Timing Jumping

[John H.]

Re: Timing Jumping

Is your point distributor triggering an MSD system? If so, that would explain the apparent "timing jumping" - most timing lights don't react well at all to the multiple spark discharges at low rpm that an MSD box generates.

[Steve K.]

Re: Timing Jumping

No MSD, just points, condensor, resistor and a coil.

[Duke W.]

Re: Timing Jumping

The L-72 has ported vacuum advance, but the VAC could be picking up an intermittent vacuum signal. Make sure it is disconnected and plugged for the timing check. (Golf tees make great plugs for this application.)

You should also check that the VAC holds vacuum, and you never did tell us the VAC ID. You said the shop changed it. What's installed? Also what's the "proper" amount of shaft end play. What is the actual end play? Good diagnositcs require definitive data - numbers!

How about the dwell angle. Is it constant as you raise revs or does it vary? How many degrees variation?

Is the distributor hold down bolt tight?

Also consider converting to full time vacuum advance. This will considerably ameliorate the overheating (research archives for L-71 and L-71). The OE VAC is okay, but if not installed you need a "B20" VAC for this conversion. The coil and ballast have nothing to do with engine temperature unless the engine had a significant misfire problem.

To check the balancer, remove the bell housing inspection plate, set the engine at the timing point for #1, and apply a blotch of paint or crayon mark on the front of the flywheel.

Check with the timing light whether the flywheel mark jumps around. If it doesn't, the balancer ring is suspect, if it does there is likely something amiss inside the distributor or the timing chain is waaaaaay loose.


Duke

[Dick W.]

Re: Timing Jumping

Duke, he said that it had a new timing chain and gears so I am thinking that it has been line bored and he has ended up with a lot of slack on the new chain

[Steve K.]

Re: Timing Jumping

Duke, I agree that knowing the vacuum advance ID is important and I will post asap, but I have this juming problem whether the vac is connect or not. The shaft end play is about 9 thousanths. I have to check the dwell angle and will post. The distributor is held down firmly. I will also put the car on my lift and check the balancer as you recommended. I can do it tonight when I get home from work.

Dick, I don't know if it was lined bored but the old chain did have plenty of slop. I did replace it with a new Cloyes timing chain and gears. I also placed a thrust bearing behind the Cam sprocket along with a button on the from of the cam shaft. There should be no walking of the cam anymore.

Thanks for all the ideas and let me know if you can think of anything else. Will get back tonight.

[Steve K.]

Re: Timing Jumping

Guys,

The vacuum dashpot has a stamp on it B1. There are no other markings visable. I also tried the timing light on the flywheel trick and there was no difference. Timing still jumping around. The dwell was off by 20 so I set it to about 30. No difference. The dweel is holding steady even ass I rev the engine. I tried checking timing on other cylinders and the jumping effect is there as well. This is not unique to No. 1 cylinder.
I think I am going to pull the distributor and go through it myself to see if there is anything I can spot myself that could cause this.
Thanks again for all the support and I am open to any other ideas. I know this is going to be something simple and stupid but it sure has me stumped!

[Dick W.]

Re: Timing Jumping

Just for grins, check the advance weight springs to see if they are loose. Long shot.

[Terry F.]

Re: Timing Jumping

Does it have the original harmonic balancer on it?? Terry

[Michael H.]

Re: Timing Jumping

Duke, I agree that knowing the vacuum advance ID is important and I will post asap, but I have this juming problem whether the vac is connect or not.

Yup, I agree. Forget the vacuum advance unit, for now. That has absolutely nothing to do with your problem.
I've been following this since the beginning but I don't have any good solutions. I do have a few question though.

Does the mark appear to jump from one spot to another per engine revolution or does it seem to move to different locations randomly?

Does the mark appear to move to a different spot each time the light flashes?

What, roughly, is the range of movement in degrees?

What do you see if the timing light pickup wire is attached to the coil wire instead of #1 wire? How about #6 instead of #1?

[Stuart F.]

Re: Timing Jumping

The more common problem with advance weight springs is usually corrosion or dirt which causes the weights to stick open (advanced). I've never seen any springs pop off or break.

Stu Fox

[Steve K.]

Re: Timing Jumping

Terry,

I do not know if the balancer is the original one but it looks to be correct.

Michael,

Interesting questions:

Does the mark appear to jump from one spot to another per engine revolution or does it seem to move to different locations randomly?

The mark appears to jump per revolution. It does move to differnt locations

Does the mark appear to move to a different spot each time the light flashes?

Yes.

What, roughly, is the range of movement in degrees?

I seem to get more flashes at 8 degrees BTDC but it can flash at 20 degrees ATDC or 30 degrees BTDC.

What do you see if the timing light pickup wire is attached to the coil wire instead of #1 wire? How about #6 instead of #1?

Have not tried number 6 or the coil wire. Will try both tonight. I am also going to pop in a distributor I have out of an old nova just to see if there is a difference.

Thanks for the advise and tricks!!

[Stuart F.]

Re: Timing Jumping

Did we establish whether the engine is reacting to what you are seeing with the timing light, i.e. is the engine speed changing or running rough then smooth? If not, wouldn't you think the problem is external to the engine, like the timing light or it's connection and not a faulty distributor or balancer, etc.

Stu Fox

[Steve K.]

Re: Timing Jumping

Tried to check number 6 and the coil wire as well same reaction. Just popped in a old nova distributor out of a small block. Saw some improvments not as much jumping around. More flashes on timing tab and more flashes in the advance area (around 35 degrees BTDC). only a few after. I am going to take the weights out of the picture but have to run off to work. Will try this afternoon. I am thinking of biting the bullet and swithing back to TI. Still dealing with sticker shock!

Stuart, I have tried two timing lights and the most recent one is new. I have connected to the alternator and directly to the battery, no difference. Thanks!!

I want to thank everyone who has offer suggestion and help this is try a great board. I never give up so will find out what is going on and post.

Thanks!
Steve

[Jack H.]

Re: Timing Jumping

And, when the prior owner converted the ignition system back to conventional Kettering from factory original TI configuration, did they 'undo' the engine compartment wiring harness mods involved with running a TI ignition system? You mentioned the TI amplifier is still bolted in, but is it COMPLETELY disconnected as well?

[Stuart F.]

Re: Timing Jumping

Steve;

I appreciate what you are saying about the timing lights, but I still think whether or not the engine speed is affected and/or stability is an important item.

Stu fox