Question for GTO guys...Olds guys

[IH82BL8]

I have a friend who has a '67 GTO with a '71 or'72 455 in it. The engine has been recently rebuilt but keeps blowing out the rear main seal. Any ideas what might be causing it?

Thanks.

 

[Stuart in MN]

Are you saying it has an Olds engine?

 

[regguy1]

What does "blowing out" mean? Do you mean he has a leak he doesn't know how to stop...or the seal is somehow being pushed out?

Most of those older engines had a graphite impregnated rope seal, not the greatest setup and most always had a "drop hanging" small weeping.

This is something difficult to answer on a forum like this, the leak needs to be evaluated by someone with expertise and who knows how and what to look for.

I'd ask: is it actually a rear main leak...maybe the back of the intake manifold or oil sending unit leaks and are being mistaken for RM leak? Cam plug in back of block....rear of oil pan gasket mis-installed? I've seen many leaks wrongly attributed to the rear main.

 

[Scott P]

A little more information like requested above would be handy. How much oil is coming out. When is it coming out, etc.

 

[tfi racing]

Does it have the PCV system connected and functioning?Sounds like excessive crankcase pressure may be the problem.

 

[wornoutoldman]

If it has a rope seal replace with this http://www.allpontiac.com/rearmain_seal.html

 

[GTO]

If it has a rope seal replace with this http://www.allpontiac.com/rearmain_seal.html

Good advice,just make sure you install it correctly.
Good Luck.

 

[Chris Adams]

I have a friend who has a '67 GTO with a '71 or'72 455 in it. The engine has been recently rebuilt but keeps blowing out the rear main seal. Any ideas what might be causing it?

Thanks.

Sounds like a crankcase ventilation problem.
Or too much blow-by, often caused by wrong size rings, tapered bore, ring notches lined up.

Start with the crankcase ventilation.
It should have positive ventilation, that is, a PCV valve on one side, a air inlet, preferably filtered on the other.
When the engine is under light light load the PCV ***** the blow-by, bringing air in through the filtered vent on the other side. When the engine is under high load, the PCV valve does not ****, and the blow-by must escape, normally out the filtered vent. If one or both parts don't work, the pressure tends to push the real seal out.
Check that first.

On a real race engine you vent the blow-by to the headers with an anti-backfire valve in the middle.

FYI, blow-by occurs on all engines, even ones with 'zero gap' rings.

 

[IH82BL8]

I assumed the only 455 was an olds engine.

The leak is coming from the rear main seal. He's replaced it 2-3 times since rebuild.

I haven't seen the car but apparently the seal is being pushed out of place and a lot of oil is getting past it as a result.

He suspects the PCV valve too, but I think it sounds more like hydrostatic pressure than air pressure. To me, if it were air pressure, it seems like the valve cover gaskets would go first.

 

[larry_g]

I'm guessing here that if your correct in thinking hydrostatic pressure then someone has probably plugged the drain in the main cap that prevents a buildup of oil pressure on the main seal. At no time should the main seal have pressurised oil on it. Next time it comes apart for a seal check for RTV in the drain, and for a good surface on the crank journal where the seal rides. Also check crank end play to determine if that may be a factor.

lg
no neat sig line

 

[Stuart in MN]

I assumed the only 455 was an olds engine.

Buick, Olds and Pontiac all had 455 engines. If it is a Pontiac, as mentioned above they used a rope seal for the rear main. They can be tricky to install, plus the original seals had asbestos in them and new ones don't, so they don't work as well. The BOP rubber seal in the link above is a good alternative.

 

[Chris Adams]

I assumed the only 455 was an olds engine.

The leak is coming from the rear main seal. He's replaced it 2-3 times since rebuild.

I haven't seen the car but apparently the seal is being pushed out of place and a lot of oil is getting past it as a result.

He suspects the PCV valve too, but I think it sounds more like hydrostatic pressure than air pressure. To me, if it were air pressure, it seems like the valve cover gaskets would go first.

Never the valvecover gaskets. I have seen the front and rear seal blown from the motor, without breaking a seal on the Valvecover gaskets. They will take about 30-60 lbs of pressure without losing seal, if they are cork, and siliconed neoprene will handle even more pressure. rope seals can't take twenty pounds. Even rubber crank seals start to weep at twenty pounds.

