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  #16 (permalink)  
Old 06-13-2010, 10:27 PM
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Quote:
Originally Posted by techinspector1
Thanks Eric, missed the part about the longer rods for that crank. I don't know about the rest of you, but I'm not beyond doing a little whittling on the bottom of piston skirts for clearance. I've done it several times before on other motors and never had a problem. Of course, you have to keep the weights the same. I remember taking a half-dollar sized dollop out of some BBC pistons for crank clearance. I put that motor together for a friend of mine and last I heard, he had fragged 3 drivelines, 2 converters and a transmission, but the motor hadn't missed a beat.
Inspector, I've cut on piston skirts before without problem too but in this case it is the pin boss below the pin in the piston that won't clear the counterweights of a 6" rod internal balance aftermarket crank. You would have to turn the crank counterweights undersize and then load the crank up with Mallory to get the balance back. Might as well start with the 5.7" rod crank as the counterweights will already clear and then just load it with Mallory to get internal balance.

I still feel too many people who don't NEED internal balance are having it done. My gosh, how did any performance engine survive before we started to modify everything for internal balance

Must be the magazines...

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  #17 (permalink)  
Old 06-14-2010, 01:02 PM
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Quote:
Originally Posted by deiselpower
Hello, I was looking to upgrade my 355 with the 60103 lunati cam Brodix Ik

200's, I was looking around for a new 3.75 stroke crank to use with 5.7'' rods

and internal balance.I was looking at scat website but they don't have any

unless I go to the 6.0'' rods, after I looked on summit and the only crankshaft I

could find for my application was Eagle and I heard (also read on here) that

they are made very poorly. I have a budget of $400 without machine work so

forged isn't necessary. Should I go with the Eagle or some other company. T

Thanks
Your budget will drive you to a cast crank, try to sping for steel rather than iron if you can as they will put up with more abuse and last longer. Problem with cast cranks as there isn't enough space to counter the moving part weight with a cast counterweight unless Mallory metal is put in it, this gets really expensive really fast, so if you just have to have internal balance you're dollars and reliabilty ahead to spring for a forging which due to the denser materail will usually balance interanally. Keep in mind that the need for internal balance is really only in high RPM, high output engines. For lesser engines, external balance is fine, especially when you consider that even internally balanced engines are balanced bearing bay by bearing bay, all production style cranks under balance the inner throws and make it up on the end throws, hence the big counterweights at either end where the center throw counterweight deficienies are made up.

SCAT makes a nice shaft, Eagle had some problems with thrust journal surface quality and rod journal widths a few years ago, current production appears to have corrected these issues.

Rod length will dictate the piston you use, a 6 inch rod on a 383 stroker drives the pin into the oil ring pack which requires a steel support ring to position the oil ring over the pin hole. While these seem to work well, it is a potential failure point that isn't present with a 5.7 inch rod and piston combo.
Getting the rod past the cam is a problem with either rod, best solution is a cap screw rod as you will probably have to grind for some clearance and from my perspective I rather shave a little off just the rod rather than both rod and bolt head where a conventional nut and bolt systems is used.
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Old 06-14-2010, 03:04 PM
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The reason why I want to keep the it internal was to keep my damper and flywheel but it doesn't really matter just trying to save a few bucks. I'll just get the external balance and take it to the machine shop to get balanced with the new pistons and get my engine builder there to give it a going over and go from there.
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Old 06-14-2010, 05:04 PM
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I have been running an Eagle cast 3.75" stroker crank with 5.7 rods in my 2 piece rear seal engine, for the last 4+ years, without problems.

I purchased the kit and had it installed by The Engine Store in Winona, MN.
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  #20 (permalink)  
Old 06-15-2010, 03:24 PM
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Quote:
Originally Posted by deiselpower
The reason why I want to keep the it internal was to keep my damper and flywheel but it doesn't really matter just trying to save a few bucks. I'll just get the external balance and take it to the machine shop to get balanced with the new pistons and get my engine builder there to give it a going over and go from there.
Balancing prices vary all over the place as it's an hourly cost thing where an easy job takes a couple hours and runs about 180 dollars here in the U.S. A complicated job can run upwards of 3 hours and will cost around 270. When the need for Mallory metal becomes involved you can add another hour or two, which will add 90 to 180 dollars for labor plus the Mallory metal. This stuff costs about 2 dollars a gram with 200-300 grams being a pretty typical requirement to bring a crank into balance when it's required. So you can pretty easily find yourself staring down a 1000 dollar cost to balance a 300 dollar crankshaft.

When you look at where balance with Mallory metal can go, spending the up front money for a forged crank that is balanced without Mallory metal due to its greater material density, and/or hunting down rather expensive ultra-lite rods and pistons; or using a less expensive cast steel crank and going with replacement externally balanced damper and flywheel becomes an effective cost trade. Unfortunately, it is difficult to pin point the cost of balancing till you have the hardware in hand and actually can measure the weighting requirements. Of course for the better or worse by then you own it and are forced down whatever path that leads too.

Bogie
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Old 06-15-2010, 03:46 PM
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You Can Purchase , Direct From Scat Or Other Suppliers A Complete 6" Rod Rotating Assy. That Is Internal Balance And Does Not Require Mallory Metal To Balance. Then You Use Your Stock 350 Type Dampener And Flywheel/flexplate[neutral Balance]. I Bought Mine From Comp. Products 3 Years Ago, Have Put 9k Miles Seen 7k Rpm Many Times,no Problem Other Than Like Someone Already Stated, Oil Control [consumption ] Is A Bit Of A Problem.
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