Rear Main Seal

[351c1971]

My mechanic had problems with the rear seal in the Fel-Pro 351c engine overhaul gasket kit. I believe he used a Mahle rope rear oil seal. Also, the hatched oil reliefs on the rope seal crank will have to be ground off to use a rubber seal. Otherwise, it will leak.

 

[Steve McMahan]

I wish I had a solution for you. It sucks to spend the money you did and have this annoying issue. I’m in then same boat, but not in the money department. Since mine was a new crank sleeve job, and a one piece seal to boot, I guess I have no one to blame but myself.

It doesn’t help me feel better about it, but I’m going to try and live with it this next year; have a great drip pan with the Ford logo under it and the leak isn’t so bad that the likely undercoating I’m going to get will be minimum. I’ve decided driving it around, only local drives, is more important to me that pulling it and trying again.

So, whatever you decide, know you’re not alone in the dammed if you and dammed if you don’t camp. I think this hobby required it.

 

[Bobby]

Bobby,
I didn't see this mentioned but, a note from a previous post stated that the flywheel bolts should have sealer applied when an aftermarket crankshaft is used in a build.
Thanks, Jay

The crank flange is not in contact with the rear of the block and spins free in the bell housing. putting sealer on the flexplate bolts would be moot.

 

[351c1971]

• My new Ford flywheel bolts came with Teflon tape on the threads.
• The ARP flywheel bolts did not.
• The Ford shop manual calls for coating the flywheel threads with "oil resistant sealer".
• I have also seen red Loctite recommended to seal the threads on the flywheel bolts.
• I used blue Loctite to seal the threads on the flywheel bolts on my "H" code 351c.​

I guess there are differing opinions on this.

 

[c9zx]

Most, if not all of the aftermarket crank flywheel bolt holes are through drilled. If no proper sealant is used oil will come around the threads. Guess how I know this. I hope you get it fixed. Chuck

 

[boilermaster]

Bobby,
You might try researching Fel-Pro 2902 rear main oil seal for 351c and 351w.
Drag racers used to run them when using stroker cranks.
The main difference seems to be all about the existence of the ( hatched grooves } or lack thereof.
Supposedly this seal had it's own grooves for use of a stroker crankshaft that did not.
This seal was discontinued by Fel-Pro, but folks still claim to use them.
as c9zx stated about the thread sealant, I put that ---- on everything pertaining ford crank flywheel bolts.
Also manual and automatic's use different length bolts at the crankshaft rear.
Boilermaster

 

[donkost]

I wanted a little more pep for my pony. This stang did not have the performance suspension as it is an H code as built. I dont plan on going to the strip nor do I plan on losing control, totaling my babe and getting myself killed. The HP is there if I need it but I want to go balls to the wall it will be for a few seconds and not trying to get a 12 second quarter mile. Way back when.....all the muscle cars that were customized had the jacked up rear....it was cool and still is for me!

My personal preference is a stock "ready to pounce" stance, but the rear lift on your car is very tastefully done. Yes I remember those days and pretty much everyone did it. Rear main seals can be tricky on a number of different engines. The rear main seal on the Pontiac 400 in my '68 GTO weeped a bit decades ago. At least your rear window is not perpendicular with the ground!

 

[Spike Morelli]

I just want to hit on a few points here. There was some mention of a "3/8ths rear crankshaft spacer that would cause the timing chain to bind".....FALSE
The crankshaft thrust bearing is the #3 main bearing ,and therefore, is only adjusted a matter of thousanths of an inch, prior to crankshaft installation.
Someone mentioned never hearing about useage of RTV on main cap and seal halves.....FALSE, You must apply a small amount across the cap surface sides, where it sits against the bottom of the block to prevent oil seepage. Some assemblers will install the main seal with no RTV, if it works for you, fine. I prefer to put a very small amount on the seals where they sit in the groove, stagger the parting lines, and carefully, sparingly, put a dab on each end. While we're on the subject of main sealing, the original oil seal was a rope, and is , even today, a good and reliable seal. However, most builders and enthusiasts prefer the neoprene or silicone two-piece units. Many of these "modern day mechanics" lack the tools and skills to effectively install and utilize rope seals. On top of this, many assemblers and hobbyiests fail to realize that these cranks have a Factory knurling on the sealing surface, designed to pull oil towards the crankcase to inhibit seepage, and that this knurling must be polished down, when using a modern two-piece seal set. Believe me....if these Jackwagons didn't see the pin in the rear main cap seal groove, they didn't see the crank knurling either, and shouldn't be doing engine work. The assembler must apply an assembly grease to the crank surface, or the seal can burn up and leak. Maybe they have previously only worked on Chevys.
Post #15 has me baffled. Why would anyone try to put in piston #1 ( or any pistons at this point ) , if the rotating assembly was in a bind??????
Now, "The machinist mentioned that the rings were a tight fit", RED FLAG, any competent machinist will at least check, if not gap specifically, all of the rings, prior to any assembly, including the oil scrapers, and a complete deburring.
Honestly, based on what has been said, this engine build makes me concerned, I believe the term these days is "Sketchy"

