Stupid question of the day -replacing rear main seal

[Gary S.]

Good morning to all. My car is out of storage and I am seeing some oil at the rear of the block/front of the bell housing on the cardboard drip mat that I put down. I intend to clean the bottom of the engine, oil pan, and bell housing with a detergent and then drive the car over the next couple of days to see where the oil is originating. I have been reading here that potential causes of oil are the rear main seal, front of the Muncie (obviously that would not be engine oil ) and oil pan leaks. I will investigate these over the next few days but my question arises from reading the 1966-82 Corvette Shop Manual, page 6-6. I have a really stupid question. If, big if I hope, I wind up replacing the RMS, the manual doesn't state that the transmission or bell housing have to be loosened or removed. Do these two need to be pulled back, in the event that I wind up going this route? I still have lots of investigating to do but wanted to read as much about this as possible. A search here provides a wealth of information to include the proper Fel Pro parts for both the RMS and oil pan and the techniques involved in this.

The car is a mid 40k mile LT1 with close ratio Muncie and very original with undisturbed drive train components.

[Joe R.]

Re: Stupid question of the day -replacing rear main seal

Gary,

Clean it and see where it drips. Would not be concerned with an occasional drop or two from the rear main seal. There are not many that aren't a little wet especially after a PA winter.
You don't have to remove the trans to get to the seal. Just remove the oil pan.

JR

[Edward J.]

Re: Stupid question of the day -replacing rear main seal

Gary, the oil pan can be removed without disturbing the trans or bell housing. the older small block Chevy engines oil leaks are among the worst to try and make them 100% leak free. Do a careful inspection of the rear corner's of the valve cover, this is a common area that runs down the back of engine and looks to be a oil pan/ rear main seal. this is a easy inspection just take your finger and wipe the corners and look for a leak.

[Gary S.]

Re: Stupid question of the day -replacing rear main seal

To add to my initial post, this all started last winter as I prepped my 72 for hibernation. I changed the oil and filter but only got 3 quarts of oil out of the pan. I was startled to say the least. I put a plastic piece down (actually an old election campaign sign) down because of the occasional drip from either the transmission, differential or engine and this is in a friend's garage. Yesterday, upon removing my plastic board, I noticed a fairly large pattern of oil under the oil pan/bell housing, perhaps 4-5 tablespoons, sitting on the surface of the board. Investigation showed a "ready to drop" drip on the bottom of the front of the bell housing and it was engine oil colored. In addition, while I know that Muncies are known to leak, I add a small amount to my Muncie about every other year.

Joe,
I plan on cleaning it today and driving it, getting things nice and warm. Then I will watch while it is on jack stands to see where this is originating.

Edward,
Reading the forum here I did see that valve covers can leak and I plan on checking that. I have owned this car for about 17 years and have never changed the VC gaskets so this is s possibility. In addition, after it is cleaned up and on jack stands I am going to inspect the back of the block.

thanks to all,

Gary

[Mark E.]

Re: Stupid question of the day -replacing rear main seal

Gary,

Neither the bellhousing nor transmission need to be disturbed to replace the RMS. Unbolt the idler arm from the frame, push the steering linkage down a bit, remove the starter, flywheel inspection cover, oil pan and windage tray. Rotating the engine so the timing mark is at 6 o'clock moves the crank counterweight up so you have easier access to the oil pump and rear main.

Take your time cleaning and prepping all mating surfaces, sparingly use anaerobic sealer on the shaded area shown in the manual, and make sure to install the seal with its lip pointing forward.

Good luck.

[Mark E.]

Re: Stupid question of the day -replacing rear main seal

Remember RM seals leak only while the engine runs, while drain plugs and valve covers continue to leak after shutdown. This may help locate the source. Several good threads about this.

[Gary S.]

Re: Stupid question of the day -replacing rear main seal

Mark,
I have spent the last day and a half reading all the threads on RMS leaks and Muncie leaks. I know I am not the Lone Ranger here.
Thanks for the comments.
Gary

[Carl N.]

