How To Repair your Zenoah Exhaust threads using a Helicoil thread repair kit

[Rototerrier]

So you just stripped out your zenoah gasser engine exhaust bolts? Whether you over tightened the bolts or the bolts came loose and the vibrations trashed the threads, this is the solution you are looking for.

First of all, Helicoils have nothing to do with helicopters nor are they designed specifically to fix engines used in helicopters. They are just a brand of thread repair and get the name from their Helical design. These kits come in a variety of names and can be found in various sizes at different retailers.

Heli-coils
Fix-A-Thread
Recoil
Prime line
Perma-coil

Unfortunately, they cannot be found in our size at any retailers. Autozone, Advance Auto Parts, Napa Auto Parts, Orielly Auto Parts, Ace Harware, etc.. all carry some form of thread repair kit and they all stop at 6mm.

For our size Zenoah engines (G23, G26, G240, G270) we need 5mm x 0.8 pitch.

I needed my repair kit immediately because I am about as impatient as a person can possibly be. I just happen to have a McMaster distribution facility about 40 minutes from my house. So I hit the McMaster website and found a Recoil kit by looking up helicoil.

The exact kit I purchased can be found at McMaster under part number: 91732A946

I purchased the 5mm x 0.8 Recoil kit. It does not come with a drill bit or tap wrench. This kit comes with 7.5mm helicoil inserts. 10mm coils would work, and might even be better. There is certainly enough depth for them and if I were to do it over, I would get 10mm inserts. McMaster only sells the 10mm kit as a part of a larger kit that costs over $50 and you would still need to purchase the tap wrench. It's your choice what kit to get and from where, just ensure it is 5mm x .08 and the insert length is at least 7.5mm.

$35.51 Recoil Kit
$8.00 for a good tap wrench
$5.00 for a 5.2mm drill bit
------------------------------------
Approximately $50 for the entire repair kit

They actually made a mistake on the McMaster website and listed the required drill bit size as 5.3mm. That is absolutely incorrect! When you purchase the Recoil kit, the box clearly states a 5.2mm drill bit is required and this little typo cost me a hour long wait at will call while they swapped out bits.

The procedure is actually quite simple, but it is always nice to see exactly what you need to do before you do it. I couldn't find this exact information anywhere and the uncertainty of what I was about to do was a bit disconcerting. Being faced with having to purchase a repair kit that costs as much as a replacement cylinder head can be a bit of a tossup. And not knowing if it would actually work worried me a little as well. Reading that it works is nice, but seeing photos would have been even better.

Step 1 - Open up the kit and prepare your tools





Step 2 - Prepare and drill out the hole

I applied a small amount of oil to the hole and then very slowly drilled it out using the 5.2mm drill bit. It took no effort at all to drill out.





Step 3 - Tap the hole

Secure the tap into the tap wrench and very slowly turn the tap into the hole. Work slowly and apply a very light amount of pressure to get the tap started. Once it starts, allow the tap to pull itself in. Tap all the way through until the tap spins freely.




Step 4 - Insert the Helicoil thread insert

Adjust the stopper on the insertion tool so that the helicoil tang rests dead center of the slot at the end.



Slowly screw the helicoil into the newly threaded hole.



Screw the coil about 1mm past the front of the hole.



Step 5 - Break off the tang

Using the supplied tang breaker or a small screwdriver or anything else that will fit through the hole, just tap straight through the hole against it and it will easily break off.



Step 6 - Test your screw and install your pipe




You're Done

I hope this helps thoroughly explains what is involved with repairing your 5mm Zenoah threads. As you can see, it really is quite simple and as long as you have an extra $50 bucks to spare, stripping these threads shouldn't be anything to worry about.

[gorden]

Good info and very skilled as well.

[winginit69]

Thats good info, but for $38 i would just replace the whole head.,

[Rototerrier]

Originally Posted by winginit69

Thats good info, but for $38 i would just replace the whole head.,

It's not for everyone and would depend on your existing head. This being a $500 Hanson, replacing the head was not as simple of an option. But yes, if you are running stock it would be cheaper (the first time) to just replace the head but if you then strip that head then you would have been cheaper getting a helicoil kit. As always, it's all about the numbers.

[winginit69]

Sorry! you are correct. I didn't think if it was a mod motor. Bill

[gill4321]

Also you would have to break in the motor again if you get a new head right

[Doug Darby]

What size and pitch is the tap?

I might have missed that?

[Rototerrier]

For our size Zenoah engines (G23, G26, G240, G270) we need 5mm x 0.8 pitch

[LG-Viking]

If I'm not mistaken the Helicoil repair will also make it stronger than original...

[Doug Darby]

I just purchased a helicoil repair kit from Grainger that was a 36 piece kit with 5, 7.5, and 10mm inserts plus the drill and tap and tool for $36.99. They are on closeout and deeply discounted. Will report on quality after IRCHA.

[Tag1260]

Mind a little tip? Stuff your exhaust port with some paper towel or a small piece of rag to help keep metal chips out.

[Doug Darby]

Yes for sure. I put tape over it to make sure nothing accidentally got in.