valve seat angle options

Cannot locate the thread, but I recall years back there was talk of cutting different angles for exhaust and intake seats. 45/30 on the exhaust and 46/31 on the intake. Can anyone share some practical experience or informed opinions?

Thanks

My first combat valve job was attempted by a profe$$ional shop and they promptly destroyed the exh seats. After that I decided I could wreck it for free rather than pay some one to wreck it. Now I do seat and guide changes and reaming and grinding all on my own now for almost 30 years. Occasionally I do a friend or club members exhaust port repair or valve job.
MY only personal experience is with my Snap-On motorized grinding stones valve tool chest. Got a good deal on it, as it was a snap-on dealer repossession from a harley shop. Almost brand new/unused. Retail with a few extra accessories was a bit under$3000.
I cut the standard 45-46 deg valve area. Seat width is very important. Where I differ is, the valve OD to the edge of the seat/aluminum casting. I custom adjust the grinding stone of this angle to absolutely not touch the head casting. It is a shame the butchery done by one piece cutters. Once you wreck the head what are you going to do?
I would like to think I am stingy to not grind a lot and allow a few valve jobs before needing to change the seats.

acadian said:

Cannot locate the thread, but I recall years back there was talk of cutting different angles for exhaust and intake seats. 45/30 on the exhaust and 46/31 on the intake. Can anyone share some practical experience or informed opinions?

Thanks

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I'm confused what you mean by a 45/30 on the intake and 46/31 on the exhaust. Did you mean a 45/46 seat on the intake and a 30/31 on the exhaust? Or are you referring to a "two-angle" cut where the seat is 45 and the topping cut is 30?

I've never run across anyone who does a 30 degree seat on a Norton head, either intake or exhaust. But I'm sure someone has at least tried it. I knew a tuner back in the '70s who had tried a whole range of seat angles on a Norton head, checking the results on his flow bench, but I don't recall if he ended up with anything significantly different than what other tuners used. Assuming you are referring to a 30 degree seat angle, there are proponents of the 30 degree seat angle on the intake, primarily because it flows more air at low lifts. But it also usually flows a bit less at high lifts, and doesn't self-center on the seat as well as a 45 degree cut. The 30 degree seat doesn't seem to have any advantage on the exhaust side.

I started out doing Norton heads with an old Black and Decker stone seat grinder, doing a 3-angle cut with a 45 degree seat, 37.5 degree top cut, and 62.5 degree bottom cut, blended into the bowl by hand. I got those numbers from a tuner I respected, who had put in a lot of time on developing the porting and seat profiles with flow bench and dyno testing, so never tried anything else. I eventually stepped up to using Serdi style profiled cutter blades in a milling machine. As dynodave mentioned, the Norton head has some special requirements to avoid butchering the area above the intake seat, but it can be done by using more than one cutter profile (and a little hand blending in the case of fitting larger valves).

Ken

lcrken said:

Or are you referring to a "two-angle" cut where the seat is 45 and the topping cut is 30?

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Yes, this.

Thanks for the feedback, I'm limited to Neway cutters

Been involved in 'one angle,' 'three angle,' and 'five angle' valve jobs on competition engines. Frankly, can't imagine either of the multi-angle valve jobs making any practical difference (power increase) on a Norton motor.

MexicoMike said:

Been involved in 'one angle,' 'three angle,' and 'five angle' valve jobs on competition engines. Frankly, can't imagine either of the multi-angle valve jobs making any practical difference (power increase) on a Norton motor.

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Well, you would get disagreement from pretty much all the well known Norton race bike engine builders in the last several decades, based on flow bench results, dyno testing, and race results, but everyone is entitled to their own opinion.

Ken

The whole port design VS +or - 1/8 of an inch of the 45 degree valve seating surface?
A basic principle that stuck out in my mind in 1967 as a high school senior while studying formula one engine design as my senior drafting class project to draw an engine.
IIRC according to the reference book of F1 engine design, all engines make peak power at the exact same air velocity at the valve. As valve size and lift change the rpm goes up or down to suit then obtaining the magic velocity.
I have been looking like crazy to find a copy of that engineering book. I do still have a copy of my 3 liter engine drawing in my 12th grade drafting class folder. LOL
I think the port as a whole is in general, more important than 3 or 5 tiny flat cut angles to simulate a curved entrance and exit from the valve seat.
Look at the disaster of the combat or RH4 port. That may explain why my (28.5mm) 1-1/8" RH1 head on my combat bottom end made more power than the 32mm RH3 head 06-3327 ?.
Not really trying to dissuade anyone's views.