Helicoil Question

[Carl Walichnowski]

2 of the 4 threads were stripped due to what I think was over tightening the bolts when tightening down a upgraded head. I brought the subject up in the beginning of the summer prior to my MB accident and several people suggested getting helicoils to best fix the problem. It’s now time to have my MB fixed and apparently I misplaced the helicoil and can’t locate the post that had the sizes. I have a Grubee Skyhawk, can anyone tell me what size Helicoil I have to buy?? Thx

 

[FurryOnTheInside]

Welcome back, Carl. How are you doing, healing up well I hope?
The 66cc engines have M8 studs. The Helicoil kit will include the necessary drill bit and tap to fit.
Make sure your crankcase is well sealed against swarf. I used PVC electrical tape to seal the crankcase and I used silicone lube spray as my cutting fluid which helps keep the finer swarf down.
A tip that @gary55 suggested is to also do all the work with the engine horizontal.
When you put the studs back in they shouldn't be torqued into the case/Helicoil but just tight and blue loctited. Then you can torque the nuts.
I used red loctite between the case and Helicoils (after finding a horrible cavity in the cast case) though it may be overkill.

Happy Time crankcase helicoiled

• FurryOnTheInside
• Aug 24, 2017

Tapped and installed Helicoil with red loctite. Hopefully this will hold.
Did all four cylinder...

 

[crassius]

check your studs if they are 8mm, then they may be 1.0 thread or 1.25 thread some are even 1.0 on one end and 1.25 on other end

 

[FurryOnTheInside]

Yeah mine were 1.0 pitch, M8 fine thread at the case end and 1.25 pitch, M8 normal thread at the head end. That's why I needed to use Helicoils when I was upgrading the studs to grade 8.8.

I don't think a recent Grubee Skyhawk has this problem though? Aren't the studs supposed to be already good in these?

 

[motorizedbikeguy]

I would use red loctite when installing the studs, not while installing the helicoil, and then let it set for a full 24 hours. Just keep in mind that the casting between the stud holes and the interior of the crankcase has a good chance of cracking. In my experiment, a 50/50 chance. If you get a helicoil set, you might as well helicoil the exhaust holes while you're at it. There's plenty of casting surrounding them, unlike the cylinder stud holes.

The cracking and bulging in these pics happened after riding for a while, probably because of the rapid expansion and retraction of the thin bit of aluminum in relation to the steel helicoils. It didn't happen while installing the helicoils.

 

[gary55]

Yeah mine were 1.0 pitch, M8 fine thread at the case end and 1.25 pitch, M8 normal thread at the head end. That's why I needed to use Helicoils when I was upgrading the studs to grade 8.8.

I don't think a recent Grubee Skyhawk has this problem though? Aren't the studs supposed to be already good in these?

Yours was a different condition than most. All of the engines I have worked on have the same threat pitch on both ends of the studs. As crassius said the pitch is different on different manufacturers.

 

[Carl Walichnowski]

Welcome back, Carl. How are you doing, healing up well I hope?
The 66cc engines have M8 studs. The Helicoil kit will include the necessary drill bit and tap to fit.
Make sure your crankcase is well sealed against swarf. I used PVC electrical tape to seal the crankcase and I used silicone lube spray as my cutting fluid which helps keep the finer swarf down.
A tip that @gary55 suggested is to also do all the work with the engine horizontal.
When you put the studs back in they shouldn't be torqued into the case/Helicoil but just tight and blue loctited. Then you can torque the nuts.
I used red loctite between the case and Helicoils (after finding a horrible cavity in the cast case) though it may be overkill.

Happy Time crankcase helicoiled

• FurryOnTheInside
• Aug 24, 2017

Tapped and installed Helicoil with red loctite. Hopefully this will hold.
Did all four cylinder...

Thanks for asking, I’m doing fine. I healed up from my injury pretty well and I’m ready to start riding again once my repairs are done and all this snow melts. The info on the helicoil is useful, I’m going over the weekend to see if they’re available from AutoZone in the size I need. I’ll keep you posted on the progress. I think I recall that it wasn’t recommended to use a tap & die set, the helicoil is the definite way to go correct? Thanks!

 

[Frankenstein]

Thanks for asking, I’m doing fine. I healed up from my injury pretty well and I’m ready to start riding again once my repairs are done and all this snow melts. The info on the helicoil is useful, I’m going over the weekend to see if they’re available from AutoZone in the size I need. I’ll keep you posted on the progress. I think I recall that it wasn’t recommended to use a tap & die set, the helicoil is the definite way to go correct? Thanks!

These aluminum parts that for all we know have recycled horse hair mixed into the melting pot, yes a helicoil just goes a long way, it's also a nice way to fix something when you f*** up if the engine still has life left in it.

 

[motorizedbikeguy]

Thanks for asking, I’m doing fine. I healed up from my injury pretty well and I’m ready to start riding again once my repairs are done and all this snow melts. The info on the helicoil is useful, I’m going over the weekend to see if they’re available from AutoZone in the size I need. I’ll keep you posted on the progress. I think I recall that it wasn’t recommended to use a tap & die set, the helicoil is the definite way to go correct? Thanks!

I would get one of those after market kits with the metal case. Much better deal. I've had no problem with mine.

 

[crassius]

as I've mentioned before, if the metal around the failed threads has taken much hammering or twisting or bending during the time the threads were failing, then it may be too fatigued to be repairable

inspection for this would be to look to see if surface has a grainy or dusty look to it