Timing Chain / Camshaft position problem - Pontiac G8 Forum: G8 Forums - G8Board.com
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post #1 of 7 (permalink) Old 07-28-2016, 07:38 AM Thread Starter
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Timing Chain / Camshaft position problem

I posted this on the Cadillac forum and I haven't gotten much feedback so I'm posting it here.

I recently purchased a 2004 CTS with the 3.6L engine. I bought it cheap due to the timing problem. The timing chain broke on the previous owner. He had the timing chain replaced. The car would start and run ok-ish but idled rough. The mechanic did the job again the car ran the same. After that the previous owner decided to unload it and I bought it.

The codes are P008, P0016, and P0017. I've done lots of research and reading on those codes and the combination of those codes with respect to the 3.6L engine. I looked at the camshaft position values with a Tech2 and I found something I don't understand. This is what is going on:

1) Clear the codes
2) Start the car from cold, idles a little rough, no check engine light
3) Monitor the CMP (camshaft position) values with the Tech2

At first "Int. CMP Angle Bank 1" is at 37 degrees and the desired is 0 degrees. The other three camshafts show 0 degrees for both the actual and desired angle. All four CMP band commands are 6%. After a short period of time "Int. CMP Angle Bank 1" works its way down to 0 degrees. The command to that camshaft actuator is always 6%. I don't understand what is going on. The codes that eventually show up are for both the intake and exhaust camshaft position on bank 1 but I never see anything odd on the Tech2 for the exhaust side.

A video of the Tech2 screen is below:
https://www.dropbox.com/s/otzdykyarx...S_CMP.mp4?dl=0

I have tried swapping the camshaft position sensors around but the problem didn't change. I also pulled out the crankshaft position sensor and used a borescope camera to verify that the reluctor wheel was correctly positioned on the crankshaft. It looks like the next step is to pull the front of the motor apart but I'll wait a few days to see if anyone has other suggestions.
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post #2 of 7 (permalink) Old 07-30-2016, 08:13 PM Thread Starter
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Today I disconnected the cam actuators to see what would happen. The intake cam position on both bank 1 and 2 showed 39 degrees out on the Tech2. After looking at the pictures of the cam gears I think the guy who put the timing chain on managed to use the wrong timing marks. The cam gears have two marks, L and R. The two marks look to be about 40 degrees apart. So, I'm going to take it apart and see.
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post #3 of 7 (permalink) Old 07-30-2016, 08:47 PM
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I think you have a winner here. I just looked at the cam gear orientation required for that engine. Each intake and exhaust (labeled) cam gear, has 2 distinct timing marks stamped on them. Both are stamped in the apex of the gear teeth. One is a*triangle* an one is a *dot*. Those timing marks appear to be stamped about 35 to 40 degrees apart. It is mandatory to rig the chain (from the cam to the crank) on the *correct* timing stamped mark, based on which side (left or right bank) that cam is located at. Sure sounds like the (mechanic in charge) so to speak, picked the wrong timing marks on that one bank, both times.



Kinda looks like I'm sorta repeating a lot of what you have already said. Shows how fast I guess I'm reading, but having a brain that can't process it at the same rate.. Sorry
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post #4 of 7 (permalink) Old 07-30-2016, 10:34 PM
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I think you are on the right track, I remember almost using the incorrect markings myself, they are different (though I don't remember exactly how they differ)... but the correct ones didn't stand out as predominantly as the incorrect ones.
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post #5 of 7 (permalink) Old 08-01-2016, 07:41 PM Thread Starter
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It turned out not be what I guessed before about using the wrong timing marks on the cam gears.

I took the top and front off of the motor and got to the timing chains. By eye it looks like the passenger side is off by two teeth. The cam gear has 32 teeth so 2 teeth would be 22.5 degrees of cam rotation or 45 degrees of crank rotation. The Tech2 is showing 39 degrees between the cam and crank but it doesn't say if that is cam degrees or crank degrees. I'll assume it is crank degrees. I'll realigned the timing components and put it back together this weekend (that's the plan anyway).

We all know that when you spin the motor after lining up all the gear and chain timing marks that they "never" ALL line up again. Out of curiosity I figured out how many crank rotations it actually takes. The timing components are as follows:

Crank gear - 24 teeth
Idler gear - 27 teeth on the big wheel, 18 teeth on the small wheel
Cam gear - 32 teeth
Primary chain - 78 links
Secondary chain - 92 links

The 18/27 idler gear is a 2/3 reduction so the one rotation of the crank moves the primary chain 24 links but only moves the secondary chains by 16 links. The cam gears are 32 teeth and 32/16=2 so we have the 2:1 ratio of crank rotations to cam rotates that you have to have for a 4-stroke engine. The math gets tricky when you factor in the length of the chains to figure out how many cranks rotations are required to get back to where ALL of the timing marks on the gears and chains are lined up again. The answer is 43506.
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post #6 of 7 (permalink) Old 08-02-2016, 10:28 AM Thread Starter
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I found an extra factor of 8 so the answer is actually 5382. Still a bunch of rotations by hand......
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post #7 of 7 (permalink) Old 08-08-2016, 06:33 PM Thread Starter
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It's all back together and the car runs great.

Once you get all of the gear and chain marks lined up there is a pretty easy check that you can do. Mark the crank gear and a spot on the motor (not the chain) as a reference. You can pick any tooth and associated point on the engine that is easy to mark. Rotate the crank 46 times. Your crank reference marks and all four cam gear/chain marks should line up. If they don't you either didn't rotate the engine 46 times or the timing isn't right. The idler gear/chain will NOT line up but that's ok.
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