1st Gen R53 Cooper S Low compression across the board. Verify timing? Bent valves?

Discussion in '1st Generation: 2002–06 R50, R53 & 2004–08 R52' started by silence238554, Feb 22, 2016.

  1. silence238554

    silence238554 New Member

    Dec 6, 2015
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    So, I've been troubleshooting my car's rough idle / inconsistent vacuum issues ever since finishing my head gasket job last fall. After taking it to a shop, turns out it has low compression across the board:

    #1- 130
    #2- 135
    #3- 125
    #4- 145

    The way I see it, there are two possibilities- The timing is off by a tooth or so and the exhaust valves are opening too early, or-

    I second-guessed the timing on re-assembly & ran it off by a tooth for about a minute. It started to sound like a diesel so I shut it off. Here's the full story-

    Please keep in mind that I did all this last September, so I don't really remember the specific reasoning as to why I did this, but here goes-

    I used white out to put reference marks on the chain & cam sprocket. With the timing chain tensioner out, I rotated the crank until the cam sprocket turned 360 deg. I think this was to bring it's arrow back to facing up without rotating the engine backward. Unfortunately, this caused me to lose my reference mark on my timing chain. However, I believe I did the rest of the head gasket job without moving a tooth.

    So then, I got the engine re-assembled and started it up. It struggled to fire & idled pretty terribly, so I second-guess the timing. Looking at the position of the cam gear & comparing it to a "before" reference photo (also referencing a mark I'd made on the crank pulley), It appeared to have skipped a tooth. So then, I moved the cam gear counter-clockwise by one tooth. I believe this would retard the timing? Fired it up, it ran fine for a few seconds, then slowly started to get more & more valve train noise, eventually wounding like a diesel & I shut it off after a minute or so.

    Wanting to make sure I had the timing correct, I pulled the timing cover only to discover that it was actually correct the first time, so I placed the chain's colored links on the crank & cam sprocket's corresponding arrows & have been running it that way ever since.

    If you've made it this far, I have two questions:

    Is it possible to have bent valves from running the engine one tooth off?

    Is it possible for the timing to "look correct" based on the links / marks but still be off??

    From what I have heard, this is an interference engine but will only hit if it's "way off". I've also heard that if you're lining up the links & sprocket marks, your only two outcomes would be to have correct timing or to have it 180 deg. off, resulting in a running engine but with crank & cam sensor fault codes.

    I currently have no codes.

    Any input on this would be greatly appreciated.
     
  2. Eric@Helix

    [email protected] New Member
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    K, I skimmed your post. Being functionally illiterate that's the best I can do without pictures, so forgive if I missed something in my response.

    -You could be off a tooth. It wouldn't bend valves if you were, but you'd be down around 30 hp. Call me if you want a quick and dirty way to diagnose this.

    -Your compressions are actually not too far apart, cylinder-to-cylinder. That's a good thing. The numbers are a little low, but that could be your gauge or that your car is cranking with a weaker battery. If you had a bent valve or two, your compressions would be all cattywhumpus, and you'd likely have misfires.
     
  3. BlimeyCabrio

    BlimeyCabrio Oscar Goldman of MINIs
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    Are you SURE you don't just have a vacuum leak somewhere? Lots of places to leak on a mini, it's a very common problem after reassembly...
     
  4. nkfry

    nkfry New Member
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    You could be a tooth off, but like Eric said; your compression numbers are within ~10% of each other. Deviance over 10% is cause for concern.

    It sounds like you have a vacuum leak somewhere.

    By it sounded like a Diesel, was it clattery? Almost like the timing tensioner hadn't been popped before starting?

    Do all of your lifters have the caps on them still, or were some of them broken off during the head work?
     
  5. silence238554

    silence238554 New Member

    Dec 6, 2015
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    Thanks Eric, I may give you a call tomorrow about that quick & dirty diagnosis. I'm actually going to do my own compression test tomorrow as well just to verify the shop's numbers.

    I'm pretty damn sure. I rigged up a PVC cap to pressurize everything from my air inlet hose & have fixed every leak that I can hear or see by squirting soapy water. I've done this whole process about 5 times.

    Nah, it's wasn't clattery, I can post a video on here later that I took of it that shows exactly how it sounded. I actually popped the timing chain tensioner with the timing cover off so I visually saw it go out & tension the chain. As for the lifter's caps, I have no idea. I don't even know what those are but I am suspecting the machine shop may have dropped the ball somewhere at this point. Care to elaborate on what I can look for if I pull the valve cover?
     
  6. silence238554

    silence238554 New Member

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    Okay, so yesterday I ran my own compression test & came up with:

    Cyl 1- 150psi, 10 strokes
    Cyl 2- 157psi, 10 strokes
    Cyl 3- 140psi, 12 strokes
    Cyl 4- 148psi, 10 strokes

    So then, Cylinder 3 seems to be a bit of an issue but my numbers certainly aren't uncharacteristically low across the board as the shop had led me to believe. I used the same gauge on the same day to do a compression test on our other R53 that runs great & it was also in the 150's so I know my car's in the right range.

    I also verified that my timing is, in fact, correct. After speaking with Eric @ Helix, I pulled my valve cover, rotated the crank 'till the two round holes in the cam gear were perfectly level with the top of the head, then used a long 1/4" extension to verify that all cylinders were sitting at the same height, and they were.

    Finally, I ran a test similar to a leak down, where I pulled the valve stem out of the compression test hose & used it to feed compressed air into the combustion chamber of each cylinder while at TDC & listen for air leaks. On every cylinder, air was leaking very slightly out of the dipstick tube, meaning past the rings, but nothing through the valves.

    So in a way, I'm back to square one, with the symptoms being:

    -Very unenthusiastic starting

    -When RPM drops to idle, it does not fall to a solid 800 RPM. Rather, it will usually fall under, possibly bog a bit, then eventually correct itself.

    -Lazy throttle response

    -Lumpy, resonant idle (all stock mounts)

    My possible suspects are:

    -Throttle body

    -Partially clogged Cat

    -Still a damn vacuum leak somewhere that I haven't found

    Any suggestions at all would be greatly appreciated!!
     
  7. BlimeyCabrio

    BlimeyCabrio Oscar Goldman of MINIs
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    I'm a big fan of vacuum leak. But you know that already. ;-)
     
  8. silence238554

    silence238554 New Member

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    That would be fantastic, do you know of any sure-fire way to test that I haven't tried?

    -smoke test
    -positive pressure applied through intake / spray soapy water everywhere / listen for hissing
    -spray brake cleaner across every potential leaking seam & listen for changes in idle
     
  9. DneprDave

    DneprDave Well-Known Member
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    I wouldn't use brake cleaner, the ones I'm familiar with are not flammable and can, in fact, release some nasty gasses, when burned (phosgene).

    Better to use propane to look for vacuum leaks, as it is a fuel and it will affect the idle, if you get it near a vacuum leak.
     
  10. BlimeyCabrio

    BlimeyCabrio Oscar Goldman of MINIs
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    Starting fluid spray works well, also.

    But your pressure or smoke test should have found it. Another possibility is failing MAP or TMAP sensor.
     

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