Last year my 71 T120 starting fouling both plugs. Checked everything and decided to pull the head. The head gasket was leaking oil and as predicted the small washers had created the depressions. I bought an interchangeable Pilot Type - Counter bore tool from Enco for a little more than $30.00 with the pilot and did mine on my drill press at about 500 RPM, it worked great and put in the hardened washers. The 0-ring under the washer trick is a good idea.
Interesting point about also putting the same seal on the valve stem.
Yeah, I got the idea from Pete R. Some oil gets through the splits in the valve stem collets, then runs down the stem into the guides and the combustion chamber.
If you place the O-ring on the valve stem before you offer the collets, the O-ring will nest in the taper of the top collar. Any oil coming through the collets will be deflected off the valve stem and top collar. This helps keep the oil out of the valve guides and combustion chambers.
According to John H. this mod was used alot on VW's too.
Last edited by JubeePrince; 01/03/123:02 am. Reason: clarify O-ring procedure
'77 T140J "Vintage Bike". What's in your garage?
"The paying customer is always right."
Fitting round pegs into square holes since 1961...
The best way to fit the O-ring is to put it on the stem above the top spring collar.The collets then push it down into the taper of the collar. Another thing you can do is sharpen the top of the guide like a pencil,about 120 degree included angle.A small flat on the top of the guide bore is OK,but you don't want a chamfer to collect oil.