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00 Stock banshee fresh rebuild, low compression


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I just rebuilt this stock banshee with 1mm over pistons.  It was already .5 over, and .75 wouldn't clean it up enough.  Got it bored and gapped and put together.   Compression is only 110 on 1 cylinder, and 115 on the other. 

Im wanting to mill the stock head some to get compression up a little.  I want it to be 93 octane still.  You think I can take .020 off the head and still not have any detonation issues?  

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  • 2 months later...

Are you holding wide open throttle during the compression test? Stockish bikes only need around 120-125. Not holding the throttle open could bring it down. You want to keep kicking with WOT till the gauge won’t go up anymore,even 20 kicks is fine. Also the engine should be cold.

If you have low compression i wouldn’t mill the head to compensate,just asking for trouble.

Unless the kicker feels very loose or it won’t start,I wouldn’t worry about testing compression on a fresh build till it is broken in.   Your not going to get accurate numbers because the rings have not been seated

 after breakin 5 psi difference is still ok,as long as it doesn’t go further.

 

Edited by Burt Reynolds
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  • 3 weeks later...

The engine should be broke in.  I have 20-30 min of run time on it.  Piston/ring clearances are all within factory spec.  Bike just doesnt want to start. Seems that the compression is to low.  Carbs have been cleaned and checked 3 times.  All jets pulled, all passages verified.  Seems to only hit on 1 cylinder most of the time.  Switched spark plugs/wires, still same cylinder.  I think bumping compression a little will help.

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  • 3 weeks later...

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