ES125 cylinder barrel problem

[Neil Wisbeach]

Hi everybody!

I am currently restoring a 1970 ES125 with a fellow MZ devotee and have run into a problem with the barrel. The threads inside the exhaust port are very worn and the nut will not tighten up resulting in as much exhaust leaking out as goes through the downpipe.

So…….does anyone have a barrel and piston they would like to sell or alternatively, does anyone have experience of a good place which would fix it (possibly a steel insert or similar?)

Many thanks for any help/advice offered!

Kind regards, Neil

[‘AAA Dummy]

I HAVE NOT HAD ANY PROBLEMS LIKE THIS MY SELF BUT WHY NOT TRY A HELICOIL TO REPAIR THE BARREL

[Derek Reynolds]

BMW’s have a similar problem on the air heads. The solution there is to have the head machined and a bronze insert installed threaded in, and threaded to take the aluminium retaining nut. Maybe worth talking to BMW onwers, or Bob Porecha in Sydenham.

[Neil Wisbeach]

Hi there!

Many thanks to you both Stefan and Derek! Hopefully I’ll get it sorted now that I know!

Kind regards, Neil

[Brian]

Hi

Sorry for the delay I’ve just seen the post.

This happened to me on a Supa 5 where the best engagement I could get was about 10 to 15 degrees without a gasket, somehow it worked like this and stayed on whilst I was fettling it. The thread at the front of the port was chewed up but it looked OK at the back. The exhaust nut was in a bad way as well.

I removed an exhaust nut from another Supa 5 and this was undoubtedly better but not good enough, maybe half to three quarters of a turn thread engagement with a gasket.

Looking at the exhaust nut it was obvious that it wasn’t threaded to the end so I basically ground it back on the bench grinder until there was a good full thread at the end. I also bevelled the inside to match the exhaust pipe. I must have ground away about 6mm/quarter of an inch.

This now screws on about 3-4 full turns with a gasket and is rock solid.

Try it, you’ve got nothing to loose as you need to be fitting a new exhaust nut and gasket if you get the thread reclaimed.

Brian

[Brian]

Hi

Can I just clarify something from my previous response.

This is where a picture is worth a thousand words but here goes:-

I beveled the inside of the exhaust nut using the bench grinder. This was done by rotating the exhaust nut by 45 degrees horizontally on the vertical axis and pressing the 12 and 6 o’clock positions of the exhaust nut onto the corner of the grinding stone, applying gentle pressure and rotating the exhaust nut.

This will bevel the inside of the exhaust nut to about 45 degrees which was close enough for me. If you was a better match then rough it out using this method and then hand finish by whichever method works for you.

You must use gentle pressure and keep the exhaust nut rotating as the grinding stone is not designed to take side pressure. So if you are in any doubt don’t do it.

Eye protection should be worn as a minimum, but a full face mask is better, and a filter over the nose and mouth.

Now whilst I think the trouble and expense of getting the thread reclaimed on a BMW head is probably justified I think with an MZ barrel it would be more cost effective and easier to get a barrel from a vehicle dismantlers.

Brian

[Neil Wisbeach]

Hi Brian

Sorry for the very late reply but I used your suggestion and……it worked! The exhaust port is now leak free. Many thanks for the advice.

Kind regards, Neil

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