Pot metal carbs???

[Guest]

The threads in my Marvel carb (where the primary jet screws in) are all most non existant. I can only tighten the jet finger tight. Therefore the gasket does not seal and therefore gas leaks out around the base of the jet (emptying the float chamber when parked).

Is there anything I can use to seal these threads or the gasket to the jet and the carb????

Is it possible to restore these threads??

Or is it time that I seriously rebuilt one of my spares using the different body and the internal parts that I know work.

Any opinions appreciated.

I need my car every day so the repair has to be something that I can do in an evening.

Thanks Guys.

[Mark Shaw]

Sounds like you need a new carb, but for now you can try Viton gasket material or you might use super glue until you find another carb. Either one is compatable with gasoline.

[carbdoc]

Reid,

If you are indeed fortunate enough to have a spare carb, I would go that route -- at least substitute the bowl body containing the bore into which the jet screws. I would not recommend epoxy becuase, if that jet should come out, you could have a dandy engine fire working under your hood.

The pot metal of 1930 was of uniformly poor quality, so repairing threads in it (especially odd-size thereads which I recall those jet bores to be) becomes just about impossible without having the metal around them fall apart.

Good luck, and let me know if I can be of help.

Jeff

[Guest]

Thanks to both Mark Shaw and carbdoc. I have three days off Sun, Mon and Tue so I guess I will transfer parts.

One other question. Should Cork floats be shellacked??? I have never refinished mine but I notice that an odd little bit of cork breaks off now and then and it has always appeared to be bare cork.

[Ivan Saxton]

First things you need are thread pitch gauges, and a set of honourable oriental number drills. You use the use the shanks of the number drills to measure the worn hole diameter, and using this as a root diameter measurement, look up a proprietry thread chart which every restorer must have in their workshop, and just see if you are lucky enough to find an oversise tap size with the same pitch or very close to it. Bearing in mind that there might be few turns of thread on the brass jet, you may even be able to bluff it with a metric size. Also, it will be the tops of the threads in the hole that will be worn, so chances are the slight change of pitch will not matter much. One sries of thread that can be very handy in small diameters is British Association (BA).

Then you make a new jet to the oversize thread in the lathe, otherwise as close as possible to the original. I used to make quite a few bronze replica Zenith 105DC carbs when people needed them for Stutz and Lancia Dilambda, and everthing was new, homemade. I stockpiled batches of components that I made, so I have jets and other items in multiple sizes according to the originalm specificvation of the car each carb was going onto. (Of course, there was a lot of "knife-and-fork" work in that.) I would turn the diameter, face the seat, counterbore the end, then drill the jet orifice with the lathe on maximum speed with the correct size number drill held in a pin vyce by hand. The counterbore will centre the hole, and by holding the pinvyce by hand you can feel and hear what is happening. You use a dip in light cutting lubricant. Drill plenty of depth so you have the orifice through when you part off and counterbore the other end and cut the screwdriver slot. To cut the thread I have made little die-holders which mounts in the tailstock. If I have to do it by screwcutting, I turn the work in the spindle by hand. I got pinvyces from a

manufacturing jewellers supply house.

For a sealant in a doubtful spot like this I would mix up a thick paste of shellac in ethanol. You still use your red fibre washer. I suspect the last thing that will worry you is that the thread is sealed with a low-grade glue which is impervious to petrol.

Victoria B.C. was one of my parents favourite places on earth when they visited it in 1938. I have only been as close to it as Portland Oregon where we visited friends with a Mercer 6. I could happily go to live in a place lkie that, too. (By the way, did liquid nitrogen help with the stuck accelerater pump?)

Regards, Ivan

[carbking]

Most cork float were originally sealed with "orange shellac", which was then baked in an oven. Modern fuel (at least what we are blessed with in most areas of the USA) will cut orange shellac like a hot knife will cut butter. We suggest sealing new (never in fuel) floats with 2 coats of POR-15.

As far as the pot metal repairs (most pre-1935 pot metal), the best advice I can give is DON"T!!! If it is important to have the original type carburetor, take the damaged piece to a foundry specializing in "lost wax" casting, and have a new casting cast from aluminum. If originality is less important, one can find numerous newer carburetors (Stromberg, Zenith, Carter, etc.) all of which are MUCH better than the original.

And to add to Ivan's comment: the beginning of a set of jet drills is a U.S. standard number drill set of numbers 1 to 60 and 61 to 80. One will notice that there are "skips" in the coverage, which may be filled by acquiring fractional metric drills (don't expect the local tool store to stock them, or even know what you are talking about, but they are available).

Jon.

[Guest]

Thanks Ivan.

I actually got around to trying the liquid nitrogen last night. It worked perfectly. So now I have one carb that is half working (on the car), one carb that is incomplete and enough original old pieces for two complete carbs that should, would or might work. This weekend will tell.

[Guest]

Thanks Jon.

Plese see my reply to Ivan

[Rusty_OToole]

Could you Helicoil the threaded hole? Just asking.

Cork floats need to be sealed. Have heard of using leftover gas tank sealer for this. Just paint the float and let it dry.

[Guest]

It took more than a weekend but I made one good carb out all that I had. I made a metal float of of some scrap brass I had left from model building. Took a pattern off the cork float, cut three pieces and with some delicate soldering it seems all okay. I also bored out the pot metal housing and made bushings for the throttle shaft to turn on, it idles at the same place all the time now . It actually runs better than for many years.

Thanks for all you hints and help guys.