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Discussion Starter #1
Machinest that has my SC block is telling me that he wants to "mock up" the block w/rod and piston at corners to determine squareness (or lack of!!) of block. I want him to make deck surfaces parallel and even relative to the main journels. He says he has no way to do that-------he's beginning to worry me!
I am going with long rods (6.2) and a Diamond piston set with correct compression height. I need to know correct deck height after squaring and honing BEFORE ordering pistons. I cannot order pistons without knowing deck height because compression ratio is affected! I also want minimal material taken off of decks---just to square them, no more.
Before I really show my posterior maximus and possibly get it kicked-------can someone with machine shop experience on these blocks please help me understand why my machinest cant use the Main journels as a reference.
Help would be greatly appreciated. I am in a holding pattern until I can resolve this issue!

TX Yardbird
 

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yardbird said:
Machinest that has my SC block is telling me that he wants to "mock up" the block w/rod and piston at corners to determine squareness (or lack of!!) of block. I want him to make deck surfaces parallel and even relative to the main journels. He says he has no way to do that-------he's beginning to worry me!
I am going with long rods (6.2) and a Diamond piston set with correct compression height. I need to know correct deck height after squaring and honing BEFORE ordering pistons. I cannot order pistons without knowing deck height because compression ratio is affected! I also want minimal material taken off of decks---just to square them, no more.
Before I really show my posterior maximus and possibly get it kicked-------can someone with machine shop experience on these blocks please help me understand why my machinest cant use the Main journels as a reference.
Help would be greatly appreciated. I am in a holding pattern until I can resolve this issue!

TX Yardbird
How does he reference his decks then before he machines them?

http://www.rcsoa.com/Block Decking.html

...but this isnt the biggest problem in this area. You're going to see a lot more issues caused by variations in piston pin height and rod length than deck alignment. (cranks can be off too, but are usually rather precise) Welcome to the world of blueprinting. How accurate do you want to be with the CR?
 

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Discussion Starter #3
TX for replys--big help

Silverbird---the link was great. I thought blocks were mounted in machine by a rod through the main journels. Mill (or hone) must move across decks perpendicular to Main saddles----suspicions confirmed! I do not expect perfect tolerences, just trying to get close and cover worst case senerio from factory. I expect aftermarket pistons (Diamond) and rods to be very close----hopefully! Using "mock up" method---deck measured from piston to deck---would still have crank throw variations affecting measurements. Crank variations probably acceptable for this application but want deck referenced to Mains. It seems machinest wants me to order pistons and rods first--then he will fit. Now I can hold my ground and insist on my instructions. In order to tell Piston mfg. what comp. ht. (which affects compression and valve clearances)

Miller1995---Tx After decking machinest can make bores perpendicular to deck (and mains) when doing overbore (.020)

Now if I can just decide on going to chevy journel size and use 6.25 eagle rods! Will this crank be weakened too much?

yardbird
:)
 

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Yeah.................uh i had no idea what i was talkign about there so i deleted the post.

-Sober Miller
 

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Discussion Starter #5
Miller1995--
Tx for your reply anyway------I sure cant prove you dont know what your talking about!

Silver95bird---
To answer about CR----My understanding about Long Rod engines is that they will tolerate more compression even on pump gas. I think I saw a reply by Dr. Fred (and others) that around 8.75 is reasonable. I may try for around 9.0 in a Long rod motor. I want it as high as reasonable. If I overshoot slightly, I see water/alcohol injection as a remedy. Have been looking and reading about it for years. The GN buick boys seemingly have it down to a science----see their sites. More compression also helps when not in boost. Of course other factors have to be considered, but I want all the compression I can without getting into trouble. That is where I depend upon the expertese (?) of the people of this board.
Tx again
yardbird
 

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What you will want to do in order to get the most even measurements with reference to deck height (and therefore CR) is to measure the distance of the pin CL of the piston to the top of the piston. Then measure rod length, on each one, CL to CL. put the longest rod with the shortest piston, etc. until you're done. Even "professionally machined" pieces come with a bit of variation. The other half is balancing. Balance all rods (with caps) - measure them all and make every rod the same weight as the lightest one if possible without removing too much material. Then do the same for the pistons, and then assemble the rods(w/caps)/pins/clips/pistons and balance those against each other too. Evening the weight will result in much smoother operation (and less stress on the crank due to varying forces). As far as journal size, keep this in mind: the larger the main journals, the stronger the crank - BUT the larger journals will also have a larger bearing surface area, which will increase friction. I don't know exactly what the sizes are you're talking of, so I can't really comment any further yet.

