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Cam position deviation improves with mileage


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Let me post the numbers first, and then add some background.

52,251 miles Cam Pos 1 -4.42 deg. Cam Pos 2 -4.25 deg.

52,998 miles Cam Pos 1 -4.05 deg. Cam Pos 2 -3.92 deg.

My car had only been driven about 2K miles in the two years before my purchase (at 51,348 miles). I put in some fresh gas and a bottle of Techron. The dealer put in a fresh change of M1 0W-40 just prior to my purchase.

The car ran a little bit rough at first. My thought was it needed to be driven and let the detergents in the gas and oil do their thing to unstick engine internals. So I drove it out onto the country roads at a good clip and almost always at least 40+ miles at a time.

I checked the cam pos deviation when my Durametric first arrived, at both idle and 2K rpm. Same numbers (posted above).

Last week John talked me into checking the calibration of my temp gauge using the Durametric. While I had it hooked up I checked the cam pos deviations again. To my surprise they had improved over the previous readings about 750 miles earlier.

This is very odd. I would have thought that it would "all be downhill" with mileage. Have the detergents in the fresh oil, and the driving good distances with the engine hot, cleaned out some gum in the valve train? Is there any other reason that the cam pos deviations would get better with driving?

Edited by Dennis Nicholls
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The cam values will vary with temp. In my case, the bank 1 values will vary almost 1 deg depending on temp.

I would start with a new baseline, making sure the car is completely warmed up, especially the oil temp and then check again after a few hundred miles.

To my understanding, the deviation does not get better over time.

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Let me post the numbers first, and then add some background.

52,251 miles Cam Pos 1 -4.42 deg. Cam Pos 2 -4.25 deg.

52,998 miles Cam Pos 1 -4.05 deg. Cam Pos 2 -3.92 deg.

My car had only been driven about 2K miles in the two years before my purchase (at 51,348 miles). I put in some fresh gas and a bottle of Techron. The dealer put in a fresh change of M1 0W-40 just prior to my purchase.

The car ran a little bit rough at first. My thought was it needed to be driven and let the detergents in the gas and oil do their thing to unstick engine internals. So I drove it out onto the country roads at a good clip and almost always at least 40+ miles at a time.

I checked the cam pos deviation when my Durametric first arrived, at both idle and 2K rpm. Same numbers (posted above).

Last week John talked me into checking the calibration of my temp gauge using the Durametric. While I had it hooked up I checked the cam pos deviations again. To my surprise they had improved over the previous readings about 750 miles earlier.

This is very odd. I would have thought that it would "all be downhill" with mileage. Have the detergents in the fresh oil, and the driving good distances with the engine hot, cleaned out some gum in the valve train? Is there any other reason that the cam pos deviations would get better with driving?

The hydraulic tensioners get varnished up or clogged with crap, fresh oil and some miles often cleans them out, tightening the deviation values. They also tend to tighten up when the car is fully warmed up.

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All measurements were made with fully warmed up engine (driven 20+ miles).

I'd thought that the deviation was mostly due to the wear on those plastic chain rail guides. I didn't realize that the tensioners would contribute this much.

Not driving these cars seems to be a bad idea. The car sat on the dealer's lot for 7 months and probably only was driven from the front of the lot to the back of the lot for washing.

The car runs so much more smoothly since I drove it about 2K miles since February.

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All measurements were made with fully warmed up engine (driven 20+ miles).

I'd thought that the deviation was mostly due to the wear on those plastic chain rail guides. I didn't realize that the tensioners would contribute this much.

Not driving these cars seems to be a bad idea. The car sat on the dealer's lot for 7 months and probably only was driven from the front of the lot to the back of the lot for washing.

The car runs so much more smoothly since I drove it about 2K miles since February.

Wear pad wear is obvious; you get weird deviation values and plastic bits in the oil. The hydraulic tensioners have been updated a couple times since the M96 was introduced, but customers often balk at spending hundreds of dollars on parts alone to replace them. When we get a car in with obviously bad wear pads, we always quote on replacing the tensioners at the same time, that way the customer gets the car back as it should have been new.

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