desmojon 851
Hi everyone
I've fitted 916 valves into my 851 with new valve guides and professionally ground in. The reason for using them was to be able to use the wider retaining half rings not for any power increase. I mean the seats are still the same. The engine runs fine below 8,000 but over that it starts coughing. Any ideas. I thought it might have to do with the valves being slightly prouder in their seats, changing squish and compression?
Any thoughts welcome.
Best
Jon 😖
outtacontrolla
If you have put bigger valves into the same size seats , the valve will be shrouding the port ie stopping good gas flow and ruining the top end gas flow !
griff851
What size valves, 34/30 34/31, 37/30 ? What is the piston valve clearance? Like at 8k is it possible the squish too close to max and your pistons are tapping a valve?
Mr.R
Open the seats to match the new larger valves,there's enough meat in the '91 seats to do this.
Then either get the bike custom mapped or fit a chip from a '92 851 Strada that had 33/29 (standard 916 sizes) valves as standard and of course check all your clearances as Griff's posted.
Steve R
