Compression numbers ?

Discussion in 'Sportster Models' started by Maustarman, Feb 7, 2015.

  1. Maustarman

    Maustarman Active Member

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    Hi there
    Could anyone help me out here.
    I'm trying to figure out that the compression *PSI numbers* should be for a 1988 hugger 883 with a 1200 upgrade.

    Thank you in advance
     
  2. BUBBIE

    BUBBIE Well-Known Member

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    Did you use the Stock 883 heads? What pistons ?

    IF So you will have More compression than a 1200 stock motor. Tough trying to figure out. Take a reading and let us know what it is and go from there.

    I had a 883 to 1200 build but used Wiseco 10.5 x 1 pistons and Stock heads from the 883...

    POWER HOUSE...

    signed....BUBBIE
     
  3. Maustarman

    Maustarman Active Member

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    Thanks..

    Yes, The heads are 883 heads. Not sure what pistons are in there.

    Tested the compression and I'm getting
    - 225 almost 230 PSI in the Rear
    - 215 in the front cylinder after installing a thicker head gasket because I was having valve to piston contact in that front cylinder.
     
  4. Jack Klarich

    Jack Klarich Expert Member

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    883 valves flow better than 1200:D
     
  5. BUBBIE

    BUBBIE Well-Known Member

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    IF you don't like the compression, you could install 1200 stock heads but that would Deflate the POWER...

    I think I would have done Both heads with that thicker gasket so they match.

    That is the pressure I remember in Stock 883 heads.

    Brings back memories of the POWER in my sport conversion.

    Having valve contact Might be you have other than stock flat-tops in there. What did the top of the piston look like when you did the gasket change?
    Totally Flat? or Grooved top. Was it level or recessed OR Out in the cylinder..?

    Better be using Slow burning High Octane gas or you may have Early Explosive actions that will do damage. No Lugging that motor.:newsmile07:

    OH Yes, BET you have to Hang on with both hands when twisting the wick...:D

    signed....BUBBIE
     
  6. Maustarman

    Maustarman Active Member

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    Yes, I've been thinking that is better go with ticker gasket in the rear too.
    I'm ok with the compression the way it is if it is healthy. (Had some ppl telling me that was way to high and not good)
    With the gasket the piston looked slightly recessed not flat with the gasket.
    Tell me more about the slow burning octane fuel if you could pls. (I'd like to have a better understanding)

    Haven't taken this baby out with out the ticking noise...but, before .....man! That was awesome :)
    Definitely looking forward to take it for spin

    Thank you
     
  7. dolt

    dolt Senior Member Contributor

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    Already commented on the OPs CCP in his "broken crankshaft" thread.

    JMHO but those CCP numbers are too high for a "street" motor; very hard on lower end, battery and starter; the OP needs compression releases.

    Using a thicker head gasket to eliminate valve to piston contact a missed shift or high rpm valve float is going to be disastrous. The pistons should have been removed and the valve reliefs fly cut. .030" valve to piston is the minimum by most use .060" as the "safe" piston to valve clearance. That little indent on the top of the piston could become a "hot spot" and with the compression that high, "dieseling" and/or detonation could be issues as well.

    I wish the OP good luck but IMHO, should have taken the process further to mitigate future issues.:coffee
     
  8. Maustarman

    Maustarman Active Member

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    Thank you...
    I took care of the intake leak I had in there and took the bike for a 1 hour ride..
    When I got back I rechecked the compression and this time things looked much more normal..
    Front
    ImageUploadedByTapatalk1423523117.413395.jpg
    Rear
    ImageUploadedByTapatalk1423522992.608008.jpg
    Don't know if the problem before was the vacuum leak or the fact that I was cold