Rotating assy balance

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I doubt there is a gram of difference in each of those speed pro pistons hes got, but I could be wrong. To the OP, I would get a T gage and a micrometer, torque the rod caps to spec and then measure the big end hole diameters, and compare to factory specs for that engine with those rods. Do it with all the caps on the original rods, write down your measurements, then put them how your machinest said to put them and measure them again. Note the differences in diameters. Ultimately the onus is on you to make sure its all 100% correct on assembly including making sure ALL the oil passages in the block and crank are clean and blown out. Typically if the end user assembles it there is no guarantee or warranty. Had he assembled it, and it blew up, it would be his responsibility to make it right. Also ditto on the weld dingleberrys on the crankshaft.
 
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I think my dilemma is all the videos and such I've watched, the components all are measured and then weighted to the lightest piece, so the bob weights are the same. None of the components in my assy weigh the same. Plus, the machinist only gave me new positions for four caps, what about the other four?
I appreciate everyone giving advice but y'all ain't making me feel any better. Just sayin'.
I'm gonna have to go back to machinist on Monday, he got some 'splainin' to do.
 
Tays340 said:
I don't have a pic of the piston rod assy. The rod end has been heated to get the wrist pin in. I don't think I can easily press them out, but, naive.
The big end has been machined so probably align bored. Looking at the numbers more, maybe he is trying to get each journal weight close. Still, his sharpie only tells me where 4 of the caps go. Not a happy camper.
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Why would you need to remove the pistons at this point?
 
Tays340 said:
I think my dilemma is all the videos and such I've watched, the components all are measured and then weighted to the lightest piece, so the bob weights are the same. None of the components in my assy weigh the same. Plus, the machinist only gave me new positions for four caps, what about the other four?
I appreciate everyone giving advice but y'all ain't making me feel any better. Just sayin'.
I'm gonna have to go back to machinist on Monday, he got some 'splainin' to do.
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Don’t confuse Bob weight with what your rods weigh. That’s only part of it.
 
yellow rose said:
Don’t confuse Bob weight with what your rods weigh. That’s only part of it.
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After watching several videos on the process, seeing that each end of the rod is weighed and then belt sanded if needed to get within tolerance, same with wrist pins and pistons if needed so each assy is within x grams of each other, then do the math build the bob weight etc which is why I took it to a professional(?) to begin with. But, just looking at the caps for #5 & #6 there is no way those two rod ends weighed within tolerance, and they're on the same journal.
I've got another bottom end. I'm feeling I need to start over. I've got too much invested in my Mopar to have the bottom end malfunction and I ain't feeling good about this.
 
Tays340 said:
After watching several videos on the process, seeing that each end of the rod is weighed and then belt sanded if needed to get within tolerance, same with wrist pins and pistons if needed so each assy is within x grams of each other, then do the math build the bob weight etc which is why I took it to a professional(?) to begin with. But, just looking at the caps for #5 & #6 there is no way those two rod ends weighed within tolerance, and they're on the same journal.
I've got another bottom end. I'm feeling I need to start over. I've got too much invested in my Mopar to have the bottom end malfunction and I ain't feeling good about this.
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Take your other bottom end to somebody else.
 
Tays340 said:
After watching several videos on the process, seeing that each end of the rod is weighed and then belt sanded if needed to get within tolerance, same with wrist pins and pistons if needed so each assy is within x grams of each other, then do the math build the bob weight etc which is why I took it to a professional(?) to begin with. But, just looking at the caps for #5 & #6 there is no way those two rod ends weighed within tolerance, and they're on the same journal.
I've got another bottom end. I'm feeling I need to start over. I've got too much invested in my Mopar to have the bottom end malfunction and I ain't feeling good about this.
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I had to go back and look at your picture. I’m ASSuming it’s 1-8 from left to right. If that’s correct then you are saying the number 5 cap is heavier than the number 6 cap by looks? It very well may be.

Again, I’m saying you don’t weigh the caps separately from the rod. They are weighed together by the end.

Just an FYI so you know. Chrysler had the most piss poor balance tolerance in the business. I’ve seen rods that were 30 grams (could have been a bit more than that) from the heaviest to the lightest big end. All on the same crank. They used what I’ve been told was “mass balance” and I’ve yet to get a definitive answer to what that even is. I know they didn’t shake but that doesn’t mean they were balanced to a reasonable amount.

The only way you will ever know if the shop didn’t balance the crank correctly is to knock the pistons off the rods (a giant pain in the *** if you don’t have the right tool and fixtures and if you don’t the possibility of breaking a piston is much higher than actually getting one of without breaking it) and measure each end on a scale. And then you have to weigh all the pieces, make up the Bob weights and spin the crank to see where it’s at. You’d literally be paying for a second balance job.

