Rotating assembly balancing after rod or piston change

[S4B5Quattro]

Hello all,

I was wondering if any tech experts or experienced builders could share their thoughts and knowledge on this topic. Especially any experience with the 2.7 liter engine.

If changing for example only rods (from stock to like either Pauter (lighter) or IE (heavier)) then what has been the actual measured difference when unbalanced (the first balancing machine reading before the crankshaft counterweight machining).

From what I´ve read, if the weight difference per rod is in the range of 10-30 grams,
was there alot of balancing work needed? Or was the result still within a certain limit?

I´m planning a build, but an access to a qualified machine shop for this purpose is difficult. So just wondering about others experience with this work

[CELison]

You’ll hear a lot of different theories on this. Some guys just drop rods in and are fine. Others balance the rotating assembly. Obviously balancing it is ideal, but some will say not neasessary when doing just rods. There are tons of drop in rod cars making a lot of power for years. If you plan to build your heads and rev it out, get it balanced for sure, but obviously engine harmonics are a factor at any rpm, not just up top. I personally did not get mine balanced, but if I were to do I over again, I would just for piece of mind. I’m sure a bunch of others will chime in.

[zillarob]

Just the crank!?!? I balanced the entire engine before putting it in.

http://yato.com/products/5/YT-55565

[redline380]

When I put my 1.8t together, I was rather drunk. Ebay rods, no plastiguage, no balancing, nothing. Damn thing runs better than most stock motors.

Obviously balancing should be done, but you can get away without it. Some people fail to remember there is a 8-30 pound large mass on the end of the crank to help smooth things out.

[quattEUro]

[Mille Bornes]

The sheet from having my rotating assembly balanced shows initial imbalance as 22g left, 25g right.

Left and right of what idk lol but there are some solid numbers, I guess. However, that's with 3L crank, 82.5mm Mahle pistons, and IE rods

[VR6Bomber]

Will you regret balancing it, no
Will you regret not balancing it, maybe

[CELison]

Will you regret balancing it, no
Will you regret not balancing it, maybe

Exactly.

[ElementR]

It's a gamble some are willing to take. I personally would not and have always had a shop properly balance the assembly on my builds. You will get all sorts of answers. It comes down to your level of risk tolerance in the end.

[VR6Bomber]

To add;
IIRC my last crank/flywheel balance cost was $170.
I mean if there is something that shouldn't be skimped on.

[blitz2190]

compared to the price of doing it a second time because maybe it does blow itself apart, its a no brainer, you'd be hard press to find a good machine shop that charges more than 200 to balance the assembly, mine was in the 150ish area (not exactly sure, balance, hone, rod hone check/fix, and block checked cost me $500)

[redline380]

Who here has had an engine come apart because they failed to balance it?

Just wondering...

[S4B5Quattro]

Just the crank!?!? I balanced the entire engine before putting it in.

http://yato.com/products/5/YT-55565

The whole assembly of course, using bob weights etc.

[S4B5Quattro]

The sheet from having my rotating assembly balanced shows initial imbalance as 22g left, 25g right.

Left and right of what idk lol but there are some solid numbers, I guess. However, that's with 3L crank, 82.5mm Mahle pistons, and IE rods

That is interesting, thanks for sharing.
Left and right meaning (crank counterweights).
From what I´ve heard (I´ve called couple of shops) is that they balance crank assemblys down to below 0,25 of a gram (with some less than 0,1g).
Now I just wonder what the factory limit is set at?

[CELison]

Who here has had an engine come apart because they failed to balance it?

Just wondering...

I think it's hard to determine the exact cause of engine failure sometimes. Person X cracks a main. That could be due to harmonics, peak tq, high cylinder pressure, crank walk, ect. It would be damn nice to know though!

[CJ_]

The whole assembly of course, using bob weights etc.

Did you click the link? Lol. It’s a high tech device that balances the whole motor, already assembled and everything. Some even use it with the transmission attached for better results

[S4B5Quattro]

Did you click the link? Lol. It’s a high tech device that balances the whole motor, already assembled and everything. Some even use it with the transmission attached for better results

Yes, a very sophisticated device indeed

[VR6Bomber]

Who here has had an engine come apart because they failed to balance it?

