From: Dave Baker
Newsgroups: rec.crafts.metalworking
Date: 29 Jan 2001 20:06:44 GMT
Subject: Re: Engine Valve Refacing

>From: eea101@psu.edu  (Edward Allison)
>
>Is there an advantage to grinding valves rather than cutting them on a
>lathe with a carbide tool bit?  It seems people are willing to pay
>hundreds of dollars for old valve grinding machines on Ebay.  Thanks,
>EEA


For speed and quality of finish you can't beat a proper valve grinder. Over
here old Black and Decker or Wolf grinders don't go for much money usually
unless you buy through a dealer. I paid £100 for mine several years ago and
it's worth its weight in gold. Must have put thousands of valves through it
since then.

On a lathe you get push off and chatter on valve steels, especially on 21/4N
stainless exhaust valves. Makes it tricky to get a perfect finish. You need a
collet chuck too ideally, or at least lots of messing about on a 4 jaw to get
perfect concentricity. a good enough way to do a one off set but I wouldn't
want to have to use a lathe all the time.

The thing that most people get wrong is lapping the valves in. The best way to
lap valves in is DON'T !  It always leads to a concave seat face because most
of the lapping action takes place in the centre of the seat width. Use very
fine paste for no more than 10 seconds just to check that everything is true.
If it isn't then lapping won't solve it - a proper seat and valve recut is
needed.

I can put a heavily lapped valve in the grinder and watch it cut just at the
outer and inner edges of the seat to start with because the middle of the seat
is abraded away. A race customer used to collect cylinder heads from me ready
to fit and then lap the bloody things in for another several minutes per valve
because "that's what they used to do in the old days". Every time his heads
came back for refurbishment I had to cut several thou of concavity out of the
valves and seats to put right the damage he'd done.


Having a well rounded education ought to mean more than having degrees from the
school of "My Dad Always Said", the college of "It Stands To Reason" or the
university of "What Some Bloke in the Pub Told Me".
http://www.pumaracing.co.uk/