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Collection, Preservation and Display of Old Lawn Mowers

1932 24" Dennis Z Type ignition timing

I have a 24" 1932 Dennis Z Type. Took the engine apart to sort some oil leaks and other issues out, at the time didn't realize the ignition gears didn't have alignment marks.

It is all back together now after some trial and error changing the timing I got it to run. Now it is difficult to start and I would like to verify that it is timed up correctly. Was running well before the rebuild.


Does any one have any ideas on how to verify the timing?

If I had another one I would take the side cover off and count gear teeth to the mark.


They way I worked out where to start with my trial and error was to align all other timing marks with piston at TDC, counted the number of teeth (32) then 360 degrees divide by 32 gave 11.25 degrees. Worked out the point where the ignition snapped to create the spark, advance the ignition to 11.25 degrees before TDC.

This setting gave me some life out of the engine. After a lot of manual priming it ran and ran well, idled nicely picked up nicely. Went to it the next day and it fired with out any manual priming again running well.

2 days later wouldn't start with out lots of manual priming. It used to start well before the rebuild. It has good compression, the spark is very strong, and fuel is definitely getting up.

I have spent nearly 30 hours on this machine so far and had the crank/ flywheel re-machined . It is good to cut grass this season if only I could get it starting reliably.


wristpin Thu, 16/02/2017

Not a very scientific explanation but I think that some of your issue between days 1 and  3 could be down to weather conditions. I believe that in cold damp weather the long inlet tract can lead to vapourised  fuel condensing on the walls of the manifold without reaching the cylinder. 

As far as timing goes it may be worth turning the engine past tdc to trip the impulse on the mag and then turning it backwards to check the point at which the contact breakers just open / close in relation to the piston position . This should show you how accurate, or otherwise, your setting up procedure has been.

I do have a spare engine with an oil leak from the timing gear cover which will have to be dealt with at some point but at present it is buried under lots of other bits and pieces.