3 angle valve cut...

[Scooter]

Hi All

Can anyone out there advise me on the effects of 3 angle valve cuts - performance/efficiency gains if any and does it effect the longevity of the valve to face seal compared to a conventional single cut? Just wondering if it would be a worthwhile procedure next time I have the head off my FZR 750.

Thanks in advance…Scooter.

[dragracer1951]

I ALWAYS do 3 angle unless it's a race motor and it gets a 5 angle.
a three angle cut just needs to be carefull that the width of the contact surface is consistant across 20 valves.
Three angle cuts control the contact surface width better than single cuts...

[Scooter]

Thanks for that...

I am assuming that the increased contact surface area of the valve face would more effectively (particularly the exhaust valve) dissipate heat to the cylinder head material? Do valves tend to be more robust with multiple angle cuts?

[gane]

Intresting question, and one which has been much on my mind for recent seconds. first thought is that by having 2 relief cuts one can control the height of valve area in combustion chamber thus aiding cooling from fuel / exhaust flow and where on valve face contact is made. thus centering wear area at valve face. 2nd is that cutting results in more uniform contact area for better centering of valve / seat wear and seated valve face. 3rd is it requires less spring tension to seal a smaller contact area. a 1mm uniform width seat is standard for most japanese bikes, a happy medium of wear charactaristics, sealing area and heat dissapation. 5 and 6 angle valve jobs include cutting the valves for better flow characteristics. just some random thoughts , perhaps someone more experianced than I can shed more light on the matter. luck G