Ideas on Stripped Bolt Hole ???

[Gordon Gould]

I have and old stand alone trail mower. The two 1/4-20 caps screws that hold the intake manifold/carb/air cleaner to the cylinder have always vibrated loose. (I use red small screw lock-tite and it hold for a year). Well I finally stripped the lower hole. It has a B&S engine.



My plan was to Heli-Coil it but I'm not so sure now that I started and I am looking for ideas. I need to remove the muffler because it blocks access for the drill bit and tap. I got the muffler lock nut loose with a cold chisel and hammer and then a 14" pipe wrench to turn it out. It came very very hard. I was hoping when the lock nut got to the end of it's threads the muffler would start to turn out of the cylinder but I just stripped the lock nut. I also tried turning the muffler can with the pipe wrench but it finally just turned were the can is sweaged around the exhaust pipe. So now I know from the force I have already used that to get the muffler off I will need to use a pipe wrench with a pipe extension handle after I cut off the lock nut. I am worried that that much force may ruin or rip out the exhaust port pipe threads. ???? and I'll be even worse off. Being an aluminum motor I have not tried any heat on the exhaust pipe. My experience with aluminum engines is minimal.

There are a couple good threads at the bottom of the bolt hole that are not stripped out. I am wondering if it would be better to get a 1/4-20 stud down into them along with some kind of magic heat resistant epoxy or something (if it exists help me out) and then use a nut to hold on the carb instead of the cap screw.

Your knowledgeable thoughts, tricks, and ideas are needed. Thank you

gg

 

[dragoneggs]

I like the stainless helicoil idea. Should be fairly easy to install in the aluminum.

How hot does the manifold get? Do you have an infrared thermometer? That will tell you if an epoxy would have a chance. JB Weld epoxy supposedly will be okay at 500degF continuous but I personally think that is a little optimistic especially if torqued down very tight. It will creep. If you use epoxy, make sure the inside wall is very clean (abrade with sandpaper and acetone wipe) before bonding.

 

[JRobyn]

Lots of cycles of your favorite penetrating oil and heat (like a propane torch) on that muffler might just do the trick. It will probably take several days of soaking.

If you have enough metal left on the stripped hole to drill just a tiny bit deeper, then clean up and extend the 1/4x20 threads and use good studs, I would absolutely give that a try. I'd use studs even if you do wind up having to heli-coil one or both holes.

 

[BigRol]

Every time I think J-B weld can't do a job I finally try it and it does, amazing stuff. Good luck

 

[dragoneggs]

Lots of cycles of your favorite penetrating oil and heat (like a propane torch) on that muffler might just do the trick. It will probably take several days of soaking.

If you have enough metal left on the stripped hole to drill just a tiny bit deeper, then clean up and extend the 1/4x20 threads and use good studs, I would absolutely give that a try. I'd use studs even if you do wind up having to heli-coil one or both holes.

I thought about drilling and tapping a little deeper but only if I knew what wall thickness I had left!

 

[mrmikey]

Drill and tap up one size to 5/16 you don't have to go any deeper.
For the muffler, cut it off leaving the stub pipe in place, get a hacksaw blade and cut into the threads from the inside of the pipe parallel with the pipe to split it and use a chisel to fold one side of the split pipe in. The slice that'll end up in the block won't hurt a thing.......Mike

 

[Gordon Gould]

Thanks all. I think I can manage the hole OK. Getting the muffler off is the question. Actually the hole is already deep enough so that I could use a bottoming tap to gain some thread w/o drilling if I don't use a coil. It seems a Heli-Coil might be better. Using studs in place of screws sounds like a good idea. Cutting off the muffler sounds like the safest way. Not much fun though.

gg

 

[Egon]

Drill and tap up one size to 5/16 you don't have to go any deeper.
For the muffler, cut it off leaving the stub pipe in place, get a hacksaw blade and cut into the threads from the inside of the pipe parallel with the pipe to split it and use a chisel to fold one side of the split pipe in. The slice that'll end up in the block won't hurt a thing.......Mike

Sounds good.

 

[Gordon Gould]

Sounds good.

If I put a 5/16 hole thru the intake manifold ear there will be nothing left. I need to stick with 1/4 I think.

gg

 

[Patches]

I'm pretty sure you can find a 5/16X1/4 stud at a fastener specialty store; you can then rethread the hole to 5/16" and have the 1/4" end of the stud exposed to fasten the carburetor on