Exhaust valve leaking fixed just to return again

[Boertjie]

Hi All,

On my 77 R100S I noticed a "missing" sound on the left cylinder by the exhaust and I did a leak down test which I could feel air coming out the exhaust. I pulled the head and pour some gas onto the valves and I could clearly see the exhaust valve leaking. Simple valve grinding seem to did the job and surely the missing and leak was gone after testing and idling a few minutes. I drove around the block a couple of times and when I let it idle again the missing was back, and the leak down test was again positive with air coming from the exhaust.
Now in haste I did not pull the dipstick to check if air was also leaking there in the leak down test. The bike also do not use excessive oil or something like that.
I will also do a compression test first thing in the morning.
Any thoughts about why the valve keep on leaking?? Guides seem good.

Regards

Boertjie

Johan Cornelissen
South Africa

[Deleted User 287]

Check the grooves in the top of the valve stem that the retainer lives in. They may be getting thin.

[Ray from Indiana]

You may have a warped head. Distortion from the warp makes it tough for permanent set even after a valve seat cut.