Timing is Changing itself

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Timing is Changing itself

Postby Brooks » Sat Aug 25, 2018 10:38 am

Bike was running great, took a couple rides around town rode about 15-20 miles and then all of a sudden the bike was running like it was starving for gas. So did a little investigating and the only thing left to check was the timing. Well the timing was off, when I checked it, it was at .150. So put the timin back to .218 (7/32) btdc and then the bike ran like a champ! Well recently the bike was running the same crappy way so checked the timing and it was off again. I know this can happen. But my theory is the crank shaft is slipping slowly, is this a common problem with these bikes or should I look somewhere else. Just want suggestions before I pull the motor. 1950 125S
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Re: Timing is Changing itself

Postby stanley » Sat Aug 25, 2018 7:16 pm

what year and style of motor are we talking about gen or magneto if its a gen are you sure you have the key in the armature or the right armature with the tang to hold the timing cam in place
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Re: Timing is Changing itself

Postby Brooks » Sat Aug 25, 2018 11:44 pm

It is a 1950 125S has a generator and im pretty sure everything is in its place unless the monkey who owned it before me didn’t put something back the way it was supposed to be
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Re: Timing is Changing itself

Postby stanley » Sun Aug 26, 2018 10:39 am

what did you change to reset the timing the points plate the points or the points cam
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Re: Timing is Changing itself

Postby Brooks » Sun Aug 26, 2018 10:58 am

The points plate with the two adjustment screws
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Re: Timing is Changing itself

Postby hennesse » Sun Aug 26, 2018 11:05 am

Brooks,

I think Stanley's right - either the circuit breaker cam 30020-47 is moving around, or the armature is moving on the flywheel shaft. I really can't see anything else causing the timing to change itself.

The cam has a notch which mates with a tang sticking out of the armature - this keeps the cam synchronized with the armature. The armature is keyed to the flywheel shaft - this keep the armature synchronized with the flywheels. One of these parts is loose/worn.

No reason to pull the engine. Take off the side cover, so you can get at things. You should be able to check the cam - remove the bolt, and see if the cam is a good fit on the end of the armature or whether it moves around.

Checking the armature fit on the flywheel shaft is a little more difficult. I think two bolts hold the generator body on. You'll have to be very careful with the brushes !!! The armature is a light press fit on the shaft, and it requires a Special Harley Tool to remove. Maybe Stanley has an idea for an improvised tool. Anyway, the armature should be a tight fit and not move around on the flywheel shaft.
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1951 Spare Parts Catalog
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Re: Timing is Changing itself

Postby houserjw » Sun Aug 26, 2018 1:28 pm

I don't mean to interrupt but I'm setting the timing on my 1949 125 and the manual I have says it should be 13/64. I know this isn't a big difference but would it matter or which measurement should I use?
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Re: Timing is Changing itself

Postby hennesse » Sun Aug 26, 2018 4:37 pm

Here are the relevant pages from the Model 125 (revised 1-48) Riders Handbook. Information on later models from the 1960 Service Manual

Model 125 - points gap .020, timing 7/32" BTDC, spark plugs .025 to .030
Model 165 - points gap .020, timing 13/64" BTDC, spark plugs .025 to .030

Hummer - points gap .018, timing 7/32" BTDC, spark plugs .020
Super 10 (and later) points gap .018, timing 13/64" BTDC, spark plugs .020

Don't think that 1/64" is going to make a heck of a lot of difference

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Model 125 Riders Handbook
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Re: Timing is Changing itself

Postby Brooks » Sat Sep 08, 2018 1:06 pm

Every suggestion checks out... key is in the crankshaft to hold on the generator. Cam is not loose. Put in new brushes and springs maybe that will help. Can’t help but think the overheating issue is causing the timing to change. Just can’t figure out why it’s overheating...suggestions?
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