# 1969 GTO rear main seal replacement



## GTOmoe (Jan 13, 2009)

Morning GTO Guys,

It appears I have a rear main leak which started sometime after the last oil change in late March this year, I just noticed after a long drive last weekend, the motor was completely rebuilt 4 years ago, seems a little strange it started now, although maybe not. Anyways very disappointed to say the least.

 A BOP viton seal was used. I am looking for someone to replace the seal. I am located in Algonquin Il. 60102. Any recommendations on who can do this would be greatly appreciated. Thank you


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## Lemans guy (Oct 14, 2014)

Before I pulled the engine to replace the seal; I would put in an "ME Wagner" dual flow PCV Valve. That often stops all these oil leaks. Especially one like yours with a newBOP viton seal. The seal leaks from too much crankcase pressure. the ME Wagner valve will pull a vacumn 99% of the time in your crankcase relieving that pressure. You would be lucky if your current PCV pulls vacumn 30% of the time.

The wagner valve is also tuned by you to your engine, with a vacumn gauge, so they dial in nice,...they are $130,...but cheaper than an engine pull and reseal. Try that first. Go to ME Wagne's website and review their data.

I have no connection with them, just use it and recommend it cause it works!


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## Mine'sa66 (Oct 30, 2019)

Lemans guy said:


> Before I pulled the engine to replace the seal; I would put in an "ME Wagner" dual flow PCV Valve. That often stops all these oil leaks. Especially one like yours with a newBOP viton seal. The seal leaks from too much crankcase pressure. the ME Wagner valve will pull a vacumn 99% of the time in your crankcase relieving that pressure. You would be lucky if your current PCV pulls vacumn 30% of the time.
> 
> The wagner valve is also tuned by you to your engine, with a vacumn gauge, so they dial in nice,...they are $130,...but cheaper than an engine pull and reseal. Try that first. Go to ME Wagne's website and review their data.
> 
> I have no connection with them, just use it and recommend it cause it works!


I agree with this 100%. If you want to do a test before you spend the money for the pcv valve, I'd rig a good old fashioned breather onto a valve cover. Might vent more than you want for everyday driving, but if your main seal stops leaking with a vent, you'll know the pcv will fix it.


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## PontiacJim (Dec 29, 2012)

Also, what size engine? The 455CI cranks have a factory serration on the journal that the oil seal sits on. The serration will tear up a Viton seal if it is not smoothed down. It was designed to work with the rope seal, not the Viton seal.


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## GTOmoe (Jan 13, 2009)

Mine'sa66 said:


> I agree with this 100%. If you want to do a test before you spend the money for the pcv valve, I'd rig a good old fashioned breather onto a valve cover. Might vent more than you want for everyday driving, but if your main seal stops leaking with a vent, you'll know the pcv will fix it.


Hi Jim,
Thanks for the response. I have a breather on each valve cover, so I think I am vented enough. The engine is the original 69 400 block which after the rebuild is now a 461 stroker, it was built by Coil Racing in McHenry Il. A new crank was installed, I believe it was a Scat or Eagle Crank , I'll have check with him on the crank serrations, although we discussed rear seal options at the time of rebuild and decided on the viton solution because I had a 65 Tripower GTO and used the BOP viton seal on that motor with no issues.


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## GTOmoe (Jan 13, 2009)

Lemans guy said:


> Before I pulled the engine to replace the seal; I would put in an "ME Wagner" dual flow PCV Valve. That often stops all these oil leaks. Especially one like yours with a newBOP viton seal. The seal leaks from too much crankcase pressure. the ME Wagner valve will pull a vacumn 99% of the time in your crankcase relieving that pressure. You would be lucky if your current PCV pulls vacumn 30% of the time.
> 
> The wagner valve is also tuned by you to your engine, with a vacumn gauge, so they dial in nice,...they are $130,...but cheaper than an engine pull and reseal. Try that first. Go to ME Wagne's website and review their data.
> 
> I have no connection with them, just use it and recommend it cause it works!


Hello Lemans Guy thanks for the message, I have a breather on each valve cover, so I think I am vented enough. I have read about the ME Wagner PCV earlier this year.


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## PontiacJim (Dec 29, 2012)

GTOmoe said:


> Hi Jim,
> Thanks for the response. I have a breather on each valve cover, so I think I am vented enough. The engine is the original 69 400 block which after the rebuild is now a 461 stroker, it was built by Coil Racing in McHenry Il. A new crank was installed, I believe it was a Scat or Eagle Crank , I'll have check with him on the crank serrations, although we discussed rear seal options at the time of rebuild and decided on the viton solution because I had a 65 Tripower GTO and used the BOP viton seal on that motor with no issues.



