2eighTZ4me Posted June 25, 2010 Share Posted June 25, 2010 1 = 708g 2 = 706g 3 = 705g 4 = 706g 5 = 704g 6 = 704g Less than 1% difference amongst the crew. Do I get them down to the gram? If so - where do I take off material. My guess is toward the top, as that's where the most (for lack of the word I'm looking for) "weighted centrifugal motion"??? Shot peening after that and then bushed for JE pistons with the spiro locks.........want to make sure it's "right" - BRAAP, Tony D - race motor builders???? Quote Link to comment Share on other sites More sharing options...
MONGO510 Posted June 25, 2010 Share Posted June 25, 2010 the rods are balanced at both ends. It will take a special scale to balance them correctly. Big ends are matched, small ends are matched, Total wieght is matched. This is not something that can generally be done at home. Mongo Quote Link to comment Share on other sites More sharing options...
2eighTZ4me Posted June 25, 2010 Author Share Posted June 25, 2010 Yeah - I pretty much got that from the Honsowetz book - but for a homebuilt job - I guess that answers my question - ain't no sense in it. I got a couple pistons that are a wee bit heavier - I can match them up with the lighter rods. Even for the balance, the rotating mass will be "better" balanced than a motor that nobody took the time to match up - course - I realize it could work to my detriment if the centrifugal rotating forces are balanced "off" (90 degrees out of phase) - but I guess I'll take my chances - it's a stroker and it won't see more than 7K - I got a badass Rebello BHJ damper for it.... Quote Link to comment Share on other sites More sharing options...
hoov100 Posted June 25, 2010 Share Posted June 25, 2010 speedwaymotors.com sells a rod balancing stand and a digital scale that works pretty good. Quote Link to comment Share on other sites More sharing options...
Tony D Posted June 27, 2010 Share Posted June 27, 2010 the rods are balanced at both ends. It will take a special scale to balance them correctly. Big ends are matched, small ends are matched, Total wieght is matched. This is not something that can generally be done at home. Mongo I completely, totally, 1,000,000,000,000,000,000% disagree! This is EASILY done at home with some hardwood dowels, (or teflon) and a drug scale from Harbor Freight! Making a rod balancing jig is not a big deal. Friction is almost a non issue if you make one using some aluminum and a 1/4" rod to support the end not being weighed. I have been balancing at home since the late 70's and can usually get them identical. I would at a minimum get them all to weigh the same. What you have is a gross number, what you need are two more measurements, 'big end' and 'small end'... You can do this in a pinch with some fishing string to hold up the end you aren't weighing. using a jig makes for a faster process though. With digital scales being available that weigh to 0.1 of a gram, there really isn't a reason not to get end-to-end weights to that tolerance at least. A 2gm variance rod-to-rod would not do for me. Not in a street car. Hell, not even in a Chevy! Quote Link to comment Share on other sites More sharing options...
Tony D Posted June 27, 2010 Share Posted June 27, 2010 (edited) Rod Balancing Jig #1 Impressive Rod Balancing Jig This looks like the one I built in the 70's from Finch's Book That should get it rolling... Read the link on the 3200cc Corvair Engine. Guys complain about having to measure stuff on a Datsun 'look where I came from!'LOL I'm guessing your comment about the stroker is based on your decision to use cast pistons, and not some internet myth about some arbirtary limit of '7500 rpm harmonic'... Oh gawd I hope it's not that... Edited June 27, 2010 by Tony D Quote Link to comment Share on other sites More sharing options...
Daeron Posted July 10, 2010 Share Posted July 10, 2010 (edited) Have you read the sticky on How To Balance Your Valvetrain?? The process is much less complex than even that. Valvetrain has many many more and different types of parts that need to be balanced and matched.. You only have six piston rods. I haven't ever actually done it myself, but I would be with the "Yes, get it taken care of now that you are thinking about it, because you are thinking about it" school here. Edited July 10, 2010 by Daeron Quote Link to comment Share on other sites More sharing options...
spork Posted July 10, 2010 Share Posted July 10, 2010 Maybe I'm out of order here, but if he's going to get the rod bushed for a full floating pin, I'd want to have that done first and any other re-sizing that might need done, then balance. I'd hate to have to do them all over again. I second the balancing at home, pretty easy to do with the right jig. Just make sure that everything you do is repeatable. If your jig isn't quite right, you'll find that you can set up and take off the same rod several times and get several different weights. Once your Jig is good to go, life is easy from there. Don't forget to have the rod bolts installed that you plan on using as well. Quote Link to comment Share on other sites More sharing options...
SHO-Z Posted July 10, 2010 Share Posted July 10, 2010 Very OLD SCHOOL, 60 years ago my dad raced a midget with a V8 60. He balanced the crank rods and pistons together as a unit. He set up a jig having the crank mains sitting on razor blades and basically balanced it so no matter where it was rotated to it would not roll. From his stories this was how all of the race guys use to do it. And they did turn some R’s on those old flat heads! Quote Link to comment Share on other sites More sharing options...
SHADY280 Posted July 10, 2010 Share Posted July 10, 2010 balance is super important, i skipped out like you and thought the extra money/time and small variance wasnt all that important. its close enough. yeah i should have never done that. now im thinking about pulling the motor to do it after near 40,000km. it runs like a champ, but after running in another persons ride that was balanced to perfection, ill never do that again. lesson learned Quote Link to comment Share on other sites More sharing options...
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