replacing the rear main seal in a 67

[William G.]

Hello,

After rebuilding the 327 engine and reinstalling it in my 67, after initial start up, there was oil under the car. I have visually inspected as much of the rear of the engine area as I can see, so I suspect I had the wrong main seal in the gasket kit. I have since purchased the correct seal, according to a Restorer Magazine article and will be doing the repair this spring.
What I would like to know is if anyone has done this repair without removing the engine from the car?

Bill

[Edward J.]

Re: replacing the rear main seal in a 67

Bill, I always like to check the valve cover gaskets at the rear portion of the head, they tend to leak down the back of the engine and make the leak look like the oil pan or rear seal. Also the rear seal on the intake manifold can have a leak at the corners All easy to inspect, I take a finger and run it along the lower edge of the valve covers, and rear side of intake. if all looks good, recheck the oil pan torque. I always add a few extra pounds to the torque wrench once its been run a few warm up cycle's.

[Joe R.]

Re: replacing the rear main seal in a 67

Bill,

Yes, I have done many rear seals, even on a 58 with a rope!

Don't worry! It's not a hard job and we're here to help.

JR

[William G.]

Re: replacing the rear main seal in a 67

Thanks guys,

All of this started two years ago in late May when I decided to reinstall the original 327 in the car. I had rebuilt the short block the year before. I've worked on a lot of cars over the years and pulled the engine out of this car twice before, so I was not expecting for it to take all summer and fall.
Once I had the engine in and started the first time, there was a lot of metal banging going on. Concerned it might be a loose rod cap, or main, I dropped the pan. All was secure on the bottom end. The noise was caused by missing one pair of rocker arms. Got called into supper half way through the process of setting the lifters! It was a good thing I found that, as I also found a rocker stud that was pulling out. Had to take the head off and go back to the machine shop!
After getting everything back together, now in late November, with temperatures falling into the low forties, I got it fired again. The next morning I found the puddle of oil under the car. I am really hoping it is the oil pan gasket, but I would think if it were that, I would see oil dripping off the drain plug and I did not! The next week, I started the car and drove it from my workshop into our garage and sealed it up in the winter bag.
This past summer, I unzipped the bag just to check for mice and to put in more mothballs. Looked in the pan I put under the rear of the engine and there was again an 8" puddle of oil. I've already declared to the wife, I will fix the car this year, protest from her, or not!

Bill

[Joe L.]

Re: replacing the rear main seal in a 67

Thanks guys,

All of this started two years ago in late May when I decided to reinstall the original 327 in the car. I had rebuilt the short block the year before. I've worked on a lot of cars over the years and pulled the engine out of this car twice before, so I was not expecting for it to take all summer and fall.
Once I had the engine in and started the first time, there was a lot of metal banging going on. Concerned it might be a loose rod cap, or main, I dropped the pan. All was secure on the bottom end. The noise was caused by missing one pair of rocker arms. Got called into supper half way through the process of setting the lifters! It was a good thing I found that, as I also found a rocker stud that was pulling out. Had to take the head off and go back to the machine shop!
After getting everything back together, now in late November, with temperatures falling into the low forties, I got it fired again. The next morning I found the puddle of oil under the car. I am really hoping it is the oil pan gasket, but I would think if it were that, I would see oil dripping off the drain plug and I did not! The next week, I started the car and drove it from my workshop into our garage and sealed it up in the winter bag.
This past summer, I unzipped the bag just to check for mice and to put in more mothballs. Looked in the pan I put under the rear of the engine and there was again an 8" puddle of oil. I've already declared to the wife, I will fix the car this year, protest from her, or not!

Bill

Bill------

If you decide that the rear main seal is the problem, you need to carefully inspect the seal surface on the crankshaft. If the surface is damaged in any way, especially grooving or nicks, installing a new stock-type seal is not going to help, at all. If the only damage is a circumferential groove caused by the old seal, you can get around this by using a special seal with an off-set lip. Other damage may be irreparable.

In addition, when installing the seal, you need to follow the instructions in the factory service manual and apply sealer to the area adjoining the seal ends as depicted in the manual. Failure to do this WILL result in a leak.

[Mark E.]

Re: replacing the rear main seal in a 67

The FSM has a detailed procedure for replacing the RMS. Follow it closely. Also, this forum has several threads with a lot of good tips.

As you search for the leak's source, remember oil only leaks past a RMS while the engine is running, so dripping stops a few minutes after shutdown. Oil leaking past valve cover gaskets tends to drip longer after shutdown (hours, maybe a day or two) because oil will pool at the rear of the heads. Oil leaking past the drain plug will drip continuously with the engine running or not.

[Michael M.]

[Joe L.]

Re: replacing the rear main seal in a 67

I would just add a recommendation for the Fel-Pro 2912 seal and not the 2900. The 2912 is more expensive, but it’s a fluoroelastomer (brownish in color) compared to the 2900, which is silicone and blue in color. The fluoroelastomer has superior heat and chemical resistance properties.

Just follow the Fel-Pro instructions using the installation tool and offsett the seal halves and main cap parting lines. Also apply RTV where recommended on the main cap.


The first pic shows half of a blue 2900 on the left and the 2912 on the right. The second shows where to apply RTV to the cap.

Mike------


The Fel-Pro 2912 or its GM equivalent, GM #10121044, are THE ones to use. The GM seal is often a different color than the Fel Pro but it's the same. I've actually looked at Fel-Pro 2912 that had GM #10121044 embossed on them. I'm sure that was a mistake but it confirms the source and quality of the GM part.

