but I just can't figure out what. I runs soo good. Powerful, smooth, responsive, sounds great with the split exhaust, good oil pressure and decent mileage. Just can't seem to fix the rear bearing/seal problem.
I don't know if the bearing goes and take the seal out, or if the seal goes and then the bearing.

Sorry for the looong post, I just don't know where else to turn.

Chuck

Good idea to check for roundness and taper on the rear crankshaft main. Also check for actual size, maybe it wasn't ground to .020 as the rest are....

John

I am wondering if the transmission is putting extra stress on the crankshaft due to a balance problem or worn bushings. This may be a real problem at 3500 RPM. The extra lateral movement is damaging the seal and that is why it only lasts several hundred miles.

Not sure if it would cause a problem or not but does the crankshaft have a pilot bushing for a standard transmission installed causing things to be to tight????

I had similar issues with my '62 235 in my Bel Air. Seized the rear main 3 times. 4th time we shimmed the rear main, it was fine, but took out the rod bearings on the center 2 cylinders. For what it's worth, mine came from the factory with the rope seal. After the first time we used the neoprene seal. I wanted to keep the 235 but it was too much headache. It's a way better car with the SBC now, even though I'll get attacked for that.