720 ran fine this AM, now it won't start, sounds like timing??

[kilohertz]

HI guys,
Happy new year!
My 720 has been running great for the last few years, and had it running this morning and ran fine, plowed the driveway, it's cold, -15C and has been for a few weeks now but it still starts fine and runs great. Anyway, went in for lunch and came out and tried to start it and cranked like it was out of time, could hear the cylinders pushing against the spark, then a huge bang, backfire out the exhaust. Tried again, same thing, like it was out of time and BANG! WTH! Pulled the plugs, checked compression, all okay, checked the timing mark on the crank and housing, lined it up and the rotor looks like it is about 20 deg out, which according to the goofy timing procedure, seems right. The service manual says that the timing is 23 ATDC with the lines aligned, and the rotor pointing to #1. Also says to time it at 1800 RPM. Well I can't get the thing running to time it with the light.
What could have happened over lunch time to throw it out of time? Like I said, it ran fine all morning then wouldn't start and backfired when I tried.
ARG!
Your thoughts?
Thanks

 

[kilohertz]

Well, I guess I should have just thought it out before I posted, but I think I have figured it out, won't know until morning, but my thought is.....
Been -24C for a week now, dam cold, started fine this morning, timing was okay, after she warmed up, advance weights did their thing, advanced, then when I shut it off, the thick grease/lube/sludge whatever may be in there, stayed advanced, went to start it and it was at full advance, stuck, which is probably why it sounded like it was pushing against the power stroke, and then backfired....I pulled the disti and the rotor shaft is definitely stiff, I can turn the rotor against the shaft, and it sticks where I leave it...it's inside warming on the wood stove tonight...in the morning she gets a thorough cleaning and relube with lighter oil.

Hope that's it......sounds about right to me...
Seem like a decent diagnosis?
Cheers

 

[thynes]

Well, I guess I should have just thought it out before I posted, but I think I have figured it out, won't know until morning, but my thought is.....
Been -24C for a week now, dam cold, started fine this morning, timing was okay, after she warmed up, advance weights did their thing, advanced, then when I shut it off, the thick grease/lube/sludge whatever may be in there, stayed advanced, went to start it and it was at full advance, stuck, which is probably why it sounded like it was pushing against the power stroke, and then backfired....I pulled the disti and the rotor shaft is definitely stiff, I can turn the rotor against the shaft, and it sticks where I leave it...it's inside warming on the wood stove tonight...in the morning she gets a thorough cleaning and relube with lighter oil.

Hope that's it......sounds about right to me...
Seem like a decent diagnosis?
Cheers

From what you describe, it is likely the problem. How does the bottom of the cap look? Are there any carbon tracking marks? Please give us an update when you get it running. Tim in Mass

 

[kilohertz]

From what you describe, it is likely the problem. How does the bottom of the cap look? Are there any carbon tracking marks? Please give us an update when you get it running. Tim in Mass

Well she is alive and well again. Gave the weights and shaft a good cleaning and lube this morning, cleaned the cap and noticed a fine crack between the center post and one outside post, only on the inside, not on the outside...so internet research to find the right cap, rotor and points and went into town armed with the details, got the parts, put it all back together and she fired within a half revolution. Checked the timing and it was spot on, even after putting in new points. Guess I got lucky. Ran it for 2 hours of snow plowing and ran smooth as can be.
So for anyone else with the Prestolite distributor IAD-6004, which I think was pretty common on the Wisconsin engine VH4D etc., the Borg Warner parts are
Cap C110
Rotor AL81
Points A81
Also, found other #'s that seemed to cross but these were in local stock and matched what I brought in.
Cheers!

 

[thynes]

Well she is alive and well again. Gave the weights and shaft a good cleaning and lube this morning, cleaned the cap and noticed a fine crack between the center post and one outside post, only on the inside, not on the outside...so internet research to find the right cap, rotor and points and went into town armed with the details, got the parts, put it all back together and she fired within a half revolution. Checked the timing and it was spot on, even after putting in new points. Guess I got lucky. Ran it for 2 hours of snow plowing and ran smooth as can be.
So for anyone else with the Prestolite distributor IAD-6004, which I think was pretty common on the Wisconsin engine VH4D etc., the Borg Warner parts are
Cap C110
Rotor AL81
Points A81
Also, found other #'s that seemed to cross but these were in local stock and matched what I brought in.
Cheers!

Sounds like you are good to go for another few years. Happy New Year! Tim in Mass