Hello all- I'm new to this forum; hopefully that won't stop y'all from providing some useful advice. My car is a '67 coupe trans-am clone which I built back in the 1980's. In the 90's I vintage raced and ran a number of track days with it but in recent years wife/kids/budget have prevented such eccentric pursuits. Up until about a year ago the car had a 12.2:1 .040" over 302 which I changed to a 9.75:1 331. Fairly big (.560"/.530" lift) Crane flat tappet mechanical cam, Ford Motorsport 'J302' heads w/ 1.94"/1.60" valves, MSD ignition, 650 dp Holley, early Torker intake. Don't know the hp/tq numbers but in 302 form it dyno'd at 385/375 respectively. When I first put this engine together as a 302 JBA in San Diego assembled it for me (I normally do such things myself)and it ran pretty strongly until I inadvertently boiled all the water out of it by leaving the radiator cap off for a few precious moments one race weekend. I refilled it then and had no further problems until several weekends later when it blew a gasket. At the time the heads were cut for Fel-Pro 'Loc-Wire' gaskets. I verified that the block decks were flat and square, had the reciever grooves recut into the heads (as well as having them resurfaced) on two more occasions and it still wouldn't hold a gasket- it would run for a couple two or three hours then POP!-another $130.00 pair of gaskets shot. Wanting to street-drive the car (when it's running right it's a mind-warp to drive) I decided last year to build up a lower-compression, pump gas-friendly stroker, and shave the heads flat, eliminating the troublesome and pricey O-Ring gaskets. The car ran bitchin' for awhile (probably no more than four hours total) when a couple weeks ago it suddenly developed a severe miss from 2500-5000 rpmunder moderate to hard acceleration. I checked the tune, made sure the float levels, etc were OK and took it out again last weekend. This time (with fresh plugs) the problem got worse- it was running so badly as I approached my house that it wouldn't idle anymore and I had to coast into my driveway. As the engine got hotter it just ran worse and worse. I attempted to start it again the following day; it did start after a little prodding and seemed to idle OK after a few seconds, so I shut it off, pulled all the plugs and did a dry compression check with the throttle open. Compression was 150-135-135-150 on each side (1,4,5,&8 were 150 lbs., 2,3,6,&7 were 135 lbs.). No water in the oil, no oil in the water, and it's not pressurizing the radiator (yet). Also no overheating problems- just one wicked nasty midrange miss that gets worse the hotter the engine gets. I'm by now no novice when it comes to building engines but for the life of me I can't seem to get to the bottom of why this thing keeps popping head gaskets. I would gratefully welcome any expertise any of you could provide regarding head sealing techniques, advice about INEXPENSIVE aftermarket heads, or whateverinsight of you may with what it takes to make an SB Ford run reliably. Thanks much in advance to any who may wish to step up and help.

 

What Kind head bolts are you using ? There are a ton of reasons....The block can be warped also. Just went thru that with a company car.Blew a HG in the weirdest place just to find out the block had a few low spot (in every place the HG pushed out). It could be lifting a head. But what the HG looks like afterears will tell you alot also. It's got to be pretty bad to pop an O-ring gasket. Did the heads show any pitting from detonation ?
Have you checked the valvesprings to see if any are broken ?Does idle get worse as it heats up, or all around ?

 

It's got ARP studs in it, the valvesprings are all fine. I know it was a pretty lengthy post, but on this most-recent rebuild I had the O-ring grooves machined back out of the heads and just ran a conventional gasket since I had dropped the CR by about 1.5. There was some very minor pitting in between the valves on a couple chambers but the two machinists that I spoke to regarding that both assured me that it looked worse than it really was. At this point I'm open to any and all suggestions but I'm certainly not rich and I'm not into throwing good money after bad. I've occasionally seen '69/'70 351W heads on fleabay for reasonable prices (half of what I paid to have a set prepped years ago) and have thought about going that route. At any rate I'll pull the heads and check everywhere for flatness, and gladly solicit any more ideas....

 

If the o-ring groove was machined off the head, that's an awful lot of milling. What do the plugs look like, can you post pics? Do you know what the cc on the chambers is now? There's not an o-ring reciever groove in the block, is there?

 

Think your looking at a warped deck, or pinging problems. But I'm leaning towards the block. Where exactly do the gaskets blow. Same spots ?

 

Max depth on the reciever grooves was .014" if I remember correctly, and prior to having them milled off I had them recut to the proper depth which of course didn't fix the problem. The J302 heads have pretty fat decks which should have allowed such milling without any problems, and I had them pressure checked to make sure they weren't leaking internally.The chambersmeasured 60cc which (again) was giving me a CR of 9.75:1 with a .039" thick (compressed) gasket, and there were no grooves cut into the block. Until the problem re-occurred the plugs were fine; since I was running 91 octane Cali-swill I was being careful not to go toolean so as the motor was loosening up on break-in I was progressively leaning it down, eventually settling on #66 & 76 primary / secondary jets with a 6.5 power valve. Also, I was only using 34 degrees total timing which is supposed to be pretty safe by all the expert opinion I've read or heard. When I pulled the plugsmost recently they were wet/sooty/black which seems to me to indicate that the motor just wasn't burning the gas that it was being fed (not a mixture problem but rather a combustion issue). Once I get it torn down (I'm now in the Over 50 Club so this may take a little time!) I'll try and post pics of the gaskets and block decks for your perusal and again much thanks to anybody who is kind enough to take the time for a reply.