9.0 CR doesn't sound too terrible, however the boost level affects this a lot. I'm not sure about whether the long rods are any better as far as reliability goes... the nice thing about them is that if you don't like them, you can change them later. If you machine the head shorter and the CR is too high, you're SOL. For any given boost level and CR, there is a certain amount of pressure (force) on the bottom end. I don't see how the rod length changes much except for changing the total angle in the X direction (left-right) that the rod moves... which does reduce stress, but that is very minor compared to the stress of the piston pushing down on the rod. What octane fuel are you running or going to run? This car is going to need a dyno tune IMO to get the EEC settings right. I'm sure there's more I'm thinking of, but I can't remember it right now. lol. Let's see where this leads first.
Tom


yardbird said:
I expect aftermarket pistons (Diamond) and rods to be very close----hopefully! Using "mock up" method---deck measured from piston to deck---would still have crank throw variations affecting measurements. Crank variations probably acceptable for this application but want deck referenced to Mains. It seems machinest wants me to order pistons and rods first--then he will fit. Now I can hold my ground and insist on my instructions. In order to tell Piston mfg. what comp. ht. (which affects compression and valve clearances)
Now if I can just decide on going to chevy journel size and use 6.25 eagle rods! Will this crank be weakened too much?
To answer about CR----My understanding about Long Rod engines is that they will tolerate more compression even on pump gas. I think I saw a reply by Dr. Fred (and others) that around 8.75 is reasonable. I may try for around 9.0 in a Long rod motor. I want it as high as reasonable. If I overshoot slightly, I see water/alcohol injection as a remedy. Have been looking and reading about it for years. The GN buick boys seemingly have it down to a science----see their sites. More compression also helps when not in boost. Of course other factors have to be considered, but I want all the compression I can without getting into trouble. That is where I depend upon the expertese (?) of the people of this board.


yardbird
:)
 

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Discussion Starter #7
Machining issues resolved! Suspicions confirmed---another machinest will use Main journals as reference for decking block, not mock-up method. Hopefully back to 2 steps forward 1 step back---not the reverse!
Silver95bird--
My interest and information on Long rod engines comes from several articles, particularly those on 351W w/400 rods. torque specs, tolerance for higher compression even on 87 gas, and better breathing for less ported heads are very interesting to me for my application. Since I will have to order custom pistons anyway to accomodate clean-up necessary on bores, why not go for a long rod setup. I have no facts to prove that they are really worth the effort, but this will not be the first time a hot-rodder has "winged it"!
6.2 rods are available w/351 journel sizes (2.31), same as our 3.8's. 6.25 rods (which would increase R/S ratio slightly more) are available from Eagle, but are Chebby journel sizes (2.1--I think). I believe that some do not recommend taking our rod journels down to that size because of loss of strength.
I do not expect to do a lot of expensive blower and plenum work, maybe pullies. Head work will have to be done early to determine volume for comp calculation. Cam will be relatively mild----520 or less lift probably, w/low to mild duration figures. Of course exaust work will be first along with eec tuning. Still have numerous issues to resolve, but will try to get engine machining started in right direction.
Feel free to PM me if you think of anything else. I have good amount of engine knowledge, but have never done a V6 or SC'd engine.

Tx Yardbird
 

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A longer rod is nice, but the piston pin gets moved closer to the piston face. I'd be worried about the pin bore and the oil ring intersecting (causing oil burning). Also as the pin gets closer to the crown the strenght of the crown is compromised. Long rod engines seem to work quite well for N/A applications but under boost I would be a bit worried. Just something to think about, but you may have researched this already and found it to be safe. I'm quite interested in your results:thumbsup:
 

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Discussion Starter #9
Rancherlee--
After checking with mfg's , I understand piston compression hts approx 1.18 and over can avoid intrusion into oil ring groove. Probe advertises a piston for their envir certified 347 that uses a 1.18 compression ht w/offset pin that does not get into the oil ring groove. I think I read a mag article about it. Mag articles can and often do get people in trouble, you can't automatically assume they know what they are talking about. Looks so far that Diamond will be piston of choice---dosnt mean others are not good! 6.2 or even 6.25 (if available) rods require a comp ht around 1.25 to 1.34. w/10 to 15cc dish to keep comp ratio low 9's or less. What I dont know is effect on skirt length etc. Dont think rod will have clearance problem. My plans dont take this engine to ragged edge in any area and other variables must be accounted for. Have read some of your posts and replys-----respect your opinion.

yardbird
 
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