We have a 2007 Mini Cooper S. We recently had the timing chain and timing chain tensioner replaced by our mini dealer. The car ran well afterward with the exception of a minor surge up and down in RPM when idling. This was minor but you could see the needle bounce. Then one morning all of a sudden, within a couple thousand miles of the timing chain work, the car won't start. It just tried to turn over. I had it taken back to the dealer and they found out that the compression on all cylinders is low. 60 psi on cylinder 1 and 50 psi on all other 3.

I am worried that this has something to do with the timing chain work but they say they have checked the chain and it is properly timed. Do you guys have any suggestions? could there be something with the timing chain that they are not seeing? Any other issues that could be addresed before pulling the head like they are suggesting? Thanks for any help.

Car has 73k miles on it.

 

Am I understanding correctly, your Mini dealer replaced timing chain and related components and right afterwards there was a minor idling surge, then one morning 1000 miles later you had an even bigger problem do to low compression, is that correct? Absolutely could be related! I think it should be standard practice to check the compression on any engine receiving a new timing chain.

Could be that your valves may have collided with the pistons when your timing chain was rattling around or even have the timing chain jump off a few teeth causing enough minor damage that wouldn't show up right away. When or if you decide to pull the head you'll know if the valves collided with the pistons if your valves ate bent.

 

Is there a way to prove that it was due to their work on the timing chain? Or am I just stuck?

 

Not an expert, but you need to first understand what caused the failure. It seems unlikely that the valves were damaged before the timing chain change but the compression failure occurred only afterwards. What might be more likely, is that the timing gears were not tighten properly during the change, causing the timing to slip. The driving gear and the two camshafts gears are only held in place by friction, so insufficient tightening might allow them to slip.

 

I would have them reinspect it, might be that a bolt came loose on install or previous damage from the timing being off, but they should have seen that when it came in for the chain.

 

If compression is that low across the board it sounds like they timed the engine improperly or didn't torque things to spec and you had exhaust valves contact the pistons. I've yet to see intake valves crash, but I've also never seen an engine that far out of time.

Which would only be caused by install error, otherwise this problem would have been evident before they did the work.

You can have a leak down test done to confirm where the compression loss is, but if you just had a timing chain done chances are they crashed exhaust valves into the piston.

They can also remove the spark plugs and use a boroscope to check the pistons for valve contact, it'd be on the half of the piston closest to you (exhaust side of the engine).