OK, the 400 crank will not have the serrations. I used the BOP seal on a former 400CI build with no issues either.


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## GTOmoe (Jan 13, 2009)

Yeah I am really not sure what happened, it was good for 4 driving seasons and then something went wrong. I read online somewhere yesterday when the car sits for long periods of time the rear main seals can get deformed into an out of round shape and start to leak. Not sure if that is the case. Joe


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## Lemans guy (Oct 14, 2014)

I would just note that vent and vacumn ain’t the same..you must have A PCV in the valley pan, and two air vents on the valve covers.....it could still hold quite a bit of pressure...

The vacumn positively reduces the pressure, A standard PCV may not reduce it enough.

my 461 strokes leaked from a brand new one piece bit on seal,....until I installed the Wagner valve...then no leak...so just a suggestion to maybe try before a bigger job....

you need the vacumn pulling hard and the fresh air vent to work correctly,.....And relieve the pressure.....


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## Lemans guy (Oct 14, 2014)

Look at this way,...vents allow pressure to go out the breathers....that is where you get the oil residue on the valve covers (Also your rear main seal)....the “Pressure” has to be relieved..

but the vents are not there nor designed to relieve pressure, they are designed to let fresh air in.

the PCV Vacumn relieves the pressure,by suction and thenthere is no pressure, there is a vacumn and oil does not-blow out the breathers or your seals....


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## Mine'sa66 (Oct 30, 2019)

Lemans guy said:


> Look at this way,...vents allow pressure to go out the breathers....that is where you get the oil residue on the valve covers (Also your rear main seal)....the “Pressure” has to be relieved..
> 
> but the vents are not there nor designed to relieve pressure, they are designed to let fresh air in.
> 
> the PCV Vacumn relieves the pressure,by suction and thenthere is no pressure, there is a vacumn and oil does not-blow out the breathers or your seals....


Agree totally.
I should have said to get it well vented and see if your seal leak lessens. If it does, you can be pretty confident that more positive ventilation will make it even better.
Sounds like it's pretty well vented. You could pull the guts or drill a hole right through the plug in the PCV valve to see if a greater pull will help. Might run funny (Idle poorly), and you don't want unlimited vacuum in there, but this is just a test to see if venting effects your seal leak in any way. Maybe a good idea to just get the adjustable one anyway, they're $100-something not $1000-something.


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## Lemans guy (Oct 14, 2014)

Good advice,...those Wagner valves are $130 or so....and you can put it in yourself

stay with it sounds like a cool car


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## GTOmoe (Jan 13, 2009)

Lemans guy said:


> Look at this way,...vents allow pressure to go out the breathers....that is where you get the oil residue on the valve covers (Also your rear main seal)....the “Pressure” has to be relieved..
> 
> but the vents are not there nor designed to relieve pressure, they are designed to let fresh air in.
> 
> the PCV Vacumn relieves the pressure,by suction and thenthere is no pressure, there is a vacumn and oil does not-blow out the breathers or your seals....


Morning,

After reading the replies, it definitively make sense, I will call Wagner on Monday. They do offer a 30 day risk free trail. You are right, its way easier and less expensive than pulling the motor, thank you for the help and explanations, its greatly appreciated. Joe


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## Lemans guy (Oct 14, 2014)

That is a good move,...it may fix it....it may not....but the Wagner valve will improve your engine running anyway, and extend it’s like.

talk to Wagner, you may have to set the cruise idle and cruise circuit on the valve more than once if the first try does not relieve the pressure, the normal setting on that 461 I think is 1 and 1/2 turns out initially. I had to go out 2 1/2 turns on the idle circuit (of the Wagner valve) to relieve the drip. Talk and work with them they are very helpful and knowledgeable.

it could be your seal is bad or flawed or catywampas in there and the Wagner valve won’t help....then you may still have to pull the engine.

But I would try the Wagner first, and keep it as it will do many good things for you going forward.


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## BearGFR (Aug 25, 2008)

PontiacJim said:


> OK, the 400 crank will not have the serrations. I used the BOP seal on a former 400CI build with no issues either.


My Eagle 400/461 stroker forged crank _does_ have serrations - FYI.

Bear


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## PontiacJim (Dec 29, 2012)

BearGFR said:


> My Eagle 400/461 stroker forged crank _does_ have serrations - FYI.
> 
> Bear


That's interesting. I stand corrected. I also read ALL factory Pontiac cranks have the serrations, but some are well worn down. From the Tin Indian website, "The only time we have seen the serrations be too aggressive on aftermarket cranks is when Eagle first came out with their aftermarket cranks which was quite a few years ago."

