Repairing Stripped Threads on a
Mercedes-Benz Ponton Solex 32 PAITA Carburetor
This topic was covered by the International Ponton Owners Group (IPOG) forum, and provides a variety of tips and thoughts on repairing stripped carburetor threads.
Figure 1. Solex 32 PAITA carburetor (Type W121 190 Ponton sedan) with accelerator pump visible on the side.
Photo courtesy: Ron Bunting (Brisbane, Queensland Australia)
Q: Some of the threads on my Solex 32 PAITA carburetor have disintegrated, and I'm ready to re-tap the M4 bolt holes, and trying a Helicoil insert. Has anyone had any success with this approach? The four M4 bolts hold the small pump onto the side of the carburetor (activated every time the accelerator pedal is sharply depressed). I think this is where there are air/petrol leaks, which makes the pump unable to squirt petrol through the injection tube. The car runs okay at idle but falters on acceleration.
Malcolm Hobson (Haddington, East Lothian, Scotland) – 11/11/19
A1: The carburetor bodies are only pot metal, and not very durable once the screws get re-tightened. A Helicoil at M4 is pretty small. It is a good idea to grease a screw, then put some epoxy, such as JB Weld or Devcon into the hole, and then screw the greased screw into the hole. The grease allows the screw to come out after the epoxy has set. There will always be a bit of excess, thus the need to remove the screw. Finally, the face can be finished for the pump.
Ron Bunting (Brisbane, Queensland Australia) – 11/13/19
A2: The threaded holes for the accelerator pump are notorious for stripping, so now we Helicoil all of them in each carburetor we do. The problem results from a combination of the pot metal aging, and the fine thread pitch they used. The thread is 4 x .75, but Helicoils only come in 4 x .70, so the screws have to be replaced. Can they be repaired in place? I don't think so. The time you attempt to save by not removing the carb(s) will be spent trying to drill a hole upside down, then tapping it with the Helicoil tool, then threading the Helicoil and getting it just the right depth below the surface. All of it blind. I use magnifying glasses to make sure I get the Helicoil just the right depth below the surface. So, I would not suggest trying to do this with the carbs in place. While you're in there, consider Helicoiling all the holes in both carbs, because over time, the others will eventually pull out.
Will Samples (S&S Imports / Texas) – 2/6/11
A3: I would just add that these screws should be tightened with a torque screwdriver and with some Loctite on the threads. It is very common to overtighten them, and therefore destroy the threads. Loctite preserves the threads as well as keeps the screw in place. Use the low strength Loctite for this purpose.
Tore Johansson (Karlskrona, Sweden) - 11/26/19
Created: November 24, 2019 / Jeff Miller
Last Update:
November 26, 2019
© www.mbzponton.org
Return to the Ponton Workshop page
Return to the Mercedes Ponton page