Lister D Inlet/Exhaust Valves

After removing the head to have a little look.... I then decided to remove the valves to see how bad they are....

anyway, to cut a long story short, from the parts lists etc it appears that inlet & outlet are the same part number...

but... on mine, the inlet valve is bigger than the exhaust... the ports are the same, but the valve itself is a lot "meatier" the exhaust is so small that after grinding the edge of the valve are right on the sides of the hole for the port.... if you ground it any more it would actually not even be seating any more...

so, my question is.... could it be that my exhaust valve has been replaced in the past with the wrong one? or could it have actually burnt away??

when I removed it the exhaust valve had not even been seating at all... (even though the engine ran okay...) both the valve surface and seat were totally covered in carbon...

should I buy a new exhaust valve ?

what year D type is it?? I am pretty sure 1 of mine A 39 maybe a 38 has a thin edge inlet valve and a thicker exhuast valve..

my inlet valve is much meatier than the exhaust valve. i could have a look and see if there is the part number on my valves tonight if you would like?

Should it make a difference one being thicker..

I understand that the original design had a thin exhaust valve and a thick inlet valve. That's probably counter-intuitive, but was that way for some reason.

The reason might be as simple as someone getting them round the wrong way on Lister D No 1 (first one made) and always been like that since.! Or (more likely) there's some engineering reason for this arrangement.

The exhaust valve is usually the hotter running, so it seems strange that this is a thin one, and the inlet thicker where thickness isn't really needed.

Ok, thanks for that.

there was some numbers on the "meatier" inlet valve, whilst the "thin" exhuast valve was with no numbers...

at least from what you mentioned about the sizes then it looks like that was what it should be .

it is a 1945 2Hp.

as long as i know that the difference in size was intended... I shall leave it how it is (it was very tempting to swap them around....), and just make sure I have lapped in the exhaust valve good enough.

maybe the reason for the thinner valve is to prevent less heat absorption?? ie whilst a thicker valve would be stronger... it would in turn dissipate more heat into the stem..........

The reason for the thicker headed inlet has been much debated up on, and no one seems to know the answer! Some say that it was to create a swirl effect for the incoming mixture, some say that the inlet was thicker as (on normal rotation engines) it was closest to the spark plug and got hot. Anyway the thicker one is definately the inlet!

Pete.

I could understand if it was just the inlet valve being bigger to let more air flow in but not for it being thicker unless it was for some kind of early swurl pattern. Give Stationary engine parts a call see what they say about the valves (pretend to be a valve buyer LOL) see if they just sell just the one type now.

Stu.