 

[boilermaster]

Spike Morelli,
Just a little clarification here.
I stated that I never heard of using RTV on seal halves and rear bearing caps (very true), I prefer to use an anerobic sealant ( does not require the presence of air to cure).
The 1972 shop manual states (pg.21-01-11) to dip the seal halves in clean engine oil.
it also states do not apply sealer to the area forward of the side seal groove.
A thin coat of oil resistant sealant is to be applied to the main bearing cap at the rear top mating surface ( to seal the rubber end seal).
What I do find interesting is that the official shop manual states that for 1972 model engines (except 240 cid use a split lip seal. I have no idea if ford did away with the (factory knurling or not.
The 1971 Boss 351 was reported to have come with a split lip rear main seal, however, I cannot substantiate or disprove that claim.
What is clear is that Bobby is using an aftermarket stroker crank, and I don't see that he stated (or knows) if his crankshaft has the knurling's that would be a great question for him to ask the manufacturer, as well as what seal works best with their applications.
Boilermaster

 

[Spike Morelli]

Boilermaster, It's OK, if anerobic style sealant works for you, then by all means do what works. Some people prefer it. my intention was to verify that, yes, RTV is commonly used. "Anerobic" sealants were not in common useage when these cars were originally built. I was the primary engine builder at Valley Head Service in Los Angeles, for 14 years, before moving here to Boise Idaho, where I continue to do engine assembly work for Westside Racing Engines. I have been employed in this capacity many years, and I don't think I have mislead anyone in my observation of the afforementioned procedure. I hesitate to even comment lots of times about what I read now and again on the boards, because I don't want anyone to be offended, or think that I'm some know-it-all, however, I do have many years of hands-on experience with most ALL domestic makes, most vintage engines and a smattering of Import engine work.
It is apparent that there are a number of "hobbiests", that don't build engines for a living, that are trying to find answers to their dilemas. Hopefully, I've helped.

 

[boilermaster]

Spike, no offence taken whatsoever
I wouldn't call myself a hobbyist either 20 + years of dealership experience.
Now days I'm just an old, retired guy that never gave up working on cars.
Today I watched a half dozen video's on rear main seal installation, and none met with my approval.
and I fully understand that anyone can join and participate on a forum, regardless of knowledge base.
100% want to help Bobby get this issue resolved.
Boilermaster

 

[Cleveland Crush]

Hello all! I’ve been working my 1972 Mach 1 since purchased in April 2018. Recently, I had an engine built earlier this year. It’s has 1972 CJ 351 block and is stroked to 393 with an eagle rotating assembly and trickflow 2V aluminum heads, etc, etc. I had it machined and assembled at a local machine shop and then had it dyno’d. During the dyno the rear main seal blew out. I returned the engine to the machine shop to have the seal replaced. I provided a new fel-pro rear main seal for installation. The machinist dug the bad seal out of the trash and showed it to me. It appeared to be heat fatigued and brittle. I figured that it was the result of the high rpm’s of the dyno and the initial break-in. After dealing with rough idle issues and shifting problems with the new rebuilt AOD transmission now the rear main is leaking again! What gives? Any ideas or fixes?

Bobby, Is your engine only leaking at the rear seal? Check the front seal behind the balancer for leaks also. This could help verify potential line bore issues. Secondly, do a leakdown test to determine what level of blow-by you have. I'm using positive thinking here...hopefully and maybe your rings are not seated; no main seal will stand up to excessive crank case pressure. Good luck on that annoying issue and keep us posted.
Chris