I don't get your diagram... it just means your chain is longer than it should be. As it ages, it stretches longer and the joints between the links wear, also adding play and length to the chain. With it being longer, it's not pulling the sprockets on the cam at the right timing. If you have a big rubber band on your ps pump for example, instead of a belt, the rubber band will stretch and the PS pump won't turn as soon because the stretch means the engine is turning and causing the band to stretch instead of turning the pump, until it hits the point where it won't stretch anymore and the pump begins turning. Same with the timing chain. The difference is it doesn't snap back once it's stretched out, it just gets longer, which is why you need a tensioner to take up that slack at the end. Otherwise there's all types of slap in the chain and when you shut the engine off, the cam may want to spin and the engine not want to (because the valve closing wants to close all the way) and the slack would allow it to jump a tooth... catastrophic engine failure.

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2021 Charger Scat Pack Widebody "Sinabee"
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Previous:
1972 280SE 4.5
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Hi ptspringer

remember that as the crank turns clockwise you can never actually have loose chain on the right hand side of the crank. it will always pull the rhs cam to keep the chain tight between the rhs cam and the crank. any looseness can only happen between the crank and the lhs cam as you face the engine and that should be taken up by the tensioner.

If you turn the crank by hand clockwise till you line up the cam timing marks and then look at the crank and see it is after top dead center by 5 deg (and you are not using a vernier so there is some slop in the system) then the most likely thing is that you have wear on the spockets and the chain is sitting on the cam sprocket a little lower than it should and you see a little movement past TDC on the crank

you should still get the nobel prize for the drawings though
cheers
barri

__________________
61 Austin mini
67 Lotus 7
74 450sl
76 Cadillac 8.2l (501 ci)

some new cars

megasquirt conversion on:
djet 74 450sl http://www.mercdjetmegasquirt.britautorepair.com/
cis 76 450sl http://www.merccismegasquirt.britautorepair.com/

the best view is always from the point of no return

Now you know why the Noble Peace Prize for chain stretch is so hard to get, there are competing theories!

I'm thinking my chain was stretched, and beyond the limits of my 37 year old tensioner. Then the extra slack would be taken up by the crank sprocket - by rotating slightly out from under that chain.

Otherwise - the distributor timing would not be so far off.

Just another theory like
a) the chain is a rubber band theory
b) the crack gear is worn theory
c) the tensioner is shot theory
d) the earth is flat theory

maybe 3 out of 4 are right -

Three-way split??

BTW - how long is a new chain?? My stretched one 0.3734 " or 9.48 mm per link.
-

__________________
1983 500 SL (Gone )
1972 350 SL 4.5

I can tell you right now if you can get string theory or even hyperstring theory and trimeric photon theory in there, you are a certainty for the prize

__________________
61 Austin mini
67 Lotus 7
74 450sl
76 Cadillac 8.2l (501 ci)

some new cars

megasquirt conversion on:
djet 74 450sl http://www.mercdjetmegasquirt.britautorepair.com/
cis 76 450sl http://www.merccismegasquirt.britautorepair.com/

the best view is always from the point of no return

Why not just do it the correct way to start with
Remove distributor.
Turn the engine so both valves on number one cylinder are closed and the piston is a Top dead centre. (poke a peice of wire in there to confirm you have the right cylinder,you can feel the piston crown) and the timing mark on the damper is at Zero. Now get the distributor minus cap ,but with the rotor in place. Look at the side of the distributor body lip. There is a tiny notch. this indicates number one lead position .
look down the distributor body at the hold down screw slot. in the center of the arc is where you want the hold down bolt to be.
Hold the distributor in place in the engine mount and aim the center of the arc at the hole for mount hold down screw.

Turn the rotor approx 25mm anti clock wise. place the distibutor in it's mount and slide it in. The rotor should turn to meet the mark on the body as it sits into place.

If you don't get it right the first time ,keep moving the rotor anti or clockwise until the distributor fits down snug and the rotor is aimed squarly at the mark.
Now check the plug leads are in the correct positions on the cap.
screw the hold down screw home,replace the cap and number one plug .Then replace the cam cover . Connect your timing light and start the engine. Adjust timing to specs.
You will find your leads and connections will now be more "relaxed" in position without having tight leads on one side and loose on the other etc etc .

Now ,for a quick lesson on why the tiiming chain should be replaced every 100,000 .
it's not a matter of slack or adjustment or the tensioner.
The link bushes wear and the chain becomes longer.
Simple?
When the distance between crank centerline and cam centerline is moved back because the chain is longer,the timing becomes retarded and the engine is low on power.

No amount of tension on any chain will alter this simple fact of mechanics.
Hold a used chain against a new chain and often the difference in length can be as much as 3 inches.

Nice lesson on setting the distributor, but it requires a lot of work.

Better to understand fundamentals of chain stretch theory, and then fix the critical flaws.

Currently there are four theories in play.

a) the chain is a rubber band theory
b) the crack gear is worn theory
c) the tensioner is shot theory
d) the earth is flat theory

Now you are proposing a 5th theory:

e) the chain is three inches longer than needed theory.

I'm afraid you won't be sharing the Nobel Peace Prize on chain stretch theory with the three of us - although you seem quite conversant on the subject ;-) , your theory is a sub-theory of a), and your estimate of three inch stretch seems a bit large compared to data.

Please consider the test of General Relativity proposed by Einstein - the advance of the perihelion of Mercury- similar in many aspects to Chain Stretch Theory.

"The advance of the perihelion of Mercury was a longstanding problem in celestial mechanics. Careful observations of Mercury showed that the actual value of the precession disagreed with that calculated from Newton's theory by 43 seconds of arc per century."

Not 60 degree stretch in .37 centuries

PLEASE - this is serious science here!

__________________
1983 500 SL (Gone )
1972 350 SL 4.5

what work? It is how it is done and probably takes ten minutes at most to acommplish. If you hold your old chain up next to a new one you will see the obvious difference in length. it's not science ,just simple basic mechanics. I do this all day, every day ,never bored with it either.