New valves.

MikeG

MikeG

VIP MEMBER
Joined
May 31, 2012
Messages
1,242
Country flag
1971 750 engine with standard head and valves. I'm putting new AN sourced valves in. Just wondering if having the seats cut and valve face ground is a must if you can get a decent seal by hand lapping. Going back to my misspent youth I remember more than once just replacing the bad valve giving it a hand lap and away we went.
 
I hate having to take something apart after thinking I had fixed it. If it were me, I would take it to a machine
shop and get the seats cut etc and say I will lap the valves myself!!
 
MikeG said:
1971 750 engine with standard head and valves. I'm putting new AN sourced valves in. Just wondering if having the seats cut and valve face ground is a must if you can get a decent seal by hand lapping. Going back to my misspent youth I remember more than once just replacing the bad valve giving it a hand lap and away we went.
Click to expand...
I always hand lap. If I get an even marking all the way around the valve and seat somewhere in the 1/16" range, I consider it good unless the leak test I do after cleaning all and finally installing the valves shows something - never has, but I do the test anyway.

I even try it if I change a guide. That's more 50/50. If I do cut a seat, I do the most minimal possible. I don't do anything to new valves except clean and lap.

This works very well - way better than a stick with suction cups: https://a.co/d/eAMXMjv
 
If hand lapping does the job then away you go, only exception is if you have access to a Neway seat cutter. With new valves and having a Neway seat cutter I would cut the seat and then call it a day.
 
kommando said:
If hand lapping does the job then away you go, only exception is if you have access to a Neway seat cutter. With new valves and having a Neway seat cutter I would cut the seat and then call it a day.
Click to expand...
Which of the Neway kits is good for Norton heavy twins?
 
I did not buy my set solely to cut 45 degree seats but to also cut 60 and 30 degree to unpocket well worn seats and improve flow with 3 angle seats.

So 234 for 30 and 45 degree and 205 for 60 degree.

I also worked on the assumption that Neway were being conservative with their diameter range and by moving the carbide cutter further up and down in the groove they would cut a larger and smaller seat. Testing once I had them in my hand confirmed this suspicion. The carbide cutter blades are solid and will cut well outside the published diameters. So this sets covers Tiger cub to 850 Commando.
 
Last edited:
Unless the guides have been replaced, re-cutting the seats may not be necessary. I would lap the valves enough to leave a witness mark on the valve as well as seats that have been darkened with a black permanent marker. This will indicate where the valve head and seat interface. If the interface is too close to the edge of the valve or seat, cutting the seat would be necessary.
 
That's what I used last time and it worked a treat. My little valve spinner device flew apart so I thought why not just chuck the cordless directly onto the valve stem?
It worked much better than the rubber thing ever did.

Glen
 
kommando said:
I did not buy my set solely to cut 45 degree seats but to also cut 60 and 30 degree to unpocket well worn seats and improve flow with 3 angle seats.

So 234 for 30 and 45 degree and 205 for 60 degree.

I also worked on the assumption that Neway were being conservative with their diameter range and by moving the carbide cutter further up and down in the groove they would cut a larger and smaller seat. Testing once I had them in my hand confirmed this suspicion. The carbide cutter blades are solid and will cut well outside the published diameters. So this sets covers Tiger cub to 850 Commando.
Click to expand...
I found using the three different angle cutters had a beneficial effect. A ridge above the valve seat might not be good. In our town, the best engineering shop is the one that does the car work.
 
You must log in or register to reply here.
Back
Top