Forum

[Midge]

Does anyone have any tips for grinding in the valves? I've been trying to seat the inlet valve for ages and I still have light showing through in one place. Its almost as if the valve is wearing but the seat isn't. Maybe the seat needs recutting, should I keep at it or give up.

[Dennis C]

Hi, What other work has been done if any? valve guide replaced ETC.

[Alan R]

Hi MIDGE----------Unfortunately you can't give up, because the bike wont work because there be no suction so no fuel/air gets in so no BANG and the bike won't work because there be no suction so no fuel/air gets in ---etc, etc, etc... First}--- as per DENNIS C ie]-- what else have you done to it ????If that's a new seat or guide then a re-cut(just a skim, mind) is usually called for..But if not}- try another valve in there...If there's still light either the seat or the guide is off-angle....NIL CARBURENDUN BASTARDO !!!

[Midge]

It starts and runs fine although compression is leaking of course. Engine is in bits to cure a crankcase problem and I only noticed the valve problem while I was inspecting the head. Valve and guide run true so I assume its the seat. Its a tuned 500 head by the way, so has the larger valve and bronze guide.

[Dennis C]

If you are certain that both the valve seat and guide are firmly fitted, then I would guess that the seat has not been cut correctly from new, in this case the only real answer it to recut the seat, but before doing so be 100% certain that there is absolutely no chance that the seat or guide has moved.

[Phil Ashbrook]

First re cut the seats with tripple angles and lap in with coarse paste and stick ( rotate the valve , up down with 1/3rd turns till you get a grey band on seat and valve , then continue on to fine paste ) .
You can make pencil marks on the seat to check its even all around , with the valves in you can check for leaks by pouring petrol in the combustion chamber with the head upside down , good valve guides are a must .
This might be a good time to fit a new oversize exhaust valve which will help prevent the valve sitting too low on the seat and very much improve gas flow and help prevent valve burn out .
Many exhaust valve seats actually drop out from 1990's bikes so this is something to keep in mind as well .