Hey guys, I can't find any threads on the balancing of my 400 I am rebuilding. My issue is that I wanted to balance my rotating assembly and my machine shop Reconditioned my rods already with ARP bolts and installed my Tim meyer/ KB Hypereutectic pistons without balancing. I don't have another flywheel so I told them I needed to do all of the balancing last when I get the flywheel from the engine already in my truck once I was a little further along with the other parts I need (cyl heads, cam etc) They said that would be fine because they could still balance it all later since it's externally balanced. Now they are saying they have to disassemble the rod/ pistons to balance everything and there is a high chance of breaking my pistons during disassembly/ reassembly... I really don't want to bust pistons and have to spend $400 on ANOTHER set of pistons. Does anyone know if the assembly can be balanced properly WITHOUT disassembly of the rod/piston?


To balance a assembly you measure the rod bearing, big end to get the rotating weight TIMES 2 (for two rods on the journal) + reciprocating weight rod small end, piston, wristpin, rings, oil @2grams dived by two, then multiply by # of pistons, which is 2 pistons per journal = Remove weight from heavier side (crank vs rod/piston)


In theory couldn't you just weight the "small" end with the pistons and rings and wristpin installed then weigh the "big end" to come up with your bob weight then find the dynamic balance on the crankshaft, harmonic balancer and flywheel; then proceed with the balancing without breaking stuff?


I'm in a major funk, first I was thinking well its stock turned .010/.010 crank, stock rods (w/arp bolts) it shouldn't be that far out of whack until I started thinking about the taller compression height AND .040" overbore... It's got to be heavier than stock slugs right?? Goin crazy, need help PLEASE.

 

It can not be balanced properly with the pistons mounted to the rods.

 

Ok, let me ask you this. Can you come up with a baseline weight and determine which pistons need to come off to balance? I don't want to break stuff. Lol

 

I myself am not a machinist, how ever i have had maybe 15-20 racing engines balanced over a 28 year racing career. Ive had any where from a 350 cu in. all the way up to my last engine was a 762cu in. and every single engine was balanced with the rods off the pistons, i even spent time with the shop that did the balancing work and watched, they told me it cant not be balanced properly with the pistons mounted, i did the same thing yrs ago like you did,THATS how i know.

 

Well S$%t... I guess bein young dumb and full of c%m still rings true, like my dad always says. Haha.


Thanks for your input partner, this really sucks. I didn't think my machine shop would fail to mention a pretty important aspect before embarking on reconditioning the rods and installing the pistons. lol


One good thing than came about it is the fact that I have already blueprinted all the main and rod bearings, piston to cyl wall clearances, cut ring end gaps and have checked my deck height before buying a new set of heads. (Kinda got screwed with using my stock heads also) hahaha


I used to build my dirtbike from front wheel to rear wheel including the engine by myself when I was growing up racing motocross with some help from dad but, mainly he would point me in the right direction and make me learn on my own. I never realized how much more there is to building a thumper V8 from top to bottom. With age comes wisdom.. And the trials and tribulations of building the first engine from ground up. Haha


Looks like I'm gonna have to bite the bullet on this one and hopefully they don't break any pistons..

 

Why don't you ask Tim????? Seriously, what do the other forum participants know better than Tim Meyer about pistons he designed and sells?

You can get all sorts of opinions here.

I'm betting the pistons are either the same weight or else a little lighter.

I'd run the doggone thing the way it is.

Yes your machinist COULD weigh the small end with piston pin and rings. He could weigh every one. It'd be a pain and may not be that accurate because of the friction of the pin, when weighing the big end. He might refuse saying it'd be too inaccurate and I couldn't blame him.

Part of balancing is weight matching. So what happens if the pin ends differ in weight? Pretty hard to get at the balancing pad on the pin end of the rod when it's in the piston. And pretty hard to drill the pin pads on the piston with that connecting rod flopping around.

So the best way would be to press pistons off the rods, balance and press them back on. I used to pay $7 for each piston so that'd be $112 extra work, plus the $200+ balancing. Plus disassembly and cleaning everything, it adds up. Every time you press on or off a piston there is a chance to break it, and rings can break on disassembly or reassembly. I can see this costing way more than $400.

