green72
Well-Known Member
In the process of putting a plan together for my slant. I’ve read a ton on here and the info is priceless. I want to raise the compression on this engine. What determines if you mill the head or the block or both?
Mill head or block or both?
- Thread starter green72
- Start date
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The block should be decked regardless. Chrysler's machining tolerances were pretty sloppy. The deck heights on the older engines were almost always too tall from spec and crooked. You want to assure the deck is square with the crank center line and also in spec. You'll also want to get the head milled to at least assure it has a smooth and flat sealing surface. From there, it's a matter of personal preference as to how much you remove from what.
What I always do to make those determinations is mock up assemble what I have. This can be time consuming if you're going to bore the block, since you'll need to bore first, then come back and do the mock up assembly to measure the deck clearance of the pistons at TDC. Once you get that figure, you can proceed with your decisions regarding how much you want milled from what.
At least, that's how I do it. I'm sure there are other methods, but that works best for me. Some people like just using the "math" on everything and figuring from there, but I like taking actual physical measurements from the actual parts you plan to use. Much less room for error.
What I always do to make those determinations is mock up assemble what I have. This can be time consuming if you're going to bore the block, since you'll need to bore first, then come back and do the mock up assembly to measure the deck clearance of the pistons at TDC. Once you get that figure, you can proceed with your decisions regarding how much you want milled from what.
At least, that's how I do it. I'm sure there are other methods, but that works best for me. Some people like just using the "math" on everything and figuring from there, but I like taking actual physical measurements from the actual parts you plan to use. Much less room for error.
green72
Well-Known Member
Great info thanks
I was just reading some of your other posts
I was just reading some of your other posts
Just remember that whatever you machine off of the block or heads, you can't put it back. If this is just an exercise in upping the compression, do it with pistons. Just square the block and heads, flat and straight.
pishta
I know I'm right....
I just saw an AL slant block at the fall fling get sold. That deck was gonna have to be milled to clean it up.
There are no pistons for the slant 6 to raise compression using matched factory parts. Unless he wants to use the 198 connecting rods and Chrysler 2.2 4 cylinder pistons, the only way he has to raise compression is milling the head and or block, OR expensive custom pistons to match the 225 connecting rod length and crank stroke. Milling is by FAR his most cost effective option. There'd be no reason he'd need to "put it back" anyway.
my68barracuda
Well-Known Member
If you are only taking the head off and not doing any block - bore work just mill the head.
If you are doing a complete rebuild there are some advantages to taking a cut on both.
Do the block machine first, you will want to have the pistons you plan to use in hand so the machine shop can get the bore size right.
Get the bore and any crank work done then get the block back from the machine shop.
Install the crank with the bearings. If you are using stock style press in pins, have the MS turn one piston pin down so it is a press fit. Then install a piston, no rings necessary in bore 1 and get the piston recession number. Use the same piston and rod in bore 6 and get the piston recession number. Be careful here, some piston top have a slight crown to them. Put a mark on the piston top with a magic marker and measure from the same spot on the piston each time. This will tell you if a front to rear angled clean up cut on the block is necessary to straighten up the block. I normally cut .010 on the block to get a new flat gasket surface
Using what was cut from the block and your new piston you will have the piston recession numbers to calculate what needs to be cut from the head to hit your target compression ratio.
Last but not least, machine shop hot tanks do a good job cleaning the exterior of blocks - heads- cranks and depositing debris in the oil lines. When you get those major components back from the MS, prior to assembly use plenty of hot water, Dawn dish soap and the right size and length of bottle brushes to scrub all oil lines and bolt holes. Use compressed air to dry throughout and wrap each in a large plastic bag till it is assembled. Eastwood has a water soluble rust inhibitor that is good as a final rinse. The parts still need to be 100% dry.
If you are doing a complete rebuild there are some advantages to taking a cut on both.
Do the block machine first, you will want to have the pistons you plan to use in hand so the machine shop can get the bore size right.
Get the bore and any crank work done then get the block back from the machine shop.
Install the crank with the bearings. If you are using stock style press in pins, have the MS turn one piston pin down so it is a press fit. Then install a piston, no rings necessary in bore 1 and get the piston recession number. Use the same piston and rod in bore 6 and get the piston recession number. Be careful here, some piston top have a slight crown to them. Put a mark on the piston top with a magic marker and measure from the same spot on the piston each time. This will tell you if a front to rear angled clean up cut on the block is necessary to straighten up the block. I normally cut .010 on the block to get a new flat gasket surface
Using what was cut from the block and your new piston you will have the piston recession numbers to calculate what needs to be cut from the head to hit your target compression ratio.