Re: Stupid question of the day -replacing rear main seal

Also check the back of intake manifold, as it might be the leak.

[Joe L.]

Re: Stupid question of the day -replacing rear main seal

...the older small block Chevy engines oil leaks are among the worst to try and make them 100% leak free.

Edward------

Yup! If I ever found a Chevrolet engine with a 2 piece rear main seal that was absolutely, 100% leak-free, I'd be absolutely, 100% astonished.

[Gary S.]

Re: Stupid question of the day -replacing rear main seal

I have uploaded some files of the oil leak(s). This is getting interesting. I don't relish the idea of power washing so a rattle can degreaser may be in order along with warm water. As you can see there is more oil on the rear than anywhere else especially about the oil filter. There is oil on the front of the pan where it meets the block and you can clearly see where the oil is and isn't on that nasty looking pan. The fun part is that under the gunk below the exhaust manifold there appears to be missing paint in the shape of an "HT" that is handwritten in fairly large letters. Would this be an assembly line grease pencil designation?

Once some guests leave, I am going to wash this down and then drive it until nice and warm. Then I am going to let it sit for a while.

In reading search results here, I see that Fel Pro makes a one piece blue oil pan gasket. Has anyone had good luck with this and, of course, it won't judge well. Secondly, anyone care to share with me (so I don't have to search ) for the source of a good looking (judge-able) valve cover gaskets?

Thanks for all the hints so far guys.

Gary

[Mark E.]

Re: Stupid question of the day -replacing rear main seal

Hard to tell much from photos. The engine doesn't look as dirty as you describe, though.

Is that fresh oil on the block above the filter? That probably isn't from the RMS. Look at the valve covers, intake and oil sender. The oil in the front may be harder to trace... oil pan, oil galley plug, front cover, front seal...

Instead of using an engine degreaser, consider Dawn dish soap diluted in hot water and applied with a spray bottle. It works just as well, is much safer for your body and environment, and smells nice. Spray liberally but in a targeted manner to the engine when it's warm (not hot) to the touch. Let it soak, then use a soft bristle brush to work off the grime. Rinse with water, repeat as needed. This method is also more gentle on original markings you might find, and leaves no residue.

When nice and clean, you can more easily locate the leaks. You may need to resort to using an oil dye and UV light.

[Joe L.]

Re: Stupid question of the day -replacing rear main seal

I have uploaded some files of the oil leak(s). This is getting interesting. I don't relish the idea of power washing so a rattle can degreaser may be in order along with warm water. As you can see there is more oil on the rear than anywhere else especially about the oil filter. There is oil on the front of the pan where it meets the block and you can clearly see where the oil is and isn't on that nasty looking pan. The fun part is that under the gunk below the exhaust manifold there appears to be missing paint in the shape of an "HT" that is handwritten in fairly large letters. Would this be an assembly line grease pencil designation?

Once some guests leave, I am going to wash this down and then drive it until nice and warm. Then I am going to let it sit for a while.

In reading search results here, I see that Fel Pro makes a one piece blue oil pan gasket. Has anyone had good luck with this and, of course, it won't judge well. Secondly, anyone care to share with me (so I don't have to search ) for the source of a good looking (judge-able) valve cover gaskets?

Thanks for all the hints so far guys.

Gary

Gary------


It looks to me like you probably have some oil leakage from a variety of sources, including valve covers, oil pan side gaskets and end seals, and, possibly, rear main seal and front cover seal. You also have some leakage from the oil drain plug.

For the oil pan, I recommend the Fel-Pro 1 piece gasket. It's Fel-Pro OS34509T, assuming your oil pan is an original (which, based on condition, it looks to be). This is as good as it gets for oil pan sealing. Install it exactly per the instructions which come with it.

