Good or low compression for future track bike?

Discussion in 'Tech' started by dallen.helmer, Nov 2, 2019.

  1. dallen.helmer

    dallen.helmer Well-Known Member

    I picked up a 2015 r6 for 900$

    Didn't know mileage didn't have a key was told 300 miles which was a lie.

    Got the keys made, turns out it has 23k

    Started digging into the bike before I track it or plan to part it out.

    Compression tested the motor I'm getting 175-180 on all cylinders ice cold.

    Whats everyone's thoughts?

    Imma get one more compressions tester. Seems like this one is leaking a little bit.

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  2. Spitz

    Spitz Well-Known Member

    Sounds low but verify with a different tester surely. Not suprising given the mileage.
     
  3. dallen.helmer

    dallen.helmer Well-Known Member

    Think it's worth a rebuild at this point? Trying to decide between part out or invest money and make it a track bike

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  4. pscook

    pscook Well-Known Member

    I'm not too familiar with compression testing on a bike with fuel injection, but on a carb bike you either remove the carbs or hold the throttle wide open to get a stable reading. Did you remove the throttle bodies or hold open the butterflies? Did you put a few drops of oil in each cylinder and get different numbers?
     
  5. MurfSVR

    MurfSVR Well-Known Member

    Pretty sure compression test on a cold engine will give a bad reading. Also, thought that a leak down test is more telling.

    If all four cylinders are pretty close in your compression test that’s a good sign.

    Before you run it check the valve clearances and clutch plates (do the clutch spring mod while you’re in there).



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    jksoft likes this.
  6. dallen.helmer

    dallen.helmer Well-Known Member

    I removed everything all the way to the intake valves showing. I didn't add oil to it yet because I wanted another tester to back up the results I'm getting.

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  7. dallen.helmer

    dallen.helmer Well-Known Member

    Well it ran for a little bit but after further investigating I found bad fuel in the gas tank along with rust. The Bike been sitting up for a while with alot of mileage. I'm trying to test engine internals before I start throwing money at it to make it a track bike I'm just trying to find out if 175 PSI to 180 are good enough compression readings to continue life to a track bike or part it out and find another one in the future.

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  8. TWF2

    TWF2 2 heads are better than 1

    What elevation did you test at?
    At my house that would be good number :)
     
  9. dallen.helmer

    dallen.helmer Well-Known Member

    3ft Louisiana we are almost under water.

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  10. TWF2

    TWF2 2 heads are better than 1

    I would put fresh fuel in there, change oil and hit starter button.
     
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  11. dallen.helmer

    dallen.helmer Well-Known Member

    Then test the compression after? It ran decent before the bad gas started kicking in.

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  12. TWF2

    TWF2 2 heads are better than 1

    Yea, or leak down or put it on dyno. I would take fuel pump out and make sure there is no bunch of rust there and clean that fuel tank.
     
  13. Banditracer

    Banditracer Dogs - because people suck

    I wouldn't say those were bad numbers for a cold motor and they're all pretty close. If it's just going to be a track day bike I'd just run it.
     
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  14. Spitz

    Spitz Well-Known Member

    Probably will need some money stuck into the chassis as well. I'd be pretty pissed if someone lied about 20k miles difference, they straight up fucked you.
     
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  15. dallen.helmer

    dallen.helmer Well-Known Member

    I mean I gambled on the milage I hot wired the key switch to get the cluster up. To show milage but it only gave me codes I figured if the motor was shot it's worth more than 900 in parts. Either way it was a deal in my mind.

    But from what I'm seeing 180-175 it's a bad compression for a ice cold motor. Imma do a leak down test to give me greater detail.


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  16. IrocRob

    IrocRob Well-Known Member

    My copy of the service manual says 198-254 psi with proper valve clearances and a fully warm engine.
    I have never done cold/hot comparison checks to see what the typical difference is although
    your cold numbers do seem to be low to me. PM sent
     
  17. PistolPete

    PistolPete Gone sailing...

    I would clean the tank and lines, run it hard for a while to free rings and clean valve seats etc, and do the next check hot. Bet you see an improvement.
     
  18. dallen.helmer

    dallen.helmer Well-Known Member

    Going to bump this one more time I ordered a leak down tester but I was testing my vavle clearance. I know how to get TDC and all that to test them but I use to be a auto tech. I just want someone to back up my theory/knowage. I don't think where on the cam lobe it self, you test whether it be TDC or tip of the cam lobe facing to the sky as long as there is no pressure applied to the bucket it's all testable correct?

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  19. Spitz

    Spitz Well-Known Member

    TDC compression on each cylinder. Keep clear when pressurizing the cylinder and I recommend not trying to hold the engine from rotating, at least we don't with car engines, they will throw your ass on the ground if you're not on the mark and the engine spins a bit.
     
  20. dallen.helmer

    dallen.helmer Well-Known Member

    Okay and what about valve clearance I'm testing them right now with the cam Lopes facing up rather than top dead center to me it should be the same thing since both ways are not putting pressure on the valves. Because as of right now my valves are in Spec the way I'm doing it

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