erratic timing on 360

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smokinnjokin

smokinnjokin

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Gentlemen,
Had this problem on a thread long ago, figured I would just start fresh and lay out everything.

1967 satellite 2-door; 727 with 3.23 sure grip and 360.
Cam is comp xe 262; Edelbrock 500cfm carb and performer rpm manifold. Full tti headers and 2.5 exhaust system.

Motor is a freshly rebuilt (by a 3rd party machine shop), low compression 360 with pertronix and halifaxhops recurved oem distributor.

Runs beautifully, starts right up, plugs are spotless and the car pulls hard. Been driving for about 6 months now and trying to solve the issue:

The timing jumps back and forth by about a 5 degree sweep. At idle, it is very noticeable; its very hard to get an accurate reading because it Varies constantly between 2 reading about 5 degrees apart. Note: it does not 'wander' gradually between timing marks, but rapidly jumps back and forth. The issue is consistent across the rev range, but is most noticeable at idle with the flashes slowed down. Because of this variation in timing, I have to keep the timing pulled back to 13/33 to avoid detonation (remember, this is an auto with no mid-throttle lockdown on the trans linkage) even though the motor really wants to run beautifully at 16/36. Based on what the light is showing, actual timing is varying by a solid 5 degrees so at full throttle.

Here's the troubleshooting I have done. Sent the distributor back to Ray to check over and spin on his machine. New cap, rotor, wires. Everything checks out, no change. Changed the distributor intermediate shaft, fearing slop. No change. Ignition system seems solid. Again, great idle, clean running and fires right up no drama.

So that leaves me suspecting the timing chain or gear; it does not appear they used a tensioner because there is some delay when turning over by hand for the distributor rotor to turn. What I don't understand is that if there was somehow excessive slop in the chain, why would the timing jump cleanly back and forth... wouldn't it wander around gradually as the chain flexed under load?

What should I check next here, I am scratching my head.
 
You nailed it Joe the slop in the chain. Set the crank to 0 tack the dist cap off, turn the crank in the "slop" direction and as soon as the rotor turns stop and see how many degrees the crank turned. Should noy be much. Also is it original?
 
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What i dont understand is how chain slop can cause the timing to jump cleanly between two settings, it literally snaps back and forth.
I have had a light on engines with worn sloppy chains before and never seen that.
 
Not sure but if it is timing jumping around not much else. How many degrees is it the slop? Think this way the timing chain drives the camshaft which drives the oil pump and the distrib, you know 2 of them ar right. Cams dont flex so not much else or the timing light is funky.
 
I get same results with 2 lights, plus you can hear it in the idle and see it on a vac gauge, so it is really happening. Also, there is absolutely no noise, rattling or anything coming from timing chain or fuel pump area to indicate a sloppy chain or loose cam gear or anything. Its really weird.
And yes, my measured slop does seem to be around 5 degrees.

My next step is to just go ahead and take the front end apart, but i have a sinking suspicion a fresh chain and tensioner wont make a difference. The snap back and forth between two settings just screams electrical problem, like its alternating between firing on leading and trailing edge of distributor contact or something. It can’t be crossfiring, that would show a way bigger variance than 5° and it would not idle or run as well as it does. Again, no misfire, clean plugs, no backfires. It just acts like an engine that is alternating between two timing settings that are both within acceptable parameters.
 
There’s a point where the valve springs will cause the cam to “jump” forward this will cause the timing to advance for a period of time til that play is taken back out of the chain due to rotation of the engine. If that makes sense, best way I know to describe it.
 
Have you checked for play in the intermediate gear/ bushing?
 
Also- this “third party” machine shop- did they actually replace the cam shaft bearings? I’ve seen cam shafts “jump around” due to paper thin bearings. Causes major timing issues, idle issues, vacuum issues and stress.
 
The vacuum advance can cause instability even when disconnected.
 
67Dart273 said:
Have you checked for play in the intermediate gear/ bushing?
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Yes, i replaced the i-shaft due to minor wear, no change.
Syleng1 said:
Also- this “third party” machine shop- did they actually replace the cam shaft bearings? I’ve seen cam shafts “jump around” due to paper thin bearings. Causes major timing issues, idle issues, vacuum issues and stress.
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Don’t say that... my worst fear. Im already irritated they did not use a tensioner.
CUDA69 said:
The vacuum advance can cause instability even when disconnected.
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Wouldn’t this have been apparent to ray when he checked the distributor and spun it up? What am I looking for to rule out vac can?
 
