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#1
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Measuring deck heighth
Ok all you engine builders, I gotta question for ya. I gotta bored .030" over 68 440 block that I am going to put 8.5 slugs in. It has already been rebuilt once and I'm assuming the standard shaved deck was around .020"? How do you measure deck height? I have a pair of 12" and 20" calipers as well as a 8" depth caliper and your standard dial indicator. In 68 I believe 10.25" slugs were used but since I'm adding a centrifugal s-charger, I need to know how to measure my block. All you're input is well appreciated. Ya'll have a good one.
J-440 |
#2
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Who cares what the actuall deck height of the block is. You need to know the distance to the deck above the piston. Install a piston/rod/crank and measure. Only way to know for sure. Something to be aware of is that when you install only one rod on a journal made for two is that if the rod slides over a little it will change piston deck height. Make sure you keep it against the cheek. Another thing. Take some masking tape and wrap it around the ring belt until the piston will just slide up and down the cylinder. This will keep the piston from rocking without having to install rings.
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#3
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I'm just guessing, but I think he want to know the height so that he can buy the right pistons.
If you haven't bought the pistons yet, how do you know which ones to buy with an unknown block? |
#4
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But that's the point, all the blocks are unknown. Build tollerances were horrible. Spec's more like speculation.
I think the most usefull spec, you need is pin height. You should be able to measure the pin height of your existing piston(I'm not sure how, but a piston manufactureer should have a picture of that spec) and use that, with your measured deck clearance. Should help you. Even then you may have to mill the heads, or pistons when assembling to achieve an exact ratio. |
#5
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Maybe i misunderstood. Use the stock unmachined deck height of 10.72" for your calculations to get a ball park of what piston compression height you need. Then do a mock-up and measure piston deck height so you can caluculate compression ratio. I assume this is what your wanting to do. For ex. 10.72-1.875(half the crank stroke)-6.768"(rod length) =2.077". Now just as the block deck height may not be correct you also have to assume that the rod lengths aren't perfect and the stroke length isn't perfect either. Assuming the above measurements are correct and with 0cc valve reliefs we have approx 8.88:1 with a .086" deck height, 85cc chambers and a 9.9cc gasket. This piston has a 1.991 compression height. Now your in the ball park. Now you have to do an actual mock up so you can measure exact distances to know exactly what your compression will be. Don't rely on unassembled measured distances.
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#6
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kinda hard to mockup a piston/rod assm. in a cylinder that hasn't been bored yet. Boring should always take place after the decks are done. Most Mopar blocks are way out of spec & should be square & parallel decked.
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#7
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As far as I know, the engine was rebuilt only 1 time. Anyone know what your typical machine shop shaves the block? I'm guessing around .010"? And yes the block is .030" over, my Eagle rods are coming in as well as the bearings. The reason I'm asking is because JE has to make my pistons for my application. Stock compression on a 68 440 was around 10:1 I believe. The new pistons will be dished and I'm looking for 8.5:1 compression. I have a lot of room to play here and maybe I'm just being paranoid but it still helps to ask you guys.
J-440 |
#8
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Ok guys, let's fill in the blank. JE wants to know these last specs. I would really appreciate the help. Remember, this is for a 68 440 Magnum, bored .030" over and assuming the deck was shaved .010" during the first rebuild. Oh yeah the crank is also a stock forged unit.
Block height: Deck Clearance: Compression height: Thanks and ya'll have a good one. J-440 |
#9
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Engine Specs
At Chrysler Engineering we would put an arbor in the main bearing bores without the bearings. You then measure the distance between the deck and the arbor. Add half the diameter of the arbor and that is your deck height. Deck height = distance from center of mains to the deck surface.
Deck clearance is the relation of the piston top to the deck. Older "B" engines had a positive deck clearance. The piston at TDC was .010 above the deck. The newer ones have a negative clearance. The piston is below the deck surface at TDC. Compresion height is the distance between the piston pin center to the piston top. Hope this helps. |
#10
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Calculate compression distance?
1. With your 20" calipers, measure the distance from your #1 main jurnal to the block. The calipers need to be paralled to the cylinders (Perpindicular to the deck) when used. Be sure to use the tips, not the flats of the caliper jaws inside the main circle. Do both left and right decks. They should be within a few thousandths of each other. Do the same for the rear of the block. Now you should have four measurements that are the same or very close.
2. With your 12" calipers, measure the diameter of the main jurnal. Divide that number by two. 3. Add #1 to #2. This is the blocks deck height from the center of the crankshaft. 4. Divide the stroke of the crank by two. 5. Determine the center to center length of the rods. 6. Add #4 to #5 to get piston pin height. 7. Subtract #6 (pin height) from #3 (deck height) to get the compression distance that would make a Zero deck clearance. A compression distance larger than #7 will put the top of the piston out of the block and a cd less than #7 will put the piston down in the cylinder. Billy |
#11
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I appreciate the help guys and I'm just about done with my dimensions. I've got one last question...what was the compression height on a stock 440 with 10:1 pistons in 1968. I've checked the original manuel and can't seem to find it. Thanks again.
J-440 |
#12
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PISTON HEIGHT
J-440, These numbers are from a piston chart printed by Chrysler Corp. The specs are for a 1972 model year 440 with " 10:1" compression.
Compression - MAX=10.288:1/ MIN= 9.306:1 PISTON HEIGHT- MAX=2.062/ MIN=2.057 CON ROD CENTER to CENTER- MAX=6.770/MIN=6.766 BLOCK HEIGHT- MAX=10.720/MIN= 10.730 HEAD CHAMBER VOLUME- MAX= 86.90/MIN=89.90 These specs are for the E87 6BBL (six pack) engine. As the compression drops,the piston height will drop if both the pistons are flat tops. The 1971 440 with 9:1 comp. has a piston height of MAX=2.012/MIN=2.007 . Of course all numbers are in inches. Dan |
#13
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DAHEMIKOTA, I really appreciate your help. What about the stock deck clearance from the top of the piston at TDC? This is my last and for sure final question and I'll stop buggin you guys. Ya'll have a good one.
J-440 |
#14
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PISTON DROP
1971 440 Six Pack =.010 / .035 Below the deck.
Note that some of the older "B/RB" engines had the pistons drop above the deck. My 1965 383 had -.012 above the deck.The only 1971 engines that had above deck piston drop was the 340 E55 with 10:1 Compression, and a 383 export truck engine with 7.5:1 compression. Chrysler Engineering says a minus sign ahead of the number means the piston is above the deck. Dan |
#15
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Dan, your a good man bro and I really appreciate the help. Now I can finish up my short block. You have a good one.
J-440 |
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