Recommendation for custom valve seat cutting nr London
Discussion
Can anyone recommend a machine shop near London who do not insist that their 3 angle serdi machine (which are typically setup to give 30/45/60 degree cuts) is what I need to apply to my cylinder head?
I want to make a 75 degree cut from the base of the valve seat down into the throat and top this off with either a 38 or 30 degree cut for the value to sit on.
Also, recommendations to get a 30 degree backcut on my valves would be great.
I want to make a 75 degree cut from the base of the valve seat down into the throat and top this off with either a 38 or 30 degree cut for the value to sit on.
Also, recommendations to get a 30 degree backcut on my valves would be great.
I have used two different machine shops so far on my engine refresh. Power Units in Hatfield (just off the A1) and Gosnays in Romford. Neither are in London but are on the outskirts.
I did do a thread some months ago asking about a decent machine shop in the Herts/London area. I'll dig out the thread link and post it up.
Oh and don't try and DIY. It's a specialist job AFAIK. I like to try most things, but I wouldn't try and do a 3 angle seat job at all. Porting, well that's another thing....
I did do a thread some months ago asking about a decent machine shop in the Herts/London area. I'll dig out the thread link and post it up.
Oh and don't try and DIY. It's a specialist job AFAIK. I like to try most things, but I wouldn't try and do a 3 angle seat job at all. Porting, well that's another thing....
Here's the link I mentioned http://www.pistonheads.com/gassing/topic.asp?h=0&a...
Give Steve at Roland Alsop's a shout, I'm sure he could do whatever is needed
http://www.rolandalsop.com/index.php
http://www.rolandalsop.com/index.php
caduceus said:
I have used two different machine shops so far on my engine refresh. Power Units in Hatfield (just off the A1) and Gosnays in Romford. Neither are in London but are on the outskirts.
I did do a thread some months ago asking about a decent machine shop in the Herts/London area. I'll dig out the thread link and post it up.
Oh and don't try and DIY. It's a specialist job AFAIK. I like to try most things, but I wouldn't try and do a 3 angle seat job at all. Porting, well that's another thing....
cheersI did do a thread some months ago asking about a decent machine shop in the Herts/London area. I'll dig out the thread link and post it up.
Oh and don't try and DIY. It's a specialist job AFAIK. I like to try most things, but I wouldn't try and do a 3 angle seat job at all. Porting, well that's another thing....
I've hand cut seats before. No big deal if you take your time. I specifically don't want a 3 angle seat. Flow bench results suggests there is more to be gained from other techniques on my old Alfa head. It's a cost/benefit thing though, as I don't have the cutters in the angles and diameters I need for this job!
I don't quite understand this thing about such specific number of angles, it is like the seat exists separately to the rest of the head? If you are blending in the valve seats surely you are ending up with a radius into and including the bottom cut and the same for the top cut? To be honest I tend to use 30/45/60 and a 70 or 75 to guide where to blend from and to, except when we are playing with 30 degree seats when we are using a 15/30/45 cutter and a hand cut 60 bottom cut. Same with the back of the valve, does it make an iota of difference it it is a 25/30 or 35 degree back cut as most professional folk will blend all the angles together. My Mira cutters I use are variations of single or multiple angles 0/15/30/38/45/60/75 depending on application. My SP Nuway hand cutters are 0/15/30/31/45/46/60 and 70. The Peg orbital eccentric system I have allows me to have any angle I like from 0-90 degrees. The valve refacer again allows 0-90 degrees. The starting angles required will depend on the approach angle of the throat and the exit angles/shape in the chamber and vary from head type to head type.
Peter
Peter
fergus said:
top this off with either a 38 or 30 degree cut for the value to sit on.
Also, recommendations to get a 30 degree backcut on my valves would be great.
If you have a 30' cut on a valve for the seat I don't know how you are going to get a 30 back cut too? It's just the same cut carrying on....Also, recommendations to get a 30 degree backcut on my valves would be great.
I wouldn't get too carried away with what someone says about flowbench results (and yes i've used one many a time) as it is only a guide or a tool to recognise trends which often don't transpire as you think in a working engine. Flow benches don't replicate the amount of air shifted in a port, nor do they allow for the stop start motion and recovery either.
That aside, I can appreciate a 30'seat although they don't have the longevity of a 45'.
The OP doesn't quite explain himself. I see what you mean about his 30 or 38 degree angle for the valve to sit on then he mentions 30 degree back cut to valve not 30 degree seat on valve?
From experience of 30 degree seats and conversion to 30 from 45 it is very hard to move from a 45 to a 30 as one tends to need inserts to bring the seat back to the correct chamber height and the valve itself can end up a weird shape and special valves may be needed.
We tend to use the 38 degree lead in to hemi-type chambers above the 45 seat.
At the end of the day the aim of the game is to keep flow attached to the valve seat and valve for as long as possible as it lifts away from the seat, there is no hard and fast rule for the ultimate one size fits all in terms of seat angles and things don't always happen the same in real life when the engine is running.
Peter
From experience of 30 degree seats and conversion to 30 from 45 it is very hard to move from a 45 to a 30 as one tends to need inserts to bring the seat back to the correct chamber height and the valve itself can end up a weird shape and special valves may be needed.
We tend to use the 38 degree lead in to hemi-type chambers above the 45 seat.
At the end of the day the aim of the game is to keep flow attached to the valve seat and valve for as long as possible as it lifts away from the seat, there is no hard and fast rule for the ultimate one size fits all in terms of seat angles and things don't always happen the same in real life when the engine is running.
Peter
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