You can read the entire write-up here - Will Pontiac crankshaft serrations shred / chew up a Tin Indian Performance Viton ® rear main seal


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## 64since65 (Dec 11, 2019)

Perfect timing on this serration issue. I just took a photo of this yesterday on my engine and noted that the seal lip seems to straddle the serrations. Not sure how important that is to this discussion but thought it might be interesting to see. I figured at least some of the seal should survive even if the serrations caused any damage.









The seal is actually centered on the groove it sits in; it just doesn't look like it because of the angle of the photo. Everything but the seal surface is coated in oil because it will have to sit for a few day due to another issue and these cool nights and humid days are perfect for creating corrosion. I wiped the seal surface for the photo. You can also see some pitting outboard from where the seal lip will ride but the area _immediately _outboard from the serrations, where the seal lip will ride, is smooth.


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## 64since65 (Dec 11, 2019)

In case someone else does the same thing I did, read ALL the instructions carefully well before starting to put things back together. I got the seal sanded to fit correctly per the instructions and the main bearings in. Then I read the rest of the seal instructions which said that you should fill the anti-rotation holes with silicone. The silicone takes time to dry - 24 hours for full cure - so I also had to wait for that.


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## PontiacJim (Dec 29, 2012)

Thanks for the reply and pics as these are always needed and can be used by anyone having questions in the future.  Nothing worse than having to pull the engine after it has been installed and you were ready to hop in and drive.


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## Jetzster (Jan 18, 2020)

PontiacJim said:


> Thanks for the reply and pics as these are always needed and can be used by anyone having questions in the future.  Nothing worse than having to pull the engine after it has been installed and you were ready to hop in and drive.


Great info On all this, it may be obvious to all, but what exactly is the purpose of the serrations?thx


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## PontiacJim (Dec 29, 2012)

Jetzster said:


> Great info On all this, it may be obvious to all, but what exactly is the purpose of the serrations?thx


The engines originally used a rope seal. The serrations picked up a little bit of oil that created a micro-thin film of oil between the rope seal and the crank journal to lubricate and not burn up the seal.


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## GTOmoe (Jan 13, 2009)

BearGFR said:


> My Eagle 400/461 stroker forged crank _does_ have serrations - FYI.
> 
> Bear


Thanks for the reply, I see what happened when we open it up in the fall.


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## GTOmoe (Jan 13, 2009)

64since65 said:


> Perfect timing on this serration issue. I just took a photo of this yesterday on my engine and noted that the seal lip seems to straddle the serrations. Not sure how important that is to this discussion but thought it might be interesting to see. I figured at least some of the seal should survive even if the serrations caused any damage.
> 
> View attachment 136057
> 
> The seal is actually centered on the groove it sits in; it just doesn't look like it because of the angle of the photo. Everything but the seal surface is coated in oil because it will have to sit for a few day due to another issue and these cool nights and humid days are perfect for creating corrosion. I wiped the seal surface for the photo. You can also see some pitting outboard from where the seal lip will ride but the area _immediately _outboard from the serrations, where the seal lip will ride, is smooth.


Thanks for the illustration


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## PontiacJim (Dec 29, 2012)

To follow up, I went and looked as 3 crankshaft rear seal journals. All do have the serrations. First pic is a 1968 400, second pic is a 1973 400, third pic is my new cast crank from Eagle for my 455.

The Eagle crank, does have a more noticeably rougher serration which may be due to its newness. The factory cranks were very smooth. I am going to use some fine emery cloth to knock down the serrations on the Eagle crank.


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## GTOmoe (Jan 13, 2009)

Thanks for the followup Jim, I talked to my machine shop all the new cranks have it. I poured in a bottle of Blue Devil Rear main sealer and the leak has slowed down quite a bit. I also changed the PCV as well.


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## 65GTOproject (10 mo ago)

Lemans guy said:


> Before I pulled the engine to replace the seal; I would put in an "ME Wagner" dual flow PCV Valve. That often stops all these oil leaks. Especially one like yours with a newBOP viton seal. The seal leaks from too much crankcase pressure. the ME Wagner valve will pull a vacumn 99% of the time in your crankcase relieving that pressure. You would be lucky if your current PCV pulls vacumn 30% of the time.
> 
> The wagner valve is also tuned by you to your engine, with a vacumn gauge, so they dial in nice,...they are $130,...but cheaper than an engine pull and reseal. Try that first. Go to ME Wagne's website and review their data.
> 
> I have no connection with them, just use it and recommend it cause it works!


I totally agree just solved my oil leak on my stroked 400 with new seals.and eagle crankshaft after dialing it in it took three tries. Zero leaks as of yesterday. Mine only leaked at 4000 Rpms and up with fuel injection and Kauffman heads. Wagner is the right thing to try.


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