350U valve timing

[linemechanic1]

This sat for a week and when I went to start it two days ago I got backfire through carb and no start> With palm ver carb for choke I get lots of pressure AND lots of suction. I don't remember experiencing that in over 50 years of messing with old gas engines. Are these timing gears or chains and do they wear enough to jump if it's a chain? It's been pretty reliable since I put the Pertronix ignition on a few years ago.

 

[504]

gear drive

 

[caterpillar guy]

Gear drive and not likely to wear enough to change timing in the last 60 years since new. I would guess your pertronix is not working right.

 

[wore out]

(quoted from post at 21:46:45 12/09/20) This sat for a week and when I went to start it two days ago I got backfire through carb and no start> With palm ver carb for choke I get lots of pressure AND lots of suction. I don't remember experiencing that in over 50 years of messing with old gas engines. Are these timing gears or chains and do they wear enough to jump if it's a chain? It's been pretty reliable since I put the Pertronix ignition on a few years ago.

Perhaps a stuck valve and/or a pushrod has gotten out of place?

 

[David G]

I would assume ignition problem, maybe wet cap.

 

[linemechanic1]

Makes sense if it's gear drive. The strong pressure back out of the carb seemed strange so now I'm thinking a stuck intake valve......more research.

 

[Bob M]

Assuming there's no valve(s) stuck open the camshaft has gone out of time. Most likely then is the cam gear hub has broken causing timing to shift. This is not uncommon since the cam gear drives the live pump. And the load imposed by the pump can break the cam gear. (It happened on my Super M, also to a friend's Super H and 400).

Quick check is to turn the crank to TDC then check the position of distributor rotor button. The rotor contact should be directly under #1 or #4 cap tower. If not the problem is cam timing.

Can verify a broken gear by pulling the live pump/distributor and peeking at the gear inside the engine front cover. If you can move the cam gear axially (front and back) AT ALL the hub has broken. The only fix is to replace with new.

 

[linemechanic1]

Three places to check—thanks to all.......

 

[Hayfarmer]

If that has same type hydraulic pump drive as M could be key sheared off in gear on hydraulic pump. Rotor may still turn just not in the right place

 

[linemechanic1]

Some dummy had #1 and #2 plug wires crossed—I'll talk to myself about that. Still a problem with running rough, back firing through carb. Pulled distributor cap—dry as a bone BUT with half a teaspoon of odd-looking, brownish chips in the cap. Clean it out and brushed up the rotor slightly but not much improved. THEORY: If the Pertronix does produce a more consistent spark would that account for the increased deterioration of the contact points inside the cap and on the rotor?

 

[Janicholson]

Comments: Pertronix ignition will mask a bad distributor shaft bushing for a while, but eventually the rotor will hit the inside of the cap, or terminals and act like a lathe. The timing and spark will also be affected because the magnetic pickup will have variable distances as it runs, and might get bad enough to hit the pickup where the points were. With the cap off, try to move the rotor Up and Down, and Toward the engine ans away. If there is any (and I mean if you can detect any) motion in that shaft the bushing and shaft are worn. Firing order is front to back 1342, with one being top right (looking from the rear) and going clockwise around the cap. Jim