About 1000 miles ago I replaced the exhaust valve & guide ( cast iron ) in the 38 ES2.
The other day I decided to remove the head due to low compression .
My exhaust guide was worn out and the valve seat had a thin layer of carbon almost all the way around except for an area about 3/16. Underneath that carbon was a badly pitted valve .The seat in the head looks perfect.
The cavity for the intake valve spring was damp with oil as it should be but the exhaust was dry and had a thin layer of carbon on the sides and around the guide plus a small amount on the valve stem just below the valve collet groove . I scraped most of it off but you can see from the photo how dry it is.
Thoughts on this is appreciated.
I couldn't find any info on valve stem to guide clearance when I did my exhaust. The shop used .004. Is this correct for both Int & Exh ?
New cast iron guides and valves for the Int & exh have been ordered.
Note: I just discovered the springs are of the later shorter version ( L 53mm ) while using the original concave top cup.
New correct 66mm set to be ordered from Paul at racing Norton.
I’ve had valve face coking…
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Valve and Guide Wear.
I had a couple of experiences of extreme valve and guide wear with a 1936 pattern 16H and put the first incident down to unwittingly using austenitic valves in grease-lubricated iron guides but your engine presumably has enclosed valves and some oil mist ?
Unfortunately, it all happened again and I believe that tight clearances didn't help.
I now use G&S plasma-coated valves (the quality is fantastic and they feel ultra-smooth to the touch) and also Miller's VSPe additive. I realise that some regard these products as snake oil, but I was desperate and the manganese additive does have some claimed valve stem lubrication properties.
I'm not sure where this chart came from or why it only includes WD16H and OHC, but my feeling is that clearances on the loose side are a good thing.
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It looks like I'm going to…
It looks like I'm going to try a bottle of lead substitute for next years riding, hopefully it helps..
The inside of the rocker box is wet with oil for both In & Exh.The carbon build up in the Exh cavity must be from the oil cooking.
One of the previous owners fitted a grease nipple to the housing, not sure why filling the cavity with grease would help.
I've heard the carbon on the valve seat stops the valve from sealing causing the seat to burn creating pits.
But why does it build up in a thin layer? One would think when the valve seats under spring pressure the carbon would be removed.
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Unanswered Questions.
It's very difficult to establish definite facts. The photo below shows my SV ex. guide at about 1000 miles. The valve stem had become an abrafile with embedded guide fragments.
I no longer use grease on the '36 pattern guides but remove the nipple and pump in engine oil before each run. In combination with the G&S valves, fuel additive and generous clearances, it has worked so far.
In the early War Department schedules, the lubricant recommended for the open guides was not grease, but "Compounded Gear Oil" which is a paraffin oil with tallow used on steam engines.
I'd think that if you have carbon on the valve seats, the mixture is too rich. On the 16H, I now use a long mixing chamber nut as it was clearly over-fuelling with the original short nut. According to Amal literature, the long nuts were for inclined inlets...but modern fuels differ in specific gravity from 1930s fuel. I don't have an answer...but there are a lot of obscure questions...not least why some of us have so many problems and others have none.
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‘“Compounded Gear Oil" which…
‘“Compounded Gear Oil" which is a paraffin oil with tallow used on steam engines.”
Compounded gear oil and steam cylinder oil are available online.
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I’ve had valve face coking and pitting and I think I blamed a rich mixture. I daresay oil could cause it too.