I get low copression (around 70 psi) in cylinders 1 2 and 4. Cylinder three has about 160 psi. What would cause this? The motor has just been rebuilt, bored .020 over has new everything. Any ideas?
thanks

 

piston rings ?

 

Did you measure the ring gaps? Were the ring end gaps spaced properly? Were the rings installed properly? Did you build enough oil pressure? Do a leak down test, it may be leaking from the head if its not leaking from the bottom end.

 

Sounds like to me only one of the pistons have the rings on them right. Time to crack it open again

 

thanks guys, I'll do a leak down test and see what happens. Knowing me though I probably forgot to put the rings on right

 

I haven't run it since it was rebuilt

 

You need to break that ---- in before you will have good compression.

 

Yeah but it ahould be better than 90 psi