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S12//SR20//HOONIGAN
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647 Posts
Discussion Starter #1
So i discovered today that my timing chain has skipped a few teeth, and im posting everything i discovered and the process i went through on here to verify that I did everything right. So please feel free to flame if by anychance I did anything wrong.. here goes.

I've finally finished working the kinks out of my motor for the past week and I went to fire over the car and every couple of cranks the car would idle for a split second then instantly shut off. So i mess with the Distributor by hand to see if the timing was just a tad bit off, and no matter how i positioned it, it ran the same. So since I cant get the car running to check timing I decide to check the timing at TDC. So i take out the plug on piston #1 and turn the crank until the #1 piston is reading 0 degrees (on the crank pulley) on its compression stroke (TDC)and I shine a light down the plug hole to verify. check the position of the rotor and its off... by alot.. I advance the distributor by hand all the way to try and line up plug #1 on the cap with the rotor and no good. ALL the way advanced the rotor points to piston number 2. Am I right? did I jump timing? I'm almost 100% on this but just want to hear a second opinion before i buy the tensioners and a cam sprokcet(s) if one of the teeth are messed up. Thanks in advance guys.
 

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The Boost Bear..Rawr!
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3,055 Posts
How many teeth do you have between cam sprocket indicators? Should be 20 pins, IIRC.
 

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S12//SR20//HOONIGAN
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647 Posts
Discussion Starter #4
I just confirmed it, took off the VC and the exhaust cam jumped by 2 teeth. thankfully no valves were dropped so i plan to redo the chain and tensioners. anyone have any tips on a fast install?
 

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Registered
SR20DE stock G20 p10 highport
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75 Posts
As JimR suggested, Check where your cams are sitting when you have turned the motor to TDC. The lobes for cylinder 1 should be facing outward. If they are aren't facing outward yet the crank pulley is saying 0*, the crank pulley could be separating from its inner rubber ring. (If the crank pulley doesn't read 0* when the dowel keys have a 10/12 o'clock orientation, the pulley's rubber ring has failed and the pulley (with the timing marks) has spun independently. Put motor at TDC and install a new crank pulley.) Finding True Top Dead Centre

If the cam lobes for cylinder 1 are not facing outwards, you need to rotate the motor until the dowel keys on the ends of the cam shafts have a 10 o'clock and 12 o'clock orientation. Verify the crank pulley reads 0*. Then reset the chain on the sprockets if necessary.

If the lobes are facing outward when the motor is at TDC, then the chain tensioner probably failed and allowed too much slack in the chain, which allowed it to skip a tooth on the cam sprockets. There should be no slack in the chain along the exhaust side (tension side) and 20 chain pins (not links) between the indentations on the two cam sprockets. (There are two pins for each link, so there will be 9 full links (18 pins) and two "half links", 18 + 2 pins = 20 pins between the indentations.)

If there are not 20 chain pins between the indentations on the cam sprockets, you must reset the chain and engage it so that there are 20 pins between the indentations.
Do do this,
Put the crank pulley at 0* TDC, and verify the cam lobes for cyl. 1 are facing away from each other.
Remove the chain tensioner, loosen the bolt on the intake cam sprocket, remove that sprocket, pull the chain away from both sprockets, and position the cams so that the dowel pins have a 10 o'clock / 12 o'clock orientation.
Loosen the distributor and slide it to the middle of the slide range. Then pull the chain slack up from the crank gear and drape the chain over the exhaust cam gear without allowing the cam to move out of 12 o'clock position.
Count the correct number of chain pins/ links between the indentations on the sprockets, engage the chain onto the exhaust cam sprocket so that the correct number of pins is had.
Be sure that the 10 o'clock orientation of the intake cam's dowel key doesn't change.
Re-fasten the sprocket bolt, and install a new chain tensioner.

The distributor only fits into the cam shaft one way, so provided the motor IS IN FACT at TDC (and not bottom dead center) then the distributor rotor has to be in the correct positon in order for the distributor to insert correctly into the end of the cam shaft.
 
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