just rebuilt a banshee top end fresh bore,pistons,rings,clips,pins,bearings did a compression test had 90 psi and 115 psi.could my crank seals be causing 25 psi difference in each cylinder.

 

Certaintly possible that you have an air leak. On a fresh bore, even if it hasn't been started yet, I'm suspect that your pressure readings are too low.

What clearance where the cylinders bored to: as in the piston to cylinder wall clearance.

Do you have the appropriate size rings for the piston size, as in, first overbore piston, first overbore rings.

A head gasket leak is possible as well.

Do you have anyway to do a pressure leakdown test. But I still am suspect of your low readings is something other than a leaky seal. We're dealing with the pressure that is above the cylinder, that is sealed by the piston and rings. There has to be something wrong there. Let me know what you find.

 

IM SURE YOU ARE AWARE....
HAVE THROTTLE FULLY OPEN....
KICK UNTILL PRESSURE STOPS RISING....
CHECK HEAD GASKET FOR LEAKS,REMOVE OR RE-TIGHTEN..
MAKE SURE GAUGE IS WELL INSERTED....
CHECK YOUR REEDS!!!!(THIS MIGHT BE THE PROBLEM)...
IF YOUR CYLINDER IS "FRESH" REBUILT CAN BE ABOUT 10-15 PDS DOWN....
I HOPE THIS HELPS

P.S. IF YOUR MOTOR IS HARD TO JET(TO LEAN,NO COLOR ON PLUGS),YOU MAY HAVE AN AIR LEAK...

 

The seals and reeds are independent of the compression. While they can and do cause problems with jetting and proper operation. If the reeds mattered with compression what would we do with the gaping hole we call the exhaust port?

Compression is a whole different function. There can only be a limited amount of problems, they all deal with the cylinder, piston, rings, head(and gasket), or gauge(gauge calibration, operation and seal).

Yes the compression will rise as the engine is broke in, but his numbers are too low to begin with in my opinion. They most likely will only rise, as stated, 10 to 15, but sometimes as much as 30.

Need some more info to get headed in the right direction.

 

The seals and reeds have nothing to do with the results of the compression test.
You must hold the throttle wide open.
if the compression is still low you may have a slight head gasket leak.
YOU DID CHECK THE RING END GAP BEFORE YOU PUT IT ALL BACK TOGETHER ???.
Other than that it might be bored over a bit to much for the pistons you got

 

ive got a 00 banshee and we done a compression check on it the day i bought it and it read 115 psi before it was broken in.after break in it was 124 psi.put on a COOLHEAD it weht to 145 psi with 22cc domes.

 

i have a 99 banshee and did a compression check on it before i put the cool head on it and it had 130 psi per side and i put the cool head on it with 21 cc domes and i have 155 to 157 psi per side

 

COUNTRY I DID FORGET TO MENTION THAT THIS HEAD HAS BEEN SHAVED@.030 PLUS ALL RING END GAPS ARE AT 12 PISTON CYL CLEARANCE IS 2.5 AND A BRAND NEW HEAD AND BASE GASKETS.HEAD WAS CHECKED FOR WARPAGE ALSO.IM BUILDING A LEAKDOWN TESTER SOON ENOUGH.THE ONLY CLEARANCE THAT HASN'T BEEN CHECKED IS GROOVE CLEARANCE,COULD THIS MAKE A DIFFERENCE!

 

Need some clarification on the cylinder clearance. You have it at 2.5, do you mean .0025"?

The ring end gap looks good, if it's .012. A tad tight but still OK.

The ring groove clearance can have a little to do with it, but not that much. The rings can rock slightly in the groove and not seat squarely against the bore wall.

Head gasket leak??? This is my strongest contender right now that may be your problem.

Let me know about the cyl. clearance...

 

Banshee 97 are you still running on premium pump gas or do you have to run race gas? And how much did the extra compresion help your power.