Oil leaks from the rear timing cover

[David Morris]

Hi there,

All Javelin and Jupiter owners know all too well that the rear timing cover (RTC) gasket is famous for creating oil leaks. Several of us have started using the 'O' ring gasket option that has been discussed here before. I have been running this option for about a year now, and until recently I have had mixed results. It's certainly better than the original gasket, but I was still having what developed into quite serious oil leaks.

There seem to be two main factors in whether this is a successful modification. The first is that the mating surfaces on the block and the RTC need to be as near as possible true and flat before assembly with the 'O' ring gasket. My colleague, John Airey, was able to 'fit' his RTC to the block during his recent engine rebuild and found doing this while the engine was on the bench made this fitting process much easier. It's a slow process, using engineer's blue and scraping carefully until the surfaces show good even contact. It is surprising how uneven the RTC surfaces are when you start this process, probably caused by years of heavy tightening down, in an attempt to cure the leaks and this may distort the faces of the RTC? Indeed, were they matched in the factory?

My engine, although fitted with the 'O' ring gasket, has been leaking from the rear of the RTC. John very kindly spent some time a couple of weeks ago in helping me by 'fitting' the RTC to the block while the engine was in the car. We replaced the 'O' ring gasket with new 1.6mm 'O' rings, making sure that there was sufficient clearance in the gasket fixing holes to stop the RTC bolt 'pulling' the gasket when bolting down. I have found that replacing the near-side RTC bolt with a stud helps locate the gasket. We gave the gasket a smear of Loctiie 518, avoiding the 'O' rings, and tightened down. Only then did we nip up the five horizontal bolts coming in from the front timing cover, as these are trying to pull the RTC away from the block and only need to be just tight, to stop splash leaks from the front of the RTC. I had made up a new half-gasket to mate with the front timing cover, that was shaped to mate with the portion of the front timing cover that is visible arond the five bolts.

After an extended and hot road test, we were disappointed to find that the RTC gasket appeared to show leaks, even after all the hard work! Note, though, that the leaks were all on the near side!! The explanation for this was not clear at the time!

This leads to the second point. I found that the new RTC gasket was not actually leaking at all! The oil filling the near side 'trough' on the top of the engine was actually coming from the oil gauge take-off union. This drips down into the trough behind the RTC and you immediately think the gasket has failed again! There are at least two places where this oil could be leaking from. One is the small olive on the copper pipe take-off. I cured this by some boss white and some small strands of asbestos string inside the compression joint. The other point of leakage is harder to see. The Jowett oil gauge adapter is a taper fit into the rear of the RTC and the later Series 3 RTC's have a very thin cast boss at this point. They crack at the bottom and then leak away out of sight! We found several RTC's with cracked boss's. The only solution was to get these welded up and re-tapped with a straight BSF thread. We then cut BSF threads on the original brass adapters to suit. The original taper threads here were asking for problems!

So, the moral of this story is that your RTC gasket may not actually be leaking at all! If the oil leaks are all on the nearside, have a careful look at the oil gauge take-off. I found that by stuffing some clean white tissue under the oil gauge adapter and running the engine for a short while, you will soon see where the oil is actually coming from!

I hope this helps with what is one of the most annoying 'faults' on the Javalin/Jupiter engine design. I am deeply indebted to John Airey for his help in our mutual quest for dry engines! It is remarkable how, when trying the RTC on the top of the engine without the gasket in place, you might find the RTC 'rocks' up and down, showing that considerable fitting work wil be required to get the surfaces flat and true, before attempting to re-assemble.

All the best,

David Morris

[Leo Bolter]

Oh, how frustrating David! . . . but SO satisfying in the end result!

But I guess, in retrospect, your colleague John Airey's meticulous "fettling" of the "vee" faces where the RTC fits to the crankcase is something everyone should undertake when assembling a engine on the bench . . . a dummy run and careful inspection (without fluid gasket maker etc.) should be done as a matter of course, (especially in that area) even if original parts are being re-fitted, and especially so if substitute timing cover/filter housing bits are being used.

One thing I would stress when the RTC securing bolts are snugged down during this dummy run, is to check that there's sufficient clearance on the 1/4" BSF bolts that pass thorough the timing cover . . sometimes a slightly oversize drill needs to be run through one or more of the holes to prevent shear forces on these bolts preventing the back cover from being completely pulled down by it's bolts. Progressively tightening all the bolts involved when finally assembling is a good idea too.

