Question: you have 8 x V8 rods, balanced on little end and balanced on big end on a rod weighing rig They all weigh 750 grams, you machine 20 grams of the little end, weigh them and they all now weigh 730 grams You machine 30 grams off the big ends and they all now weigh 700 grams Are they all still in balance ?? ... If you measure the weight of the little and big ends on a rod weighing rig will they come out the same but of course lighter ?? Ricky.
The rods will be in balance with each other, but not with the crank, if that's what you mean. When a crank is balanced, the bobweights are calculated with a formula using the rotating weight and half of the reciprocating weight. The big end of the rod is rotating weight, and the small end is reciprocating weight. Both ends are weighed in order to calculate the bobweights. In order for the rotating assembly to be balanced, weight will have to be removed from the crank counterweights to account for the lesser weight of the rods.
I would say no. I have tried balancing Chrysler 440 rods, threw them up to get some what of a matching set. All with in 5 or 6 grams so thought I could balance this set, but then when weighing big ends, 20 to 30 grams off, same with the little end. Chrysler were the worst for this problem! I would try to weigh them big end matched then little end matched. Then they should be all the same, and a bob weight made up.
Rereading your question, if they were a balanced matching set to start with, then what you are asking should come out right, but would not count on it to come out right without checking each end. But taking 20 to 30 grams off a rod, is a lot of weight!!! Probably have no rod left!
Thanks guys ! The engine is not balanced yet, still mocking it up 390 FE, 040 over with a 428 crank..... the forged pistons will need around .083 shaved off Already measured, will leave plenty of top ring land and at the lowest part of valve reliefs I took an overheated 390 rod and ground a considerable bit off the top and bottom leaving some material on both ends Took just a bit off the sides, but not to the flats ... lost over 50 grams The forged pistons are already lighter before being shaved than the factory pistons so should need less mallory Ricky.
You shouldn't need any mallory metal unless you are trying to internal balance the rear of the crank. Just use a 428 flywheel or flex plate. I have done many of these in all different ways. Internal it with heavy metal in the rear, use stock 390 flywheel then. Drilled a 390 flywheel to match the 428 crank. Never had to take that much weight off the rods. I have trimmed the tops of pistons on some, but that because they were the wrong pistons to start with. But nothing wrong with that as you have made the checks you need to be able to do that. I would make sure you have at least .150 piston thickness left on the top. If not heat will dip them in the center. "Took just a bit off the sides, but not to the flats" Hopefully you didn't give it to much side clearance with that. Anyway, you will defiantly have to get a bob weight and spin that one up! You may of created more problem doing that with those rods to rebalance it.
Thanks Flatrod17 I am going to internally balance it, it is in the mock up stages and has not been balanced yet I have an aluminum flywheel, a steel flywheel, an aluminum and steel pressure plate and an automatic flywheel, all will be internal balanced I took no material off the rod sides where they contact each other or the crank, just the beams a bit to smooth them I have a 76 truck C6 built up, a Fairlane T-10 I am rebuilding with syncro lock sliders and will be set up tight and a 4 speed top loader on the way It it a 65 F100 I bought from my Uncle Robbie over 40 years ago, was my daily driver for 40 years Now it is something I want to modify just for fun, no drag racing, just cruising, car cruise in and such Have got it down to 3700 lbs, it will be around 3200 lbs when finished It pleases me to make things light and modify everything I can except my daily drivers I have a red/with a slight orange tint 2001 3.8 Mustang with 78,000 miles on it, I get compliments from young Folks, it takes me a while to realize it is old to them Ricky.
That’s good info, I assume there’s a “special machine” ? Or does a shop add the bob weight? man I gotta go to google now
What they look like: These come in sets. You match up the ones you need to equal the rod/piston weights and they clamp to the crank.
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