Oil leak after recent rebuild

[Roger G.]

I have a leak after a recent rebuild. Just noticed this the other day. The motor is a 69 427, just turned 1000 miles on the build. I first noticed this when the car was left to idle for about 20 minutes. There was about a 4 inch slick on the driveway, and it is dripping from between the bell housing and pan. The thing that seems interesting, is that I can take the car out for a drive, come home and park it, there will be only a couple of drops of oil the next morning, but if it sits and idles for 20 minutes or so, there will be a 3 or 4 inch puddle. I don't see anything from the heads or distributor, I'm thinking it may be the rear main seal, because it doesn't seem to leak when the motor isn't running.

Not sure if this is this is related, but I put a zinc additive in about 3 weeks ago at the advice of the builder. Could that be responsible?

[Edward J.]

Re: Oil leak after recent rebuild

Roger, I would take my finger and run it along the rear area of the valve covers and see if you get any oil. so much of the time I see oil leaks from the rear of the valve covers, another area is to look at the oil pressure line that feeds the gauge, Distributor base gasket area. Other wise try to re torque the oil pan gasket after a few hundred miles of driving the pan bolts tend to loose there torque some.

[Gary H.]

Re: Oil leak after recent rebuild

Use a mirror and a flashlight and see if you have a leak at the rear of the intake. Look on the drivers side and try to read the engine block casting numbers and see if the area is wet. Will present underneath the car like a rear main leak.

[Joe L.]

Re: Oil leak after recent rebuild

I have a leak after a recent rebuild. Just noticed this the other day. The motor is a 69 427, just turned 1000 miles on the build. I first noticed this when the car was left to idle for about 20 minutes. There was about a 4 inch slick on the driveway, and it is dripping from between the bell housing and pan. The thing that seems interesting, is that I can take the car out for a drive, come home and park it, there will be only a couple of drops of oil the next morning, but if it sits and idles for 20 minutes or so, there will be a 3 or 4 inch puddle. I don't see anything from the heads or distributor, I'm thinking it may be the rear main seal, because it doesn't seem to leak when the motor isn't running.

Not sure if this is this is related, but I put a zinc additive in about 3 weeks ago at the advice of the builder. Could that be responsible?

Roger------


I would say the symptoms you describe are most likely the result of a rear main seal leak. It could be the valve covers but I would more suspect a rear main seal leak here.

When installing these 2 piece seals, there are quite a few things that have to be "exactly right". First, there has to be no wear on the crankshaft seal journal. If there's any wear or damage (e.g. nicks, scratches), there WILL be a leak. Second, there has to be sealer applied to the areas adjoining the seal ends as shown in the factory service manual. Failure to do this and there WILL be a leak. Third, I recommend only using a high vacuum, fluroelastomer seal. Fourth, the ends of the seal should be "off-set" (i.e. so that one end is below the block surface and the other above the block surface).

By the way, you don't think that GM went to a one piece rear seal for 1986+ small blocks and all Gen V+ big blocks because the two piece seal worked just as well, do you?

[Mark H.]

Re: Oil leak after recent rebuild

I agree with what Joe said. The symptoms you describe are identical to what I had not only on my '76 but also on a '78 Camaro that I owned. Both times it was the rear main seal.

[Duke W.]

Re: Oil leak after recent rebuild

The rear main seal gets indicted for a lot of leaks, but if the front face of the flywheel is not wet from oil, the leak is from somewhere else.

Duke

[Roger G.]

Re: Oil leak after recent rebuild

Roger, I would take my finger and run it along the rear area of the valve covers and see if you get any oil. so much of the time I see oil leaks from the rear of the valve covers, another area is to look at the oil pressure line that feeds the gauge, Distributor base gasket area. Other wise try to re torque the oil pan gasket after a few hundred miles of driving the pan bolts tend to loose there torque some.

Thanks Edward, that would be great if the oil pan bolts solve the problem

Roger------


I would say the symptoms you describe are most likely the result of a rear main seal leak. It could be the valve covers but I would more suspect a rear main seal leak here.

When installing these 2 piece seals, there are quite a few things that have to be "exactly right". First, there has to be no wear on the crankshaft seal journal. If there's any wear or damage (e.g. nicks, scratches), there WILL be a leak. Second, there has to be sealer applied to the areas adjoining the seal ends as shown in the factory service manual. Failure to do this and there WILL be a leak. Third, I recommend only using a high vacuum, fluroelastomer seal. Fourth, the ends of the seal should be "off-set" (i.e. so that one end is below the block surface and the other above the block surface).

By the way, you don't think that GM went to a one piece rear seal for 1986+ small blocks and all Gen V+ big blocks because the two piece seal worked just as well, do you?

Hello Joe, would the crank seal journal be turned normally during the rebuild?

The rear main seal gets indicted for a lot of leaks, but if the front face of the flywheel is not wet from oil, the leak is from somewhere else.

Duke

Hello Duke, can the front face be seen with the bell housing on?

[Joe L.]

Re: Oil leak after recent rebuild

Thanks Edward, that would be great if the oil pan bolts solve the problem



Hello Joe, would the crank seal journal be turned normally during the rebuild?



Hello Duke, can the front face be seen with the bell housing on?

Roger-----


The crank seal journal is usually not machined when the crank is otherwise machined. If it were, the rear main seal would not work properly. There are no "over-size" rear main seals available. However, there are special rear main seals with a displaced lip which can be used to avoid worn (e.g. grooved) areas.

The front face of the flywheel can be observed by removing the inspection cover. This is quite easy. However, you do need to remove the starter first.

[Scott M.]

Re: Oil leak after recent rebuild

Was a Fel-Pro one piece oil pan gasket used? If so, if RTV is not applied at the mating areas at the main cap and timing cover drips can occur.

[Roger G.]

Re: Oil leak after recent rebuild

I got my car out of the shop today. I took it to Chuck and David Anderson here in Fort Worth. Their shop is full of really cool cars... There was a Duntov LT1 they were working on when I dropped mine off. They are very patient, and take time out to explain things. I can highly recommend them to anyone in the North Texas area that needs work done on their corvette.

Anyway, the rear main seal was the culprit, there was a no name seal used for the recent rebuild, which was done in another shop, out of state. They replaced the no name seal with a Felpro seal. The crankshaft was good, with no grooving, so that was good news.

I also got got them to curve the distributor on their sun machine, and I can't believe how good it runs now! It has really come to life at the lower rpm range.

[Mark H.]

Re: Oil leak after recent rebuild

Thanks for the update. I learned a long time ago to never say, "It's gotta be this" or "It's gotta be that", but with the symptoms you described I was fairly certain the rear main seal was the problem.