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Excessive Rear Main Engine Oil Leak After Installing New Rope Seal Or After Market Rubber Seal

Had a leak on rear main seal…installed new after market rubber seal with instructions to use shimmy feelers provided with seal. Buttoned everything back up and took car for a short spin then put it back on the rack…leaked worse than before from the rear main seal. Took apart again and installed old style rope seal…buttoned back up again and took car for spin again and put it on the rack…still leaking excessively than originally…! What am I doing wrong what would cause leak to be worse than originally…?

To give you all some backgrround…the block is a '54 Olds, V8, 324 ci…Old crankshaft was cracked and three main caps were broken… couldn’t find one rom a '54 engine…so I had to settle with a '55 crankshaft and all 5 of the main caps. This resulted in having to have the block cylinders, the crankshaft and main caps machined…then entire engine line-bored and center-lined…the engine went from .000 standard to under .030…all appropriate internal parts had to be replaced at under .030.

Back to leak…any thoughts as to why the new rear main seals (new after market rubber or old rope style seal) not working…would a different crankshaft and main caps from a '55 engine on a '54 block have any effect…?

Have you verified the “end play” of the crank is within specs?
Is the crank surface where the seal rides on free of scores?
I’m assuming your oil pressure is within spec, and your rear mail bearing clearance is within spec (it would need to be way off to be a factor here).

Yeah I agree with Joe. This reminds me of another poster a few months back. Blew his rear main, mech installed a new one, blew that one, mech appoxyed in another it held for a few hundred miles and blew. Turns out the end play of the crank was bad, and it was causing all the problems

I believe that the rear main cap has a weep hole between the main bearing and the seal. Enlarging that hole will relieve some pressure on the rear seal. But installing those seals is difficult.You mentioned both styles of seal but I don’t believe they are interchangeable on any engines using a 2 piece seal.

This is the kind of problem you get into when you start interchanging parts from different engine series…There are drain holes and oil slingers involved and the Mix & Match method of engine assembly ALWAYS leads to problems…Find a '57 J-2 engine, drop it in there and have some fun!

JoeMario & gsragtop: Machine shop where work was done suppose to have spec’d block and crank/caps reason for block machined and crank/caps machine then line-bored and center-lined and now at .030 under from standard. Trying to confirm with machinist that ‘end play’ of crank was within specs…how bad does the ‘end play’ of crank has to be…is there a fix…?. The crank seal surface appears to have some surface corrossion but no deep scores…can corrosion be removed with light emery cloth…and not impact diameter of seal surface…? Re-checking rear main bearing clearance again to ensure it’s within specs. Appreciate your comments…great input, gives me course of action to take.

Rod Knox: Will be checking weep hole to ensure it’s lined-up properly and not clogged up. Would enlarging weep hole cause any other issues…pertaing to specs etc…? After many complaints of installing the rope style seal and that it didn’t last long before it leaked again…Olds/GM answer was to develop the after market rubber style…however part of the seal includs two strips of gasket type material to be fitted in channel along with rubber seal (as a shim/filler)…which makes it for a more difficult install. Thanks for your comments, we had the same thoughts about the weep hole issue.

Caddyman: Good point…reason had block and crank/caps spec’d out and machined…then lined-bored and center-lined to hopefully eliminate those mix and match issues. At this point, another engine is not an option…have too much time and money invested on this engine to drop it as a loss cause…! I do appreciate you input…Thanks.

If the oil pressure is relatively high and the rear main bearing’s clearance is at the upper limits a great deal of oil will be dumping out into the gap at the rear seal. If the volume is too great for the weep hole pressure will accumulate and the seal cannot hold any pressure.

Rod Knox, will be checking oil pressure and rear main bearing clearance again. You previously mentioned that by enlarging weep hole it may help relieve pressure. What other issues or complications enlarging weep hole may surface pertaining to specs and internal/overall engine functionality…?

I am not aware of any complications of enlarging the weep hole. I have reamed out that hole on the few occasions that I replaced 2 piece rear seals on older engines to help ensure that I was solving the problem but I tried to avoid replacing those seals unless they were leaking heavily as it seems impossible to totally stop the leak unless the engine is removed, the crankshaft polished and the seal carefully laid, paying close attention to the seal when the crankshaft is installed. I have had better luck with the rope seals than rubber seals on old engines. If you want to ream the hole I would suggest you find the largest drill bit that will pass through the original hole, then ream it with the next larger bit.

