It is important that the cam does not rotate independently of the crank or you can damage engine internals. What was the setup at chain and sprocket removal (gear dots and TDC/cylinder)?


George

 

Dang wish I had snapped a picture. When I removed the timing cover the crank sprocket dot was at 12:00. The cam sprocket was also at 12:00. The cam gear behind the chain sprocket mark is at the 6:00 position. Facing the engine the cam pin is at the 9:00 position not the 3:00 position like I see in some pics. The chain had some pretty good slack but I have seen worse.#1 is supposed to be at TDC according to the rotor pointing to the 6 mark on the distributor case.

 

The whole point of the dots on the crank and cam sprockets is that they point at each other (12 and 6 OC) when number 4 is at TDC. You should move to that alignment before starting. Given that you started with something else, have the cam or crank moved since you started this? If not then why did you not just put the new chain and sprocket on? Yes the distr gets set to TDC for #1 but keep in mind that each cylinder comes up twice per cycle and the harmonic balancer ring can slip on these older engines so the crank pulley marks can be unreliable.

George

 

With all the misfires I have been fighting on this truck I just wanted to verify that what I was seeing was correct. I haven’t moved either crank or cam. Before anything was removed #1 was at TDC the harmonic balancer’s second hash mark was in line with the mark on the cover, I’m trying to say is there is a lower hash mark at about the 4:00/4:30 position. So if I install new timing set to match what was removed it should be okay? Or should I throw the old set back on and rotate to #4 at TDC?

 

I am not sure about the lower hash mark at 4 OC. Do the new and old sprockets have the exact same alignment and orientation for the pin holes, keyways and dots? IOW, are they an exact replacement? Do the new gears go on with the dots in the same place as the originals? I'm trying to understand how we got messed up here or what does not look right. Yes you should have started with the dots point at each other because that's the most accurate way to confirm sprocket/cam/crank alignment (that and #4 at TDC) but if nothing moved and the replacement set is correct and everything is the same between both sprockets then why is it not just a reassembly thing? The sprockets can only go on one way. If anyone else is following this and sees that I am not understanding something please chime in.


George

 

I will not pick up the new timing set till Monday but I will closely compare the new against the old. How do I determine #4 is at TDC, should the rotor be pointing at something to verify?

 

Pull the #4 plug, rotate the engine until you start to feel air pressure with your finger over the hole. Put a wooden dowel into the hole resting on top of the piston. Continue rotating until the dowel stops moving up. Do not rotate the crankshaft unless the camshaft sprocket is connected with the timing chain in the correct position or you could have interference problems and cause damage.


George

 

Finished the timing set replacement today. Short test drive shows the crankshaft sensor requires a relearn, TAC jumps around above idle and runs poorly, no misfires recorded or while running. I never did disconnect the battery thinking I could avoid this. Have you ever had any luck with the manual relearn procedure? I have been educating myself on fuel trims so as to understand my readings, bank 2 long term reads + 99.9, how can that be? Also my oil pressure gauge has always jumped at idle but not at higher rpm’s, does this play into anyway to my misfires? Will get this crank sensor relearn complied with one way or another this week. The Battle continues!

 

Sorry everyone I have been helping a friend cut an bale his hay for the winter these last few weeks. I did replace the timing gear set due to excess slack and have the PRC retard down to -1.3. The MAF sensor was not plugged back in ( over sight) and I have noticed I have no misfires, will do a test drive Thursday to verify this and will post the results.

 

More of the ongoing battle: determined the purge solenoid at the intake manifold was stuck closed. Replaced with new an test drive was great, no misfires, at 50 mph it started surging badly, no SES light ever came on. Scan had two codes 405/335. Both are for signal fault, one for CPS, one for EGR. How do I track these? A ground problem? Harness issues? These codes have never been seen till now.