Nailhead 401, possible blown head gasket?

[66 buick guy]

Hey guys, my 66 GS recently started missing almost to the point of not being able to drive it......I ran a compression test on all 8 and came up with 160PSI on cylinder 1, 190PSI on cylinder 2, 170PSI on cylinder 3, 185PSI on cylinder 4, 150PSI on cylinder 5, 170PSI on cylinder 6, 100PSI on cylinder 7, and 170 PSI on cylinder 8.....From what I can see through the spark plug holes atleast the top of all the pistons look fine.....I know that nails usually don't blow head gaskets but I'm leaning towards that option because both 5 and 7 are low....When the car initially started running like crap it was just like one of the carbs had a bad accelerator pump, then it progressively got worse within about 10 miles...Just started on this today.....Any suggestions?

Thank's

Mike

[suntreemcanic]

Fuel or ignition but not head gasket.

[Utah Blaine]

....When the car initially started running like crap it was just like one of the carbs had a bad accelerator pump,

What is the carb set up........2-4's, 3-2's or? Stock ignition set up or changed too?
.

[66 buick guy]

2 carter comp 600 cfm carbs, pertronix ignitor 2 ignition, Poston NH 600 cam, but 7 cranks on the motor with all 8 plugs out and only 100 PSI on cylinder 7.....The motor has been done since 1996, probably 5,000-10,000 miles on it....Being a stupid kid in 1997 (as it was my first car when I was 16 years old), I drove it around for about 2 years with BOTH rockers broken on cylinder 7....Bent push rods and all...Sure wondered why the car wouldn't spin past 2,800 RPMs back then.....She got super hot a few times back in my not so caring days......I'm really wondering if the gasket finally gave in....

Thanks

Mike

[suntreemcanic]

If your head gasket was leaking to the outside you should hear it. If it is leaking between two cylinders, those adjacent cylinders would be low on compression. If it is leaking into the cooling system, you probably would get overheating, maybe bubbles in the radiator (cap removed). You can get a chemical at the auto parts to test your cooling system for signs of combustion from leaking head gasket.

[66 buick guy]

I guess ill try the radiator chemical test first because its easier... I REALLY dont want to tear into the motor......If the head gasket ends up being bad it gives me a good reason to send the heads off to Mike Lewis at flowtech.......If I just would have kept my foot out of the pedal (it all started immediatly after a hard 2nd gear punch, spinning into 3rd gear) **** those people at the gas station for asking me "what'll she do"....Winter project ahead

Thanks guys

Mike

[My55buick]

Youre saying you rebuilt it about 10,000 miles ago right? Just making sure....

Were the heads rebuilt and are the guides ok? My firend had an old Maverick with the 200 straight six and it ran ok, but missed like crazy. His compression was all over the place, with as much as 20 psi difference on some cylinders. Turned out the valve seals were non existant on some of the cylinders. We changed all of them fired the car up and drove it in second gear to get the cylinders hot and burn everything off. Then seafoam treated it. The car had nearly even compression across the board with no more than 5 psi deviation.

I know Most nails dont have valve seals but, it doesnt mean it cant be leaking too much oil past the guides.

What do the spark plugs look like? Usually a bad head gasket turns the plugs funny colors... Kind of like grayish. If it was oil soaked you'd know to. That would be my next step.

[66 buick guy]

Correct, the engine was completely rebuilt roughly 7,500 miles ago, new pistons, .40 over bore, double roller TC advanced 2 degrees, heads were checked for cracks and any warpage at Bills machine in Omaha NE. valves resurfaced, stiffer "high rev" double springs installed for the .523 intake and .525 exhaust lift cam (that might not be exact lift), Poston high rev lifters, eelco 2x4 intake with 2 carter competition series 600CFM carbs, T/A Knock off hooker headers, straight pipes, Telesco mini starter......I think I'm just going to have to tear into the motor.....I always run ATLEAST a 50/50 blend of leaded AVGAS and non ethanol 92 octane pump gas so I cant imagine that anything happened to the valves but Ive seen more unusual things happen...Spark plugs are burning a nice light tinted brown color.....I have been running a pretty wicked timing advance, 6 degrees at the balancer and about 38 degrees total but NEVER had any timing ping......I'm just puzzled......currently changing the timing chain in my Dakota so haven't had a chance to further dig into the nail since my last post...

Thanks guys

Mike