I recently posted on plans for some performance improvements on my 16H. Despite correcting the cam timing a while back it was still struggling to do better than 50MPH on the flat.
Have found that the head on my bike had 3mm clearance over the piston at TDC without a gasket, so 4.6mm with the old composite gasket. In addition the tip of the standard spec 18mm plug was lost up in the plug hole.
I had a spare head which looked more promising both with the plug position and visually a smaller volume. And with a 0.66mm copper gasket (thankyou Sam) it was cc'd at 5.4:1 comp ratio. 30 thou off that head and 6:1 is what we have settled on. It has been briefly run at the shop but I won't get to seat of the pants test if for a few weeks as some parts including the tank are off getting a birthday paint job.
We haven't cc'd the original head but it was obviously running at well below quoted standard comp ratio, which would explain the less than startling performance even by 16H standards.
Did Norton do an even lower performance head for these things – for stationary use perhaps??

iain

Hi Iain..
I'd be interested to hear how it goes when you're done...

You need to address the recessed plug (if you haven't already)....'Shrouding' of the plug slows down combustion, in effect, retarding the engines ignition timing...and we all know they don't run well retarded....Ian

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

Will do Ian.
The shrouded plug is on the original very low comp head, the replacement (and now planed) head has much better plug placement.
So once all is back together i can do a run with the old head and then switch to the "performance" one for a quick comparison.
I hope there will be an obvious difference
iain

Hi Iain...It should be better...The American tuners tend to say if you don't have a 10% improvement you won't feel it on the road...Fortunately 10% of 14BHP is only 1.4BHP and you might get that if your luck holds up... ...Ian

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

If its an increase in speed you're after then the first thing to do is higher the gearing either at the engine or the gearbox sprockets. The WD 16H was undergeared compared to the civvy bikes as use off road was anticipated. Personally I wouldn't want to be on one at much over 50.

The M20 starts to get a bit 'vague' in the stability department at about 70-75mph....
I had it flat out on the beach up near Cherbourg and lived to tell the tale and on a good road it just 'wanders' slightly at those speeds..
I don't think I'd fancy it on a bumpy road though..or going round bends.. ...Ian

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

yea my WM20 likes to get into a tank slapper over 65 but my plunger/tele model is ok at 85mph.
why not weld up some of the combustion chamber on the Norton as i did on three M20s, makes a big difference

....Because the beautiful domed piston will hit it !

I agree Keith, 50 MPH cruising is all i would be brave enough to maintain. At present that is only vaguely possible on the flattest of roads, which there aren't too many of.
A little bit more grunt for the hills is the aim. The sprockets are already civvy spec but the throttle ceases to have any effect long before speed becomes an issue. I am planning to do the Mail Run next year - a girder fork run from Taupo to Napier. Will have to climb from sea level to 800m on the return home - it will be a loooong trip at current set up.
I dont have the figures to do the calc at the moment but the original comp ratio looks to have been well below 4:1
cheers
iain

['I dont have the figures to do the calc at the moment but the original comp ratio looks to have been well below 4:1..']

That would make it an ideal candidate for supercharging... ....Ian

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

My 16h only has a slight domed +40 piston and there is loads of room for a bit of welding plus a .6 mm solid copper gasket, then put a radius on edge of barrel plus some gas flowing on inlet and around valves/guides should make loads of difference

The combustion chamber shape reflects the piston crown. If the compression is to be raised then surely it's best carried out, as Iain has done, by simply skimming the head ? Provided that this doesn't compromise clearance above the valves, surely this is the easiest and most reliable method. It also gives some way back via a compression plate if results are not as expected.

This photo is not a scientific experiment but it doesn't seem to show a huge volume above the piston.



Here's a picture for Iain showing a selection of heads. The three on the right have all come from used 16H engines and have a plug thread depth of .733" - The one on the left is NOS in Cosmolene and has a boss that measures .867" which is a bit extreme with a .5" reach plug. It could presumably do with machining down a little. A 1/2" reach plug can measure up to about .6" before taking any crush washer into account.

Thanks Rik,
should have my bike (less the bits at the painters) back next week. Will do a comparison at that stage.
cheers
iain

Might also be worth checking out the carburetter........our 16H had a NOS WD carburettor, but when fitted with a pattern main jet it wouldn't run very well at all, but after fitting a genuine Amal 170 jet it was much improved......

Also found that the bike was particularly sensitive to any changes in needle position......and lowering or raising seriously affected the performance negatively.........

And don't get me started on the 16H-type jet blocks that often appear different to the normal type encountered on most other models........

email (option): sjmwdbikemad@aol.co.uk

Now there's an idea ..... i won't be following up on.
It would certainly be different.

Good point Steve. My original carb was more than tired so i have a new (modern) 276 fitted, but i am guilty of assuming that the factory settings would be correct and so havent played with that at all.
iain

Good things come to those who wait - received the last piece of the jigsaw back yesterday, tank from the painter. Formerly rusty pitted chrome with red panels and gold pin stripes, now rusty pitted chrome with Norton Silver panels and black + red pinstripes. Much nicer
First start up and impressed with the swifter throttle response, a quick ride up the driveway (up to second gear) and feels much more responsive.
A bit of fettling to do - getting a good backfire on the overrun at present, much to the neighbours kids surprise.
Something to keep me busy over the summer break, and it doesn't involve gardening.
cheers
iain

Summer...what a lovely thought..

Interesting stuff Iain...keep the reports coming in until you get the final result....Ian

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

Ha! Classic British understatement...starts to get a bit "vague"...

email (option): bobdukw@aol.com

I do it without even thinking Bob..If it's a force 12 storm I'll say 'It's a bit breezy out'...I don't think it's common with younger people any more though...

Personally I always think of the words of Capt.Titus Oates on the Scott expedition, when he went out into an arctic blizzard and sacrificed himself to give the rest a better chance....'I'm going outside...I may be gone for some time'....Classic...

"The British are feeling the pinch in relation to recent terrorist bombings and threats to destroy nightclubs and airports, and therefore have raised their security level from 'Miffed' to 'Peeved.' Soon, though, security levels may be raised yet again to 'Irritated' or even 'A Bit Cross.' Brits have not been 'A Bit Cross' since the Blitz in 1940 when tea supplies all but ran out."...Ian

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