Oversize Valve Stems

[hddennis]

Got an unusual question for machinists or engine rebuilders. Found a set of N.O.S, valves for my Maxwell for sale online. I was just about to buy them as spares when I noticed the box is marked oversize stems. Normally a restorer would be happy to find this as it meant he could get a little more use out of worn guides before replacing them. My problem is my 2 motors are standard bore so I think they have low mileage and probably the only reason to replace the valves would be if badly burnt or pitted from rust. My question is would it be possible to cut the valve stems back to standard?

 

Howard Dennis

[Rusty_OToole]

Shouldn't be too much problem for a good man with a lathe. But by the time your valves wear out or burn out, enough wear may have taken place to make oversize stems a good idea.

[Seldenguy]

I had a standard bore engine in one of my cars that was "owner reported, low miles". That one needed an overbore of .040 thousands to get the cylinders centered back over the crankshaft. Any time you can upgrade for only the cost of reaming the valve guides instead of turning the stems to fit old guides I most definitely would ream. But, I have done things irrational before without thinking it out. Good luck on your decision.  --Bob--

[Bhigdog]

1 hour ago, Seldenguy said:

I had a standard bore engine in one of my cars that was "owner reported, low miles". That one needed an overbore of .040 thousands to get the cylinders centered back over the crankshaft. Any time you can upgrade for only the cost of reaming the valve guides instead of turning the stems to fit old guides I most definitely would ream. But, I have done things irrational before without thinking it out. Good luck on your decision.  --Bob--

 

Especially since the stems really should be ground to ensure surface finish and lack of taper rather than turned............Bob

[Ivan Saxton]

"Oversize" often does not mean a very big increase in stem diameter. A digital calliper  will show you the difference;  but you open the guides carefully to fit with a reamer or with a "dunny-brush"  hone .  The hone gives an ideal cross-hatch surface finish.  The best instructions for this are in a DVD produced By Guy Croft, on cylinder head reconditioning.  He used to be a builder of Formula 1 racing engines,  both V10 Arrow and V8 Minardi.   Since then his work has been on the in-line 4 cylinder  Twin OHC FIAT/ Lancia engines for special purpose.

[Ivan Saxton]

I  apologise that the Post above should have been more comprehensive.  I had accumulated sleep deficit over the weekend.     You can adapt valves with longer stems, and with larger diameter heads and stems,  and I have done this when I could not access correct replacements for my Lancia Aurelia.  This may be quick and easy if you can use a centreless grinding machine to reduce the stems;  but doing it in the lathe as I did then, you have to be very careful to achieve finish and size without discrepancy of taper.  Your micrometer needs to be able to read to a tenth of a thou.       Very, very many antique cars were made long before Elwood Haynes' invention of "Stellite" , which could give poppet valves good hot-hardness,  and resistance to rapid oxidation at or near red heat.   The original valves of my 1911 4 cylinder Napier had perfect stems, but the faces on the valve heads were not brilliant.   When I heated the valve faces carefully with a carburizing flame on the oxy-acetylene torch, (as you do), even the exhaust valves  oxidized so rapidly that it was impossible to wet and build up the faces with the cobalt filler rod.   The job needed a little cunning and trickery.   I cleaned up the valve face again with the grinder, then coated it with nickel powder from a little powder-facing torch;  and the interface of nickel powder protected the valve so that the Stellite rod would wet the surface and build up in the normal way.    This accords with Tom Reece's guidelines in Antique Automobile ,  that you  Repair, or Replace As Necessary.

I guess that article of Tom's may be worthy of republication, West.

[hddennis]

Thanks Guys, it sounds like the easiest thing would be to open the original guides to the oversize.

 

Howard Dennis

[Rusty_OToole]

 I don't know how they did it when your engine was made but most oversize valves I have seen, the stems were only .003 bigger than standard, about the thickness of a piece of paper and impossible to detect with the naked eye.