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Gentlemen,

We're finishing up our racing engines for the 2016 season, and we have one with an very slight oil oil leak we havn't encountered before.

It appears to be oil getting past the washers on the two center case studs as they pass through the 3-4 cylinder head, just behind the rocker arms. Two distinct drips, one for each stud.

We've removed the fan housing and run the engine to make sure it's not the oil cooler bypass plate. Dry. We dropped the rocker arms and re-sealed the washers to the heads with Permatex, and sealed around the stud as best possible, reassembled, waited a day, and ran it again.

The two drips became one, and it was smaller than the beginning.

I'd love to hear from someone whom this has happened to before. Right where it is, on a street car, the leak could be easily blamed on bad oil cooler seals, a cracked oil cooler boss or even a leaky cooler.

FJC

Fix Found

High case pressure due to flooding carb on one side. A needle valve replacement fixed it.

There was so much gas pouring into the 3 & 4 cylinder side that gas, soot, and oil was blowing out of the header slip joints on that side. Amazingly, the engine would rev well even flooding like this.

We figure the dry sump pickup was helping by sucking out a lot of the pressure, explaining why it was leaking just on the flooding side.

FJC

Good to hear you found the problem.

I prefer Curil K2, but the Permatex will work...give the head side of the headnut washers the sandpaper-on-glass treatment to remove any burrs and ensure they're flat, then paint the underside with sealant on assembly. Sometimes the washers are a loose fit radially on the heads (esp. with m8 studs), I like to use the tip of a screwdriver to keep them centered as the nuts are tightened. DO NOT use silicon seal for the job unless you want gummi-worms plugging up the oil strainer.
Another insidious leak which can masquerade as a pushrod tube seal problem is down the threads of the rocker studs (that's why they're sealed with little O-rings). For some reason they quit machining the little "moat" around the studs on newer heads and only put in a small chamfer, not big enough for a seal to live in. Fortunately these heads seem to rarely leak there (perhaps they tightened up the thread tolerances for the studs) but it doesn't do any harm to drizzle a little sealant into the chamfer before bolting on the rockerarm assemblies.

Did the fuel wash kill your ring seal?

Hi Piledriver,

Yes, the amount of gas pouring in was so much it washed away the ring seal. Our first clue it was gas (not just a freak leak) was in taking the head off that side, and on removing the manifold, discovering one head port was absolutely full of gas!

And the engine had been running with that much gas pouring into it.

One good thing came out of this nasty incident. I found the quick and dirty way to seal behind the head washers. Just take a Coke can and cut out some thin aluminum "washers" that fit the head washers outer diameter and the stud diameter, (not the larger thread diameter). Snip the washers halfway in two so you can fit them over the studs, and seal between them and the head with Permatex, then apply your head washers and nuts,

Fantastic seal.

Of course, if you're not fighting drastic flooding, oil dilution, and case pressure, no slick tricks are necessary.

FJC