Did you put a new chain in when you installed the cam?
 
I did not build the motor. But it had a new chain and tensioner in it when sent out for rebuild. No tensioner now. Even if they recycled the old chain, it should not be this sloppy.
 
smokinnjokin said:
The snap back and forth between two settings just screams electrical problem, like its alternating between firing on leading and trailing edge of distributor contact or something.
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Maybe try subbing the ignition components one at a time to rule that out before you start tearing it down?
 
Yea, those Sun machines are pretty smooth operating, they can spin up a distributor pretty quickly. The machines are driven by an electric motor, no engine pules, no vibration, just a smooth rotation.

Now take a distributor maybe like the one you have, maybe a light spring and a heavy one pair together, typical performance minded. Usually the heavy spring fits loosely on its pins, and the lighter spring should be more taught on its bosses. Depending on your tuning you may or not want zero mechanical advance at idle OR mechanical advance just right off idle.

So while keeping this in mind, a lighter spring or one that is loose on the bosses can cause your timing to bump around. Especially on a cammed up hipo motor, just racing to get out of the garage. lol


To challenge this, take the lighter spring switch for a heavy one.... and check your timing.
 
not familiar with that camshaft, does it idle rough and lopey?
 
smokinnjokin said:
I did not build the motor. But it had a new chain and tensioner in it when sent out for rebuild. No tensioner now. Even if they recycled the old chain, it should not be this sloppy.
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It entirely depends on the quality level chain set they used. I can tell you from personal experience, if you do not spend at or around 100 bucks for a timing set, you're probably not getting a good one. You need a billet set to assure minimal chain stretch. If they put a garden variety chain on it, even brand new, it will be stretched in 15 minutes worth of run time. Most people who use those types chain sets never notice it on a light, because they normally just set the timing once and turn it loose. They're not looking for a performance timing curve and will likely never see the variation in timing.

It would also bother me if the engine went in with the tensioner and came out without. They should have replaced new with what was there doing a rebuild. Although the tensioner cannot keep the chain set from retarding due to stretch, it can and will most certainly stop a loose chain from showing variations like you're describing.

One last note. When you go to to the test turning the crankshaft, once you get it up to TDC, you will need to turn the crank BACKWARDS to check chain slop, since you will be turning the crank clockwise bringing it up to TDC.
 
Check for slop between the intermediate shaft and distributor shaft drive slot. If loose peen the end of the distributor shaft to expand and dress with a file. I've had this problem before and this fixed it. Also make sure the vacuum advance is installed correctly. The vacuum canister arm is what anchors the plate in position.
 
OK ON THE DISTRIB THIS IS THE SECOND TIME i HAVE BEEN THROUGH IT ABSOLUTELY NO ISSUES THAT i AM SEEING AT ALL. OOPS sorry caps. Joe if you want to eliminate electrical send me a list of all the ignition components you are running I can send you know/tested good ones to replace one at a time to try. This is a weird one. I really want to know what it is.
 
halifaxhops said:
OK ON THE DISTRIB THIS IS THE SECOND TIME i HAVE BEEN THROUGH IT ABSOLUTELY NO ISSUES THAT i AM SEEING AT ALL. OOPS sorry caps. Joe if you want to eliminate electrical send me a list of all the ignition components you are running I can send you know/tested good ones to replace one at a time to try. This is a weird one. I really want to know what it is.
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Well just holler about it Ray! LOL
 
My guess is the timing components, the shop may have cheaped out & put Chineseum chain & gears in it. As RRR said, $100.00 for quality timing components is on the mark.
 
Don't forget that 600 rpm is just 10 revolutions per second and the plug only fires once every second revolution, so 600 rpm is just 5 firings per second. This is plenty of time for a sloppy chain to dance around.
There is an easy test for a sloppy chain. Post #2 covered it
 
I have a new Rolon chain for a Pontiac, free....
One side of the links says Rolon. Other side says India.....
 
Had this same issue on my Dart, it turned out to be operator error. One of my plug wires wasn't fully seated. Timing jumped around exactly as you said and once I went through all the nightmare scenarios I found one ignition wire that wasn't "clicked" tight
 
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