Helicoil suitable.

I'm rebuilding the rear bevel/drive unit on a Moto Guzzi, and the "oil level plug" thread is in poor condition.

I could easily helicoil it, but am unsure if helicoiling is likely to be oil tight, and therefore wondered if this was a good idea or not?

Other options are to tap out to 12mm, but I'd prefer to keep it standard (10mm) if possible.

Regards,

Reggie

Since the plug is a straight 10mm thread I doubt it was sealing on the thread itself anyway. It probably seals with a washer. To Heli coil the thread and not have trouble with the repair you'll need to load the insert to the outside while the Loctite sets up. Just install the coil all cleaned up with brake clean in a clean hole with Loctite on the outside of the insert and a dab in the hole. Install the proper bolt with anti-seize on it and tighten it slightly to pull the insert toward the outside of the case. Leave over night before removing the bolt and it will never give you an ounce of trouble.

Thanks for the quick and comprehensive reply.

I understand :shock: :shock: The loctite will assist in sealing the external threaded portion and hold the helicoil, and yes, it does seal with a washer.
I have some bearing fit loctite to hand, I assume that this would be suitable?

Reggie.

I think the bearing fit Loctite would be fine. A lot of guys don't load the insert toward the side where the load will eventually be and thus the Loctite is evenly distributed over the coil both front and back of each thread. By giving it a bit of a pull load toward the side where it will be during service you create a metal to metal contact on that side and the Loctite moves around to the back space between the aluminium and the stainless steel insert. My friends tease me but I have great luck with Helicoils. Remember to use anti seize on the bolt you use when you first let it set up. (but only a little bit)
Cheers, Dan.

Dan, thanks again. I will proceed this morning.