Joined Nov 2001
17K Posts | 774+
Ely, England
as discussed recently the 37s from OEM are £62 plus VAT in the UK so thats £73 per inlet. the problem as you know is that they tulip if revved on OEM cam and valve springs.
i have had a few machined down that had gone south. suprisingly they can be saved at 36.8mm and with a taper around the base edge as well.
TUNING
the width of the seat on even the standard valve is quite wide and effectively the seat hammers at the 60% of the valve it contacts and obviously can't touch the rest - inside the port.
by feathering the back of the valve down and into what is now an even wider seat you are actually tuning the bike. gaining power! the reason is because the threshold the mixture has to travel before it can spread out is shortened.
how to do it?
well some use an engineer.
or
i know someone who uses a felt tip pen and smears all around the valve face. then just kisses it in with some lapping paste leaving a shiny silver ring through the felt tip. he then places a drill upside down in the vice and places his valves in the drill. then having turned it on he gets a 4" grinder and get this...by hand right... he grinds the felt tip away with the grinder (old P60) whilst the valve spins in the drill, then he finishes it off with jizer on some P400 wet 'n dry!
fruitcake!
regards
Taffy
i have had a few machined down that had gone south. suprisingly they can be saved at 36.8mm and with a taper around the base edge as well.
TUNING
the width of the seat on even the standard valve is quite wide and effectively the seat hammers at the 60% of the valve it contacts and obviously can't touch the rest - inside the port.
by feathering the back of the valve down and into what is now an even wider seat you are actually tuning the bike. gaining power! the reason is because the threshold the mixture has to travel before it can spread out is shortened.
how to do it?
well some use an engineer.
or
i know someone who uses a felt tip pen and smears all around the valve face. then just kisses it in with some lapping paste leaving a shiny silver ring through the felt tip. he then places a drill upside down in the vice and places his valves in the drill. then having turned it on he gets a 4" grinder and get this...by hand right... he grinds the felt tip away with the grinder (old P60) whilst the valve spins in the drill, then he finishes it off with jizer on some P400 wet 'n dry!
fruitcake!
regards
Taffy