For the valve covers, I recommend Fel-Pro #1604 "Cork-Lam". These are a rubberized cork with a steel core. These have been around a long time but I've never found anything better. These are 1/16" thicker than original but that difference does not affect visual, installed appearance by very much. Yes, maybe some judges can detect the difference but so be it. If you want exactly original cork gaskets, Dr. Rebuild is where it's at. Either the Fel-Pro 1604 or Dr. Rebuild's are "4 hole" gaskets, not the common aftermarket and GM SERVICE "6 hole" gaskets. The "6 holers" are to accommodate 55-59 "staggered" bolt pattern valve covers as well as later style covers. These are especially "bad news" for small blocks with aluminum valve covers as they have to be trimmed to fit properly. This creates a weak spot in the gasket.

For rear main seal, use Fel-Pro #2912 or GM #10121044.

Your oil drain plug gasket was originally fitted with a nylon gasket. I expect that judges may look for this as the edges are visible. These nylon gaskets do not seal well. GM went through several iterations of improved gaskets which superceded the nylon. The latest, which has actually been around quite awhile now, is a gasket featuring a soft metal frame bonded to an elastomeric seal. These are GM #14090908. They appear very "hi-tech". They leak, too, though. So far, I have NEVER found an oil pan drain plug gasket that does not leak, at least a little.

If you use an aerosol degreaser, be careful not to get any on plastic or rubber parts; it will attack and degrade them no matter what it says on the can.

The "HT" you mention sounds like the engine suffix code often seen in crayon on the side of the block. However, the strange thing is that this code was last used for 1968.

[Gary S.]

Re: Stupid question of the day -replacing rear main seal

Mark,
Most of the oil is assumed to be fresh and, of course, the oil above the filter didn't migrate up so it must be coming down. I used detergent and hot water through my garden hose and I will let the engine dry tonight. I am going to diagnose the leak by driving it, once dry, and seeing where the leaks originate.

Joe,
Once I got under the car, it was obvious that there were multiple sources. I am going to take care of all the gaskets (thank you for saving me the trouble of searching for the valve cover gasket number) in the next day or so. If I need the RMS, I had already noted your response in several other posts about the Fel Pro 2912. I am going to try and take a picture of the crayon marking on the block. It was dirty, I was tired but there is either something like that there or it is a very interesting anomaly.

Thanks to all. Stay tuned for results.
Gary

[Patrick H.]

Re: Stupid question of the day -replacing rear main seal

I'd fix the others and leave the rear main seal & oil pan for last. For one, they can be done at the same time. Second, they take a lot more work to fix. The Fel-Pro one piece gasket works great and is reusable. However, it's bright blue, and even if you paint the edges orange the paint will likely fall off. I would think about trying some primer made for plastic followed by engine orange if I were going to do it again. Third, a lot of oil on that engine is coming from above.

I have fixed oil leaks by replacing the rear main... and not fixed them. My 71 leaks as it sits now, but its not worth fixing.

I also use ARP thread sealer on oil drain plug threads, and it helps. It only takes a tiny bit to work.

Your crayon marks should be CKY, written upside down.

For the valve cover gaskets, it sometimes helps to put a thin layer of Permatex copper RTV on the upper surface of the gaskets and then lay the valve cover on top of them. Do this on a smooth surface, glass if possible, and then place a weight on the valve cover. Be sure that the bolt holes all line up when you do this. A day later when the RTV has cured you can install them. In doing so you seal the gasket to the cover and eliminate one path for leaks, and don't have to rely on uneven torque from the valve cover bolts. I also use an inch-pound torque wrench when installing valve covers to be sure I don't overdo it.

[Gary S.]

Re: Stupid question of the day -replacing rear main seal

Good points Patrick. I have located some valve cover gaskets and they will be in my garage by noon tomorrow. I do agree, as I mentioned previously, that some of the oil seems to come from above, especially the left rear valve cover area as Mark E. points out. By actually putting the car on ramps and crawling under there it was obvious that the oil is mostly (hopefully) coming from above. This will be done is stages - no need to fix it if it ain't broken. The only guessing point is at the front of the oil pan where it has an obvious bit of oil as evidenced by my first photo. It is the dark spot directly in the center of the photo between the timing chain cover and oil pan gasket. That will be investigated after I do the valve cover gaskets.