[Mark E.]

Re: replacing the rear main seal in a 67

Just follow the Fel-Pro instructions using the installation tool and offset the seal halves and main cap parting lines. Also apply RTV where recommended on the main cap.

Offsetting the RMS halves is one of those controversial practices... it's not part of the FSM procedure but many do it anyway. I follow GM's procedure with good results. What does Fel-Pro's instructions say?

Regarding sealant, I recommend an anaerobic product, not RTV, for the main cap. Use sparingly, and only in the shaded area shown in the FSM.

[Michael M.]

Re: replacing the rear main seal in a 67

Offsetting the RMS halves is one of those controversial practices... it's not part of the FSM procedure but many do it anyway. I follow GM's procedure with good results. What does Fel-Pro's instructions say?

Regarding sealant, I recommend an anaerobic product, not RTV, for the main cap. Use sparingly, and only in the shaded area shown in the FSM.

Here's a better pic of the Fel-Pro instructions.

[Mark E.]

Re: replacing the rear main seal in a 67

So it looks like Fel-Pro and the Service Manual differ about installing the seal with an offset.

The Service Manual is old... maybe GM has a TSB recommending installing an RMS with an offset?

[John M.]

Re: replacing the rear main seal in a 67

William,
I don't want to complicate the issue but I have twice seen leaks back there due to the pipe plugs at the back end of the oil galleries improperly
installed and tightened. Could be somewhat similar to the rocker arm at suppertime.. Be sure to have a look while you're under there.

[Jim T.]

Re: replacing the rear main seal in a 67

Do you have a picture of the installation tool? Looking farther in the posts I saw the supplied tool.

[Joe R.]

Re: replacing the rear main seal in a 67

As you search for the leak's source, remember oil only leaks past a RMS while the engine is running, so dripping stops a few minutes after shutdown. Oil leaking past valve cover gaskets tends to drip longer after shutdown (hours, maybe a day or two) because oil will pool at the rear of the heads. Oil leaking past the drain plug will drip continuously with the engine running or not.

I want to second Mark's observation that an 8" puddle of oil is unusual for a rear main seal unless the car was parked with the engine running for a long time. When the engine is not running there is very little oil against the inside of the rear main seal. The entire rear main journal is above the normal oil level in the pan.

You should probably check the oil level to make sure that the pan has not been over-filled, but aside from that I think the evidence points to something other than the rear main seal.

I once had a hard-to-find leak at the back of my '67 327 that turned out to be because the rubber seal at the back of the intake manifold had "squished out" at one end and left a large open gap into the lifter valley. The leaking oil covered a large area at the back of the block and made it hard to determine the source.

I suggest that you proceed methodically and make sure you determine the source of the leak before you start replacing gaskets. You mention that one head has been off and the oil pan has been off, so the possible suspects include a valve cover gasket, an intake manifold gasket, and the oil pan gasket. Also, as John MacRae has noted, the rear oil galley plugs are a possible suspect, since the short block is a fresh rebuild.

I seem to recall that there is a dye that can be added to the oil that will make the oil glow under an ultraviolet light. This might help you determine where the oil is coming from.

BTW, if you end up pulling the intake manifold, I highly recommend that you omit the rubber end seals and use a bead of RTV such as Permatex Ultra Copper instead. I first learned about this method from a posting by John Hinckley on this TDB, but since then I have seen it described in various car magazines as well. I have now used this method several times with excellent results. I think it is far more reliable than the rubber end seals that the factory used.

[Joe L.]

Re: replacing the rear main seal in a 67

I want to second Mark's observation that an 8" puddle of oil is unusual for a rear main seal unless the car was parked with the engine running for a long time. When the engine is not running there is very little oil against the inside of the rear main seal. The entire rear main journal is above the normal oil level in the pan.

You should probably check the oil level to make sure that the pan has not been over-filled, but aside from that I think the evidence points to something other than the rear main seal.

I once had a hard-to-find leak at the back of my '67 327 that turned out to be because the rubber seal at the back of the intake manifold had "squished out" at one end and left a large open gap into the lifter valley. The leaking oil covered a large area at the back of the block and made it hard to determine the source.

I suggest that you proceed methodically and make sure you determine the source of the leak before you start replacing gaskets. You mention that one head has been off and the oil pan has been off, so the possible suspects include a valve cover gasket, an intake manifold gasket, and the oil pan gasket. Also, as John MacRae has noted, the rear oil galley plugs are a possible suspect, since the short block is a fresh rebuild.

I seem to recall that there is a dye that can be added to the oil that will make the oil glow under an ultraviolet light. This might help you determine where the oil is coming from.

BTW, if you end up pulling the intake manifold, I highly recommend that you omit the rubber end seals and use a bead of RTV such as Permatex Ultra Copper instead. I first learned about this method from a posting by John Hinckley on this TDB, but since then I have seen it described in various car magazines as well. I have now used this method several times with excellent results. I think it is far more reliable than the rubber end seals that the factory used.

Joe------


Yes, a failed rear intake manifold seal is a distinct possibility. I also agree that the use of the traditional rubber seal included with the gasket set is absolutely not advisable. GM stopped using these end seals in the early 80's and changed to formed-in-place RTV. That's all I use and originality be damned in this case. I recommend either Permatex Ultra Copper or Ultra Black. Both are high temperature and extremely oil resistant.