I would expect he is romping on this engine, the seal is going either at maximum vacuum or minimum.

Good luck with it.

 

[GTO]

Buick, Olds and Pontiac all had 455 engines. If it is a Pontiac, as mentioned above they used a rope seal for the rear main. They can be tricky to install, plus the original seals had asbestos in them and new ones don't, so they don't work as well. The BOP rubber seal in the link above is a good alternative.

The rubber rear main seal on BOP site is a Viton brand

 

[mrbelvedere]

I'd be checking for excessive blow-by or a defective PCV as well, the PCV valve should rattle when shaken, and blow-by should be evident on a hot engine with the oil cap off, the draft should be feel-able with a hand hovering over the opening, and get worse as the RPM's increase.

Just a note, in my experience, rope seals do not like synthetic oils at all.

Installing a rope seal properly is tricky, I'd go with a retrofit rubber lip seal as mentioned above.

 

[bgott]

Is he using a lip seal, and maybe he is installing it backwards?

 

[02hawk]

First of all....If it is a 455 it's probably a Pontiac Engine. The cause is too much crank case pressure...In a street pontiac, usually the PCV goes from the valley pan and gets vented into the intake. If the engine is not producing a good amount of vacuum under light load the oil will find the easiest way to escape....normally I have vented my Pontiacs with breathers on the rocker covers...or in the case of a high horse power deal, I vent from the covers to the exhaust collectors....In a race car you install a vacuum pump and venting is not required....The rope seal in the rear on a Pontiac is a weal spot. You get him to go to BOP performance and order a Viton rear main seal. This will solve the rear main leak.....

Sometimes the oil gets blown out the valley pan cover and goes to the back of the engine and it is a mess. guys sometimes think because of the volume it is the rear main seal.
Get him to go to www.performanceyears.com ....go on the forum...thats where all the pontiac guys hang out.

Putting an Olds engine into a Pontiac is heresy and requires a severe beating...Except for the 78 T/A's but I ain't goona talk about that

 

[69lm69gp]

The are a few little details in this thread that are incorrect. The original rope seal was made with asbestos and the replacement without the asbestos didn't work well. Then cam the BOP seal made of Viton (trade name of DuPont fluoroelastomer rubber). The BOP seal works well but can have issues if the rear main cap has been machined too much and the grove for the seal is no longer round. The newest seal is the graphite rope seal from Best gasket and all the reports over at the performance years forum is that it works well.

While none of this will necessarily solve the OP friends issue I felt it was important to pull together all the bits of information to make it clearer. I have been a member of the performance years forums years and I recommend your friend ask the question over there after doing some research as I am sure this has been asked there many times.

 

[GTOGreg]

If it is indeed too much pressure, which I would find strange for it to be emanting here instead of somewhere else, I would first check the PCV as others have stated. There are two good seals out now for pontiacs; the BOP seal and Best graphtite seal. I much prefer the latter in absence of the old asbestos style rope seals - those are the best but have been phased out obviously. They pop up now and and again on the Bay. Go with the Best rope seal and you will be fine. With the BOP seal, just make sure you have a concentric mating surface around the rear main journal and the cap.

 

[MBfreak]

I work quite a lot om MB engines from the sixties. Cast iromn block, alu oil pan.
After the last bearing there is a slinger ring that throws oil film off. The slinger ring is some 10 mm bigger in dia than the shaft and has a sharp edge. Then comes the sealing surface for the rope seal. The sealing surface has a "impeller" built in in the form of a very fine pattern made with a 120 grit paper at 40 degrees to the shaft axis and turned so as to pump oil back into the engine. There is a procedure in the old shop manuals from MB how to restore this using hand tools only. The rope seal is a graphite/rope type with a square section. Get hold of a dowel with the seal area dia-1 mm, and roll the seal in place with that, DO NOT HAMMER. The halves shall be cut off 0,5 to 1 mm proud of the surface of the block/pan. Needs a real sharp knife, seals are 12x8 mm and tough.
Lubricate with moly grease and assemble engine. Never leaks.

It is also possible to machine the block/pan to install a modern sealing ring.

Crankshaft must be straight to within 2/100 mm , and crankcake pressure must be low.


Has always worked well for me, over a period of 40 years and LOTS of engines.

Ola