Leaks from other sources around that area? Of course, there's the "old leaking at the top crankcase join" problem that can fool one into suspecting the RTC gasket is leaking (see: http://jowett.net/forum/viewtopic.php?f ... lit=Vacuum)

PLEASE NOTE: The images below show the difference in "meat" surrounding the oil pressure off-take in the 2 RTC examples I have on hand (there could be other variants about, of course). Interestingly the one with the least thickness at this critical point is the RTC with the large oil passage ports to improve the lubrication flow! This is supposedly a later improved version . . . . and it IS in the passage department! Still I really do think your idea, David, of ensuring the taper threaded boss doesn't split by making the thread parallel is a cracker ( pun?!) one . . . . provided a good Locktite product is used on the thread to seal it! Please DON'T use a fibre washer under the fitting's hex . . the hex is relatively small and as such would not support the washer sufficiently . . and anyway fibre washers are notoriously known to split!

Although it doesn't show in the perspective of these two images, the "boss" for the fitting stands about 10mm high in both instances (Not nearly flush with the rest of the casting, as it appears to be here!).

"LARGE OIL PASSAGE" REAR TIMING COVER COVER



"SMALL OIL PASSAGE" REAR TIMING COVER COVER

Talking of splits, reminds me of the reason I first developed the aluminium plate/O ring solution . . . a standard gasket was in use on our Javelin and it poppped a section out of the side at the main port carrying the oil from the pump. The car was travelling at about 50 miles/h at the time and the drop in oil pressure wasn't noticed . . . until the windscreen "oiled up"! This "jet" was about 5mm x the gasket thickness (say 0.75mm) . . the main jet must have been aimed right at the fan . . . WHAT A bleedin' MESS !!

Keep up the good work, David and John . . . and for reporting it so eloquently . . . there's no potential for ambiguity in what you have written above!

Cheers. Leo.

[TedAllen]

Join the club, Leo....mine blew up on the Skipton to Kirkby road 5 or 6 years ago. It's aim wasn't as good as your's, though.
It always ran with no oil pressure on the clock but when we pulled in for a coffee I saw the front o/s wheel had a lot of oil on it.

Wheel bearing, was my initial thought but when I saw the big trail of oil down the car park, I knew differently. the gasket had blown on the nearside and was aimed perfectly at the hub and wheel. At least, i knew the oil pressure was good !
Another trip home by truck !

Ted

[David Morris]

Hi Leo and Ted,

Thanks for the excellent photos Leo, they show clearly the problem with the Series 3 ( large oil ways) RTC's. Yes, we did check the clearance on the holes through the front timing case cover for the 1/4" BSF bolts. By the way, I have made mine all five bolts now, rather than the original central one being a stud. I think I have run a 7mm drill down these holes in the past for just this reason.

By the way, I have tried 2.4mm 'O' rings as an experiment, but they collapsed into the oil ways. I assume there was not enough 'land' on the block face to support the whole of the ring surface? We are also using Vitron rings, as the Nitrile ones are borderline on the temperaature that our oil runs at. I believe our engines operate the oil at temperatures higher than the water, hence the need by Jowett's for oil coolers? Certainly, I have burnt my finger on a hot dipstick!

I think Drummond Black kindly checked his stock of RTC's for me and found he had about five versions! It's just some of them that show the thin boss that you illustrate. You would have thought that Jowett't must have realised that they were heading into problems with this thin boss and a taper fitting? The Centenary Year Book that we had presented to us at Wakefield shows a photo of the hotel car park at Crieff. Our Javelin is the only one with her bonnet up and a can of oil beside it! John and I were busy changing the RTC gasket in the car park! But I recollect we used a conventional one then, before we got into our stride with the 'O' ring versions.

Like you Ted, I have had trails of oil behind me on the road from major leaks in this area! However, so far I have always thankfully managed to get her home. Just at the moment there is a trail of oil leading from about 1/4 mile away, going past our house and right back into the garage from the last disaster!

Thanks to you both for your comments.

All the best,

David

[TedAllen]

Collectively, we must be like Exxon Valdiz in this club.
The annoying thing is, now I seem to have an oil tight engine, and at a max of 60 psi, I wouldn't expect it to blow the RTC gasket, I do have great splodges of black all over the drive. I thought it was oil but, as per my sump thread, I now realise its unburnt petrol with soot from inside the exhaust. You can see it round all three exhaust pipe flanges.

Ted