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What should my cylinder PSI be?

Discussion in 'Motorcycle Tech Talk' started by Screamer, Feb 12, 2007.

  1. Screamer

    Screamer New Member

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    I have a 2001 Road King with a Big Bore kit, forged pistons and stock heads. The engine has 93,000 miles on it and I was curious about how the compression was holding up. I checked it and the front is 130 psig and the rear is 122 psig.
    Does anybody know what it’s suppose to be?
  2. whacker

    whacker Active Member

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    cylinder pressure

    If motorcycles are anything like automotive,I think they should be within 10 percent of each other,I was looking in my manual to see if I could find anything on compression,but there was nothing on it....Sorry not much help...
    Last edited: Feb 12, 2007
  3. kenfuzed

    kenfuzed Administrator Staff Member

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    Compression tests can sometimes be deceiving. I prefer a leak down test which will narrow down any problem to a specific area. Of course you will need a compressor to run this test. You can buy testers at any autoparts store or online for cheaper. Most come with common plug adapters which will fit your Harley.
  4. chucktx

    chucktx Moderator Staff Member

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    from the readings you posted, i dont see a problem with compression. are you having trouble?? or just curious!!
  5. Screamer

    Screamer New Member

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    To Many Miles?

    Thanks, I'm not having any trouble with power, in fact it seems to still be as strong as ever. It doesn't smoke, it does use/leak a small amount of oil. I do have a problem with it stalling at high speeds (I covered that in another thread) but I don't contribute that to compression. The dealership didn't want to work on it and "waste" my money on a bike with so many miles so I wanted to get an idea of what kind of shape it was in. I don't mind rebuilding the top end but I don't want to get into the bottom. I figured if the cylinders were still in fairly good shape the bottom would probably be OK.
    My believe has always been that normally the bottom end would last through one top end rebuild.
    Is this a reasonable assumption?
  6. chucktx

    chucktx Moderator Staff Member

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    i havent heard that before. i have rebuilt many pans and shovel top ends without touching the bottom ends. and these were my machines. i would think that if you are not racing ie...abusing, the engine i would think you would get a number of top ends to bottoms. that said, i am not sure how strong the bottom ends on the new engines are, compared to engines past. i have a twincam with 19,000 miles on it now. i parked my pan of over 20 years and started riding modern.....so far, so good
  7. 2fastnaz

    2fastnaz Moderator

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    I would say those are good numbers for 93,000 miles. ANd yeh I think the dealers blowing smoke up your ass too. I haven't dealt with the block heads much but if I got 30,000 out of my shovel top end I was pretty happy and I got 3 top ends to one bottom.
    Riding in 120 degree heat has alot to do with how long mine last I'm sure. YMMV
  8. Screamer

    Screamer New Member

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    My only other experience was with pans too, but that was a long time ago. I know they lasted a long time compared to the top end but I'm going on 100,000 with this top end.
    I don't expect to get 200,000 out of the bottom end but I have a noise that sounds like something squeaking in the engine. It started after I had the cams and everything changed in the cam chest (at an independent shop). I had a dealer’s shop recheck the installation and they said everything was fine. It sounds to me like it’s in the heads. I am considering changing out the heads with a spare set I have just see if it helps. While I was in there, I thought I would rebuild the cylinders if they need it but I’m thinking right now they do not. I just replaced the throttle body to try to eliminate the stalling problem I have and as soon as I get by the dealer to buy a new battery, I’ll give it a test run. If the noise is still there, which I’m sure the T B won’t help that, I’m thinking about switching the heads and not do anything to the cylinders (unless a visual inspection shows a problem).
    Does this make sense or once I’m in there should I just go ahead and spend a few more bucks on the complete top end.
    What a quandary, if the noise is still there after a top end rebuild, then I’ve got to have a shop do the bottom end and all that time is wasted.
  9. hotroadking

    hotroadking Super Moderator Staff Member

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    Did the shop put in adj pushrods? Could be rubbing in the tubes if they didn't swap out the tubes, the lower is a bit wider for the adjustable pushrod

    You can take a flat blade screwdriver and touch the metal tip to the motor move around and listen with the handle to your ear to isolate the sound.

    Noise travels a lot on HD's
  10. Screamer

    Screamer New Member

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    They did put adjustable push rods in and I don't know you had to use bigger covers. That explains why they replace the stock ones, I thought they were just being wasteful when they gave me my old parts back and there were the old covers.
    Thanks for clearing that up.

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