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I think I screwed up again
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Joined: Dec/19/2007
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Points: 302 		Post Options Post Options   Thanks (0) Thanks(0)   Quote BDCVG Quote  Post ReplyReply Direct Link To This Post Posted: May/22/2012 at 7:43pm
Well it has the 1/2 head bolts I got it out of a 1970 AMX 28 years ago, I still have the 291-c dogleg heads. 10 years ago when I first had the block worked on the machine shop decked it but didn't record how much. They were also supposed to align hone the main caps whish the current machine shop says were off. I can go the shop tomorrow and look for the part #s to be sure.
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Points: 302 		Post Options Post Options   Thanks (0) Thanks(0)   Quote BDCVG Quote  Post ReplyReply Direct Link To This Post Posted: May/22/2012 at 7:47pm
Lol so I have 2 of the most knowledgeable AMC motor Guys here one says one says put it together and run it. one says run from it. Now I am confused lol
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Points: 302 		Post Options Post Options   Thanks (0) Thanks(0)   Quote BDCVG Quote  Post ReplyReply Direct Link To This Post Posted: May/22/2012 at 7:51pm
Originally posted by SKeown SKeown wrote:

 
 I would question that, that's .038 off a 1970 block. Are you sure it's a 70 block, what size head bolt holes does the block have? If you determine it's a 70 390 block, I would be scared to death to proceed based on that measurement.
 
 I carefully measured the four corners of my current block using a 12" calipers, but wanting to be as exact as possible I paid one of Houston's most respected builders to check it with his BHJ fixture. Fortunately being his finding was much different than mine I ordered pistions based on my measurement and they ended up exactly where I wanted them. Every time I commision machine work I hold my breath, because I've had bad results from some that are considered top notch.
 
 I would bet you either have an early 390 block decked .005, or they are way off on their measurement.
 
 
 I think they are off on the measuring, My caliper is not big enough to check it. My locating dowel were not the step dowels . Although it would not surprize Me if the shop I had it at 10 years ago screwed up decking the block.
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The trashed pistons are already off the rods so I can't measure that way either.
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Points: 2027 		Post Options Post Options   Thanks (0) Thanks(0)   Quote SKeown Quote  Post ReplyReply Direct Link To This Post Posted: May/22/2012 at 8:44pm
 
 Okay, I would say it's a fair assumption it's a 70 block. Line honing shouldn't alter the deck height much at all, but at this point I would be very cautious, because who knows what the block has been subjected to? You cain't use one of the new pistons for measurement purposes because then you'll likely have trouble returning them. The deck height may be 9.170, but I would make absolutely certain, this is an area you can get in real trouble.
 
 If you still have an origional piston, you could have it fitted back to a rod and after determining it's compression height and the rod's actual C to C length (the rods may have tampered with at some time) you can fit it together and varify the deck height. Other options are having a second person measure it for you or get a 12" calipers and do it yourself. By all means I would be absolutely sure before making another move in acquiring pistons.
 
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Points: 2027 		Post Options Post Options   Thanks (0) Thanks(0)   Quote SKeown Quote  Post ReplyReply Direct Link To This Post Posted: May/22/2012 at 9:11pm
 
 
Originally posted by BDCVG BDCVG wrote:

Lol so I have 2 of the most knowledgeable AMC motor Guys here one says one says put it together and run it. one says run from it. Now I am confused lol
 
 To eliminate confusion ask yourself if you want it correct or good enough. Altering engines for performance use allows for good enough, but that aint me.
 
 At this point and provided you varify the block's 9.170 height, and based on you're reluctance to wait for custom pistons to be produced, you may be a candidate for good enough? In that case I would sincerely say good luck in dodging detonation.
 
 SKeown
 
 
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I'm at work so I check back in here on My breaks, at this point in time I think just getting everything back from the shop and measuring Myself. If I measure from the main journal to the top of the deck and add 1/2 diameter of the crank do I also add the thickness of the bearing shell? The crank had to be turned to .020 undersize so if the oil clearance is .002 then the bearings would be .018? Which would give Me 9.188 which would make more sense no?

Edited by BDCVG - May/22/2012 at 9:20pm
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Points: 302 		Post Options Post Options   Thanks (0) Thanks(0)   Quote BDCVG Quote  Post ReplyReply Direct Link To This Post Posted: May/22/2012 at 9:25pm
I am convinced that custom pistons are the way to go , I don't want the flt-tops and if Mr. Curtis still wants them that's where they will go. I just want to make sure I have the right #'s to get what I want which is a .045 quench and around 10-1 ish compression. I am in no hurry I'm just in a bad situation because the car is not at My primary residence, the lifter failed at My work station and I'm cramped for space and don't have all My tools.
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Points: 302 		Post Options Post Options   Thanks (0) Thanks(0)   Quote BDCVG Quote  Post ReplyReply Direct Link To This Post Posted: May/22/2012 at 9:27pm
The advice I have received so far has kept Me from accepting "good enough" and has kept Me motivated to keep from rushing into a 2nd debacle>
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Points: 2027 		Post Options Post Options   Thanks (0) Thanks(0)   Quote SKeown Quote  Post ReplyReply Direct Link To This Post Posted: May/22/2012 at 10:06pm
 
 I don't understand how a lifter failure led to piston damage, but you're on the right track seeking 10:1 & .045 P to H clearance. Anyway, forget about the crank and bearings, just measure the main bore and add half that to the measurement you get from the top of that bore to the deck. Take you're time and stay at it until you repest the same finding. Check all four corners and formulate an average. If the block has already been decked by .038 you don't want to go more unless the thing is really off from front to back. If one side is much different from the other, you could have the high side machined to duplicate the other.
 
 You might be able to get away with 10.4:1 compression provided the P to H was at .040?
 
 SKeown
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