Pulled a head on Elvis and sure enough, 3.75" stroke so it's a 239. Bore is about 3.20 by dial caliper (don't have the right tool), leading me to believe that it has been bored out a bit. Very little ridge, looks pretty fresh, been running very rich. So some P.O. yahoo put Mercury 8CM heads on the engine after boring it out. The lower compression that I'm seeing is probably due to the head change.

I'm in Winston-Salem, NC and have a pair of nice 8CM heads that I'd like to trade for an equally nice set of 8RT heads (or 8BA if they are the same...)

Also broke one stud off almost flush with the deck at the start of the thread. I'm putting PB Blaster on it every few hours, any good threads on in-truck broken stud removal?

 

Sorry for the bad luck doubled there. At least you know now why the consistent low compression over all the cylinders. On the broken bolt, there's a few options and none are easy at all. If there is any of the bolt up high enough you can weld a nut to it and try to remove just like a bolt. Drilling into it and using an easy out is another option, but you have to be careful to drill the bolt only, not the threads, and not to break the easy out either. Using some heat right on the bolt might help. It's just not easy getting in there to it unless you have the engine out or front end off.

I don't have any spare heads. Joblot lists them for $65 each. LMC has them listed for $49.95 each. I'm sure you'd hate to drop the money into new ones, but unless you get them from a very trusted source or can measure them, you might want to avoid getting used ones. You never know over the last 50 years how much they've been milled down. You'd go from low CR to really high CR, or might even damage a piston.

Good luck,
Scott

 

Check flatheadsforever.com and redsheaders.com for tips to removing broken studs in the flathead blocks. There's many other methods availables as well, but those sites will get your mind to thinking

 

Sounds painful.

 

I've got some 8BA heads here in Conn. if you want them, free!! Just pay shipping.

Barry

50 F-1

 

Is there any difference between 8BA (car) and 8RT (truck) heads?

 

8BA have more compression. THe EAC Merc heads have the same ratio as the 8RT heads, so I'm told.

Barry

50 F-1

 

Just checked out the Red's Headers site, liked the welding the nut on idea. There was also an article about using sleeves to drill out the offending bolt remnant. Anybody try that or know who has sleeves like that?

-Scott

 

Congratulations! This is much simpler than a rebuild, isn't it?

If you haven't pulled the other head yet, you can "usually" avoid broken bolts by tightening a little first, with a hand breaker bar, then use an impact wrench to loosen. Slow'n'steady is actually likely to snap them.

I would certainly defer to Barry, but I didn't think there was a difference between 8BA and 8RT heads. Other than the oil pan, and some carb differences, I don't know of any real differences between the car and truck engines (cam, etc). I always wondered why they bothered to cast different numbers into them.

That sucks about the stud. Can you MIG weld pretty well? Personal opinion, one of the better methods is to put a plain steel (i.e., not cad-plated) nut over the stud, and weld inside to what's left of the stud. The heat this puts into the stud does as much good as anything, and after continuing your PB for a day or two, you can put a wrench on the nut to back the stud out. Be sure to clean all the PB out of the area before welding with brake system cleaner or similar, or you'll have a brittle weld.

 

I'm no expert on flatheads, I just posted what I've read. If there's any experts reading this post, please step in and set the record straight. I know it's been beat to death here before! I'm having an early senior moment (51) on this!! Heh heh!!

Barry

50 F-1

 

How about if all you guys that have heads put a spark plug in them and measure the cubic centimeters of water they hold. Then you can compare and see if they are different. If one persons holds 38cc and another holds 50 cc the guy with 38cc has a higher compression head.

Also if you have good Mercury heads you can get them shaved down to raise the compression. Make sure you check the clearance between the valves and the head first. Heck you might get enough shaved off to raise the compresion up to 8.5:1. The should give you more power and better gas mileage using modern pump gas.

 

8RT heads are no better than the 8CM; true CR in a 239 comes in around 5.8. 8BA and EAC are close to each other and EAB are the best for compression.

Any flathead can easily be cut up to .060 to clean up the surface and/or raise the CR a bit. Stock 8BA volume is 76cc and the EAB is 71cc

 

Excellent info! Thanks

 

There are a number of threads right here on broken bolt removal - search on broken bolt, and perhaps candle wax (one of the "cures"). Good luck.

 

Here ya go! This was the most recent thread about broken bolts. Has some good tips (and some stupid ideas, too).

https://www.ford-trucks.com/forums/s...d.php?t=440077