I’ve got a significant oil leak around the head of the large center bolt in the oil filter of my xk120.
It’s kind of surprising since last summer in an effort to eliminate various small oil seeps I “rebuilt” the seal around the head of that bolt. Where the bolt passes down through the head of the filter assembly there’s a machined recess that accepts what looked to me like a square-edged O ring, or it might be a black fiber washer. In any case if was pretty hard and not flexible so I assumed that it had hardened since it was the original 60+ year old part. I replaced it with a new similar O-ring which was slightly thicker and slightly smaller in OD. And for good measure I added a stat-o-seal washer above that on the bolt. It worked- no leaks and I drove the car about 400 miles that way and then stopped driving around the middle of November due to the weather.
So now I started it up again a couple of days ago planning to go for a ride and during my “pre-flight” I found a small, but steady flow of oil coming out from under the bolt head. I checked and it was tight. I’ve now taken the whole thing apart again and find no damage or wear that I can see. Kind of strange- the car sits there doing nothing for a couple of months and on its own it develops a leak! And no, I don’t think it can be seal shrinkage since both of the new ones are Buna-N.
Hold it up to your computer screen. Oh, yeah, I can see it from here.
Buna-N is only rated for 225 deg F. It may be that you have cooked it.
Viton Fluoroelastomer would be better, rated for 400 F.
I have in my notes that the bolt is 5/8" diameter and the recess in the head is 1" diameter.
There should be a flat washer on there.
You might try McMaster-Carr part 1170N81 at $5.39 for a package of 5, or 6540K177 at $7.81 for 10.
I don’t think the stat-o-seal is necessary if the square section o-ring fits tight on the bolt.
Many thanks for your response, Rob. Maybe Buna-N was the wrong choice- frankly, I didn’t pay attention to the service temperature when I ordered them. (I got them from McM/C too, BTW.) Viton looks like a much better choice.
I agree that the bolt is 5/8" and the recess is 1" ID. The bottom of the milled recess is a little uneven, but I measure it at about 0.10" deep so I guess the nominal 1/8" thick O-ring should fit well with a little compression.
The parts book just lists it as a “rubber washer” with a part number, but no details on dimensions. In any case it seems like a good idea to replace it after all these years.
Yeah, I would have posted some pictures, but I haven’t figured out yet how to do that. I haven’t used the new site very much, so although it’s probably easier, I still don’t know how.
No, I didn’t mean anything disparaging, I was just remembering a joke we used to make back in the early days of the internet before we could post any kind of picture.
The bottom of the milled recess should be smooth, so you might want to try a file or a scraper on it if you can get one in there. Or sandpaper if nothing else.
Just to close the loop on this one, I’ve finally solved the leak problem by applying hylomar to the clean metal surface of the recess, installing a square cross section viton o-ring on top of that, then putting a stat-o-seal washer on the center bolt and then assembling the whole works with the OE flat steel washer on top.
Whew.
I did all of that because without the hylomar and the stat-o-seal and using an X- cross section viton o-ring it still leaked as before.
So now I don’t know which one of the three additions solved the problem or whether it took all three, but I’ll take it.
Well done, Bruce!
Hylomar has fixed a leak or two on mine.
That sealing surface looks like it has experienced aluminum corrosion at some time in its life. It should be smoother than that.
Future plans might include setting it up in a Bridgeport mill or a good drill press and using an end mill cutting tool in there. Any machine shop can take care of that for you.
Rob
