Exhaust threads stripped !

[lilchunkyboy]

hi, I have a 80cc 2 stroke engine that i have have ridden for a few months now. In general almost everything is going well, just yesterday noticed my exhaust was quite loose. I went to tighten the bolts and it just wouldn't tighten. The bolts i use are allen key bolts that has worked really well for the past few months. I flashed a light to the thread holes to see they are completely stripped. I cut some a bolt in half and used them as studs,i hammered it into the holes. for a moment i thought i had fixed it, when tension came when tightening the nut as it should, it twisted the bolt with it... I have posted this because im quite stuck on what to do, helicoils ? any ideas on for a quick fix

i am considering riding with no exhaust...

 

[Greg58]

You can thread the holes with a larger tap, use studs with thread locker, the low grade aluminum won't last long if you take the exhaust on and off much. Always add a hanger at the rear of the muffler, that will save the studs from stress and flex.

 

[lilchunkyboy]

ok, should the tap be the size of the stud ?

 

[Greg58]

1/4 28 (fine thread) is the next size that is possible, aluminum needs fine threads. Use a bottom tap, it will thread all the way down as the name applies.

 

[Greg58]

The chart below should help.

 

[Greg58]

If you want to stay with metric 7mm would be next, Home Depot and Lowe’s have them in the specialty section.

 

[wrench]

1/4 28 (fine thread) is the next size that is possible, aluminum needs fine threads. Use a bottom tap, it will thread all the way down as the name applies.

Not sure where ya heard that Aluminum needs fine threads?
I would suggest tapping the stripped 6mm bolt hole to 1/4" x 20 as the threads are more course and hold better than 1/4" x 28 fine thread

Tapping a stripped 6mm threads to 1/4" x 20 is a common fix in aluminum M/C cases
Courser threads are less likely to pull out - especially exhaust threads

 

[wrench]

ok, should the tap be the size of the stud ?

Yes

 

[mapbike]

I also use 1/4 x 20 for fixing stripped out M6x1.00

Has always worked very good for me

 

[Greg58]

If all the threads are pulled out this may not help, anytime I’ve tapped aluminum I’ve had better results using NF taps, and since the fine thread is slightly larger I thought it might have enough bite to hold.

 

[curtisfox]

Kind of the same way with woo course thread for soft wood, fine thread for hard wood.........Curt

 

[lilchunkyboy]

used a tap and die set. tapped the holes and and inserted the studs,then screwed the nuts on. The exhaust seems to be holding up fine, need to reinforce the rear of the muffler.

 

[Testname111]

Purchase a new cylinder, they cheap

 

[Denis Zen]

I am just throwing this out there...

I used those aluminum brazing/welding rods to fill the holes with and retapped them on a friend's bike and it worked great.

But they arent cheap. Helicoil or Retapping larger or buying a new one would be cheaper and faster.

 

[Elterrible]

Drill them out and heli coil. Only way to solve it for good. I did my intake, exhaust, and mounts