I`m rebuilding an Alpina engine at the moment, M115 and the exhaust thread is no good. I remember seeing some helicoils or a solid inserts for sale to go into the exhaust port on the early engines. I can`t find them now though. Does anybody know of a place that sells them. Cheers Graham.

Edited February 17, 20188 yr by bullylover

I like Würth Time Sert very much these are a bit more "durable" espacially for threads that have to carry a lot of stress.

I've repaired the threads to the rear shock mount to my Bultaco Sherpa and one mount to the bash plate mount to my
SWM with them, with very good result:

 

You find them at E-Bay the initial package is worth the money. Look up Time Sert and M 8 f.e.

Timeserts are best seen a lot of helicoils fail in aircooled stuff, just make sure you fit them properly,good luck.

https://www.dirtrider.com/features/protips/141_1102_how_to_repair_a_thread

But I now have to correct myself if it is the very big thread which is in likewise diameter then the exhaust port then I would recommend laser welding which can be done without overstressing the old cylinder.

A good repair shop that will do this but in Germany:

https://www.worb5.com/werkstatt-instandsetzung-hebebühne-motor-zündung-zündkerze-reparatur-reifen.html

They do all things you need to do too repair two strokes they tune scooters in all sizes vintage and modern. These guy have a cylinder of my bike just now and are reshaping the ports and in- and outtake + reshaping the head for better performance. Nice guys easy to talk and to negotiate with.

Thanks Patrik. Germany is just a bit to far for me as I am in Australia. It looks like I might have to just make an insert and make the hole in the exhaust port larger and heat shrink the insert in there. Finding a tap that size might be fun though. I have never made any threads on my lathe and it is an imperial lathe so making a metric thread could be fun. Or I could just take all of it into an engineering shop and get them to do it which is probably the smart thing to do. Cheers Graham.

1 hour ago, bullylover said:

Thanks Patrik. Germany is just a bit to far for me as I am in Australia. It looks like I might have to just make an insert and make the hole in the exhaust port larger and heat shrink the insert in there. Finding a tap that size might be fun though. I have never made any threads on my lathe and it is an imperial lathe so making a metric thread could be fun. Or I could just take all of it into an engineering shop and get them to do it which is probably the smart thing to do. Cheers Graham.

Graham, George did mine by using a milling machine to enlarge the hole and then welded in the aluminium insert that I had bought from Keith Lynas. He said next time I needed one done, I should consider cutting a bigger diameter thread in the cylinder and make a new steel nut (male piece) to suit the bigger diameter thread.

On 18/02/2018 at 6:04 AM, bullylover said:

Thanks Patrik. Germany is just a bit to far for me as I am in Australia. It looks like I might have to just make an insert and make the hole in the exhaust port larger and heat shrink the insert in there. Finding a tap that size might be fun though. I have never made any threads on my lathe and it is an imperial lathe so making a metric thread could be fun. Or I could just take all of it into an engineering shop and get them to do it which is probably the smart thing to do. Cheers Graham.

How about trying to use the later double spring retainer as on the later Sherpas and MX models. Heat shrink around the exhaust port on an aluminuim barrel could be problematical with loosening etc. I’m sure that there are really large Helcoils available and there are also solid thread inserts on the market. Alternatively you could open out the exhaust entry ( damaged thread area) to accept a new short pipe threaded to match with an internal diameter as the original screw in front pipe sleeve. I wanted to say plumbers thread tools if you follow my drift.???I hope there’s some useful ideas here to sort your problem. Good old Google should have some answers too!