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| I found an NOS set of Jahns Racing Pistons and have a set of good ECZ-G heads to re-build.
Stroke is gonna be different cause I had the mains on a 312 Crank turned down to a 292, using 312 Rods and this new set of Jahns Pistons in a 292 Block.
How much can I safely surface off the bottom of the heads? And what implications are there when I have the block decked?
Thx all for your patience and willingness to re-open this post after all my false starts last night!
Keep it Kool, Keep it Old School, David |
She's a Marriage Wrecker, a leak in our Savings Acct, and a Demanding Mistress. Skirted, Curves, N plenty of sass for a 53 yr old Dame. I'm gonna primp her one vintage find at a time, until she turns over N screams! 292 with a 312 Crank / Rods, Jahns Racing Pistons, High Ratio Rockers, Mummerts Cam, High Volume Blueprinted Oil Pump, 3 Deuces, Ramshorns, Sheifer Forged Alum Flywheel, 3 Spd Overdrive, alittle Vintage Bling, and as much Mojo as I can squeeze out of her! |
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| | The only way to really tell now is to assemble a couple of rods and pistons to the crank and see where you're at. If it looks normal, take a used gasket and install the head with clay on top of the piston, roll it thru by hand CAREFULLY. You may hit something, so don't force it. You then pull the head off and measure the clay thickness. You will know exactly what you have. If the crank was ground correctly, your stroke has not changed. It's still 312. If it was offset ground, all bets are off.
Frank/RebopBristol, In ( by Elkhart) 
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| The crank must still have the 312 stroke. Offset ground mains won't work favorably at all.
Norcross, GA |
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| | Nope, they werent offset ground... I sent my crank across the country to Memphis and had Mummert's shop of choice do the work. So the question I'm sweating is: Pistons are Domed...
The machine shop doing my heads said there was enough corrosion on the head surface they needed to be milled 15 thousandths.
I thought I read in a post long long ago you shouldn't mill more than 10 off heads?
Thx for the reply's, David
She's a Marriage Wrecker, a leak in our Savings Acct, and a Demanding Mistress. Skirted, Curves, N plenty of sass for a 53 yr old Dame. I'm gonna primp her one vintage find at a time, until she turns over N screams! 292 with a 312 Crank / Rods, Jahns Racing Pistons, High Ratio Rockers, Mummerts Cam, High Volume Blueprinted Oil Pump, 3 Deuces, Ramshorns, Sheifer Forged Alum Flywheel, 3 Spd Overdrive, alittle Vintage Bling, and as much Mojo as I can squeeze out of her! |
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| | | Supreme Being
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| | David: .015 won't hurt your heads. You'll be using thicker than original head gaskets anyway. John in Selma, IN
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| | How much compression will you be running? You might want to make sure the heads are posted before continuing work on them. Here is a link to a previous thread about posting http://www.y-blocksforever.com/forums/Topic12729-3-1.aspx How will the engine be used? Much above 9.5:1 and you'll probably need octane booster or racing fuel. With domes and G-heads you will be well above 9.5. Assuming 10cc domes and 0 deck, you will be near 10.7;1.
Norcross, GA |
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| As Charlie mentions, you’ll need to clarify if your heads are posted or not. And then compression ratio (CR) will need to be figured. Using 10cc’s for the dome volume for the Jahns pistons should get you in the ballpark for that part of the calculation. Anything over 9½:1 CR will not be pump gas friendly so also keep that in mind. You didn’t mention what bore size you’re shooting for but 10.3:1 CR is where your combination will be at if at 3.800” bore (+0.050” over), 312 crankshaft still at 3.44” stroke (regardless of the main size), 0.010” in the hole, 10cc for the dome, compostition head gasket, and the heads being milled 0.012” (67cc). The CR is still too high for pump gas with this combination. Substituting a set of 471 truck heads (still big valve) that are milled the same 0.012” will reduce the CR to 8.82:1 without changing anything else. But if you’re going to use those G heads with no more than a 0.012” cut, then the domes will need to be cut down to a 3.5cc dome volume to get the CR to 9½:1. This is all figured on the aforementioned 3.800” bore size and 0.010” piston to deck clearance so if your bore size and or deck clearance is different, then the CR will also change.
  Lorena, Texas (South of Waco)
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| | | Supreme Being
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| I missed the "mains" part, was thinking rods. 312 to 292 sizes on the mains won't affect the stroke. You can check with Jahns, or clay it up as I said earlier. But, measure the bosses on the heads and find out if they/ve been milled before (good chance) they are supposed to be 1.000" originally. That will tell you how much has been removed previously. It's academic really, if you have to take .015 off, then you have to take .015 off. Like John said though, another .015 won't hurt anything.
Frank/RebopBristol, In ( by Elkhart)
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