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Help me understand

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Bus Driver

04-01-2007 14:14:13

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My first car was a 1933 Chevrolet bought for $25.00. So I have been around for a while. On several forums, one sees sometimes posts that suggest that an engine has "jumped time". I do agree that such could happen due to wear of gears, timing chains and sprockets, etc. But such posts always suggest retiming the engine and continue running it. Has anyone actually seen some condition, other than loose distributor or magneto clamp, that causes an engine to change timing while exhibiting no other problem before or after the timing change? Single cylinder engines are not what I am describing here. It seems to me that "Jumping timing", if it happened, would be expected to happen again almost immediately. And the camshaft probably would be involved so that ignition retiming would not help much if at all. So are these other people just wrong or do I need a better understanding? Are these other folks just offering baloney?

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B-maniac

04-02-2007 19:11:22

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Re: Help me understand in reply to Bus Driver, 04-01-2007 14:14:13

Like said in post below , the gears and chain are so sloppy that when they reach a certain point of wear they will jump over a couple teeth when you shut down the engine. Right before it stops turning it will snap back momentarily from compression and cause the chain to jump teeth. Depending on the amount , it might try to start the next time or it might pop through the intake etc. Just depends on where it came to a stop. Could be so far off it will hit valves into pistons when you try to start it. Yes it is real. If it only jumped one tooth you may be able to re-time the dist. and get it to start but won't have any power. Probably jump again when you shut it off again. Good test is to turn the crank while watching the rotor in dist. If you can turn the crank back and forth a 1/2" or more without the rotor moving then you need to replace gears and chain.

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Oldmax

04-02-2007 05:09:12

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Re: Help me understand in reply to Bus Driver, 04-01-2007 14:14:13

I had a 56 - 292 ford that the timing chain got so lose that it would jump over the teeth . but new sprokets & chain solved the problem .

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Howard H.

04-01-2007 21:04:55

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Re: Help me understand in reply to Bus Driver, 04-01-2007 14:14:13

Thats a pretty good story about the '33 Chevy! What year did you purchase it? Do you still have it??

I had a 534 Ford irrigation engine act up one time similar to what you are saying - took me forever to realize the drive gear on the distributor had sheared the roll pin that held it to the shaft. The gear was still pretty tight on the shaft, but would slip every so often...

Howard

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MarkB_MI

04-01-2007 18:46:03

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Re: Help me understand in reply to Bus Driver, 04-01-2007 14:14:13

I had a '73 Cougar with a 351 Cleveland. One day I noticed it really didn't seem to have power. So I put a timing light on it and sure enough, the timing was retarded several degrees. I reset the timing and everything was fine for a couple of days. Three days later it wouldn't start. The camshaft sprocket was completely gone. 20-20 hindsight, but I should have known something was up when the timing changed for no apparent reason.

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Crem

04-01-2007 19:10:42

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Re: Help me understand in reply to MarkB_MI, 04-01-2007 18:46:03

Yup, sometimes you could set the timing back again twice and get away with it but soon you would be tearing it apart. The timing chain jumping usually wouldn't happen while running but rather at shutdown or start-up.

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dave guest

04-01-2007 18:30:17

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Re: Help me understand in reply to Bus Driver, 04-01-2007 14:14:13

Do all my own work. Wrenching that is. Never saw an engine jump time. Bought several that were supposed to have done that. Never found any. And I looked real hard, too. Mechanic friend had service station for 20 years told me he never saw one either.

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Walt Davies

04-01-2007 16:47:48

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Re: Help me understand in reply to Bus Driver, 04-01-2007 14:14:13

My Case LA has done it twice on me real irritating. Some how the darn thing just jumps a dog or two and won't start. The last time i got it real tight so far so good,
Walt

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Crem

04-01-2007 16:33:50

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Re: Help me understand in reply to Bus Driver, 04-01-2007 14:14:13

I can remember back in the late sixties or seventies when some of the timing gears were made of a material that wasn't metal, and the timing chains and gears became worn, they would skip a tooth and cause the timing to be off. You could re-time the ignition again, but the valve timing would be wrong.

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frankiee

04-01-2007 14:45:13

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Re: Help me understand in reply to Bus Driver, 04-01-2007 14:14:13

I in fact heve seen it with a Dodge station wagon.
Mechanic friend moved the wires around. I dont know if he moved the dist. or not.
But it ran after.
I asked why and the mechanic friend why he did and and he said so we could drive it if we had to.
It ran poorly but it ran and kept running.
Car got a chain and gears next day. Drove there.

Come to think of it. I did a belt on a Dodge 2.2 and missed by a tooth and the car ran. Ran bad but it ran. I promptly redid the belt.

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Bob

04-01-2007 14:23:09

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Re: Help me understand in reply to Bus Driver, 04-01-2007 14:14:13

Outside of a timing chain jumping a tooth or two; on engines so equipped; or a key wearing out in an "accessory drive"; IMHO; the "jumping time" thing is 99% "BS"... either a confused operator; or someone has tampered with the machine.

(This does NOT apply to breakdowns where the engine has to be repaired before it will run again... such as broken gears.)

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Allan In NE

04-01-2007 14:23:04

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Re: Help me understand in reply to Bus Driver, 04-01-2007 14:14:13

Yep, You be right.

I've worked on a trainload of the devils and when they actually jump time, they flat don't run.

What people are probably referring to are the old mechanical point ignition systems. When the points wear, for every 1 degree of dwell change, the timing will change 3 degrees.

Allan

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JK-NY

04-01-2007 14:22:06

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Re: Help me understand in reply to Bus Driver, 04-01-2007 14:14:13

Among other things,Timing chain, gears and chain guide wear, timing belt stretched/worn or looseing a cog on the cogged belt, worn distributor gear, frozen/inoperative advance mechanism , even worn points can cause timing change but most of these issues arent permanently repaired by retiming .

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Brian G. NY

04-01-2007 16:35:09

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Re: Help me understand in reply to JK-NY, 04-01-2007 14:22:06

The early 289 Fords were notorious for jumping time. Usually at around 100,000 miles or so the timing chain would be "as loose as a goose" and this caused the problem. Almost always the car would be running fine when shut off but would not start ( or would barely run) when it was needed again. This was usually because the engine had done the "back spin" when shut down. In some cases it was possible to reset the distributer a tooth and "limp" home but the engine would be running so poorly it couldn"t pull itself over an anthill.

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Mike (WA)

04-02-2007 08:58:46

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Re: Help me understand in reply to Brian G. NY, 04-01-2007 16:35:09

I replaced the distributor 180 degrees out on a Dodge K car- it would start and idle (poorly), but die as soon as you touched the accelerator. I was surprised it would run at all.

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