I have spotted these valves on ebay for a 16H but why does it say that despite fitting models from 38-53 it says that they don't fit WD models, but why, does this prove that they did use a different combination of valve/guide materials on WD models? If so then surely this could be the solution to the wearing out of the valve guides that some 16H's have been experiencing?
http://www.ebay.co.uk/itm/Vintage-NOS-Norton-16H-valves-job-lot-of-six-/380611980143?pt=UK_Motorcycle_Parts&hash=item589e3deb6f

email (option): davmax@ntlworld.com

Dave, they are indeed 1938 pattern valves (the collet grooves are closer to the tip than on the earlier motors).

The '38 engines had oil lubricated valves and they are austenitic which is something that apparently shouldn't be used with unlubricated iron guides. It is indeed what I inadvertently did the first time and may have been the cause of my initial catastrophic ex. guide failure. It doesn't though explain why the inlet guide went the next time as they were correct ex-WD valves.

G'day Rik,
Forgive me if this was covered in your original guide failure thread (can't seem to find it) but I would have thought that rapid inlet valve and guide wear (especially as the valves were WD stock) would be caused by an over rich mixture flushing away any lubrication.

email (option): spacemonkeym@gmail.com

The only thing Rik left out is the WD 16H is called the 37 pattern engine

email (option): horror@blueyonder.co.uk

Matt, thanks for your comment. I have heard of the richness being a possible cause but it's nice to have it confirmed. The blackness on the rear stand and the amount of blowback that I suffer from do point in this direction. Nortons do blow back a bit but mine seems excessive.

It's a puzzle as I have gone as far as building another NOS carb and am running a long mixing chamber nut to lower the fuel level. Low-end pick-up was better with the higher float level so I don't want to lower it further and am a bit puzzled as to why the best-running settings of air screw, needle height, cutaway and main jet (all are leaner than standard) should be causing richness.

I really don't want to fit a Mikuni....

It's always referred to as the 1937 pattern engine but it isn't really. The engine changed for the 1936 Model year and all parts from '36, 37 and WD16H engines are interchangeable.

The 1937 civilian frames had horizontal saddle spring lugs so the WD bike is really more of a 1936 machine.

The only change that I can think of which occurred in 1937 was the adoption of the cvc dynamo instead of the three brush system (but everything in service was retro-fitted anyway).

Hi Rik, by blowback do you mean it's spitting back through the carb? If so, thats a sign of it being too lean. My ES2 used to do it a lot and someone said that was the reason. I put the choke on and it stopped.

My 16H stand is black but when I look at the plug it's very clean, which I am finding worrying on an old single. I think mine is running too weak and maybe needs a bigger main jet. This may also be the reason it doesn't go very fast and doesn't like it when it's hot.

email (option): horror@blueyonder.co.uk

No, it certainly doesn't spit back but with the slide raised, it's possible to see fuel vapour being blown back out of the carb. My first thought was valve timing but both in. and ex. are open the same amount at tdc, as they should be. It must be over-fuelling somehow but I can't work out why.

I don't get the colour at the plug that I'd expect from the soot at the end of the silencer. I put it down to modern fuels. Mine's a flyer by the way and doesn't seem to get unduly hot, although the oil tank gets pretty warm when compared with the Commando.

Hi Rik
my 16h has always had a bit of blow back, in fact over time its discoloured the oil tank permanently. My plugs also on the light side but I don't think there's anything wrong. Both my 16h's where like that I think its just the way they are.

Spitting back in the carb as the throttle is opened indicates weakness...Blowback of 'wet' fuel indicates an overly rich mixture, but not necessarily throughout the carbs operating range...It can be hard to pin down at exactly which point the mixture is over rich and rapid opening of the throttle with the bike on the stand can induce this condition when nothing is wrong...Ian

email (option): ian@wright52.plus.com

I read somewhere that M20's are prone to spitting back through the carb with a risk of the carb catching fire!

Old Wives Tales..Like sidecars coming off, bikes firing every other lampost, and sidevalves that would go uphill downdale in top gear with the wife and nine kids in the sidecar....Whoever said that didn't know much about M20s... ...Ian

email (option): ian@wright52.plus.com

I've just remembered where I read about M20's catching fire. It was on the "Facts" page on this website!! So it must be true

Lot's of things are stated as 'fact' when in 'fact' they are based on anecdotal evidence or oft repeated 'folk lore'...Like buried Harley Davidsons and Spitfires.. ....
I've owned numerous M20s/21s over about four decades, have covered a lot of miles (I've done over 100,000 mls. on just one of them) and have never experienced this 'tendency'..I've also never met a current or past M20 owner in that time who has described a similar experience..That's not to say it's never happened but the M20 is no more prone to it than any other bike...it's a myth...Ian

email (option): ian@wright52.plus.com

If I open the throttle 'sensibly' then I don't see any blowback but in use, it definitely occurs. This could be because my preferred fantasy when I'm out and about is flat-on-the-tank Jimmy Guthrie rather than bolt upright 'Jack Service'

Maybe drop bars and rearsets are the next modification Rik

email (option): horror@blueyonder.co.uk