Valves - how to identify ?.

[Josh Cox]

Evening,

How do you identify the difference between inlet and exhaust valves ?.

My A10 has a cast head the inlet and exhaust are very very similar.

The only different I can see is that the exhaust valves appear to have a bit more of a lip on the seated face ?, am I on the mark ?.

The part numbers are obscured.

[chaterlea25]

Hi Josh,
Test with a magnet
"Normally" exhaust valves are made from austenitic steel which is non magnetic!
some BSA ex valves have G2 marked on them
Poor quality pattern valves may be magnetic (Bin!)
If all 4 valves are non magnetic I would go with the wider seats on exhausts
Regards
John O R

[Josh Cox]

Chaterlea25,

It would appear you hit the nail on the head:

The old valves are as you said, the inlet were magnetic, the exhaust were not.

Have been given a set of hardly used valves, they are all non magnetic, two have a bigger, higher and rolled lip on the mating face, which I will use as exhaust, the only other difference I could find is the distance between the top of the collet recess to the top of the valve was slightly different, also agreeing with your statement (the exhaust valve was slightly longer).

Many thanks,

Josh
The one on the right is the exhaust.

[chaterlea25]

Hi Josh,
Just to confuse you some more,!!!!!
looking at the photo you posted it looks as if the seating on the left hand valve is more marked (slight pitting) as if it had been used as an exhaust valve,
Sometimes you can see the ex valve will be discoloured further up the stem than the inlet from the heat
I'm not sure what effect the lip would have on the exhaust side??????
So more confusion???
I did not make any remarks as to the valve lengths, I have some new old stock valves (somewhere) I will try and dig them out and measure the lengths
Regards
John O R

[Josh Cox]

Again on the money, the ones on the left were used as exhaust valves on the old engine.

Have worked on Helicopter engines, they also use a lip on the exhaust valve, the way it was explained to me, I must add we were both well pickled at the time, was that the lip starts to obstruct the airflow before the seat shuts it off, at the time I thought he was talking through his rear end,,,,perhaps not as it would turn out.

[olev]

Here is a couple of valves supplied with a reconditioned A7 head I just bought.
They are supposed to be toyota valves touched up in a lathe.
They are slightly bigger than those in the original head.
He has fitted inserts and machined the guides to take seals.
Can't make up my mind about fitting the seals. any suggestions??
cheers

[chaterlea25]

Hi Again,
I have seals on my SR head and very tight clearances on the guides, NO PROBLEMS (so far)
over 8K miles,
Interesting theory about the lip??? Josh, even though I have seen a lip left on the outer edge of ex valve seats supposedly to stop ex gasses curling back into the cylinder
Cheers
John

[olev]

Nice work John O
I assumed the nice shiney valve was the intake and the black one would be exhaust.
Your magnet test tells me I was wrong and they are the other way round.
cheers

[BSA_54A10]

They are shinny because of the high nickel content of the high temperature alloy.
The intake is a much lower alloy as it rarely ever gets really hot as opposed to the exhaust the runs some where between bright red and yellow hot.

[RichardL]

No kidding? I never thought about them changing temperature color, but suppose it makes sense. I may have to go look up at what color vs. temperature they start to get soft. Do you happen to know?

Richard L.

[BSA_54A10]

Around 900 to 1100 C.
That is why vintage bikes used exposed sodium filled valves, to stop them welding closed.
The seats can dump the heat into the head and the piston conducts it through the walls and rod and also gets oil cooling and air cooling from underneath plus dumps a bit into the incoming charge but the poor old exhaust pokes its poor little head into 1600 C gasses 5000 time a minute.
Unleaded burns a bit hotter I think , LPG burns hotter still and ethanol burns a lot colder which is why they are busting a gut to get more of it in "fuel" as the colder combustion produces far less nitrides, argonates and all the other oxadized compounds from all the weird flotsum & jetsum that makes up the last 0.5 % of what we call air.