289/302 forces water out rad. cap when cranking

I have a weird problem that seems to point to an obvious solution but I want to make sure that no one else has encountered this before and its actually something else....

I got a 289 block and heads out of 66 fairlane. the block and heads were virgin and never had any problems. Had our local Napa machine shop hot tank and bore the block .30 over and had the heads hot tanked and rebuilt with stock valves, guides, and some comp cams springs for a .512 lift cam - to accompany my Lunati Bracket Master II with the same lift. I had a 302 crank out of 77 mav, which I had polished at Napa (didn't need to turn it). I ordered a complete rebuild kit from Northern Auto Parts for a 71-77 302. I then rebuilt the motor with an old gearhead watching over my shoulder.

After I got it all together I put it on my new C4 tranny from summit and dropped it in my 71 mav, after I pulled the old I6 and accumulated what I needed for the swap (motor mounts, engine xmember, tranny xmember, ect.) I started cranking her over for the first time, for about 4 seconds, but the points weren't quite gapped right and the timing was a bit off. Adjusted both and hopped in and tried again. After about 4 more seconds I heard water gushing from in the cab (heater core) so I bypassed it (water pump directly to intake inlet behind thermostat, and went at her again.

She fired up and ran great and sounded mean. But after a couple minutes an upper chatter started to grow so I shut her off. There was extreme pressure at the rad. cap. I took off the valve cover and intake to find that the #1 pushrod was bent. I had used the original 66 pushrods, so I got a new one, and after checking the lifter to make sure it wasnt collapsed, buttoned her back up.

Fired her up again and after a couple mins the pressure pushed out of the lev.r.vent cap with a high pitched squealing noise. Ofcourse I shut her down.

Ran a compression test on all 8 cyls, the passenger side (1, 2, 3, 4) averaged about 142, the lowest being about 132 and the drivers side averaged about 150 or higher. Replaced the head gasket, and fired her up again - same thing.

I disconnected the coil wire so it wouldnt run and just cranked the motor over - and it built up extreme pressure at the rad. cap.

I pulled the motor and when I drained it there was about 8-10 quarts of thick white vanilla shake. I took the heads back to Napa to have them magnafluxed - they checked out ok. I visually inspected the block and i couldn't find any water tracers down any of the cyls and couldn't find any visual cracks after i rotated it through all the strokes.

The head gaskets were, all 3, good and none looked abnormally burnt. The thermostat was not stuck, the heads checked out ok, and there was never any white smoke the 10 minutes or so that it ran. Im assuming there has to be a crack somewhere in the block, but could it be anything else?

You have a cracked head or block... Better check EVERYTHING.

Have the heads magna-fluxed... There is no way it could be the head gasket after 2 sets unless the block was milled incorrectly.

Make sure you have the CORRECT head gaskets and they match the heads AND the block perfectly

had the heads magnafluxed and they checked okay. the head gaskets are also correct, all water jackets line up perfectly and just to be sure i checked the part numbers for 66 289 head gaskets and 302 head gaskets and they are the same. also, i did put them on correctly (FRNT stamped on each gasket at the front of the block).

so the crack has to be somewhere in the block was what i was thinking but ill have to wait till I get back home (at college now) on the weekend to take the block apart and take it back to napa.

Yeppers, if the combustion chambers are good, then the block is likely kaput....

I had a pin hole in my timing cover once. Changed out the head gaskets before I figured that one out... It was only visible once it had been bead blasted, and even then it was literally the size of a pin tip. Same result on chocolate milk though...

Timing cover p[in hole will not cause Pressure in the block's water passages... As the block generally works in a vacuum when the PCV is correct.

yea, i had the timing cover bead blasted before i painted it and put it on, the same guy that helped me put it together did it at his work...

I got much more than chocolate milk though, it was like a triple thick VANILLA shake from McD's, much much more white and airiated and not a tint of dark...plus, when I drained it, it filled up one of my drain pans and then ran over for about 5 mins - amounted to somewhere between 8-10quarts...