Hot Rods Should I Get My V-8 Balanced?

I'm building an AMC 360 on a budget for endurance racing. It's a mild build with a mild hydraulic flat tappet, dual plane intake, 9:1 compression, etc. Max rpm will be 5,500.

The original crankshaft had a divot in it, so I swapped it to one I removed from my spare engine. It's .010/.010.

I am reusing the stock pistons, rods, and balancer.

It had a flexplate, but I'm running a manual, so I'm using a new flywheel.

The engine is externally balanced.

I have started ***embling the short block (have two pistons and rods in) but now I'm second-guessing my plans to proceed without getting it balanced.

Any thoughts? I've typically gotten stuff balanced, but since it's a stock bottom end and a budget build, I hadn't planned to do it.

FYI - my local machine shop will balance for $300. Will take about a week.

Thanks

 

If you’re using the same crankshaft, rods and piston’s you should be good to go. You’re also running in the same basic rpm range as the stock engine so I don’t see the need for a balance of the rotating ***embly.
It’s when you start replacing the pistons or rods with different weights or turn the crank changing the weight of the crank you need to balance everything…

 

With all the changes you are making, definitely "YES". I always balance any rebuild beyond a simple "ring 'n valve". My machinist has a deal with a guy at the balance shop to do it for $150 during a normal rebuild, so it's a no-brainer" for me.

 

I agree with @tubman. Especially since you changed out the crankshaft and you said it's for endurance racing. I realize you said you're doing a budget build, but to me spending the $300 upfront would save a lot of time, money, and headache down the road.

 

Balancing has proven to add longevity and more smoothness overall versus non balancing/spend the money and never wonder “What if I had not balanced???”

 

In a word, yes.
You build power with the heads, cam, carb etc, and build reliability by getting the bottom end right. For endurance racing you want the engine to last long, and the cheapest budget build is the one that lasts a long time - even if it was more expensive to build.

 

@Fordg***er1

 

Yes, it came from the factory somehat wonky and ran a long time that way. Engines are very forgiving, but they also reward getting it as right as possible.

From long experience, we now line hone, square deck and balance all our builds. The parts cost, R&R costs, cleaning, dis***embly, re***embly costs are the same whether the machine work was done right or not. As a percentage of the total, balancing is ant****e. Do it.

jack vines

 

Do you already have the flywheel and clutch? Is the flexplate/flywheel part of the external balance?
If you already have those and the crank has been changed along with going from flexplate to flywheel I'd consider it, but it's your money and late night thoughts.
I know the slippery slope of While It's Apart and stuff adds up. I don't know what another 'good running' 360 is in your area. So the question is, can you get another long block if this one dies in the middle of race season, how much and how long until it's swapped out?

 

I've never built a motor that I didn't balance.

To me it was a cheap way to make sure all the new pieces played nicely together at all rpm ranges. And I like the added benefit of a smoother idling/running motor and longer life out of the engine.

Did all my motors need it? Probably not but it was cheap piece of mind and I already had the motor apart and at the machine shop so it was worth it to me....

...

 

Well, it kinda depends on what you mean by "balanced".

Around here my experience is that you provide the shop 1 rod, 1 piston with rings & bearing and the crank and flywheel that are the pieces that are actually balanced.

If one hasn't balanced the pistons and rods themselves, the "balancing" is pretty suspect.

Today, I would balance the pistons and rods myself even on a ring and valve job (and I did on an off-topic flat four with scavenged useable pistons).

There are also some pics here on HAMB of balancing stands for home balancing of flywheels.

 

Balance it!

 

Scales are cheap that read down to grams or less, get one and check the rods and pistons just to give you an idea what you are working with. I've never seen an engine come apart for not balancing one with stock parts.

 

I was at a shop where the guy was in the process of “balancing”.
This was maybe 30+ years ago.
He had a fixture that only weighed the big ends. He matched that weight to the lightest rod.
Then he would do the pistons and call it “balanced”.

Fast forward years later, I watched a video of a real balancing. The guy did pretty much the same thing, but weighed and marked each rod ***embly, with rings and bearings for each, then clamped 8 weights on the journals and spun the crank, drilled here and filled there based on what the machine told him to do.

I mention all this just to make you aware of what can be done, or maybe should be done?

I’d ***ume for 300$ the second way I mentioned would be done, but may want to ask what/how the balancing is done ahead of time.

 

I already have the flywheel. The machine shop didn't ask for the clutch.

I have a spare 360 in the shop. The engine I'm building is technically the backup, but they guy who is supposed to be building the primary engine is an unknown commodity and I don't think he's started on the build yet.

thanks

 

The shop asked for 1 rod, 1 piston with rings and con rod bearing, crank, flywheel, and balancer.

I do not plan to weigh and grind all the rods and pistons so I can get them to the same weight. I just that's overkill for an engine that won't make north of 350 hp and won't see the far side of 5,500 rpm.

Thanks

 

I reload my rifle ammo, so I have some very accurate scales. But that's a rabbit hole that I don't want to head down at this point.

Thanks

 

At that price I’d consider it

I’ve never balanced a thing

but I just cruise em

 

They'll be doing something similar to the second option, but they only have one rod and piston.

Thanks

 

I dropped off parts with the machine shop to get balanced a few hours ago. They said it should be done by Thursday.

Thanks for all the input.

Scott

 

I always look at a decision with the thought of weighing.
"How does it feel later, after, when you think after you might have done better, but didn't"

 

The shop only wants one piston and rod ***embly, and I expect with the rings and rod bearing so they know the bobweight. The factory had matched them close prior to ***embly, so no need for them to have them all.
For those considering balancing their own rods keep in mind that the pin end and big ends are weighed separately, a rod is suspended from the pin end for example, using a stand and then only the big end is placed on the scale, then the big end suspended and the pin end weighed. The rod has both reciprocating and rotating weight.

 

Yes, the piston had rings and a rod bearing installed. Thanks

 

EVERY SINGLE TIME

 

Balance job is done, and I'm glad I did it. Shop called to say that the rotating ***embly was waaaaay out of balance. Would have shook my teeth out.

Thanks again for all the input.

 

MAY YOU TURN MANY SMOOTH LAPS!

 

AMC engines are a bit strange. I have had problems when changing the flywheel. Even with correct one from the dealer.
A friend (bit time AMC nut) insists they need to be balanced for any performance use. Especially when you mix parts.
I see you did do it. You will be glad you did.

 

I understand the decisions made. Here’s a series of articles by Ted Eaton of Eaton Balancing on engine balancing in general. Not real technical, nor marketing for his services, but good background.

https://www.eatonbalancing.com/category/balancing/