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Timing Chain Question


keithb7

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First off, my car is running great. No concerns. 

I got to scratching my head about camshaft timing. Hypothetical question here:

If a flat 6 old mopar timing chain skipped 1 tooth, is this enough to see low compression? Would a simple compression test reveal lower numbers across all cylinders?

I tend to think a compression test would reveal low numbers. No?

Normal symtoms would probably include poor running engine. No acceleration. Backfiring. Exhaust noise through carb. Correct? 

To check cam timing , am I correct to say rad, fan,  crank pulley and front timing coverre to come off?  Depending on model of car.

Could valve timing be verified another way? Using #6 TDC locator hole in cylinder head and checking valves? Maybe by using a degree wheel? Or no, best to just access and view timing gears?

Thanks. i just love learning more on the old engines. Keith

 

Edited by keithb7
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A vacuum test would be more accurate diagnosing valve timing issues. You say it is running OK, what leads you to suddenly question valve timing? There are a host of other things that might make the difference between OK and great that I would check before suspecting timing chain issues. 

Simple test, pull the plugs, remove the dist cap.  Rotate the engine by hand while observing the rotor movement. Can you rock the fan back and forth without the rotor moving?  How far? Or hook up a timing light, at idle do the timing marks wander or are they steady?

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I have driven some junk, had a old 77 toyota pickup with a 20R motor. The chain stretched so far, the timing changed depending if you had your foot on the gas or coasting down a hill.

The chain was so loose it was slapping the side of the timing chain case and nearing breaking through. I put a new chain in it and it ran great again.

 

Then I had a 72 cj5 with a 304 headers carter 4 barrel, I romped on it going through a mud hole and timing chain did jump on that one, crank it over and carburetor shot gas on the windshield with the hood removed.

But I do not think it is going to affect your compression, just the timing, by the time it got so bad to affect the compression would have much bigger issues.

 

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I don't think it can happen, skip a tooth. You can check valve timing with the marks on the vibration damper. Pull the front valve cover and watch when the intake and exhaust valve  opens.Their are factor specs for this degree location and you can verify with the pointer location on the vibration damper.   

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@greg g My car is running great as mentioned. I am enquiring about valve timing just to learn from other's experiences. I have no symtoms with my car. 

I was reading about someone else's troubles, and I've reviewing my own depth of knowledge on the. Subject. 

Peresonally, when I look at the front timing gears on a flat 6, and the chain length, I too have trouble believing the chain could skip a tooth. I am in agreement that there are many other questionable parts and systems on the car that I would inspect before ever looking at the timing chain. 

I am merely asking to further my knowledge on the subject. 

Thanks. 

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2 hours ago, Los_Control said:

I have driven some junk, had a old 77 toyota pickup with a 20R motor. The chain stretched so far, the timing changed depending if you had your foot on the gas or coasting down a hill.

The chain was so loose it was slapping the side of the timing chain case and nearing breaking through. I put a new chain in it and it ran great again.

 

Then I had a 72 cj5 with a 304 headers carter 4 barrel, I romped on it going through a mud hole and timing chain did jump on that one, crank it over and carburetor shot gas on the windshield with the hood removed.

But I do not think it is going to affect your compression, just the timing, by the time it got so bad to affect the compression would have much bigger issues.

 

I've welded up 2 timing covers from 22R engines in the past, one was my own and another for a co-worker. Pretty common for them to get sloppy and wear out the guides, then  get into the cover.

 A few years ago I bought a Jeep CJ5, It had a very worn 304 V8. I did some tuning on it, trying to get it to run better. I went through the normal stuff, plugs, wires, cap, button. Rebuilt the carb. Still it ran kinda odd, had like a come and go kinda feeling or surging I guess I should say.  Finally I checked the timing chain, I have never seen one with so much slop. I took pics even a video of me pushing it over and touching the block. I really couldn't believe it could run as bad as it was worn or hadn't jumped time.  They say AMC engines don't oil well in the timing chain area. I replaced it with a True Roller, Dual Roller from Cloyes. Still running great to this day.

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As mentioned rotate the crank back and forth and watch the dizzy rotor and how much rotation delay between the crank and rotor. This gives an idea how sloppy (loose)  the cam chain is.

A new chain and gears ...the rotor follows the crank back and forth  rotation exactly with no delay.

With a worn chain and gears there might be 20 degree's of crank rotation before the rotor even begins to turn. 

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4 hours ago, Dodgeb4ya said:

As mentioned rotate the crank back and forth and watch the dizzy rotor and how much rotation delay between the crank and rotor. This gives an idea how sloppy (loose)  the cam chain is.

A new chain and gears ...the rotor follows the crank back and forth  rotation exactly with no delay.

With a worn chain and gears there might be 20 degree's of crank rotation before the rotor even begins to turn. 

LIKE.

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I had a 55 Plymouth, nice car,  (75000 miles, 1970)  the timing chain skipped a tooth while starting the engine.

It ran smoothly but had absolutely no power.  A timing light revealed the problem.  In a pinch, you could advance the timing and run some distance but my car decided to act up right in my driveway.   In over 50 years I have encountered a skipped chain on our favorite flatheads only twice.

  Usually you can hear the chain hitting the cover at idle, long before a tooth is skipped.

 

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Looking at how close the gears are on these motors I doubt they would skip.

30 yrs ago I put a new cam, lifters and timing chain in my everyday driver '77 diplomat w a 318. The timing set was TRW double row chain and gears. Once assembled the car ran sort of okay, but ran what I would call "heavy". Turned out the timing chain timing marks were one tooth off on the cam gear. AAAaagh. Corrected that and it ran very well. From then on I either check these marks against a known good piece, or centerline the cam to verify correct timing. Lesson learned the hard way. 

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