Back cut valves

[Jhonno]

I tagged this on the end of my previous thread, but it is probably one on it's own..

Back cut valves..



Are these worth doing? (Old valves..)

The exhaust valves in particular seem to be worthy of it..

Edited by Jhonno on Tuesday 17th July 19:20

[Jhonno]

Oh OK..

It's not removing lots of material, just a small chamfer to lead into/out of the seat cut? Seems to be a common thing with Yank V8's amongst other things.. Valves are just stainless. Not sodium filled or the like.

[Jhonno]

No, not what I meant!

Just to add a small 30/32° chamfer to lead out of the exhaust seat surface.. Possibly in on the inlet to, depending on how it sits on the valve seat (need to check with engineer's blue)..

Picture is just to show the shape of both valves.. Reference to the exhaust valve was because it is has a much more defined ridge after the seat surface...

It seems to yield some decent results on various engines, looking at flow figures.

Apparently I need to work on my communication skills in this forum!

Edited by Jhonno on Tuesday 17th July 19:36

[Jhonno]

Like this..

[Jhonno]

Thank you..

Interesting information there. Possibly not worth it for my valves then.

[Jhonno]

tapkaJohnD said:

jhonno,

what you suggest is part of the 'three-angle valve cut' concept. See http://johnmaherracing.com/tech-talk/3-angle-valve... and many other references.

John

John,

Yes, this is indeed the theory I've been reading up on.. I'm yet to find a negative result for it.

[Jhonno]

Mr2Mike said:

stevieturbo said:

No it is not worthy of another new thread.

And no, I would not randomly be removing lots of materials from valves...especially exhaust valves.

I did my apprenticeship with a lad who tried to waist the valve stems in his Escort Mexico using an old lathe in our machine shop. The material was so hard that even carbide tools struggled, and he ended up with a terrible finish with some nasty ridges and grooves. Needless to say, one of the valve heads dropped off within a few days of using it, trashing the engine.

Ouch! I hope I'm not at that level!