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I recently purchased a 2012 825i at auction. The machine has 2900 hours. The engine is running rough and has a knock (or a tick, not sure I know the difference). I am going to list what I have done to diagnose the problem and I am looking for suggestions on what else to do before pulling the motor and opening it up. I started off by changing all the fluids. No noticable shavings in the oil. I also drained and replaced the gasoline. I have pressure tested the fuel pump, which is a little below spec (40 psi). I have tested resistance on all the coils. The resistance is the same for all, although I can't find a spec to compare it to. I replaced the spark plugs. I have done a compression test on all three cylinders. They are all at 100 psi, give or take a few. I believe this is a low, but that could also be my compression tester. I have checked the timing belt. It is in time and the belt looks to be in good shape. I also did a leak down test on the cylinders and only had small amounts of air escaping (well within tolerance) from the dipstick tube. I have never worked on a DOHC motor before, but I have rebuilt other types of motors. I have a copy of the service manual. Any suggestions on testing before I dig into it?
 

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I recently purchased a 2012 825i at auction. The machine has 2900 hours. The engine is running rough and has a knock (or a tick, not sure I know the difference). I am going to list what I have done to diagnose the problem and I am looking for suggestions on what else to do before pulling the motor and opening it up. I started off by changing all the fluids. No noticable shavings in the oil. I also drained and replaced the gasoline. I have pressure tested the fuel pump, which is a little below spec (40 psi). I have tested resistance on all the coils. The resistance is the same for all, although I can't find a spec to compare it to. I replaced the spark plugs. I have done a compression test on all three cylinders. They are all at 100 psi, give or take a few. I believe this is a low, but that could also be my compression tester. I have checked the timing belt. It is in time and the belt looks to be in good shape. I also did a leak down test on the cylinders and only had small amounts of air escaping (well within tolerance) from the dipstick tube. I have never worked on a DOHC motor before, but I have rebuilt other types of motors. I have a copy of the service manual. Any suggestions on testing before I dig into it?
 

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What were the leakdown test results?

100 PSI compression seems low as for some reason 170 PSI sticks in my mind, but I could be way off.

Have you checked the valve lash? In the past some owners found the valve lash too tight causing an issue.

Also check your spark plug wires real good.

Good luck!
 

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Discussion Starter #4
Leak down results were right around 15% and were pretty much the same for all three. Would valve lash being too tight cause a tick or a knock? I havent checked it, but will as I start to dig into it. Fortunately this is gator number two, so I still have something to drive around!
 

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I was thinking the low compression numbers.

Knock sounds like a bearing issue.

Tick is usually associated with too much valve lash.
 

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Discussion Starter #7
And I got a different compression tester. Gonna test again to see if the cylinders are low or if the tester is bad.
 
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