Timing a Z

[dlp]

I read in a post some back that if you advance the timing one tooth on the cam it will give it more power. Am I recalling this correctly? If so, will doing this on a mag engine help or just make the hand crank a flying weapon? Thanks!

 

[buzz36]

not sure aobut more power but if you advance the timing one tooth you may live to regret it on a cranker i did this to a model T engine and it though me across the room
do you have a mag style early Z i need info for the one i just bought

 

[Anonymous-0]

Advancing the timing this way is really hazardous because if you get it pre-TDC the piston fires backwards. I remember Dad and his friend discussing this at an auction back in the 60's. His friend held his arm out sideways and swung the forearm. The surrounding crowd about all had a similar story.

 

[dlp]

Right now I'm building an engine for my '37. I have 4 mags that I will be building one out of. I figured that would be the answer I would get on the timing issue. Just was curious. I didn't figure it would be any different than my other types of engines with mags. What info were you needing?

 

[Anonymous-0]

I am under the impression that advancing the cam timing helps power most when the engine is turning a bit faster than what is considered stock RPM for a moline engine. It helps by opening the exhaust valve earlier in the cycle. Of course, the spark timing is advanced more at higher speeds too to get the mix burning well when the piston crosses TDC.

If your tractor has a magneto, you are much more limited to stock RPM and timing. You have to time the mag so it fires at TDC (Or just after TDC. read your manual) when cranking, otherwise it'll break your arm. And then when it does start, the flyweights in the impulse coupling immediately fly to the advanced position and stay there regardless of the speed of the engine. As far as I know, most tractor magnetos do not have timing advance that varies with RPM.

For instance, the magneto on my JTU has a 35 degree impulse coupling. It is about right for mid throttle or a little faster, but the engine labors a bit at idle because the timing is really a bit too high.

 

[Anonymous-0]

I have a "semi-stock" UTU puller that I advanced the cam one tooth. My tractor has a distributor, when I first put it back together just to get it running, I timed it to fire a little early because I was warned that if it fired late it would tear up the starter. It fired well enough to run and then I fine tuned timing from there. As for power, I will say this: advancing the cam gear one tooth on the crank is a poor man's cam grind, it really didn't give me any more top end horsepower but the tractor is night and day different in regards to torque. Once under load and the engine pulls down a little then it seems to hold on forever and lugs like you wouldn't belive. I think it's an excellent adjustment for a stock tractor or even a tractor that's been tweeked a little.

 

[MMark]

I have done this to 3 tractors (2 Z's, 1 R) It will help the low and mid speed torque, It will help HP by about 1 or 2 HP. My 37 Z with 1/8" over bore made 37 HP before and 38 HP after. My 49 Z with 1/8" over bore made 42 HP before and 44 after. Torque during the pull was noticably more. Mag and/or distributor timing should not be affected. Take off the bearing blocks holding the cam, the cam will drop down enough to rotate. If you think about it the only thing you are doing is changing where the valves open and close. You have not changed where the crank is or where the drive gear for the mag or distributor are. If I remember right the cam gear has 60 teeth which should relate to about 12 degrees cam timing change. (360 / 60 = 6) The cam turns half the speed of the crank so (6 x 2 = 12). That means the intake and exaust valves will open and close 12 degrees (of crankshaft rotation) sooner. Remember the crank and mag gears have not changed in position, the plugs will fire in the same place as before.

Mark Damewood