Leaking rear main seal - sometimes!

Have you considered the source of the oil to be ZF oil leaking from a front input shaft seal?

Is it clear that the leaking oil is engine oil?

Larry

quote:

Is it clear that the leaking oil is engine oil?

Yes

Hi Push, crankcase pressure is a good thought.... What are you running for valve cover breathers?

factory Ford stock crank or stroker?

I'm using a PCV system, set up as described by the manufacturer. A breather in one valvecover connected by a hose to the airfilter, and a pcv valve in the other valvecover connected to carburator vacumm.

The engine IS a stroker, 4.17 stroke 427 9.5" Deck Winsor.

Christian should the PCV not be connected to Manifold Vacuum to work properly? and have you checked it is not blocked etc.?

I'm using a baseplate from a Holley Ultra which has both a power brake port and a PCV port.

I'm actually running them reversed, i.e., I'm using the PCV port for the brakes and the brake port for the PCV. To my knowledge it shouldn't make a difference as (I think) the ports are similar.

I haven't checked if the PCV port is blocked

Christian, like most things DeTomaso, repairing the seal is not a straightforward fix. This is because early 351-Cs used a 'rope-seal' in the rear main, retained by a small spike that prevented it from spinning. Later engines used a two-piece neoprene seal without the spike. From the serial #, your car may have either type seal if its never been overhauled. The rope seal is no longer available and in any case was tricky to install correctly so it didn't leak when new.

The later seal retrofits into early blocks by removing the oil pan, then the rear main cap and seal. With a small hammer & dowel, drive the little spike clear thru the main cap so it falls out the back of its through-hole. Seal the remaining hole in the main cap with a spot of RTV. Now the later two-piece main seal will fit the early cap perfectly. My spare engine (1970) had one of these and when I rebuilt it in 1992, I switched seals. Still running with no leaks!

I hope your car has been updated to late factory specs with a removable under-engine crossmember and e-brake bracket. If not, the engine & ZF must come out to drop the oil pan, as the early factory-welded crossmember will prevent pan removal. Good luck-

If it is just a few drops on the Floor it might be worth just to learn and live with it

It does not take many hot drops of oil behind the swirl of 4000rpm´s behind the Flywheel to look a lot worse than it in fact is??

btw Bosswrench it is a Windsor.

I had the same symptoms with my engine, which I also thought was the rear main seal... Turned out that the oil pan was leaking at the rear of the block - there was a slight twist to the pan's mounting surface. When I put the engine back in, I resealed the pan with some extra RTV back there, and no more leak!

as it turns out aftermarket cranks (stroker cranks) usually don't have the oil slinger that the factory cranks have. lots of guys battling rear main leaks curse the standard neoprene flavor of the day rubber seal that never has an issue with a stock crank, only to find that the now discontinued can't get them any more Super Duper fluoroelastomer seal doesn't do any better than the regular seal. then they try to blame it on the diameter of the sealing area of the crank, nope, the diameter's correct. try another Super Seal, still leaks ...

my $.02 is that there's no integral slinger on the crank & if there was it wouldn't be leaking. here's a pic of a damaged rear oil slinger on a stock crank, pretty sure stock Windsor cranks have the same?

http://351c.net/board/uploads/...eecef40db61dc221.jpg

Sirs,


I have been told that the old FelPro *brown* rear main seals worked well compared to their new replacements, which are black(?). The Speed Talk Engine Tech forum has several comments from engine builders about the lower quality of the new seals and the increase in leaks. IIRC, the good ones were made of Viton (?).

There are some sources for those. Apparently, Cometic makes a pricey brownish rear main seal. Does anyone have any experience with the Cometic rear main seals??


Warmest regards, Chuck Engles

With one h---uvalota work, a 351-W (also marked 'for 351C') teflon one-piece rear seal from Rock Auto can be adapted to a 351-C. It takes careful machining to cut away the std seal holding grooves in the block and rear main cap, but then the one-piece supposedly-lower-friction 'racing' seal will fit. I did this for a friend a few years ago but as it wasn't my engine I can't say how it lasted.

