I ordered a stroker kit for a NOS 4 bolt standard bore block I have had for years. I had it balanced but when the kit came it they had ordered .030 pistons when I specifically ordered standard 4". The vendor said no problem they will send me the right pistons. My question is do I need to send the whole assembly back for rebalancing? The vendor said they will be alright as is.

sure they weigh the same as the 1st set

They should be lighter because they will be smaller.

have to rebalance the crank

have to way light to make a difference. 25gr. even at high rpm(8500) it doesn't show up

Are you saying .25 gram or 25 grams. If you are talking 25 grams, you need to get a good balancing machine because the one I use will show a change with as little as 1 gram. You must not get the balance job real close. I use a Stewart Warner. Nothing else gets them this close. Hines is a joke.

not talking a new bal. job. 25gr more or less after a bal. been done .

If you make a change on any component of the balance job it is not balanced anymore. It doesn't matter if it has been done or a new setup it will no longer be balanced if you change the setup 25 gr. I like my engine more than that to let it go with a 25 gram change in the bobweight and not try to correct it. I have too many compliments on my balance work to not do it the best you can. Been doing it since 1975 and have done more than a 1000 balance jobs.

I would check the pistons and see what they weigh. If they are within a few grams(most likely) it'll probably be fine. If they end up being a few grams heavy it'll be very easy to match weigh them to the weight of the other pistons.

From what I've seen when doing balancing is that you just never know about pistons. I had a 420 Windsor repair job in the shop a few weeks ago and it needed one piston to fix a persistent knock. Whoever had built the engine had a 4.040 bore on all 8 cylinders and pistons designed for a 4.040 bore in seven of those cylinders with one piston made for a 4.030, giving about .015 piston clearance, ooops! So I ordered a single and it was within 1 gram of the .030 piston I replaced! These were Mahle pistons.

I was told that there could be a change of up to 10gms and it would be alright. The new pistons they claim will be 4-6gms lighter. Should pursue this issue with them, after all it was their mistake.

i guess you never over or under balance , thats all you end up with- over or under. so you did 1000 jobs. most use 4 or 5 gr of oil, now how much oil is on the crank at any given time. with that, what happens when trays/ scapers and all that good stuff is used. ask this of a bal, shop that has done over 10K bal. jobs and is aircraft cert.

So your saying 4-6gms shouldn't matter?

The 4-5 grams of oil is what is figured that is inside the oil passages in the crank. The 427 FE steel crank is figured with 15 grams because the rod journal is hollow, I guess you have to do balance work to know that. If you are so much of a expert, how many balance jobs have you done personnaly? Don't criticize some one if you don't know yourself. It is according to the rpm range of the motor on what you do on over-under balance of the crank.

seems like the guy just likes to find ways to spin people up

forgot the Boss 429 , now how would i know that

Hey Rich ,4-6 grams lighter is real close, probably closer to 4.To me that's not a big deal. With engine machining i'm more concerned with human error or that's good enough, was your assemble balanced to zero? or did they leave acouple grams. Are your bob weights equal? these are questions to think about.If your gut is telling you to send it back,maybe you should send it back.

It was done at a very high profile shop with an excellent reputation. I am just looking for other opinions to make sure that they are not blowing me off and saying it's close enough for a street motor. What would they do if it were a high profile racer? Would they say the same thing? It should be OK.

I allow 3 grams for oil. I think you need to get your pistons and weigh them and then make a decision. Don't be surprised if they are within a few grams. I'd say if it's 5 grams or something don't worry about it. If they are heavier by a small amount it'll be easy to match them to the old pistons.

I'm not so sure how I feel on overbalancing theories really. Can anyone tell me why it's better? Or why some way of balancing is better at a given rpm? I've never used overbalancing on any V8 I've always used 50%.

One thing that's for certain is that when I put an engine on my dyno and fire it up I can generally tell if the balance job is good or not. A good one will run smooth, a not so good will shake the stand. Not all that much but it's noticeable.

How good are stock balance jobs? Best V8 I can think of was my Mercury Flat head which had less than 4 grams of imbalance at either end. Also, I had a stock assembly 429 that I checked that was within 5 grams, I'd say that's great. I've had 454 Chevy engines that have been 75 grams out at each end with all the stock stuff and that's a LOT! A 400 Chevy without a balancer is a few hundred grams out and that's so bad you don't want to run the engine.

Hope this helps some...

I would have it balanced again, but I would not send it back to the vendor to have it done. You were concerned enough to have requested it done in the first place. Get it done right. It's better than wondering after it blows up "maybe if I had balanced..."
If you were a "high profile" guy, they'd balance it again, and again...and again.
bop

I'd say that if you have the old pistons it'll be a simple matter to find a scale and then match weigh them if you know someone who mixes car paint their scales will measure down to 1/10 gram which is WAY closer than they need to be.

Either way it's really not a big deal to calculate a bob weight and rebalance the assembly. The tough part is already done and that's the match weighing of all the parts.

Carl, I do not try to spin people up, but Rich asked for help and the answer he got was if it was within 25 grams it would be OK. I sorry to step on toes but I don't want anyone to do my engine that will allow that much of out of balance. Rich if the pistons are close enough to match, run it, but if not, do the best thing and rebalance the setup. You will have peace of mind and know you have done the best for the motor. Sorry to piss anyone off but I do not want to see anyone tear up a engine, even if is not a Ford.

I think you misunderstood me that remark wasn't about you

25gr is what i found not to be a problem. not spin you up but that tells me you never tried it. i did and found no effect on a small block going to the bottle and changed wrist pins. also and even across all 8 pistons so it changed the balance by less that 1 1/2 percent. that leaves me to think you find and over/under bal, not acceptable. a lot do find that it is. I have my why of doing , you got yours just like you don't care for hines, while i know some that like them better than sw. ask a chevy guy what he thinks of Fords

Most people like a Hines because you can take a do-dah of the street and he can run the machine in 10 minutes. Did a check between Hines and Stewart Warner years ago and the Hines could not pickup what the SW could. So you get a balance job that is so so. If thats what you like, I glad you don't do my motor.

I spent years justifying hard bearing machines (hines) to the owner of company I ran, these machines rely on rigid structure and calibrated load cells to be accurate. They are preferred for repetitive work (same part over and over). They are easy to use and train on. These machines measure movement against zero as a reference. Because they dont need to run with and without "trial weights" they are faster in producing results (first run gives you corrections to apply). The hines machine cost a helluva lot more than an IRD or SW machine.

I spent years using soft bearing machines (IRD and SW), these machines are very capable but are more "art form" than hard bearing machines. A soft bearing machine spins rotor first without and then with a "trial weight" in each plane that gives vector and degree of change. This change is used to calculate correction.

Either one is capable of good work. Hines is probably more reliable for the masses (considering new guy doing work, etc.). The IRD/SW type machines are more prone to operator error (my opinion). I defer to no one on an IRD machine but dont hold a candle to my buddy Don on the SW balancer. I can use it but the damn thing will always have "voodoo" aspect to me.

I think a soft bearing machine may be capable of more accurate corrections. I also think that the operator is a big deal.

Read up a little on hard and soft bearing machines. Be at least able to think in terms of "G"'s, mils, or inches/second acceleration. These are the basic units of balancing. Talking to your shop's balancer about what units he works in will at least make him think he should do a good job for you.
Shane