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BullDoozer

Timing marks off on cam sprocket

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Howdy folks I recently purchased this 720 and I’ve been chasing problems from the very start. I think I’ve narrowed it down to one final mistake from the previous owner. When I got the truck, my distributor would have to be fully advanced to get the timing at 0* tdc. I knew this was screwy so I went to the oil pump spindle to figure out why it was off. Sure enough, when at tdc on compression stroke it was almost 180* off from where it should be. I reindexed it to the proper position and was able to get my timing in a normal 5* btdc with the distributor pretty much in the middle of the adjusting bracket. After doing that the engine ran much much better but I’ve noticed a lack of acceleration on take off and a definite cam rattle. This was confirmed when I pulled the valve cover off and saw score marks towards the front of the cam between the lobes, petering out towards the firewall. I set the engine to tdc again and examined the cam sprocket in relation to the shiny link on the timing chain that the previous owner replaced. It is 2-3 teeth off where my manual says the “bright” link should align with the #2 punch hole. Is there any easy fix that wouldn’t require taking the front cover off and just reindexing the cam itself? Thank you for any response I’m losing my mind over this thing. 

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Usasaly the person who removen the dist put it back in 180 off and the rotor locks stillits its orginal position in the spindal. so one can move the plug wires 180 deg and that will still work. Just the vacuum advance will be 180in the opposite direction.

 

so more or less one can install the oil/dist spindal off and one can install the dist house 180deg off

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The bright links are only for the initial placement of the chain and sprockets. As soon as the engine is started the bright links become random and line up maybe every 20 turns so don't go by that.

 

Set TDC exactly* and only by turning clockwise. If you over shoot don't just back up, but back up 1/4 turn and try again even if it takes a dozen tries.

 

*This is absolutely critical so use the notch on the crank pulley and the timing scale for ignition.

 

There is no TDC mark on the Z series head for cam sprocket checking so what I do is look through the top hole in the sprocket and directly between the two rocker arm towers for a small vertical casting mark...

 

Txj05Jv.jpg

 

The back of your cam sprocket should have a V or U notch in it. Confirm that the V is below or perhaps just slightly to the right of the line and NOT to the left of it. Like below...

7IjLfsA.jpg

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Thank you both so much for your detailed responses, I’m gonna give ‘er a look see when I have a chance. Would the cam being slightly out of time be the cause of the fairly noticeable rattle when I first accelerate on the next gear? There is noticeable chatter that isn’t just the rocker arms. Scoring seems to be in between lobes right before the first set of rocker arms worse up towards the cam sprocket and definitely lessens as you follow the cam towards the firewall. Loose timing chain? Valve lash needing adjusted? I’m stumped. 

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I am at the point of reinstalling the head on this '82, 720, Z22 and find following Mike's instructions, getting the notch to align with the casting mark, the intake valve on #4 has started to open.  Is this going to be a timing problem?

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I think all engines above the L16/18 came from the factory on the #2 hole BUT this is for new timing components and allows one more move to the #3 hole to compensate for chain stretch or having the head milled down. This should be checked and the sprocket moved if this is found to be the case. If #3 hole doesn't bring the cam into spec then the timing components should be replaced with new.

 

A moderately stretched chain has the effect of causing the cam events to be later than they should be. This would slightly favor top RPM at the expense of low and mid power and torque.

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