I just installed the engine in my 1927 Sport Touring can of worms project. Its in another thread. When I put the carb on, it started leaking. I had already rebuilt this carb last fall, and it was in good running condition. But due to needing to overhaul the engine the carb sat all winter. When I tore the carb down today to see what was wrong, I found that all the tops of the threads for the brass bowl drain valve had torn off. They are the cast iron threads inside the cast carb body. The brass drain valve also had the threads flattened out. After cleaning out the metal thread parts, the drain valve would then "strip out" and no longer tighten up. Just before I removed the carb from the engine it had quit running and would no longer start. During the carb teardown I noticed the metal "teeth" had worked there way into the spray nozzel and were not letting enough gas thru the nozzel to run. I have rebuilt lots of NH carbs and have never seen this happen. Also, I did not have the drain valve cross threaded into the carb. So cross threading could not be the problem. The carb was also an above average condition carb that I used to rebuild. It was not a rusty junker. I found another original Ford drain valve with very nice threads and it screwed into the remaining threads very well and tightened up. I am glad because I thought I was going to have to rebuild another NH carb body and throw away the one I was using. I have reinstalled the carb on the engine and I can now hand crank it again with one short pull of the crank. Has anyone seen this happen before .???
Did you chase those threads before rebuilding it?
No, I did not chase them. But the drain valve would screw in with my fingers.
My guess is there has,over the years been some water/corrosion there and you disturbed enough to shear away the threads. You might want to keep an eye out for another carb body.
I have plenty of NH carbs to rebuild. That is one of the items I hardly ever sold. I always kept them "just in case" or to help someone else out. So thru the years I may still have 75 or more. I just hated to see a good uncracked body do what this did. And it takes a couple hours to properly clean the body up. I always melt out the plugs so I can clean the internal passages and then re-plug the casting. I have rebuilt dozens of these carbs all with very good results. But this is something new to me.
The thread is 9/16 x 24. Should have a tap that size for NH's. Cleans up the threads.