Looking at them with your eye or weighing them on a scale means nothing. Is there any thing other than visually looking at the stuff that makes you think they didn’t get it right? I’m asking because I still don’t know why anyone would tell you swap caps from one rod to another one. That makes no sense.

If you need to verify something, take the rods and pistons to a different shop and have them remove the piston and end weigh each rod and let you see how close they are. Even if there is a 5 gram spread between the rods it won’t make a pinch of **** difference.
 
Tays340 said:
After watching several videos on the process, seeing that each end of the rod is weighed and then belt sanded if needed to get within tolerance, same with wrist pins and pistons if needed so each assy is within x grams of each other, then do the math build the bob weight etc which is why I took it to a professional(?) to begin with. But, just looking at the caps for #5 & #6 there is no way those two rod ends weighed within tolerance, and they're on the same journal.
I've got another bottom end. I'm feeling I need to start over. I've got too much invested in my Mopar to have the bottom end malfunction and I ain't feeling good about this.
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Imo you are way over thinking this! Take that bottom end back to the machinist have him figure out what cap goes where and run the thing. There is a ton of very knowledgeable engine builders on here telling you that the balance is acceptable put the correct cap with the correct rod and put the thing together. Iv been there before and stressed over the little stuff but trust what these guys are telling you your balance is fine the caps being mismatched is not! There is no need to remove the pistons from the rods or start over. Just figure out what cap goes where.
 
yellow rose said:
I had to go back and look at your picture. I’m ASSuming it’s 1-8 from left to right. If that’s correct then you are saying the number 5 cap is heavier than the number 6 cap by looks? It very well may be.

Again, I’m saying you don’t weigh the caps separately from the rod. They are weighed together by the end.

Just an FYI so you know. Chrysler had the most piss poor balance tolerance in the business. I’ve seen rods that were 30 grams (could have been a bit more than that) from the heaviest to the lightest big end. All on the same crank. They used what I’ve been told was “mass balance” and I’ve yet to get a definitive answer to what that even is. I know they didn’t shake but that doesn’t mean they were balanced to a reasonable amount.

The only way you will ever know if the shop didn’t balance the crank correctly is to knock the pistons off the rods (a giant pain in the *** if you don’t have the right tool and fixtures and if you don’t the possibility of breaking a piston is much higher than actually getting one of without breaking it) and measure each end on a scale. And then you have to weigh all the pieces, make up the Bob weights and spin the crank to see where it’s at. You’d literally be paying for a second balance job.

Looking at them with your eye or weighing them on a scale means nothing. Is there any thing other than visually looking at the stuff that makes you think they didn’t get it right? I’m asking because I still don’t know why anyone would tell you swap caps from one rod to another one. That makes no sense.

If you need to verify something, take the rods and pistons to a different shop and have them remove the piston and end weigh each rod and let you see how close they are. Even if there is a 5 gram spread between the rods it won’t make a pinch of **** difference.
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I admit I have no clue.
The #6 cap is virtually unmolested while #5 cap weighs 20 grams less. Yes, I measured it 3 times. I just don't see how those two rod ends came close to weighing the same. I would feel better if all the caps were sharpied, ...maybe. I was expecting some caps to be worked but... If I put the assy's together the way I stamped them the weights are within 8 grams lo-hi. What's that? 3 post-it notes. As far as swapping the caps around, eesh. Again, he only marked four.
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Maybe this is why the old man acted like he wanted to hire me after asking me to explain how to balance a rotating assy.
 
Tays340 said:
I admit I have no clue.
The #6 cap is virtually unmolested while #5 cap weighs 20 grams less. Yes, I measured it 3 times. I just don't see how those two rod ends came close to weighing the same. I would feel better if all the caps were sharpied, ...maybe. I was expecting some caps to be worked but... If I put the assy's together the way I stamped them the weights are within 8 grams lo-hi. What's that? 3 post-it notes. As far as swapping the caps around, eesh. Again, he only marked four. View attachment 1715747937 View attachment 1715747938 View attachment 1715747939 View attachment 1715747940 View attachment 1715747941 View attachment 1715747942

Maybe this is why the old man acted like he wanted to hire me after asking me to explain how to balance a rotating assy.
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I’m saying that is perfectly normal. You just can not weigh that stuff apart like you are. It’s the visual thing that’s got you going. That’s 100% NORMAL. On some of the balance jobs I’ve done I had to use core rod I had laying around to get a set I could balance.

