drifting timing (caution VERY long winded!)

[elwood blues]

A little background, I have a 1978 CJ7 pretty much stock when I bought it. Okay, it was bone stock except the seats when I bought it three years ago. Last spring I started this project. I wanted to get rid of my single barrel YF carb and I didn't want to spend the money or from what I read take the time to swap in a Weber. So, I picked up a really nice Motorcraft 2100 1.08 venturi carb. I bought a used 2 barrel intake from a 1979 CJ and I bought a brand new exhaust manifold. While I had the intake and exhaust manifold off I put in a new exhaust too, new headpipe, no cat, a flowmaster 40 and a tailpipe. I also stripped anything even remotely related to the emission control stuff. So I replaced every piece of vacuum line I could find, because now it's all different.

Did a full rebuild on the 2100, stripped it down to parade rest, replaced everything that could be replaced, power valve, accelerator pump, choke, float, needle and seat, everything. I also found smaller jets for it too. I got it all put together, had some timing issues initially, but got it all worked out and it seemed to run pretty well.

Until, the Ford Dura-spark module crapped out, again. So, I decide that I'm not going to replace that piece of junk again. After a lot of research I buy a Summit Racing street and strip ignition control module and matching coil. New Accel non-resistor plugs and new Taylor 8.2mm AMC 258 i6 / 4.2l specific plug wires. Plus a remanufactured distributor, new cap and new rotor. I finally got it all together and she ran. But never ran well. I never got smooth idle or drastic change in throttle response that everyone else raved about.

So, I picked up a different version motorcraft 2100, this one is an even older version. Again, full on rebuild, everything I can think of. Slap this new carb on, it still runs like , possibly a little worse.

Last night I finally, after the CJ's sat for close to two months, got the original motorcraft 2100 swapped back on and got her fired. It's been cold here, so I had to manually adjust crank up the idle speed to keep her running for a while. It's still running like , so I decide to throw the timing light on it, just to see.

As I listen to the engine idle up, then back down, shake and shimmer, darn near die, then idle back up again. I hook up the timing light, and stare down at the timing marks, in rhythm with the engine I watch the timing drifting back and forth. High idle, the timing reads 12 degrees BTDC, when it idles down and starts to shimmer and shake, I can watch the timing mark move down to probably 6 or 4 degree BTDC. Back and forth it goes, even after it's warmed up.

I'm completely and totally confused. After a session on chat here last night we came to a concensus that it's probably something with the vacuum advance, or a vacuum leak. If anyone else has a good idea, please let me know, I'm pulling my hair out.

P.S. If it counts for anything, I have a distinctive valve-train (I'm pretty sure it's a lifter) ticking noise. Funny thing is, as you adjust the timing more or less BTDC, the ticking noise comes and goes.

 

[BajaEdition]

ok, I am out of my element here, I do not know much about a 78.
But. first let us GET TO BASICS, plug the vacuum line to the dist,, and see if she will run without the variance. We are checking to see if it is the distributor. if it does run now, with no wobble, we now go and get the motocraft instructions and check each vacuum port for where it goes. We need to see if everything is sucking correctly. once checked, we try again, After this, I would need to be there, I think the advice of someone else here would be prudent

 

[LongHorn]

IMHO "Baja" is on the right track. Do you know the history on the short block?

 

[elwood blues]

Got it, back to basics. Stop nuking this, it's no where near as complicated as I'm making it out to be


I don't understand Longhorn, "do you know the history on the short block"? Are you asking if I know the history of my particular vehicle, or the AMC 258 i6 / 4.2l engine in general?

 

[LongHorn]

Got it, back to basics. Stop nuking this, it's no where near as complicated as I'm making it out to be


I don't understand Longhorn, "do you know the history on the short block"? Are you asking if I know the history of my particular vehicle, or the AMC 258 i6 / 4.2l engine in general?

I was talking about "Nylon Timing Gears".

 

[elwood blues]

I was talking about "Nylon Timing Gears".

I know absolutely nothing of "Nylon Timing Gears".

 

[LongHorn]

I know absolutely nothing of "Nylon Timing Gears".

Your AMC 258 i6 / 4.2l came from the factory with "Nylon Timing Coated Gears".
A 1/8" or so thick coating of nylon that over time wears out cracks & falls off. letting your timing chain slip, changing your timing.

 

[Old Dog]

The timing should be changing with the RPM's, thats what it does. The question is, is the timing making the rpm's change or is the timing changing because the rpm's are changing.
I would make sure you don't have a vac. leak to begain with. Do the basic timing and such to see if it will smooth out.
I was also having a problem somewhat like that when I found the bad bushings in my dist. You might want to check thoes out also.

 

[Petescj]

Wouldnt that at some point throw the whole motor out of time enough to stop it and be unable to restart?

