I have been trying to recover some missing horses - 50MPH is the best i am getting on the flat and that's a struggle.
Have now played with the cam timing, NOC website had a tip about exhaust valve still just closing at TDC and inlet valve just opening - both equally open at TDC. Have moved the inlet cam 1 tooth to get this, previously the inlet hadn't moved by TDC. No test run yet.
While i was at it also checked piston to head clearance and get 3mm (0.118") without a head gasket, have measured two used composite gaskets at 1.85mm (.073"). The combined 4.85mm (0.19") is way more than the squish values Ian W mentioned recently for M20's. Plenty of room to skim the head and up the compression it would seem? The piston edge is as good as flush with the top of the barrel at TDC.
Presumably with cast iron head and barrel running without a gasket is not feasible? It is done on alloy ES2's.

email (option): braunz@paradise.net.nz

Hi Iain..Can you post a picture of the inside of the 16H head?...Ian

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

Hi Ian
pic below of two heads, internal profiles differ slightly.
Left is off my bike, dims noted earlier are from this.
Right is a spare, has slightly more clearance. Interesting that the plugs over the piston sit at different heights - the plugs are the same length.
Sparkplug also recessed deeper on the LH head - when it's fitted.
Piston top is domed, has a reasonably uniform clearance from the head over the rear half (opposite the valves).

Hi Iain..Clearances inside the head are certainly large! There are a couple of points to consider here before machining the head. Firstly, it is not good to have the spark plug recessed too far into the plug hole. 'Shrouding' the plug slows down combustion, effectively retarding the ignition.
Second, it will be necessary to remove a fair bit of material from the head to create a better combustion chamber shape and produce an effective squish area.
This will have an effect on compression ratio and while these engines can benefit from an increase, maximum compression ratio should not exceed 7-1 to avoid 'pinking' problems. In fact this is considered the practical maximum for sidevalves and my own experiments with M20s in this area confirm that.
Calculating compression ratio on the M20 with the head off is a simple matter as it has a flat piston so it only requires head volume to be measured and with that and the cylinder volume an easy calculation provides the answer.
With a domed piston head volume is usually calculated by measuring the volume with the head in place and with the piston at TDC. (though I have done it before by taking a mould of piston crown and then measured that to calculate the cc of the piston dome, factoring that figure into the head volume calculation, not forgeting the thickness of the head gasket)
Personally I would stick with the head gasket to avoid potential sealing problems.
Another factor to consider if the head is substantially lowered is valve to head clearance at maximum lift...after dropping the head it may be necessary to machine some material from the head above the valves. If that is the case at least it would help to solve the problem of the recessed plug!
So, the firt job is to try and work some of these things out before hacking your head up...As you have already calculated the internal clearances in the squish area obtain some plasticine, putty or similar and carefully 'line' the squish area of the head to a sufficient thickness to produce the correct clearance..Then replace the head, with gasket, after positioning the piston at tdc and sealing the piston to cylinder gap with some grease.
Next obtain a burette glass..these can usually be bought from chemists if you don't have one. It is basically a glass tubular container graduated up the side in cc's. Fill the glass with a low viscosity liquid such as paraffin or petrol to the upper mark.
Next carefully pour the liqiud down the spark plug hole until it is JUST at the bottom of the threaded hole. Take care not to spill any liquid...
The difference between the volume of liquid you started with and what is left in the glass is the head volume in cc's.
Take this figure, add it to the cylinder volume and divide the result by the head volume...this will give you the compression ratio.
If it is under 7-1 you are in business..over 7-1 and you will have to look at the possibility of removing material elswhere in the head to lower the ratio (and you might have to do that anyway above the valves.)
Take a look before doing all this though to ensure you have surplus material to remove from the gasket face...if you don't then welding up the head over the squish area is the way to go rather than machining the gasket face...Ian

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

Thanks Ian, will give that liquid trick a go.
There appears to be a greater clearance over the valves at full lift than there is over the piston at TDC so they shouldn't be any problem.

Hi Iain..I currently have my M20 running at a 7-1 compression ratio without any problems. The Norton has a more compact combustion chamber than the M20 so potentially may work more efficiently after alterations and there are also benefits in terms of gas flow with a domed piston..another advantage.
A minimum valve to head clearance of at least a 1/16" will be ok. Re. the spark plug position after you have made any alterations to the head it may be possible to machine a little off the spark plug seat on the outside of the head to drop it further into the hole....Ian

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

Iain, I'd suspect that the valve overlap aspect is the basic cause of your problems. It's a quick visual check that things are in the right area.

Have you been following Mike Pemberton's articles over the last couple of months in "Roadholder" ? He goes into quite a lot of detail about getting the valve timing spot on and mentions a dog-slow post-war ES2 which must have been wrong since it left the factory !

If we go back twenty years, Nortons used to charge extra for 'Brooklands Special' 16Hs which were guaranteed to have achieved 75 mph and there were also 'Brookland Road Specials' which reached 70mph. The engines were run in a slave chassis...and what happened to the engines that weren't fast enough ?...They were sold to the punters who didn't pay extra - guaranteed slow ones !

These were one piece top ends of course but it shows the effect that a side valve casting can have on performance.

I know that Ken McIntosh has raised the comp ratio on his WD16H and gave me some figures over minimum clearances but I've lost the details with a hard drive crash. Probably worth a word with him.

I'll photograph some heads later.

I'm still puzzling over why Norton made engines without valve timing marks..the inevitable result is some bikes running about with the wrong settings. Maybe they thought it added to the 'mystique'..either that or they weren't prepared to commit themselves to the exact position of the cams.. ..Ian

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

I think that you're probably right, Ian ! Pre-war Norton engines had timing marks stamped and the implication is that WD engines did also. Spare parts, however, don't seem to have been, perhaps because the gears were stamped in the engine shop after final assembly. Most ex-WD engines have undergone multiple rebuilds during a time when NOS parts were ten-a-penny.

The crank pinion has three keyways, allowing incremental adjustment of the valve timing and was also used on the ohv engines. I suppose that if stamped gears became mixed up in an army workshop, that would be worse than no markings at all.

Norton clearly didn't make the transition from a small manufacturer of selectively assembled machines to the era of mass production all that cleanly.

It is perhaps strange that previous builders don't seem to have marked their own engines once they've checked the valve timing.

The timing pinion and cams have pin marks on them which were carefully photographed and reassembly was as found, but they appear to have been set up incorrectly before my efforts.
Rik, yes i have been following the articles, and have also spoken with Ken a few times. He couldn't remember exact figures when we spoke but it may have been around a head gasket thickness that he shaved off.
I am looking into a solid copper head gasket, given the number of times the head is likely to be on and off before i am done, so may get .042" or thinner to take up some of the adjustment.
Will be test riding with the std head and gasket to finalise the valve settings before going the next step though. One change at a time.

email (option): braunz@paradise.net.nz

Have just reread all at more leisure and good feedback thanks to both.
I'm sure you are correct Rik and the cam timing will be the main root of the current under performance.
Once that is sorted the thought on upping the comp ratio is to improve upon perfection and gain a little extra hp - in an effort to minimise the length of the queues of the young and impatient behind me.

email (option): braunz@paradise.net.nz