Head gasket for a Johnson 35

Ta Daaaaaaaa! I just made an absolutely dead solid perfect head gasket for one of my Johnson 35's. If you recall, they used a full-head gasket of rubbery composition material. The stuff I used was some I had picked up in the early 1960's. I had tried to make a head gasket at that time, without any decent tools, and it was butchery. This one I made this afternoon would make Hi Johnson himself jealous.

I miked the material, and it's .020". I imagine that's a little thicker than the original, but it may not be. I don't have a fresh original gasket to measure. I would like to make some thinner gaskets, to be able to play with head space a little. Two questions for which I need answers.

(1) Does anyone know the original thickness? (The later large-case motors used a crankcase gasket, under the cylinder, and I imagine that was the same thickness.)

(2) Where would you look for a selection of thicknesses of sheets of composition material. I have checked NAPA before, and all they had was paper gasket material.

Did I say two questions? I meant three. Do you think paper gasket material would work for head gaskets?

I can't help you with the gasket thickness but I pose a question in this forum. Do you really wish to use a fibre gasket in you head. We don't use them anymore for an several reasons but the one that really struck me is the obvious. It's an insulator and isolated the head from the case creating a very hot head. Might be better to make your gaskets from annealed aluminum.

Or copper! Check the bore and see if you can't buy a few aluminum or copper gaskets for a newer engine with similar bore size. Steve

Denny: I don't know if it makes a difference, but is your Johnson 35 a Large or Small case?

Currell, Really doesn't matter what johnson it is. Lets consider that K&B, McCoy,,OS and many others all used fibre gaskets. Remember how they used to blow out, and you would have to replace the head gasket if you pushed the engine too hard. Well remember when I told you that the fox 35 was one of the worst heat pumps ever made the other manufactures wern't too far behind. The head was insulated from the case and really superheated when. the engine leaned Why do you think that the old McCoys used to smoke when they landed. Oh I know that i'm being simple in this reply but I don't want to argue engines, however those high oil content fuel didn't come about just for Fox, his was the worst, but the others needed it too just to cover all the problems that they had designed into their motors. Add bad fits and metalurgical nightmares and oil took on real significance.
It's significant that at the time Enys had a precision fit and used NO head gasket, so they never had those problems. Granted they overheated when new but mostly they survuved to have long productive lives.
Interestingly enough that is a forgotten event now that everyone uses metal gaskets, People even use the same gasket over and over and get away with it, but it relly is not recommended as it will only compress so much and then it's all over

Currell, this particular one is a small-case, the J-35.

Before I made this latest gasket, I fit a Fox 35 head gasket to the engine. It fits fine, with a notable exception. The Johnson head bolts are very close to the cylinder bore, and the Fox gasket has to be notched to clear the bolts. The notches must extend about halfway across the Fox gasket, making it pretty weak.

By the way, everyone, bear in mind that Johnsons are "steel-fin" engines. They used no cylinder liners. The cylinder and cooling fins are machined from one piece. While the later large-case motors used a composition gasket under the cylinder, the small-case motors did not.

Currell, you're running Johnsons. What's your experience with their running hot, because of the heads being insulated from the cylinder...or are you using metal gaskets? Have you tried both? Any difference?

So far I have run a Johnson S, a .35 small case, and a large case Sport Special and Stunt Supreme. I have never had the heads off of any of the engines, so I assume they have stock gaskets (I may be wrong). They all ran well, with no overheating problems. (Of course, it's usually not too hot up here in Mi). To be honest, I have never thought about this head insulation issue, and the differences of heat transfer of aluminum head gaskets vs fibre ones. Guess it's one more thing to stay awake at nights worrying about.

I like the S most of all, except that it has the Dreaded and Much Feared Fox Burp during outsides, at least on a Shoestring with a Perfect non-uni tank. Hide the children.

Surprisingly, the supposedly downmarket Sport Special also was a good runner. Lots of power.

Currell, are you using the 5%, 29%, all castor fuel in them?

BTW, I do remember as a kid having my Johnson 35 land smoking, but then as a kid I did a lot of dumb things. Actually I do MORE dumb things now, but that's just because I do more things now than as a kid. I used to run Missile Mist and needle the Johnson right up to peak lean. Overlean flights were not unusual, and if I couldn't hit the rags my buddies threw up in the air, the entire flight was overlean.

Geez,
I guess we've all probably thrown and tried to hit rags at one time or another for that over lean run.
At one time "Perfect" used to package small squares of fiber gasket material. Does someone still make it? My guess is that it might have used asbestos and is no longer made.
Some folks make aluminum gaskets out of beverage cans.
George

George: Of course, I have squirred away a few of those little Perfect gasket squares. You can get them at swaps from time to time.

Denny: I run 25% oil, majority castor, and anywhere between 5 and 10% nitro. Currell

I have an automatic transmission business as one of my pursuits. We collect a lot of surplus gaskets that are used between the valve bodies and cases on transmissions that have useable space for model engine use. This is .010" thick and can withstand the hydraulic pressures produced in transmissions. I will send some to anyone who wants it. Send me your address.

Denny:

Email me at [email protected]