Vintage valves

[ian Howell]

Following the diagnosis of a badly worn inlet valve as the cause of my 1930 Long Four 'ticking over' on only one cylinder, I discovered that the valve guided was made of BRASS and was of a slightly different design to the original item. It was badly worn - about 20thou' slop, so that was where the extra air was getting in.

I removed a serviceable guide from a 'spare' cylinder, fitted it and ground in the valve.

So far, so good. but; -

Whilst reviewing my 'stock' of serviceable spare valves I noticed that one, marked 'EN 52' has a much smaller diameter head and shaft than all the others.

Now EN 52 is a known material for exhaust valves, but the valve I found fitted with the brass guide was the same shaft size (3/8in dia) and head as the inlet valve in that cylinder. Could this mean that whoever went to the trouble of making the brass guide - possibly during wartime shortages - also had to fit an inlet valve in place of the correct item and made the 'new' guide to suit?

If the exhaust valve SHOULD be the smaller item, then I will need to revisit my latest endeavours, source from JCS and fit a correct guide with the smaller valve in my stock and regrind the whole shebang. I will also need a smaller threaded valve spring cap and end nut/cap.

Or have I got it all wrong? (Probably).

[Keith Clements]

Hi Ian, I am not conversant with that engine but I think your suposition is probably correct. Exhaust valves are usually smaller than inlet. Guides are usually cast iron. Also usually the stems are same size. Maybe a larger valve was fitted because the seat had worn too much or was damaged or cracked.
I was confused because you started by talking about a fault with the inlet then at the end about the exhaust

[ian Howell]

Keith; -

Thanks for the quick reply. full story;

After my last 'show' last year I noticed 'tickover', on only 1 cylinder - NEARSIDE.

Removed OFFSIDE cylinder to investigate - found badly worn BRASS inlet valve guide.

Removed brass guide and fitted 'spare' cast iron guide, reground inlet valve. So far, so good.

Whilst I was 'there' I decided to regrind the exhaust valve - noticed it was same size as the inlet valve.

Refitted cylinder, set tappets, reassembled engine and ran. All OK - I think.

When tidying up my remaining valve stock, all presumably Jowett as they all have a threaded 'collet' end, I noticed that one, same length as the others, has a smaller head diameter, a thinner 'stem' and is marked 'EN 52' on the head.

This is presumably an exhaust valve - correct material - but the thinner shaft is a puzzlement.

The 'scrap' cylinder that I took the replacement guide from has different sized ports and valves, as one might expect, but both guides have the same 3/8in diameter bores.

Is the 'thinner' valve from an earlier, or possibly later, vintage engine.

[PJGD]

Hi Ian;
I think, but don't know for sure, that EN52 became generally available in the late 1930's, so your valve is perhaps from a later engine — 10 HP perhaps?

Philip

[ian Howell]

Philip ; -

Thanks for that. Great to 'hear' from you again. Remember Harrogate.

I found your treatise on Jupiter valve timing. I suppose this came too late for the Le Mans team, fatigue creeps up.

Back to my 'funny' valve, I suppose it IS a Jowett item, what with the threaded tappet adjustment, but were there any other makes that used this method. We need to know these things.

Ian H