trenace
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posted October 18, 2005 01:04 PM
Does anyone have stock piston pin weight; also stock piston weight?
Does anyone have the stock piston pin weight, and/or the stock piston pin weight?
I'd like to be able to tell Falicon what the difference is in weight in case that's any use to them in making each throw balanced to each rod and piston, assuming they even bother to do that as opposed to just overall balance. It would also just be interesting to know how much weight I saved (the CP pistons are 230 g, and their pins just under 75 g.
Thanks!
  
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zrxdean
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posted October 18, 2005 01:33 PM
They don't bother with matching to piston weight, they only balance the crank as a unit. It's your responsibility to make sure all the pistons are the same. You can check with RA about all the details of balancing rotating assemblies...
Dean
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TurboBlew
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posted October 18, 2005 02:07 PM
Stock piston/ pin weighs 370grams accoring to my scale.
JE piston (stock bore) weighs 350g with pin.
Those must be some light pistons you got there..especially if 2mm over.
Like Dean says.... take a scale and make sure all your pistons weigh the same.
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trenace
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posted October 18, 2005 02:46 PM
 Edited By: trenace on 18 Oct 2005 19:00
Thanks, Turboblew!
So, adding it up, the CP assemblies (piston plus pin) are just under 305 g. That's a DAMN good savings over 350!! And I guess an even bigger savings over stock, as I though the JE's were lighter than stock, though I don't have a stock figure -- would also be interested in that if anyone has it.
And they are 86 mm bore (1287 cc).
I was indeed planning on weighing them all, but just got them in a couple of hours ago and only weighed one. Since I have eight, I'll pick the four lightest ones, which ought to cut the variation in half right there, and then if needed take a touch off the heavier ones.
That's kind of a shitty job on the crank balancing if they don't care about the individual throws. Sorry to hear that, though actually I thought that they did not bother with that but didn't know for sure. When you take substantial weight off the pistons and rods as is the case here, the individual counterweights really ought to be lighter, if they were correct weight to begin with. Maybe I have to send the crank to England to get that degree of attention to detail.
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trenace
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posted October 18, 2005 07:43 PM
Edited By: trenace on 18 Oct 2005 20:44
I should have done a search for the stock piston weight -- but had I only done so, I wouldn't have gotten the good information TurboBlew and zrxdean posted. So it's lucky I didn't until now.
Anyhow, the search turned up jimo as posting:
quote:
Bergie, My stock pistons with rings and pins weighed between 365.49 grams for the lightest and 366.65 for the heaviest. The stock rods with nuts and no bearings weighed in at 393.93 grams for the lightest rod and 420.77 grams for the heaviest rod. The factory did a good job of mixing the light pistons with the heavier rods. The difference in weight between #1 and #4 as a set, and #2 and #3 as a set was .07 grams. (#1 and #4 weighed 1573.05 grams, and #2 and #3 weighed 1573.12 grams). Jim O.
So -- the rings being about 20 grams -- the CP assemblies are about 325 grams vs about 366 for stock.
That's a savings of about 41 grams per piston, or about 11% lighter, for pistons that are 3 mm bigger bore. Seems outstanding to me! Very pleased with that.
On the rods, it seems to me jimo must have had a typo in at least one of them, as there's a vast disparity between the lighest and heaviest figures he gives yet the total weights are about the same. Given the average of his lightest and heaviest pistons of 366.07 g, and the average of his total assemblies (minus bearings) at 786.54 g, his average rod weight would from that follow as about 420.47 g.
Carillos are 350 g, and while I couldn't get an exact figure for Falicons they are apparently about the same, as their ZX-11 rod is only slightly more and they said their ZX-12R rod is a little lighter than their ZX-11 rod.
So, combined weight of the CP assemblies with aftermarket rod would be about 325 plus 350 g or about 675 g, versus about 786.5 g. About a 14% savings.
Since rpm for same bearing load changes according to square root of weight difference, this weight savings "entitles" 7.9% more rpm, or about 12,575 rpm for same load on bearings as at 11,650. Over 900 more rpm allowable thanks to the lighter pistons and rods.
Pretty damn good!!! 
So if the ECU mod is good for 12,250, with the CP pistons and Falicon rods I'll actually have less bearing loads at that higher redline than the stock assembly does at stock redline. Very nice!
Extending the redline that much also means allowing two more teeth at the rear while keeping same speeds in gears. So there's a real snowball effect from this benefit of lighter piston and rods (which of course was already a known fact, but it's nice seeing the specific result in this case.)
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TurboBlew
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posted October 19, 2005 04:03 AM
I forgot to mention....
My weights for stock with rings and pin. Same for the stock bore JEs (which are designed for 13- 1 compression.)
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VincentHill
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posted October 19, 2005 08:55 AM
Cast Pistons are lighter than Forged. That is why Forged is stronger More Density.
____________
Made History @ Daytona and still one fast old man!!
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trenace
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posted October 19, 2005 11:39 AM
Edited By: trenace on 19 Oct 2005 13:36
TurboBlew, thanks! So then the correct comparison (Both being compared with rings and pin) is 325 grams for the 86 mm bore CP versus 350 g for the stock bore JE.
Still a quite good savings! 
Also, the consistency in weight is good.
I would have to do a little statistics that I'm not going to do to figure out what the variation would most likely had been had I ordered only four pistons. (Getting 8 pistons tends to result in a wider spread than getting only 4.)
But within the eight pistons, my four lightest are a really nice set, ranging from 229.23 g to 229.43 g, i.e. plus or minus 0.1 g, which will make it easy to get them basically dead on.
The four heaviest range from 229.54 g to 230.31 g. Actually there is only one "flyer" in there, the very heaviest one... the next heaviest one is only 229.89 g.
Also incidentally it turns out I was wrong regarding individual throws. It's irrelevant for inline Fours.
Roughly as a guess... if someone had ordered only four pistons, they might well not have gotten my very heaviest piston, for example. Suppose though that they had happened to still get my lightest one and my next-to-heaviest one. In that case, their spread would have been from 229.23 g to 229.89 g, i.e. plus or minus 0.33 g.
It's also possible that mixing and matching the piston pins would get the variation closer than this.
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TurboBlew
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posted October 19, 2005 04:23 PM
Who cares if they are off a few grams?? Just put the assemblies on an accurate scale.. write down the weights for each, then scuff the tops of the piston(s) if you need to even the weights up.
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trenace
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posted October 19, 2005 04:36 PM
Edited By: trenace on 19 Oct 2005 19:05
That may be better; I have always done parts of the wrist pin bosses that seemed no harm in taking down a touch... true it's not a big deal if a set is less accurate than this because one can take more off but I kind of take it as an indicator of quality that they were close as supplied, which the plus or minus 0.1 g for the lightest four pistons certainly is.
But actually I have to take a little off the piston tops anyway due to some edges and points (nothing bad just the usual.)
The wrist pins vary quite little, only a .13 gram spread between them. That actually could almost bny itself accomodate the differences in the pistons; perhaps together with the rings that I haven't weighed yet it will be a question of removing just hundredths of a gram. Of course the differences could be bigger with no problem since as you say that's certainly correctable when it's the case. My thinking might be bogus that closeness in weight as supplied is an indicator of overall care in manufacture but it's a superstition I have.
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