Anyone know the stock compression of 1966 250 I6

[K5 Addiction]

I know I've got a problem in at least 1 cylinder as there's about 21 PSI difference between cylinder 5 (the highest at 128 PSI) & number 2 (107 PSI) but don't have a base line to know how bad off my motor is overall. Any info would be greatly appreciated.

[68gmsee]

In a stock engine, it should be the same as all 250's -around 130 psi.

As you probably know, if there's more than 10 psi difference, it's time
to start dismantling.

One quick way to see if it's the rings is to see if it blows smoke or burns oil. Or, you could squirt some oil into the cylnder and see if the compression goes up. If it stays the same it may be something as simple as a bad head gasket or a burnt valve.

[fleetsidelarry]

just to add to what 68gmsee said, I think it's 10% variation not 10 psi (about the same in this case), ('66 factory manual actually says not more than 20 lbs difference! )

remember to check compression with throttle wide open.

[68gmsee]

Originally Posted by fleetsidelarry

just to add to what 68gmsee said, I think it's 10% variation not 10 psi.....

Yeah, thanks for correction. I meant "more than 10 percent difference." At 8 AM my brain is not fully warmed up to operating temp.

I've actually seen differences as high as 15% or 17% variation on V8's that still ran okay, but on inline sixes that much difference is more noticeable.

[K5 Addiction]

Thanks for the info y'all. I knew i had a bad cylinder but wanted to know how close to stock the other 5 were. It's rebuild time for me but I'm pretty stoked to dig in. Look for an engine build thread in my future.