Tdc With Slack On Chain

[siteunseen]

Does rotating the cam backwards to get TDC, causing slack on the drivers side, have any effect on the actual top dead center?

Sounds like a no brainer question but I'm not positive about it.

Thanks

Cliff

[zKars]

Only way cam position is directly related to piston position is when they are linked together solidly. This only happens in normal rotation direction with no slack.  TDC is only to be measured at the piston, not at the balancer notch/pointer or cam plate notch as this introduces sources of error between TRUE TDC at the piston and those indicating sites. 

 

Now all that said, depends on what you're trying to accomplish.

[John Coffey]

Always rotate the engine in the correct direction to set cam timing.

[rossiz]

tdc is the position of the #1 piston and corresponding position of the crank, as they are connected. the valve train (and chain) are set to tdc, they are not at tdc... so once the #1 piston is at the tip-top of its throw, the crank is at tdc, then the valve train is set to correspond to that.

 

so the issue of timing chain slack doesn't really affect tdc, it affects the valve timing in relation to the pistons.

the tight or straight-line side of the timing chain is the critical measurement between the crank and the valve train - set by a specific number of chain links. as the timing chain stretches, this dimension gets longer so the valve train gets further and further behind the crank (retarded). the different numbers on the cam sprocket (1,2,3) allow you to compensate for this by advancing the valve train a few degrees with each setting. 

 

the chain tensioner picks up this slack and keeps the chain from flailing around too much on the loose side - too much slack and the chain can jump a sprocket tooth and bad things happen.

 

now, to your question about setting the valve train in relation to the crank and timing chain slack... if you want to have the valve train at it's correct position relative to the crank at tdc, then you need to set the crank to tdc such that you pull tension on the straight/tight side of the chain. to do this, either turn the crank pulley clockwise (tensioning the straight side of the chain) until you hit tdc, or turn the cam counterclockwise (again, tensioning the straight side of the chain). either way will work, and if you pass tdc with the crank, you can back it up with the cam. just be sure to have the plugs out so you're not fighting compression.

 

if, for example, you were to turn the cam counterclockwise (tensioning the straight side of the chain) and pass tdc, and then you turn the cam clockwise, the first few degrees of cam rotation would simply take up the slack in the chain tensioner and not be turning the crank - so you would not have a true measurement of the valve train to the crank. same thing would happen if you turned the crank pulley clockwise and passed tdc, then turned it back counterclockwise - the cam wouldn't move for a few degrees.

 

i hope this makes sense...

[240260280z]

TDC is simply putting the piston to the top of its stroke, you can do this many ways (turning at crank, cam, wheels  or bumping starter or cleverly applied compressed air).

 

The easiest way (assuming no thick radiator, triple damper pulley, ac components in the way) is to pull the plugs, put in neutral then use a shallow socket and ratchet to turn the crank cw (as viewed from in front of the car).  This direction does not loosen the bolt and replicates what the engine does when running. If you sweep past TDC, keep going and try again.

[siteunseen]

i hope this makes sense...

Yes it makes sense, thank you for taking the time to explain.  My only question is this "turn the crank pulley clockwise (tensioning the straight side of the chain) until you hit tdc, or turn the cam counterclockwise (again, tensioning the straight side of the chain)"  I'm pretty sure my crank and cam turn in the same direction, towards the driver's fender, but I'm not so sure of anything these past few days.   

 

Thank you again RossiZ.

[siteunseen]

TDC is simply putting the piston to the top of its stroke, you can do this many ways (turning at crank, cam, wheels  or bumping starter or cleverly applied compressed air).

 

The easiest way (assuming no thick radiator, triple damper pulley, ac components in the way) is to pull the plugs, put in neutral then use a shallow socket and ratchet to turn the crank cw (as viewed from in front of the car).  This direction does not loosen the bolt and replicates what the engine does when running. If you sweep past TDC, keep going and try again.

There's my problem!!!!  I've got the Yorx A/C with the compressor mounted on the passenger's fender and that big old bracket with a belt and pulley.  Probably an inch and a half of space to get to the crank nose, so I have to do it from the bottom side.

 

I've been turning the cam with Vise Grips to get TDC.  I finally see that the cam doesn't have rods connected to it and the #1 piston!  Pulled my head out of my rear end and now I can see.

 

thank you Blue, I'll figure out some way.  maybe pulling the ZX shroud off the radiator, DUH, will give some room.

[siteunseen]

Only way cam position is directly related to piston position is when they are linked together solidly. This only happens in normal rotation direction with no slack.  TDC is only to be measured at the piston, not at the balancer notch/pointer or cam plate notch as this introduces sources of error between TRUE TDC at the piston and those indicating sites. 

 

Now all that said, depends on what you're trying to accomplish.

I'm going to get to TDC via the crank nose then adjust the cam sprocket window until it lines up with the dowel plate mark.

 

Whu pea!  I've got a plan.

 

Thank you for your help and I'll figure out how to multi quote when I'm done working on the Z.  

[Zed Head]

My method is to put the car in 5th gear and rotate the front tire until the damper mark is at Zero.  That is TDC, assuming that the pulley and marker tab are correct.  

 

Then I put a wrench on the timing sprocket bolt and ease the sprocket backward to tighten the chain.  The only reason to do that is to check the cam timing relative to the crankshaft and pistons, as rossiz described.

 

 

Just saw your last post.  Looks like the filament is glowing now...

[siteunseen]

OK I'm assuming you mean the passengers side rear tire not the front tire.  I put 2 drinking straws together and rotate that tire until the straw kinda "hoovers" in place.

 

I'm going to get to work now, I'll post some pictures for reassurance.  

[siteunseen]

Yes it makes sense, thank you for taking the time to explain.  My only question is this "turn the crank pulley clockwise (tensioning the straight side of the chain) until you hit tdc, or turn the cam counterclockwise (again, tensioning the straight side of the chain)"  I'm pretty sure my crank and cam turn in the same direction, towards the driver's fender, but I'm not so sure of anything these past few days.   

 

Thank you again RossiZ.

I see exactly what you are saying now.  Two wheels turning the same direction, one pulls one pushes, that's why I can turn the cam backwards to get a tight straight side.  Like one side of an all wheel drive car. 

[Zed Head]

OK I'm assuming you mean the passengers side rear tire not the front tire.  I put 2 drinking straws together and rotate that tire until the straw kinda "hoovers" in place.

 

I'm going to get to work now, I'll post some pictures for reassurance.  

Front tire.  The whole car moves.  If you use this method while adjusting valve lash you might crush your recycle bin by accident.