1991 rm head question

[DesertVenom]

i picked up a RM125 for a $100 off a buddy who didnt want it, i just wanted the back tire off it for my XR. When you kicked it over sounded like major crank issues, but it turned out that flywheel was loose making all the evil noise. Also all the studs where pooched and messsed with and the head is warped so it leaked antifreeze like crazy no matter how tight you get it. The reason why the studs all pulled out. But i got that all fixed and ordered a new head off ebay, but when i got it, there was a slight difference in the numbers
old head - 27C E-2
new head - 27C1 E-1
does anyone know what thats all about?? they look identi i put it on and it will start with fuel in the cylinder, but its not getting gas which i will sort out later today. its a brand new rebuild with .50 over and the comp isnt very impressive, under 90 anyways. could just be my tester cause it seems to have enough when i kick it and it will start.
anyways...thanks for the help

[Dave2122]

Those are casting numbers and looks like your bike had a head from 1992. Must have been replaced at some point in its life. It does not mean it is wrong it is just when it was cast. As long as it is the 27C it is fine. You said "NEW", was it Brand New in the package or Used ?

Compression should be taken with the engine at operating temp. Also when you kcik it over you are to hold the throttle wide open to let as much air into the cylinder as it will draw (with the engine OFF of course). Not a big believer in compression tests as the tell all sign. As you stated the guage may read different.
Best way is to Mic the Piston to Cylinder wall clearance and keep track of hours on the motor after rebuild. Compression checks are ok as a stop gap measurment.