Last but not least, machine shop hot tanks do a good job cleaning the exterior of blocks - heads- cranks and depositing debris in the oil lines. When you get those major components back from the MS, prior to assembly use plenty of hot water, Dawn dish soap and the right size and length of bottle brushes to scrub all oil lines and bolt holes. Use compressed air to dry throughout and wrap each in a large plastic bag till it is assembled. Eastwood has a water soluble rust inhibitor that is good as a final rinse. The parts still need to be 100% dry.
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green72
Well-Known Member
Great info
You didn't say what the goal & budget is, as long as You are NOT going to use the long(198)rod/ 2.2 piston combo, the above is accurate. You have to modify the amount that can/should be taken off the block if You go long-rod...
Sorry for the x, but the Slanty pistons are already heavy enough for the bore, and long as a can of baked beans as is! Lol!
MOPAROFFICIAL
Oogliboogli
Whatever you mill ... you CAN put back by means of a cometic/mls head gasket.
I'd mill .020-.040 off the block and .060-.080 off the head.
I'd mill .020-.040 off the block and .060-.080 off the head.
my68barracuda
Well-Known Member
if one was using long rods and 2.2l style pistons and followed the instructions sequence in post #7 they would certainly notice that the pistons were at or nearly at 0 deck height prior to milling the block.
MOPAROFFICIAL
Oogliboogli
They are close before milling. Yes.
Got a part# for those gaskets?
MOPAROFFICIAL
Oogliboogli
Custom. 180.00 bucks.
Had some made @.080
Certainly so Sir, thus impressing the importance of making goals, decisions, & detailed checks before doing anything...
Well, that ain't too bad for a mulligan......
MOPAROFFICIAL
Oogliboogli
Nightmare at the machine shop years ago.
I wanted one of 2 heads milled...they milled both.
Mine were .055" below the deck surface. Not anymore. lol
Slantsix64
Well-Known Member
i milled my 225 .100 off the head got me right at 9:2:1 CR Went from a 120PSI to 160 PSI cranking pressure. Going to wanna upgrade that cam as well
I got my '74 slant 6 in pieces, and missing the rods and Pistons. So I couldn't get "before" readings on the piston recession. I went with stock style Silvolite pistons in the right oversize for the bore-out job, and was plenty unhappy when I measured my piston recession upon assembly was STILL at 0.180 in the hole even though I had requested a 30-thou shave off of the block deck.
As my block progressed thru the machine shop, I had requested this much of a shave, and when they said "it's done" and I asked how much they had shaved the block/ and was told that they had taken only 6 thou off/ which was all that was needed as a clean up cut. When I reminded them I had asked for 30 thou they weren't happy about putting it back into the mill to shave the rest as I had asked for. But they did. I wasn't there running the controls but I know they took enough off to eliminate the block stampings adjacent to #1 bore.that's all I had to go by, concerning before and after.
Once I got it all assembled, I had wished that I had requested an even deeper shave off the block.
I did wind up having 70 thou taken off of the head.
But for other reasons, it looks like I will have to run the extra thick Aussie head gasket, so I will wind up with a net shave of 60-thou since the Aussie HG is 40-thou thicker than the original shim steel one.
I did what I thought was a slight clean up of the combustion chamber edges and the fire ring on a more conventional replacement head gasket will (very) slightly protrude the edge of the head casting, on a couple of cylinders. The Aussie HG is meant for a bigger overbore so the bore holes in one are larger than that of a Fel pro, or a ROL, or a McCord or a Victor Reinz HG, all of which I have had here to lay on top the head to check for that.
I just have the head sitting on the block, not bolted on yet/ I need to get a piece of Plexi one of these days so I can CC the Chambers to see where the head shave left me for combustion chamber volume before I bolt that on.
As my block progressed thru the machine shop, I had requested this much of a shave, and when they said "it's done" and I asked how much they had shaved the block/ and was told that they had taken only 6 thou off/ which was all that was needed as a clean up cut. When I reminded them I had asked for 30 thou they weren't happy about putting it back into the mill to shave the rest as I had asked for. But they did. I wasn't there running the controls but I know they took enough off to eliminate the block stampings adjacent to #1 bore.that's all I had to go by, concerning before and after.
Once I got it all assembled, I had wished that I had requested an even deeper shave off the block.
I did wind up having 70 thou taken off of the head.
But for other reasons, it looks like I will have to run the extra thick Aussie head gasket, so I will wind up with a net shave of 60-thou since the Aussie HG is 40-thou thicker than the original shim steel one.
I did what I thought was a slight clean up of the combustion chamber edges and the fire ring on a more conventional replacement head gasket will (very) slightly protrude the edge of the head casting, on a couple of cylinders. The Aussie HG is meant for a bigger overbore so the bore holes in one are larger than that of a Fel pro, or a ROL, or a McCord or a Victor Reinz HG, all of which I have had here to lay on top the head to check for that.
I just have the head sitting on the block, not bolted on yet/ I need to get a piece of Plexi one of these days so I can CC the Chambers to see where the head shave left me for combustion chamber volume before I bolt that on.
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