low compression in bank 2, bank 1 is perfectly fine

trlps_

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Feb 25, 2020
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so i ended up doing a compression test on my 02 GT after it sitting for sometime and here were the results, cylinder 1-4 were at a solid 170-180, coming to bank 2 cylinder 5 was at 0, cylinder 6 was at 100, cyl.7 was at 20 and cyl.8 was at 30, does anyone have any clue as to how this can be? i did recently have the timing chain replaced but i didnt change it out myself, had someone else do it but the car drove fine after it was changed but only for maybe 2 weeks or so, does anyone have any ideas?
 
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To find the where and why of low compression, connect an air hose to each cylinder on that bank one at a time, and track down where the air is escaping. If the air comes out of your throttle body or tailpipe, burned or bent valves is your answer. If it comes up through your radiator cap, you need a head gasket. If it comes out of the oil cap, you have internal engine damage.
 
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I unfortunately don't have access to an air hose due to where the car is sitting at my apartment, but is there any way that I can run this test maybe with anything else? not sure what else I could do the test with but now im eager to run it
 
I unfortunately don't have access to an air hose due to where the car is sitting at my apartment, but is there any way that I can run this test maybe with anything else? not sure what else I could do the test with but now im eager to run it
Not really, you're going to need compressed air.
 
i did recently have the timing chain replaced but i didnt change it out myself, had someone else do it but the car drove fine after it was changed but only for maybe 2 weeks or so, does anyone have any ideas?
Yes. My guess is that the bank 2 timing chain has slipped. Piston to valve (PTV) contact was the result. I think you will have a tough row to hoe here.
 
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Yes. My guess is that the bank 2 timing chain has slipped. Piston to valve (PTV) contact was the result. I think you will have a tough row to hoe here.
I agree that this is the most likely culprit. Either a teardown of the front of the engine or a leakdown test will tell the tale.
 
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So i am having a similar problem. cylinders 1,2,3 and 4 are all running about 165psi. 5,6,7 and 8 are all running right at 180. Like a fool, i did not run a compression test before i did the timing chains, guides and sprockets as the motor was out of the car when i decided to do them. I am positive that i followed the procedure correctly and the marks on the chains lined up with the marks on the sprockets when i was complete. I even used the cam holding tools recommended by the manual. So before i go tearing down the front of the motor looking to see if one of the cams possibly jumped a tooth, is it possible i got a defective sprocket for one of the cams? Is there something else i am missing that would have the whole bank running low? Am i over thinking this? Thanks!
 
I am positive that i followed the procedure correctly and the marks on the chains lined up with the marks on the sprockets when i was complete.
Did you take pictures? Why is this important? Because it has happened more than once that the cam sensor "bump" on the left hand cam was mistaken for a timing "dot" resulting in an out of time for the left hand bank.

Obviously if the incorrect timing mark has been used the person doing the work believes they have done it correctly (but in fact not).
 
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Did you take pictures? Why is this important? Because it has happened more than once that the cam sensor "bump" on the left hand cam was mistaken for a timing "dot" resulting in an out of time for the left hand bank.
I did take pictures, unfortunately i took them after i stuck the harmonic balancer back on so you cant see the dot on the bottom, but you can see plain as day the dot in the pic on the cams.
 

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Looks good from what I can see in the pic. Obviously without being able to see the crank, we can't double check the crank dot. However based upon what can be seen in the picture the motor would be in time left to right. If out of time the whole motor would be out of time.

You don't have to tear down the front of the motor. It's possible to check timing by just removing the value covers. The down side of this method is you may have to turn the motor over by hand a TON of times in order to get the marked link and the cam dot to line up at the same time. But if you can see both cams still lining up between the dark links and the dots, IMO it's safe to conclude that the motor has not slipped time since you installed the chains.
 
Thanks,
yeah, i'm starting to lean towards slop in the cam gears them selfs. I have read a bunch of articles like this http://www.mustangandfords.com/how-to/engine/mmfp-0612-ford-mod-motor-cam-timing/ to where the cams were not perfectly timed from the factory. I wish i would have read this article before the motor went back in the car. I did just put a turbo on this motor so i was double checking things before i head to the dyno. There is a lot of things to move in order to open the front of the motor back up. I don't plan to keep this motor in the car long term anyway. I'm already thinking about forged internals and more boost! I wan't to use this motor as the learning curve for the real motor.
 

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