valves and guides for NH

[volker.halbach]

I ordered a pair of plasma nitrite coated valves from G&S valves. What still worries me is that Paul G had problems with them, and they stopped only after he had honed the guide. I'll try the same. The guy at G&S runs his valves in old bikes with 0.0015" clearance (half of what Waller recommends) on the exhaust with no problems. Incidentally, the guides I removed are exactly 1/16" shorter than the new ones.

Paul J, thanks for your offer to look for NOS guides. It would be great if I could use a pair of these guides. Actually, I first read about your research into exhaust guides in 1992 when I bought an issue of Classic Bike in Germany, long before moving to England.

[nevhunter]

The galling I'm speaking of is pressure/heat welding of small particles on the stem from the cast iron guides when lubrication is limited. Any time the stem surface is wearing rough, galling has taken place, It's NOT normal wear. Cast iron is "fruit cake" material with free and combined carbon. and some steel carbides etc. The older Silchrome ,(Silicon Chrome alloy steel) valves are much better in that regard. Industrial chrome plate is good also on stems, but has to be ground to size to be done right. Nev

[nevhunter]

Perhaps the guy at G&S doesn't run his in any side valves or cast iron heads that run really hot and have open valves. . I can't see why you wouldn't just go to what the makers recommend and avoid the risk. It's a mistake to believe they knew nothing back then. Most failures are a result of trying to run things too tight these days.. I see it pretty often. Nev

[paul.jameson]

Having gone through the box, I seem to have 2 pairs of NH NOS guides. Having run the micrometer over them, it seems I have a pair at 0.6265, an inlet at 0.6255 and an exhaust at 0.6275 o/d. Where they came from I have no idea but they were probably accumulated last century! I used to buy NOS guides whenever I could find them as they seemed to work better than newly made ones.
When I fitted the 500 engine in my Red Hunter I fitted an open valve head which did about 500 miles before exhaust valve and guide problems occurred. So off it came and an enclosed head went on and stayed there. The open valve head is on the shelf and next to it are replacement valves and guides - together with a flexi - hone for improving the inner finish. So I have gone down exactly the same route as Paul Gasson - completely independently.
From my experience, the most critical item though is the bottom ring on the piston which needs to be plain, not an oil control ring, so that some lubrication can get to the exhaust guide.
PM or email me if any of my guides are of interest to you - they are surplus to my needs.

[volker.halbach]

Nev, I have no aspirations to experiment with reduced clearances. I had asked the G&S guy what he recommends against galling, and he just had never experienced galling with his valves in iron guides, even with these reduced clearances. I had asked about honing the guides or starting with enlarged clearance. I bought the G&S valves because they are plasma nitrided, given that other people had problems with untreated "stainless" valves.

Paul, thanks for looking for your old NH guides! The smaller inlet guide sounds right; but again 0.002" difference in the OD also between your guides. I would have thought that's significant for an interference fit. I'll first check the usual outlets whether they can tell me what OD their guides have. But probably they all come from the same source. I am also wondering whether my old inlet guide can be reamed and be used on the exhaust side.

[paul.jameson]

You will find that a VH inlet guide can be used as an NH exhaust guide, if push comes to shove!

[Paul Gasson]

Based on my experiences, I would think long and hard before reducing clearances. Each time the valve picked up material from the guide in my bike, it was surprising how many times the engine turned over before I could stop it. Those heavy Ariel flywheels just keep turning! I was so lucky because my '55 NH is running a standard piston at 6.2:1 so the valve, which always stuck open, did not touch the piston, but if it had, there could have been significant damage and a much higher cost to fix it.
Completely agree with Paul J. regarding the type of lower piston ring you are using. You need some oil to get into the upper cylinder to lubricate the exhaust valve and its probably not coming from anywhere else on your engine.

[wade.edwards]

All the talk about seizures has me concerned as I have an open valve VH to start up.
Has there not been a retrofit top end modification made to supply more lubrication to the exhaust guide?

[paul.jameson]

Its called an enclosed valve head......................

[wade.edwards]

That would be historically inaccurate. Might as well scrap Model D engines and replace them with Model As. That would also be a crime