Following a recent head refurbishment on my 1960 Model 50, I experimented with a previously unused Xmas present, a cylinder head air pressure testing kit - no leakage whatsoever. As a follow up to this, I decided to investigate using air pressure to check exactly when the inlet valve opensby fitting a rubber glove over the carb intake and a timing disk on the crankshaft end. The instant the inlet valve opens is immediately obvious by observing the first slight movement of the rubber glove due to air pressure. The full two finger salute illustrated below shows the inlet well open !
http://i1236.photobucket.com/albums/ff451/PeteMcD/DSC_0005_zpsyraey0zl.jpg
Unless there is something basically wrong with my method and thinking, this indicated the inlet valve starting to open at 58? BTDC on the exhaust stroke instead of the proper 28? BTDC, in other words 30? too far advanced. Likewise, by listening for the cessation of air through the exhaust port, the exhaust valve appeared to be closing at 70? ATDC on the induction stroke instead of the required 29?, or 41? too far retarded.
The cam / pinion timing marks are where they should be as shown below:
http://i1236.photobucket.com/albums/ff451/PeteMcD/Timing%20Marks%201_zps8wgpjjpi.jpg
I am aware of an earlier thread on a ES2s ( http://www.nortonownersclub.org/noc-chat/technical1-singles-forum/315728931?b_start=0#842994503) suggesting incorrectly marked timing pinions and I also have a Wideline ES2 for which the previous owner had the engine rebuilt by Mike Pemberton, it appears that wrongly marked pinions are not unknown.
Mike's report on this states " on assembling the engine and checking the valve timing with a timing disc on the crank I discovered that the inlet valve was only starting to open at 7? BTDC. This engine must have had very poor performance when last on the road. By advancing the inlet cam by one tooth (18?) I have corrected the timing to 25? BTDC. I can only assume that the inlet pinion had been stamped incorrectly from new !!! "
My M50 engine is within a month of this ES2's, but having both inlet and exhaust pinions wrongly marked seems bizarre. Besides which, both would require adjustment by two teeth (36?) and in the opposite sense. Even that would give settings 5 or 6 degrees out. Unlike my 16Hs, the later half time pinions have just the single key slot so a 6 degree adjustment is not feasible.
During the five years / 5000 miles that I have had my M50 it has always seemed a bit down on power, particularly when tackling hills, compared to what I remember back in the day. I had put it down to rose tinted memory, being a few stone heavier and it being just a 350cc. Starting and smoothness have always been OK, the only other oddity has been an occasional backfire on the overrun which the normal checks for leakage and mixture failed to rectify.
My concern before making radical alterations to achieve nearer the correct timings is whether there is something fundamentally wrong with my method of testing and whether the M50 would show much more acute symptoms if the valve timings are actually as I have found.
Any suggestions appreciated.
P.S. Couldn't get the HTML method of direct Photobucket image insertion to work !
I like your method. You co…
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I like your method. You could also try a condom and see if that gives you more pleasure, ahem, while setting up your beloved bikes. I suspect you will find it more sensitive.
I doubt that you need to get the timing closer than 6 degrees on such a mildly tuned engine.
Should you go high-tech and borrow a dial gauge or two (as I did recently for a rebuild), the valves on most engines should have equal lift at 4 degrees BTDC. Overlap is more important than exhaust opening or inlet closing time.
It is quite possible that the engine assembler in the factory noticed the incorrect valve timing, and that the engine left the line acceptably timed, but that someone working on the engine 'corrected' the timing to the marks. When you are satisfied with the timing, don't forget to paint the correct timing points on the gears. Note to self.....
Paul