The commonly used formula for balancing a V8 isn't derived by any mathematical method, it was developed by experience. Race engine builders sometimes on purpose make the piston end lighter or heavier than the formula would suggest, it's called underbalancing or overbalancing. You don't have a race engine and I'd suggest that anything less than 1/2 ounce will probably not be noticeable in daily use.

I know a guy who substituted pistons in a V8 that each were 84 grams lighter and didn't change anything else. He bracket raced that engine for years with no noticeable problems.

R.

 

In fact I have been calling Tim with questions, and he has answered a few of them. Now I've been trying to get ahold of him through email the last couple weeks and had no reply yet..


Only reason I was asking about weighing the piston end on the rod is to find out just how out of balance they may be, if at all then remove the necessary pistons if it cannot be balanced at the crank, dampener and flywheel to keep the bottom end together but, I think I'm going to end up biting the bullet and just having the shop take them off and do a complete balancing and HOPE they don't break.


My want for balancing is longevity and reliability. I plan to and will spin the engine to 6000RPM max and while that may sound miniscule, I think we all know that an imbalance even at 2000 RPM can throw a rod through the block so I don't want to be so far off from the stock 400 setup that my counter weights, dampener and flywheel cant compensate thus reducing reliability and longevity. I don't want to be off roading in the middle of nowhere bouncing off the rev limiter and be freaking wondering if it will hold up. If it blows after doing everything right etc at that point it's out of my hand then at least I can say I did't just slap it together and crossed fingers.

 

Below is a balance sheet used.
Each part needed to be weighed and matched for weight.
Then a bob weight is assembled to simulate the weight.

If you told the shop you wanted it balanced, they really should be taking it apart to balance it correctly.

 

Awesome, thank you!
I've embraced the suck, they were supposed to balance my rods/ pistons after reconditioning them the first time but, apparently they didn't get that memo... So it didn't happen.
I already called up my shop Aimes Machine here in Reno and I am going to take my rods/pistons and matched rings to them. They're going to remove my pistons from the rods measure and balance them reinstall the pistons and record the weights. I still need a flywheel (Summit Racing wants $600, so I am trying to find a used one to turn and put back into service) so when I get that I will be taking my crank, flywheel and dampener to them to balance according to the previous weights.


Pain in the butt...

 

I dont see where anybody said they knew more than Tim, he asked a ? and i myself answered the best i could, i knew i was correct cause if i didnt i wouldnt have said anything, plus if you read above you will see that i was. Have a nice day.

 

Nothing against anyone including you, Bud. I have been on boards for years and one of my chief complaints is people who ask questions they should be asking the manufacturer or dealer or supplier. What they get on boards is mostly "rules of thumb", "what worked for me", "I heard" or "scare you to death and insist on the most conservative approach".

No way is an imbalance going to cause a rod to be thrown at 2000 rpm. It just won't happen. You may experience engine roughness, and if the flywheel is the wrong one you will experience some real vibration. What this would most affect is the main bearings and possibly the life of the crank.

Sounds like you're going to get it done right, and that's okay. I was suggesting that the allowable limits for balancing may be quite a bit looser than some people think. It's easy to say has to be within a half a gram, but the real question is, how many grams off can it be before it affects anything in a meaningful way?

R.

 

You're hitting the nail on the head. That's basically where I was going with this and will my pistons be so heavy that it will cause major issues and catastrophic failure due to such an imbalance compared to stock. I didn't change the stroke just taller and wider pistons. Either way its not the stock setup from the factory. I was skating around the issue of having to pull the pistons and possibly break my brand new pistons. I'm just gonna bite the bullet, having that question/ concern in the back of my head will drive me nuts and I won't have confidence in my build without doing so... I'm way too **** lol I'm taking my rods and pistons to the shop today in fact.

 

Your assumption that the pistons will weigh more is totally incorrect. Most high or higher performance pistons are lighter in weight than the stock pistons why are replacing.

That's why somewhere in my post I said you need to ask Tim Meyer how much the KB pistons weigh.

Then you find the weight of a stock replacement piston and go from there.

R.

 

Really? I didn't know that. I was just thinking since they are taller compression height and .040 over they would weigh more than stock. I'll have to look into that, interesting.

 

So the difference between the two weights (piston w/ wristpin) is,
OEM (federal mogul)- 771g
Tim's measurements above- 689g that's an 82 gram difference, that's spectacular lol