Pot metal carbs

[Guest]

Does anyone have any advice on removing a brass??? accelerator pump from a Marvel AA carb. I have two spare ones. I was contacted by a man who has a Pontiac that has a Tillotson carb, his car is not running and he was interested in one of my spares. I would sell him one but would not do so unless I could make it run or at least be positively rebuildable. I have tried every kind of soaking stuff for 2 years now and cannot get the pump plunger out of the body. These carbs seem quite rare. My spares ae the only two I have heard of in the last thirty years except for one that sold on ebay for around $400.00. last year. Any information is appreciated.

[Ivan Saxton]

You might try using the coefficient of linear expansion, and differential temperature for the brass plunger and pot metal body. If you can seal the valve in the plunger iwth either minimal locktite wichin or silastic, depending how easily liquid would otherwise run through it. Then lightly seal a plastic tube that will just fit in the bore to the plunger, using minimal silastic on the end surface. You should be able to get a small quantity of liquid Nitrogen from a medical practice. Medicos use it for such minor proceedures as freeze-killing skin warts. You super-cool the brass plunger while maintaining the body in a bath of warm/hot water. If you cannot find siutable size plastic tube, make on in your lathe with suitable rod stock.

I suppose it was smart and economical to die-cast components of zinc pot-metal. To be fair, probably most cars of the 1920's were built with intended useful like expectation of 8-10 years. Stutz, for instance, could never have dreamed that we would be making sg cast iron cam follower bodies after 85 years to replace diecast originals so expanded that the T-head engines would not move. I am not a metallurgist, but I understand diecast failure is most often due to inclusion of traces of lead or cadmium. Diecast carbies vary in their problem. It is fairly difficult to find a Zenith 105DC from a Stutz or Lancia Dilambda that is good enough to use as copy pattern for accurate machining. Any you probably need to be very accurate for every piece you make. I made probably a dozen fro people who needed these, and there is a lot of "knife-and-fork" work in each; and I haven't even made carbs for my own cars yet. I am pleased someone else is making these same carbs now, because I haven't been asked for one for a few years.

Good luck. Ivan Saxton

[Guest]

I have played around with different temperatures but as my carb is working I never seriously attemped removing the pump on a carb that I really only had as a spare.I certainly never thought of sealing the plunger and using such extreme cold. I do have access to liquid nitrogen and will try your suggestion.

Thank You.

[carbdoc]

Reid,

My suggestion is not as high-tech as Ivan's, but here it is:

The probable reason that the pump piston is frozen is that the bowl is made from pot-metal prior to the mid-1930s. The pot-metal cast during this period had a tendancy to "swell" (due to a high lead content, it is said).

I would recommend removing the plug directly below the accelerator pump, then removing the jet above it into which the metering rod (affixed to the bottom of the pump) recesses. You may have to make a special "forked" tool to remove the jet, particularly if the piston (hence metering rod) is frozen toward the bottom of the bore. With the jet out, insert a hollow drift of less than 1/4" O.D. (I use brass hobby tubing) which will just fit though the jet bore yet whose I.D. will fit around the metering rod. Then proceed to drive out the piston from the bottom.

You will need to clean the pison thoroughly, then try to fit it back into the bore. You probably won't be able to do so without LIGHTLY sandpapering the inside ot the bore. Don't treat the pot-metal casting too roughly during any part of this operation or it will break -- it is very weak.

Good Luck!

Jeff

[carbking]

Reid - you have two issues to contend with. As Jeff mentioned, one is the "swelling" of the zinc alloy. The other is corrosion. A carburetor is a natural Galvanic cell (two dissimilar metals in the presence of a liquid); which causes ion flow. If the carburetor were cast iron, it may be heated to burn the oxygen from the corrosion molecules, but heating the zinc alloy will cause it to crack (or worse, explode violently!!!). If you use liquid nitrogen, keep it on the pump plunger, as the extreme cold on the zinc alloy will also cause it to crack.

We have had moderate success by first boiling the unit in water, and then placing the unit in a zip-lock bag and freezing. We then submerge the frozen unit in a weak acid (vinegar, your favorite soft-drink, etc.) to attempt to eat some of the corrosion. We then apply a slide hammer and light upward pressure to the plunger. If something rare, we keep with it. With a unit as common as this one; if it doesn't break loose in a few weeks, we start with another unit.

Chances are if/when you get the plunger out, you will find that the well is out-of-round, requiring boring and sleeving for good results. If you have to bore it, a boring bar taking only 1 to 2 thousands at a pass. As Jeff stated, this stuff is extremely weak. A drill bit will normally shatter the zinc alloy.

Jon.

[forjack842]

All,

With the release of the new epoxies for gas tank sealing can this be used on the Marvel 10-725 bowl and bowl top to keep any further damage from occuring?

I've got a 29 Hudson 10-725 in perfect condition so far (nothing broken and no cracks visible yet) before rebuild and would like to apply this epoxy after the initial cleanup cycle.

Unfortunately the source of the repro bowls is no longer able to make them so that option is off the table.

Ideas....Opinions please,

THanks

Jack

[DavidAU]

If you are going to try to freeze it apart you might want to have a look at Locktite Freeze and Release which I have used and found it to work very well. About $10.00 a can here in Aust. so should be about the same in the US.

David

Welcome to: Loctite® Freeze & Release

[TexRiv_63]

There was a long thread about 4 weeks ago in the General section about Tillotson carbs and pot metal problems, titled "Correct carbs when judging, etc." The overall verdict of that thread was pretty bleak on the chances of finding any useable carbs due to the potmetal problem.

[Rusty_OToole]

Before you go nuts with the loctite and frozen Nitrogen, can you get behind it with compressed air? Usually a few puffs from the air hose will dislodge anything. A continuous blast is not recommended because it gives too much pressure and could break something.

Look for the passage where the gas comes out of the pump and see if you can get some pressure in there.