Your AMC 258 i6 / 4.2l came from the factory with "Nylon Timing Coated Gears".
A 1/8" or so thick coating of nylon that over time wears out cracks & falls off. letting your timing chain slip, changing your timing.

 

[elwood blues]

The timing should be changing with the RPM's, thats what it does. The question is, is the timing making the rpm's change or is the timing changing because the rpm's are changing.
I would make sure you don't have a vac. leak to begain with. Do the basic timing and such to see if it will smooth out.
I was also having a problem somewhat like that when I found the bad bushings in my dist. You might want to check thoes out also.

The distributor is "new" remanufactured unit I got from NAPA, can't be more than 4 months old now. Think a got a bad refurb unit?

Wouldnt that at some point throw the whole motor out of time enough to stop it and be unable to restart?

I was thinking the same thing.

 

[Petescj]

Have you had the dizzy out since it was installed? Reason I ask is you havent driven the Cj much since you changed it correct? Did it have the correct gear on it , the one that wont eat your cam gear ?

The distributor is "new" remanufactured unit I got from NAPA, can't be more than 4 months old now. Think a got a bad refurb unit?

 

[Old Dog]

The distributor is "new" remanufactured unit I got from NAPA, can't be more than 4 months old now. Think a got a bad refurb unit?

It wouldn't be the first bad rebuild. It's easy enough to look at it and see.

 

[CJ]

Sounds like a vacuum leak to me.

What I would do to be sure it is not -

1. Temporarily cap and seal all vacuum ports at the port. Disconnect all lines including the power brake booster.
2. Reset timing.
3. Using cans of ether, spray all around the carb (not into the throat), around all ports and around all gasket areas for the intake.

Take note of any RMP changes. If you have a hand held tach that would be great as they are usually very sensitive.

 

[elwood blues]

Have you had the dizzy out since it was installed? Reason I ask is you havent driven the Cj much since you changed it correct? Did it have the correct gear on it , the one that wont eat your cam gear ?

No, I haven't pulled it since I installed it. How do I know if it has the correct gear? I threw the old one away!

 

[elwood blues]

Sounds like a vacuum leak to me.

What I would do to be sure it is not -

1. Temporarily cap and seal all vacuum ports at the port. Disconnect all lines including the power brake booster.
2. Reset timing.
3. Using cans of ether, spray all around the carb (not into the throat), around all ports and around all gasket areas for the intake.

Take note of any RMP changes. If you have a hand held tach that would be great as they are usually very sensitive.

I get it, rule out vacuum leak first. I don't have a hand held tach, but I'll see if I can borrow one.

 

[CJ]

I get it, rule out vacuum leak first.

I always like eliminate the easy stuff first...

You don't have to have a hand held tach - you may not need it...

 

[rushpowersystems]

Mechanical advance should be at its lowest point at idle, you should have your vac advance unhooked when testing so vac should not be an issue.

Rotate your engine clockwise direction by hand on the crank pulley nut until you are at top dead center “0” on the timing mark. Now take you distributor cap off and make a mark on the housing that lines up with the distributor rotor. Now have someone watch the rotor as you turn the engine the other direction again by hand. When the rotor moves stop, the number of degrees shown on the timing marks is how much stretch or nylon ware you have, the chain can jump at 12 deg. never seen one move that much at an idle though.

Try this start the engine and hold your hand over the carb but don’t completely block it off, does it the engine smooth out? Pull a smaller constant vac line so that you have a vac leak, does that help the idle?

 

[Petescj]

From what Ive read about them is the dizzy has a hardend gear that eats the cam gear in its normal configuration. The cam gear on a Cj is softer and gives way. Im not sure if this is the way that would start. Im thinking youd hear something internally if this was the case. Break out a flashlite and take a good peak if you get this far. Im still with vaccum like we talked about last nite. Just giving another option to check if other suggestions dont turn up the problem.

No, I haven't pulled it since I installed it. How do I know if it has the correct gear? I threw the old one away!

 

[BajaEdition]

lots of good advice going on here
one more thing Elwood, make notes after each test, seems we are going through a lot of ground here and we need to know setings and and results from the test to further read the problem. I mean if it is a few things, we will know how each seems to be effecting each other.

 

[IOPort51]

From what Ive read about them is the dizzy has a hardend gear that eats the cam gear in its normal configuration. The cam gear on a Cj is softer and gives way. Im not sure if this is the way that would start. Im thinking youd hear something internally if this was the case. Break out a flashlite and take a good peak if you get this far. Im still with vaccum like we talked about last nite. Just giving another option to check if other suggestions dont turn up the problem.

I seem to remember reading about this situation with the drive gear but now I can not find anything on this subject. I believe what you say Pete but could you document it?