Technical 26IMB10 stud replacement

[ronstox]

Driving my '71 Fiat 500F the other day, I heard the sound of something falling off the engine and bouncing it’s way through the engine compartment to the asphalt below. I stopped and couldn’t find anything obviously amiss and since the engine was still running nicely, I just carried on my way.
It wasn’t until a few days later that I found the missing bit: the forward stud that holds the air intake pipe elbow to the top of the carburetor (26IMB10). Before ordering a replacement, I checked the threads in the carby top. As I suspected the threads were mostly gone and could not hold an M6 bolt even with Loctite.
So, what's the best way to go about installing a new stud. Should I tap the hole out and apply a Helicoil? Has anybody got another fix for this problem?

 

[Bounding Bambino]

This is actually an interesting fix.. Ideally you would do a helicoil, or more preferably a timesert. However, due to the way that the stud is fixed (fits thru carb top cover and actually threads into the body. There is more then likely not enough meat there to do the repair. The outer stud has a relatively small tab and passes thru the top cap. The inner stud threads right into the top body, and might be repairable. Level of success all depends on which of the 2 fell out. I can measure a m6 timesert if you need dimensions.

Welding the body closed then re-tapping is not likely an option either as these are made from poor pot casting material mix, and it doesn't weld nicely.. Ive tried for a different repair.

A larger stud is a possibility with a re-tap. however the top case will need to be drilled open, as well as the 90degree elbow to fit the larger stud. Belmetric has all the specialty studs one would need to tackle this. Ive ordered from them for studs to do my carb conversions. Going to a M7 might do the trick.

The other alternative is get yourself a 28IMB, and get a tad of a performance boost.

 

[Toshi 975]

I have repaired quite few of these with a simple helicoil with no problems. It is quite a common problem.

 

[ronstox]

the arrow in the attached image shows the stud that has gone astray.

 

[Toshi 975]

Yes done those, if you have lost the stud it needs to have a short thread on the bottom end so it locks in place without protruding too far inside the carb.

 

[Bounding Bambino]

Agreed, a helicoil or timesert should work on that one. there should be enough meat in the casting in that area

 

[ronstox]

Thanks for the advice, I've gone ahead and ordered the helicoil kit.
-Ron