DTSSF!
OK I think I have the story now.
After the overhaul and running good Thursday, I checked compression Friday morning (155), and went out for a 100 mile ride. Part way though, the PO's problem returned, on down shifting and coming to a stop the motor would quit. Restart, hold light throttle for a bit and it would idle just fine. Stayed that way the whole ride. Got home, down shifted the last hill. pulled the clutch, motor quit, coasted in. Later pulled the plug,
View attachment 147685
it was dry just a little dark no soot no oil, did a compression test, RH 60 pounds, CRAP! Parked it and walked away.
Did some other projects and thought on it. This morning I decided to do what I
should have done a week ago.
DTSSF!
Do the simple (stuff) first
Checked valve clearances, they were both completely tight.
Torqued head bolts, again, and set valves, all is good, runs great, compression 160PSI.
So here's my thoughts, When I checked compression and found it low, tight valve clearance on this side (IE none) was the original problem.
Unfortunately I had done some internet "research" and found several "bad head gasket was the problem " posts. I got in a hurry, EXPECTING to find a bad gasket and did the tear down BEFORE I
did the simple stuff first. Then when the head gasket appeared to have been fine, I was lost as to what the problem had been. So did the usual, fix everything near to hand, and put it back together, hope the problem disappears.
This is a push rod motor. When I first removed the head, the studs were not very tight, far from spec. These engines, like XS650's like to be retorqued, manual calls out a 600 mile from new head stud torque. My guess; it either was not done or like I did, it was torqued, valves set, buttoned back up. When the gasket squeezes down it takes away valve clearance. Way above you will find a pic of the exhaust valve not seating. Pretty sure now it was just no clearance causing it to leak.
So if I had DTSSF I could have avoided a day and half labor and $180 in parts and machining. And some choice thought RE Moto Guzzi and there engineers. Well I'll rack up some more miles, maybe check valves one more time. The interweb usually opines; keep Guzzi valves on the loose side, if you can hear the tappets the valves are happy, sound familiar?