I'd consider this a 'last resort' type of mod since it alters a rare Cleveland block. Dunno- looking at the result, it may be possible to fabricate a filler piece that once again accepts the std two-piece main seal.

And although this post was about a leaky rear main, remember that many parts houses will try to sell you a Windsor FRONT main as '351C equivalent' as rear Cleveland front seals are getting scarce. Sure, it fits but the identically sized Windsor front seal has no locating lip so you have to be very careful in seating the Windsor seal to the right depth in a Cleveland front cover. And R&R-ing such a seal requires pulling the Cleveland front cover off the block to drive the lip-less seal out.

Dear Bosswrench,


Ah, I was not clear. The fancy Cometic rear main seal is a standard two piece deal. It is NOT the one piece deal that requires the special machining.

So....anybody with experience or second hand knowledge of the Cometic rear main seals?

Warmest regards, Chuck Engles

put ' Cometic rear seal ' into the search bar here http://351c.net/board/index.ph...all-new-topics-here/

and here http://www.network54.com/Forum/119419

not the google custom search but click on the word 'search' in the forum header

Dear 4V&Proud,

Excellent. Thanks.

Chuck Engles

another stroker specific factor that just came to mind, the increased stroke may be adding to the turbulence / pressure in the lower crankcase?

I started thinkin what's the common demoninator between 351C & 351W based strokers having rear main seal problems, 1st thing I came up with is the stroke. then take away the slinger & the seal gets overwhelmed

more breather may help?

Thanks for the comments, also the ones about the 351C seal :-). That's a very valuable diskussion for everybody. I'll consideer that when I rebuild my original 351C.

The motor I'm having the problem with is as mentioned a 351w. It's a later post-83 block with the one-piece rear seal. I'm pretty sure, that when Ford changed the 351w and 302 blocks to the one-piece in late '82, the cranks were changed too. I may stand corrected here. Post-83 Ford cranks doesn't have the slinger I think. The 5.0 cranks doesn't either. So all the aftermarked stroker cranks may follow the designfilosofi of the later crank!?

In most cases, from what I've read, the one-piece is a much better design, that normally last the engines entire life, in contrast to the older two-piece.


In reality I have no other options than to try and change the one-piece seal to a better one or try to reduce crankcase pressure. Luckily, replacing the seal is pretty easy once the transaxle is out.

Any suggestions as how to improve crankcase ventilation?

Make sure the oil isn't seeping through the threads on the flywheel attaching bolts. They need sealer on them.

quote:

Any suggestions as how to improve crankcase ventilation?

what type of rocker covers do you have?

did you mention that the PCV system is in place & working?

The valvecovers are fabricated aluminum with baffles.

The pcv system is in place and I assume it Works. How do I test if it is so?

pull the PCV valve from the valve cover & hold your finger near the suction hole. it should grab your finger to it with the vacuum suction

the opposite side valve cover should have a breather or tube to the air cleaner housing for fresh air intake

the PCV valve draws fresh air from the opposite side valve cover, through the crankcase pulling out any blow-by smoke with it

adding an additional breather vent to the fresh air side cover may help a little

Momentary pulse-pressure surges affect all engines but as you say- the bigger the displacement, and the higher the operating rpms, the more pressure surges tend to affect engines. Old Triumph bikes and H-Ds both with overbore kits come to mind. 500-inch Pro-stockers run at 9000 rmps are severely affected, and I've known of some supercharged 351-Cs that regularly fogged up the rear window in a Pantera with oil from the front main seal when under even mild boost. Likely, the fogging was also oiling the clutch from the rear main but that's not visible. Off-boost, no leak at all.

Unfortunately, such pressure surge problems have no one-size-fits-all solution. What works for one motor may have no effect on another- or some negative may appear. It seems to be allied with how tightly the crankcase wraps the crank & rods, how much oil is flying around inside- which itself is affected by con-rod side clearance, oil pressure and probably many other things. Blow-by is simply poor ring seal and thats a serious problem all by itself. Good luck and let us know if you do solve the problem.