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Old 08-04-2004, 06:13 PM
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383 Crank Hits Pistons

My machinist called today - said that while assembling to set deck height in my 383 Chevy blower motor the 4340 Eagle crank, (internal balance) using 4340 H Beam 5.7" rods hit the bottoms of my pistons, which are JE blower pistons. He re-measured everything and says he's never had this happen before, the numbers on the crank are correct for my application but he thinks the crank is not a 5.7" rod crank.

Eagle tells me it happens and sometimes requires machining of the throws to avoid the collision, but is rarely found on JE Forged pistons.

Has anyone ever heard of this? The machinist says he can machine the throws but balancing will be more expensive. I can't imagine having to do this to brand new expensive parts. I may buy different pistons but would hate to have the same problem with the new ones!

Anyone using an Eagle 4340 crank and if so, what pistons worked? Please be specific, in case i need to get the same ones. I'm looking for around 8:1 with 64 cc.

Sorry for the long post, I'm fired up! Larry

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Old 08-04-2004, 10:36 PM
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Well, I'd be pissed at the piston manufactures and demand my money back for another set that will work with that setup. If anything you should grind the bottom of the piston shirts, NOT the crank!
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Old 08-04-2004, 10:39 PM
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chev hi performance

Hi Chevy hi performance mag just did an article on this in the last month or two.Can't tell you which month,mine are at work.You can probably find it on line though.Hope this helps.
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Old 08-04-2004, 11:08 PM
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I looked at Chevy High Performance's site and found an article on a mountain motor stroker project, but it didn't tell much.

These pistons were originally ordered for an LT-1 350, but my understanding is they will work in any 350 block, stoke is stroke right?!

I'm considering a set of JE 131631's, but would like to have some warm fuzzies that they'll work! What pistons are you Eagle crank 383 guys running? Camaroman7D, are you here??

Thanks, again, Larry
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Old 08-05-2004, 06:21 AM
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Most of the aftermarket crank makers specify which rod length the crank throws are machined for. What is the part number of the crank? I believe the problem lies with the crank as your machinst thinks. Turning the throws isn't an issue and would actually free up some HP but the expense of adding slugs of mallory can get pricey.
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Old 08-05-2004, 06:50 AM
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Alot of the Eagle cranks I have seen in the 3.75 stroke range specify that 6 inch rods are required. I think if you check the part number on your crank you will see the same thing. It is not the parts manufacturors fault if this is specified.

Chris
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Old 08-05-2004, 09:16 AM
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This problem is very common. I hear it every week. Cut the throws down on the crank and then it will have to be rebalanced. I would suggest to anyone to mock up your assemble before any machine work goes on. It will save you $$$ and time.

Chris
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Old 08-05-2004, 12:13 PM
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Turbo, this is a 5.7" crank, part #435037505700 - I bought 5.7" rods, so I certainly wouldn't have bought a crank for 6" rods. The rods (Eagle H beams) and JE pistons are both correct, the piston compression height is 1.425", right on for the stroke and rod.

There was no machining or balancing done, only block clearancing, what Chris mentioned is exactly what was being done, trial fitting and measuring for the decks. That's a no brainer for sure.

My issue is, many vendors sell 383 rotating kits, using Eagle, Scat, etc. assemblies, that fit out of the box so to speak, why would mine require molesting the crank to make it work. Even Eagle says they have never seen JE forged pistons be a problem.

I'm still working the problem and will post the outcome when it's all said and done.

Thanks, Larry
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Old 08-05-2004, 01:08 PM
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Larry,
The simple answer is the counter weight profile is on the large size. The chinese throw nothing away. Your machinist, sounds like he knows what he is doing, will have to put the crank in a lathe and cut the counter weights down. As Czar said this is not a bad thing, reduces windage, which is good in a stroker, and will free up some power.

Chris

Larry,
I just put 2 and 2 together on who you are. You better put the damper on that eagle crank and check the press fit. Many times the snouts on the cranks are undersized and the damper just slides on.

I don't want you to cut the counter weights and then run into this snag and eagle not take the crank back.

Chris
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Old 08-05-2004, 01:09 PM
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Well, that sucks. I thought that is might just be a part mismatch, but I guess not. I had to clearance my block and rods when I put the 6 inch assembly together in my 400. The chinese rods where suppose to be clearance for everything, but they were not. I would say that is one of the biggest drawbacks of the low buck parts is the fitment. If you are assembling yourself, it is no big deal. If you are paying to have the clearancing done......the cheap parts start to not be cheap anymore. BTW, I used the 6 inch Eagle crank with SRP(made by JE)18cc dish pistons and everything was good on piston clearance.

Chris
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Old 08-08-2004, 11:14 AM
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Quote:
Originally posted by 68NovaSS
I looked at Chevy High Performance's site and found an article on a mountain motor stroker project, but it didn't tell much.

These pistons were originally ordered for an LT-1 350, but my understanding is they will work in any 350 block, stoke is stroke right?!

I'm considering a set of JE 131631's, but would like to have some warm fuzzies that they'll work! What pistons are you Eagle crank 383 guys running? Camaroman7D, are you here??

Thanks, again, Larry
Larry, i think this is your problem. lt1 350 pistons and 383 stroker pistons are completely different and will not interchange. if your building a 383, you need to order 383 pistons. not only is the stroke different but the wrist pin location is different too. i don`t know who ordered your pistons but your engine builder should have caught that, you alway double check the part numbers before assembly.see if je will exchange the pistons for the correct ones.
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Old 08-08-2004, 01:40 PM
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jegs sells all the the same brands that you have and 383 kits.give them a call and they will help to get you straightened out.but i wouldn't let anyone grind the throws on my crank.get the right pistons.
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Old 08-08-2004, 02:15 PM
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68c, these are 383 pistons, they were originally ordered to be used in an LT-1 block, but the intended block was never an issue when ordered. Eagle tech says they have never seen a JE piston needing clearance ground in the throws, but there's always a first time. They do admit, however, that clearancing is common with some other pistons, and not a problem, seldom requiring heavy metal to balance.

I've ordered a set of 131631 JE's that should arrive tomorrow, I'm told they will work, we'll see.

Are there no 383's out there running JE pistons, if not what are you guys using?

Larry
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Old 08-08-2004, 04:02 PM
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68novaSS, you said the pistons were blower pistons right? Well they'd bit sitting at a lot closer to the crank due to the different piston pin bore positioning in an effort to lower the compression ratio. I'm sure that if you used normally aspirated pistons clearance would not be an issue. Rob
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Old 08-08-2004, 04:20 PM
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the way you worded it, it sounded like you ordered them for a 350 c.i. motor since it had the same bore size you were running. you also said "stroke is stroke, right?" which also led me to think you ordered 350 pistons. TRW selles a set of flattop pistons for a 383 that require the bottoms of the pin boss area to be shaved .020 for crank clearance. as for what club 327 said, blower pistons have a dish instead of a flattop. the compression isn`t picked buy pin location. also, blower pistons have the ring lands further down than a normal piston to help with heat issues melting the ring lands. wherever you get your pistons from you need to give the following information...


c.i.d.
borexstroke
rod length
ring size your using
cylinderhead combustion chamber volume and head gasket thickness if available

good luck getting it all worked out.
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