HOWEVER, if the rear main clearance is beyond specification, correcting that would be the first move. Plasti-gage the clearance and see what you have.

Rod Knox: Appreciate the suggestions, they have been very helpfull. To plasti-gage the clearance on the rear main bearng and to ream out the weep hole on the rear main cap probably requires exposing both buy pulling engine out and breaking down to correctly accomplish both tasks…? At this time if at all avoidable, any other possible fixes that can be done first with engine still in car…? Below is a pic of the 'old ‘54 Olds dinosur’ I’m working on…Thanks again.

When you installed the rope seal, did you cut off much? I have no experience with the particular engine you are working on but have built 2 Olds motors with rope seals. Neither leaked. I would take the rope seal and mash it as short and I can make it. Then cram as much as possible into the crevice in the block and cap. I would place a very small amount of RTV in the corners between the cap and block before installing the cap. No leak.

Again, I have not had experience with this particular motor but are you absolutely sure it is the rear main? My 455 was leaking from the block to intake surface and the leak path ended up dripping off the lip of the oil pan looking like a rear main leak. Just a different thought.

Car looks beautiful though.

One other thought, do you have a oil pressure gauge on this car? Do you know if this motor has a blind plug that has a weep hole to oil the distributor gear like the 60s blocks do? This is the biggest overlooked issue on the 60/70s block where a machine shop will install a solid plug instead of the one with a hole in it. It may be that an oil passage is not cleared correctly and you have an over pressure situation and this main seal is the easiest path of relief for oil pressure. Just another thought.

W30[post: Great suggestions, the second time it leaked excessively the rope seal was saturated with oil all around. We will go ahead and install new rope seal and do what you recommended. If it leaks again we will re-check oil leak path to confirm it’s from the seal. We will also check for bind plug that should have a weep hole to oil distributor, although oil pressure on gauge is staandard for the engine and I don;t recall shop manual addressing such a plug…? .I’ll check manual again…may have overlooked it. Thanks again…

Maybe the weep hole type plug was not used in the earlier motors. I am not positive on that. Good luck on this. I know it can be frustrating.

To All & W30post: After changing rear main seal twice…still leaks excessive…have retraced leak more thouroughly and found that lhe leak may be from what appears to be an incorrect ‘threaded plug’. Ufortunately this required dropping tranny, removing oil pan, pump, flywheel cover, housing etc. to expose rear of engine and the end of crankshaft and metal panel bolted on the rear of engine block

The excessive oil was around the plug and looked like it was leaking from there… the plug was removed and one can see that it did not match the threaded block hole. With engine on an upright position, the plug is located on the right sie of the block (picute below shows block upside down). When plate bolts and plate is removed, there is a soft freeze plug on the left and a ‘threaded plug’ on the right. The bolt size is 7/8" and the thread number is 14, with what appears to be straight type threads rather than sloted.Don’t know at this time whether the plug has a weep hole from top to bottom or just at the bottom or none at all. Again, since the one we removed appears to be the wrong plug, both in length and in type of thread, which may be why it’s leaking through the threads.

Anyone familiar with such a ‘threaded plug’ in mid year cars or later year cars…what is its function and where does that hole channel go to…? W30post: You mentioned a ‘blind plug’ that has a weep hole on it…is it located in the same area…? I couldn’t find any other threaded plug that has a weeping hole on it…? Anyone that has or knows where I can locate such a ‘threaded plug’, or anyone with an old '54 Olds engine that is willing to part out…let me know? Anxious to get this Olds on the road and cruse…!

Wow, sorry you had to go through all this work to find the leak but you chased down the source… On the newer blocks the weep hole type was behind another soft plug and leaked onto the distributor gear.

I have never laid eyes on that style block. My guess is you will need a plug here since it is to the outside of the block. I would most likely jump to a forum like to get their insight on this topic. Lots of very knowledgeable folks on that board for just Oldsmobile vehicles. That board sees a lot of traffic also.

W30post: Thanks, it was your input that led us to continue and hopefully find the right source…in replacing the right ‘threaded plug’. I’m placing another questions regarding new found source, hopefully someone out there some insight, but also going to other forums as you suggested. Thanks again…