Put the caps back on the rods they came off of, put it together and send it.

If you can’t sleep with that option, then you have to do what I said above and take the rods off the pistons, weigh all that stuff correctly and check the crank. You’ll be doing another balance job essentially.
 
yellow rose said:
Just an FYI so you know. Chrysler had the most piss poor balance tolerance in the business. I’ve seen rods that were 30 grams (could have been a bit more than that) from the heaviest to the lightest big end. All on the same crank. They used what I’ve been told was “mass balance” and I’ve yet to get a definitive answer to what that even is. I know they didn’t shake but that doesn’t mean they were balanced to a reasonable amount.
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I think you answered your own question here.
 
I built a Pontiac V8 engine a couple of years back, forged pistons, SpeedPro or Sealed Power, not sure which one, but one of the two.
Made in India.....
 
bob mCcarty said:
disagre,


-disagree , thats terrible spread on the balance
I `d be trying to get it done right some way --------and dam sure aint gonna switch rod caps around !
My 505 kit was race balanced by hughs engines , on a solid motor plate , no rubber bushings , u cant feel it running !
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I'm talking about factory balance on our old engines... I've seen 20-30 grams difference just from rod to rod. New OE stuff is much closer.
 
BTW... to keep things in perspective a regular small paper clip weighs one gram.
 
SpeedPro is Sealed Power. Their pistons are forged in India and finished in Mexico. At least that is what I have heard. The last three sets I used in Mopar 360s all weigh dame near the same. Heavy as hell but still had no problems with any of them. Nice replacement pistons.
 
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Hellrats said:
SpeedPro is Sealed Power. Their pistons are forged in India and finished in Mexico. At least that is what I have heard. The last three sets I used in Mopar 360s all weight dame near the same. Heavy as hell but still had no problems with any of them. Nice replacement pistons.
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Speed pro is sealed power and are made by federal mogul.
 
Tays340 said:
When I pulled the engine apart I stamped each rod and cap.
I am so on a budget here, New rods? They said the pistons would be destroyed if had to be changed. He did weld up the crank some and add a hole. When I put #8 cap on #5 rod it binds before it seats. I don't like it.
I thought the whole purpose of balancing was to get all the components to weigh the same before you made bob weights to balance the crank. This looks like it would shake apart and kill every bearing on cam break-in. But i'm naive. Still 13 grams between #3 journal and #4.
I guess I'm headed back to the machinist for some explanation, but, in my opinion, this is not right.View attachment 1715747234 View attachment 1715747235 View attachment 1715747236
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on the first pic , that welded in weight is sure to let go one day not the right way to put in a weight , had a buddy have a slug of mallory let go on a 440 destroyed a piston and a cylinder . why not just buy a complete kit and be done with it . and find a new machinest while your at it
 
So the parts were balanced and numbered, and you decided to explore, and now it's all **** work? No offense but step one should have been asking the machinist (with visual aids) to explain what he did for you. Nothing looks wrong to me in the work. Everything looks wrong in your approach to "checking" his work.
 
@Tays340 are you sure that's what you heard the machinist say? OR, did he tell you to "pair up" piston/rod combo 1 with 4, 3 with 6, 5 with 8 and 7 with 2. Combining heavist and lightest "pairs" and progessively matching up the most closest combos available. 2605g, 2593g, 2606g and 2595g. Still a 13g spread but a crap load better than factory. Here's some 383's fresh outa the block, with Chryslers crappy tolarances. Total weight spread of 850.0 to 817.2
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That may have been what the machinest was trying to explain to the OP, but may have not explained it well. Or maybe the information conveyed by the machinest was not fully understood, or possibly a combination of the 2. Not everybody is good with verbalization skills. Pair a certain rod with its respective cap with a certain rod on the same journal based on combined weight, and crank counterweight.
 
Here the problem lies is the caps may offset to either side, and dressing the sides of the rod, then the other side of the cap, may increase side clearance beyond acceptable tolerances.

You can usually match the cap to rod by scrutinizing/matching the hone marks . Done it a few times.
Prefer crank weight in side of counterweight, so it's "captured" , and can't fly outta the end of the counterweight on a missed shift over-rev. ( Ask me how I know ) .

I wouldn't use those rods or machinist .
 
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Hellrats said:
SpeedPro is Sealed Power. Their pistons are forged in India and finished in Mexico. At least that is what I have heard. The last three sets I used in Mopar 360s all weigh dame near the same. Heavy as hell but still had no problems with any of them. Nice replacement pistons.
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yeah they are heavy old school pistons . there are a lot of good pistons out there today that are lighter and stronger , once you're spending money do it right once
 
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