Greetings All,

I finally tracked down a pesky oil leak on the passenger side of my '84 351W. I thought the leak was coming from the 3-way junction between the timing cover, engine block, and oil pan, but I was less correct than usual. The leak was actually between the timing cover and engine block, about 2 inches above the oil pan. Quite the odd place for a leak, huh?

For a bit of background, I replaced the timing cover about 3 years ago. The (original?) water pump sprung a leak, and some of the mounting bolts that pass through the (original?) timing cover had corroded and swelled in the holes. The timing cover had to come out in pieces. I replaced it with an aftermarket (Dorman?) and it seemed okay at the time. While researching this current problem, I noticed some timing covers were different in the area that was leaking oil, but I'm not sure if the sealing area is affected. Please take a look at the pics. I'm trying to determine if there were also some differences in engine blocks and the timing cover must match.

Here is an outside view of the currently installed aftermarket version. Note the area of the leak in relation to the two adjacent bolt holes:




Here's an inside view of the same type of cover presently installed. Although it wasn't the source of the leak, this version had provisions for a front dipstick tube, which I plugged:




IIRC, this is the type that had been originally installed. Note the extra material near the area that had been leaking on the other version currently installed:



An inside view of what I think was the original style:





It's hard to tell, but the curvature of the sealing surface in that area looks the same. Also note the following difference in available gaskets. The following views are from inside the engine, looking forward.

This gasket is narrow in the suspect area:





This gasket, which I think is the type currently installed, is much wider in the suspect area. I'm pretty sure this is the type I used, as I can see that extra gasket width hanging out past the timing cover:



Any thoughts? I plan to replace the timing cover with the original style, but I'm still perplexed why the other style was leaking so badly. I retorqued all the bolts, no joy, and even loosened the oil pan bolts to make sure that wasn't holding the timing cover away from the block.

And as previously mentioned, it's only leaking from that one small area where there seems to be some sort of difference between the two styles. I have no doubt where the leak originated. I did a smoke test of the crankcase, and I had to look around to see if O. Weston Link was nearby with his camera:

 

This is a good idea. I would also use the gasket with the wide surface near the leak again. It looks like a better gasket.

Good to know that your smoke machine worked. Start a thread on how you built that smoke machine if you don't mind. Everybody doesn't smoke so some would be reluctant to use a cigar like I mentioned in the other thread.

 

I've ordered the OE style timing cover and the wide gasket. I plan to carefully check the fit before installation. When I installed the existing cover, I know I checked the fit of the gasket to that cover, but never checked the fit of the cover against the engine block. I'm still scratching my head why it leaked so badly there. From the pictures above, it appears either style should seal properly against the block. I'll know more when I tear the engine apart and have both covers side by side.

Re: the smoke machine. Yes, I can make a thread on how I built it. Might be a few days before I can get to it. The smoke machine is not much, just a mason jar, a old pencil-style soldering iron, and an inexpensive aquarium air pump. It uses mineral oil for the smoke. I just learned the hard way to drain it when not in use. I left some oil in there for several months after use and it went rancid. Stunk to high heavens. Hadn't considered that...

 

I've finished installing a new OE style cover from Dorman. I carefully compared this cover with the leaker and could see no difference in the sealing area. With the both covers, I confirmed everything lined up with the gasket and block. I checked all surfaces for flatness and made sure nothing was trapped under the gasket.

I'm stumped why the old one was leaking. I made two changes with this installation in hopes of a better seal:

1) I had previously used a copper colored RTV sealer, on the recommendation of the guy at the parts store. I've never been a big fan of RTV sealer, This time I went with my tried and true favorite Permatex #2 non-hardening sealer.

2) When I had previously installed the timing cover, I spliced the oil pan gasket. This engine has no provisions for dowel pins to align the cover. I suspect the leaking cover was not down far enough relative to the block, due to interference from the oil pan. I later went back and replaced the oil pan gasket with a one-piece rubber gasket instead of the (spliced) cork. This time, I loosened the oil pan first, which gave me room to carefully position the cover per the instructions in the service manual. Unlike last time, I know the bottom edges of the block and cover are properly aligned. A misalignment there still wouldn't explain why I had a leak 2 inches above that, so I'm still confused.

 

Did you straight edge the timing cover to make sure it was not warped? This should be SOP on all older aluminium castings.

 

Yes I did, on both covers. No warpage that I could detect.