420A rear main seal is killing me

[iron bird]

alright im to the point of hitting my 98 gs with a sledge hammer . i just replaced the rear main seal twice and both times it has leaked. i dont know what i am doing wrong or what im missing.

 

[VelocitàPaola]

Did you lube the inside of the seal with oil and lightly coat the outside with black RTV before installing?

 

[iron bird]

i did oil but no rtv

 

[1whitegsx]

You shouldn't have to use rtv on the outer part of the seal unless the mating surface is scratched or deformed in some sort. Grease works a little better on lip seals just for initial start up too.

 

[VelocitàPaola]

Corbin recommends a thin film of oil on the inside of the seal and RTV on the outside of the seal:

2GNT.com - A_Proper_Rebuild

I've always followed his recommendations when rebuilding engines and I've never had a problem.

You may also want to be sure the seal recess in the block and the crankshaft itself is sanded and free of any burrs.

 

[iron bird]

so is the seal suppost to sit flush with the block or pushed all the way in?

 

[VelocitàPaola]

It should sit flush with the block.

 

[iron bird]

alright i have no idea why its leaking the it stumps me?

 

[VelocitàPaola]

Are you sure it's not the head or one of the freeze plugs that's leaking?

 

[iron bird]

well the tranny was covered in oil and its shooting everywhere so the only thing i can figure is the rear main seal with the symptoms

 

[pboglio]

Is it leaking thru the static side or dynamic side?

 

[iron bird]

what do you mean by that?

 

[VelocitàPaola]

The transmission? Do you mean the inside of the bell housing, or is the whole transmission literally covered in oil? If it's the outside, then I'd say to start looking elsewhere...

 

[iron bird]

yea the inside of the bell housing had oil all through it

 

[pboglio]

Could also be an input shaft seal, that would be a leak coming from the other direction but still in the bell housing. Other than that, replacing the rear main seal is straight forward. Either you have a nick on the crank, or a nick on the bore that retains the outer seal. Or, the crank is not concentric with the retaining bore which would pull the lip away from the crank surface opening up a nice gap. This is the only way 2 seals are going to leak straight away. OR, you have massive blowby that would pressurize the entire oil pan assembly but I'd have to see what the pressure rating is for energized lip seals, it would have to be a fairly high pressure to do it.

 

[bullettdsm]

Could also be an input shaft seal, that would be a leak coming from the other direction but still in the bell housing.

Yup. The other "usual" culprit in that area. Are you sure you're loosing oil and not tranny fluid?

Other than that, replacing the rear main seal is straight forward. Either you have a nick on the crank, or a nick on the bore that retains the outer seal. Or, the crank is not concentric with the retaining bore which would pull the lip away from the crank surface opening up a nice gap.

This is also a possibility. partsdinosaur does sell a kit for that; 99128 C/R Speedi-Sleeve 1.257" - 1.263"

Now, you spoke about where the seal should sit. Sometimes, the spot where your seal seals on the crank, gets a wear line. To combat this, you leave your seal just 1/16th or so above flush fit. You are basically using a different part of the crank for the sealing point. Some old Mitsu guy have recommended that you do this for any crank seal install. I don't, but I haven't run into that problem yet.

OR, you have massive blowby that would pressurize the entire oil pan assembly but I'd have to see what the pressure rating is for energized lip seals, it would have to be a fairly high pressure to do it.

I'm thinking this is a bit more tongue in cheek, but an outside possibility situation. Our engines generally leak by the cam seal or the valve cover seal if there is blow by. But not out of the realm of possibility.

If that amount of blow-by was the case, then you would probably have a problem with performance.

My suspicion is the first thing that pboglio mentioned; the input shaft seal. If its not the crank seal, its generally the input shaft seal.


MB

 

[pboglio]

What you mentioned about a "wear" line reminds me of my last project. We were collaborating with Windy City Seal/Saint Gobain to design a dynamic lip seal for one of our Slushi machines. The wear surface was actually a ceramic coated stainless steel machined stub. Reason for this was that the microbes in the mixing barrel would eat the sugar in the ice and shit acid completely etching away the unprotected stainless surface on previous stub designs causing some nice leaks.

I want to say a dynamic seal in that size has a maximum shaft-to-bore misalignment of about .008" from what last they told me a spring energized seal could handle. There are minimum runout, shaft-to-bore misalignment, min. shaft diameter specs on Saint Gobains website, they probably produce that rear oil seal. The internal energizing spring is there to clamp down on the shaft if there is some wear or undersizing.

Figured I'd share, I did a shit load of FEA analysis designing a dynamic seal that would take massive misalignments and still clamp down tight and not leak without going to a multi-piece floating face seal.

 

[iron bird]

im gonna have to wait until i have another break off school but im going to look at the input shaft seal. the crank has no groove thats the first thing i checked for.