Valve piston clash

[A-BCD]

I had a mystery on my twin years back, when sometimes there seemed to be no compression on one cylinder but once started the bike ran fine, then when checking the tappets sometimes there was excess clearance on the inlet valve, other times it was too tight !! This was a loose inlet valve seat, when running it was staying place, but when the engine stopped it would sometimes slip out a bit........

 

[Bill Thomas]

The thing is sometimes its loose and then tight, So it does not sound like just a worn bush, Still finding new things after all these years !!. Cheers Bill.

 

[davidjoyner]

Sounds to me like a cam has slipped in it's wheel, being retarded the exhaust valve is clipping the piston because of the late timing. Also if you have installed Mk 2 cams, the extra lift could be binding on something....if you installed new followers, a big one is the ball ends on the pushrods not fully seating into the cup of the new followers, which then wear quite rapidly, and then eventually sink down the hole giving odd tappet settings and poor adjustment........Ahhhh, like everything on a Vincent, it all needs checking and then double checking when you change something.

Many thanks for all the suggestions for my ailments - It WAS the the camwheel that had slipped on the shaft !!!! I must have done 8,000 mls on these cams.
Bob Culver re - jigged them for me and I put a blob of weld on the inside face...sorted
Great - put it all back together - mistimed supidly once - then timed using the marks properly - started first kick VROOM - yes 2 cylinders!!
So with refurbed heads and new carbs I'm the MAN - casually idling at the lights hands off the bar at the front of the traffic. This must have been a fantastic bike new out the shop and tuned by a knowledgeable mechanic.
Sorry about the late update but always struggle to get onto website until I remember to use explorer not chrome.

 

[davidjoyner]

I had a mystery on my twin years back, when sometimes there seemed to be no compression on one cylinder but once started the bike ran fine, then when checking the tappets sometimes there was excess clearance on the inlet valve, other times it was too tight !! This was a loose inlet valve seat, when running it was staying place, but when the engine stopped it would sometimes slip out a bit........

Late reply - better than never - had the same - cracked valve seat and slipped camwheel - related???