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STS 2005 3.6L LE, SRX 2009 4.6L Northstar AWD
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Discussion Starter #1
As a result of driving on LPG, I experienced compression leakage during cold run on cyl. #1. Both the inlet valves leaked as a result of burnt valves/seats due to lean mixture burning in cyl.#1 causing a higher combustion temperature. The lean mixture was a result of bleed air being mixed at the intake manifold gasket. The bolts holding the intake manifold had become lose over time, a result of a higher expansion coefficient from the nylon-80 intake manifold in comparison to metal. The inlet manifold gasket leaked some air. As a result (now I know why.....) DTC-P0420 P0430 was set irregularly.

Since the car had ran 90k miles only and a trade-in of the car would return the scrap price only, I decided to invest in an engine overhaul.
The cylinder heads were ordered in Clearwater, Florida, tailor made with hardened valves and seats to run on LPG. I drive in Germany and LPG is available everywhere and much cheaper than gasoline, however I have re-invested a big chunk of this profit on engine overhaul....

I also replaced the timing chains and tensioners with an aftermarket/OEM set (Made in Taiwan). One of the tensioners had failed after the first 5 miles test run and I had to call road side assistance to return the vehicle to the workshop. After dismantling the timing cover, I discovered that the tensioner on the LB had returned back into the collapsed position (see pic). The chain became lose and caused a rattling noise. The hydraulic oil pressure couldn't prevent the tensioner piston from returning into collapsed position. The RB tensioner started to fail too, whereas the pin holding the ratchet had come out of the housing (see pic). However, both chains didn't jump over the sprockets. A compression test revealed no compression loss on all 8 cylinders, all over 170 psi, not bad before breaking in!!!!

The old tensioners (Made in USA) were checked and built in again. Ever since (500 miles) no failure has occurred, fingers crossed. I drive Made in USA for several good reasons.

The new cylinder heads were delivered with the VVT-sprockets mounted. My car is model 2004-2007, and the new heads were 2007-2009, both series have identical cylinder heads (with different cast numbers) however, the VVT-sprocket set has different CMP disks!!!!!!! The notches on both series are totally different (see pic with old and new ones presented in matching position). I didn't checked this when the cylinder heads were mounted, but after the test run, when replacing the secondary chain tensioners, I discovered it and replaced them with the original ones. No visible wear was seen on the teeth, even the size of all teeth was identical to the new sprockets. Before, during the failing test run I had 4 DTC codes P0361, 366, etc. all related to the CMP's on both banks.

The tensioner of the primary chain WAS WORN TO THE BARE METAL!!!!!!!!!! (see pic). I replaced it with the new one because it had a normal firm spring load force like the original one and the rack and ratchet were working properly.

I did oil changes and general maintenance every 7500 mi. or 1 year, whichever came first. I can only recommend to use premium consumables on this premium engine to prevent failure.

A returning pair of DTC-codes P0068 and P1011 haven't returned ever since the overhaul. These codes are related to a calibration issue of the ECU, however no ECU-flashing has been done so far.....

Unless other experiences with other drivers, my car's engine, (and the car) still runs exceptionally good and I hope it will for many more years to come.
 

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That's the horror story with some no name aftermarket parts for Northstar cars. I don't know why, but it seems far worse than it is for any other engines/cars. That's exactly why I stuck with all AC Delco tensioners when I rebuilt it. They get the job done.

I've seen that wear on the primary tensioner a few times. That happens for FWD as well. Not all cars suffer this, some even at high mileage, so I'd assume it has to do with the oil used during the car's life. Perhaps an additive not working really well with the material or something.
 

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STS 2005 3.6L LE, SRX 2009 4.6L Northstar AWD
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Discussion Starter #3
That's the horror story with some no name aftermarket parts for Northstar cars. I don't know why, but it seems far worse than it is for any other engines/cars. That's exactly why I stuck with all AC Delco tensioners when I rebuilt it. They get the job done.

I've seen that wear on the primary tensioner a few times. That happens for FWD as well. Not all cars suffer this, some even at high mileage, so I'd assume it has to do with the oil used during the car's life. Perhaps an additive not working really well with the material or something.
Exactly right, about the oil used and the additives. I was asking myself the same question. I use premium oil LiquiMoly with MoS2 additive, here in Germany they claim it as premium.... but here everything 'made in Germany' is claimed as premium, that's why I drive Made in USA. :)

About the tensioner set, it is Cloyes, AC Delco wasn't available at the time I ordered. The alternative is Melling. I was advised to use Cloyes......now I know better. Anyway, the original ones are built in again except for the primary chain.
 

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STS 2005 3.6L LE, SRX 2009 4.6L Northstar AWD
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12 Posts
Discussion Starter #4
Exactly right, about the oil used and the additives. I was asking myself the same question. I use premium oil LiquiMoly with MoS2 additive, here in Germany they claim it as premium.... but here everything 'made in Germany' is claimed as premium, that's why I drive Made in USA. :)

About the tensioner set, it is Cloyes, AC Delco wasn't available at the time I ordered. The alternative is Melling. I was advised to use Cloyes......now I know better. Anyway, the original ones are built in again except for the primary chain.
Thanks anyway for sharing your experiences.
 
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