not your normal low compression question

['99350t]

i got my banshee ported alittle( i would say a heavier trail port), and just installed my NOSS head with 20cc domes. and my compression is only 125 per side. i was expecting probably around 160--170. is this normal? i rebuilt my top end not too long ago( not my first or second one either) did i install something wrong on this head? or are my rings shot already? its been starting hard and kinda weak on power.

[Snopczynski]

Did you warm it up before checking, pull both plugs, kick it 5-10 times, and hold the throttle wide open?

[dlnoss]

That is pretty suspect. Does the compression guage thread in as far as the spark plug does? Throttle wide open? What was the compression with the stock head? What is your elevation?

[Snopczynski]

What gauge are you using?

[blowit]

What gauge are you using?

 

 

Yeah, I too would suspect the gauge first. If you know your top end is fresh and head is new and both sides are equal, grab a buddies gauge and try again.

 

 

Brandon

['99350t]

its a lesile (?) gauge, i didnt check it before i pulled the stock head (was on my list too) i held the throttle wide open and kicked until it stopped building pressure, (5-7 kicks) and it was right after i was done riding it. like i said its been starting hard and not running to its full potential. i hope is just an o-ring in the head or something stupid but my moneys on the rings

[BlackBarron]

you said that you rebuilt you top end, meaning you changed your gaskets? the thickness of your gaskets will change your compression to. take a piece of 1/8 soldering rod and check the squish. Mine is at .042", you dont want it under .040"

['99350t]

you said that you rebuilt you top end, meaning you changed your gaskets? the thickness of your gaskets will change your compression to. take a piece of 1/8 soldering rod and check the squish. Mine is at .042", you dont want it under .040"

 

im not following what your saying? rebuilt top end, gaskets, pistons, rings etc.

[BlackBarron]

let me break this down. the closer the top of the piston gets to the dome the more compression, so if you bought a gasket set that had thicker gaskets than that would make that distance between the piston and the dome bigger so you lose compression. :biggrin:

[Snopczynski]

you said that you rebuilt you top end, meaning you changed your gaskets? the thickness of your gaskets will change your compression to. take a piece of 1/8 soldering rod and check the squish. Mine is at .042", you dont want it under .040"

 

or over .065"

[BlackBarron]

or over .065"

 

that is correct !!!!