Just wondering...

Well that would be hard to prove,

However,
If someone building a motor isn't willing to spend 150-200 on balancing their nice new internals, they are also more likely to be skimping on other stuff too.
Essentially making their whole setup more prone to failure.

[csobel]

My crankshaft was -8.5g and 11g off respectivey. The weight difference between the stock pistons and rods and JE/RPM combo was less than 2 grams total. The RPM rods did need to be balanced end to end and sized properly but otherwise seem to be strong quality rods. The Fidanza flywheel was 24 grams off and the worst item of the lot was the Sachs pressure plate which was a whopping 46 grams off. I spent 1100 on the the entire block work of which only $200 was balancing... in this case it was well worth it at least for the pressure plate and flywheel. I wouldn’t say that 10 grams on the crank is insignificant either but compared to your average American V8 crank it’s miniscule... my guy said on average the American cranks tend to be 40-50g off.

If the engine was smooth to begin with and the new rotating assembly is very close in weight it would probably be fine. The question is—how close is all your stuff going to be? I didn’t want to skimp on anything with this build as I am hoping to put many miles on it.

Cheers,

Chris

[MacDaddy]

The guys that say you dont need to are the amatures who for one reason or another dont want to learn or feel they already know everything. You need to get it rebalanced if your changing your big end weight.

Why some engines fail and some dont, there is a plethora of reasons, improper torque procedure, cheap tools, bad tuning, could be anything.

Generally manufacturers of components write up good guides on proper installation (EG ARP’s catalog gives a great description of proper torquing of fasteners, carillo has a great write up on rods, etc) if you want to learn more.

[Scotty@Advanced]

Physics state that balancing the assembly is the proper route to take. Makes sure to exclude the flywheel, and balancer when having the rotating assembly balanced.

[VR6Bomber]

Makes sure to exclude the flywheel.

I've done 3 motors and each machine shop wanted the flywheel for balancing.
So I'm confused.

[jaychen]

I've done 3 motors and each machine shop wanted the flywheel for balancing.
So I'm confused.

flywheel should be balanced out of the box, in saying that, machine shops have always asked me for the flywheel too.

[Mille Bornes]

I had a fidanza balanced a few years ago. It was 14g off. For the current build, they balanced my ttv but I can't remember how far out it was.

[csobel]

flywheel should be balanced out of the box, in saying that, machine shops have always asked me for the flywheel too.

A good machine shop will balance the rotating assembly in several stages—first the crankshaft, then adding the balancer and flywheel assembly. This way if you change flywheels or clutches the rest of it will still be balanced. As it’s been shown above by various reports of flywheels out of balance they don’t always come balanced from the factory.

Chris

[travis_w]

Are balancers required if you have a balanced assembly?

Sent from my SM-N950U using Audizine mobile app

[okkim]

Yes. It is not a balancer, it’s a harmonic damper.

[Nollywood]

I have never had an engine apart this far, and not had it all balanced. And this is with retaining stock rods.

[blitz2190]

A good machine shop will balance the rotating assembly in several stages—first the crankshaft, then adding the balancer and flywheel assembly. This way if you change flywheels or clutches the rest of it will still be balanced. As it’s been shown above by various reports of flywheels out of balance they don’t always come balanced from the factory.

Chris

you mean a good shop will balance them separately, the only time they should be balanced together is when those parts are used to balance the crank, aka externally balanced engines. the rotating assembly should be balanced and then the flywheel by itself there is little they will be able to do with the stock harmonic dampener of this car as well.

[csobel]

Yes. It is not a balancer, it’s a harmonic damper.

Sorry my typo.

[csobel]

you mean a good shop will balance them separately, the only time they should be balanced together is when those parts are used to balance the crank, aka externally balanced engines. the rotating assembly should be balanced and then the flywheel by itself there is little they will be able to do with the stock harmonic dampener of this car as well.

Yes, that's what I meant. Sorry I had surgery yesterday and barely remember posting...