Timing Chain Slack on 1974 260Z

[AZ260Z]

I noticed the slack side of the timing chain would slap against the guide while remotely cranking the engine on and off to adjust the valves. The slack is removed while continuing to turn the crankshaft. The cam sprocket is set to timing mark #3 and I did a slack measurement test and there was just under 5 degrees of slack. Is this slapping of the chain against the guide on the slack side "normal" on "Z's'" when cranking the starter on & off in short intervals? I'm asking this because someone else who is a mechanic witnessed this and said that didn't seem right but he was not familiar with older "Z's"

[madkaw]

How do you know the valve timing is set on the #3. Did you have the timing cover off and saw the bright link on te crank gear lined up when the cam sprocket was on three?

Your in this deep now, maybe you should consider taking off the cover and start counting links!

Edited June 11, 2012 by madkaw

[AZ260Z]

How do you know the valve timing is set on the #3. Did you have the timing cover off and saw the bright link on te crank gear lined up when the cam sprocket was on three?

Your in this deep now, maybe you should consider taking off the cover and start counting links!

No, I think I misspoke about the timing being set at#3, should have prefaced this by stating that we had #1 piston at TDC and I was checking out the cam sprocket and looking for (chain stretch) or slack prior to adjusting the valves. Looking at timing mark#3(at approx 11o'clock), the groove was just to the right of the notch, where its supposed to be, but am concerned about the slapping of the chain on the guide, since the mechanic didn't think that was normal. Based on what I saw, and the before and after adjustment pictures in the Haynes manual, it appears it's been set to #2. There was no shiny link in sight.

Edited June 11, 2012 by AZ260Z
I Screwed up

[240260280z]

The timing chain slack is controlled by an oil pressure driven "timing chain tensioner". I don't think there is much oil pressure and oil flow when cranking with just the starter (~ 200rpm) so you will not see the slack taken up by the tensioner.

Slack is different from chain stretch. The slack can be caused by any or all of :

timing chain guide wear

timing chain stretch

migration of timing chain guides

incorrectly installed guides

incorrectly installed tensioner

The specification for installing the chain (with no oil pressure) is "no slack" but I have seen many instances of incorrect installation resulting in slack. It is common.

If you are concerned, you can take off the front cover, inspect and re-adjust the guides and tensioner.

[240260280z]

Forget about the shiny links. These are used for installing a new timing chain and are typically only seen aligning then (unless you are lucky). They do line up but it occurs every xxx revolutions... it is sort of like looking at the moon and every now and then things are aligned and you see an eclipse.

The way to check timing chain stretch is to get the engine at Top Dead Centre (TDC)... usually the damper pulley degree marking is fine for finding TDC.

Then look through the cam sprocket to see where the triangle aligns with the dimple in the fixed plate.

Here is a close-up:

And the full monty:

[AZ260Z]

Forget about the shiny links. These are used for installing a new timing chain and are typically only seen aligning then (unless you are lucky). They do line up but it occurs every xxx revolutions... it is sort of like looking at the moon and every now and then things are aligned and you see an eclipse.

The way to check timing chain stretch is to get the engine at Top Dead Centre (TDC)... usually the damper pulley degree marking is fine for finding TDC.

Then look through the cam sprocket to see where the triangle aligns with the dimple in the fixed plate.

Here is a close-up:

[ATTACH=CONFIG]54047[/ATTACH]

And the full monty:

[ATTACH=CONFIG]54048[/ATTACH]

Yeah, we did that and the groove in the fixed plate was just to the right of the notch, like the manual said. We even checked for stretched chain by hand cranking until the rotor started to turn, marked and then cranked in the opposite direction until the rotor started to move. It was only 1/4" which is less than 5 degrees, and from what I've read, is acceptable.

My only concern was if it is "Normal" for the slack side (driver's side) of the chain to slap the guide when you have the valve cover off and stop cranking the engine at short intervals, as in trying to adjust the valves?