Mitsubishi 3000GT & Dodge Stealth Forum banner
1 - 20 of 25 Posts

·
Minty
Joined
·
3,295 Posts
Discussion Starter · #1 ·
Forgive my ignorance, but I am curious.

Hypothetical situation #1.

I buy a block, have it bored/honed, buy some brand new forged pistons/rods, and buy a brand new forged crank from mitsu.

As long as the pistons/wrist pins/rods are very close to the same weight assembled, does this engine need to be balanced prior to full assembly/run?

The reason I ask is I have never seen the answer, anywhere. I here some people saying any and all builds MUST be balanced, where others never even mention it.

My current understanding is that if I purchased these parts, and they are all the same weight, that the crank itself should be counterweighted correctly from the factory, and I should be able to just assemble it and run with it.

Please do correct me if I am wrong. Are factory engines actually individually balanced? I would assume not, but I am the ignorant one here.
 

·
Quit while you're ahea
Joined
·
7,917 Posts
But why, like what benefit does it have if everything is so close?
Less vibration = Your engine will last longer, possibly handle more power.

It doesn't cost that much to do so with all the new parts it's a drop in the bucket.
 

·
Minty
Joined
·
3,295 Posts
Discussion Starter · #6 ·
Less vibration = Your engine will last longer, possibly handle more power.

It doesn't cost that much to do so with all the new parts it's a drop in the bucket.
Do you do it as an assembly? Or do you just do rods and crank separate?
 

·
'96 VR4
Joined
·
3,290 Posts
Less vibration = Your engine will last longer, possibly handle more power.

It doesn't cost that much to do so with all the new parts it's a drop in the bucket.
+1. What GL said. Balancing will cost about $300, and the entire assembly is balanced together - including the harmonic balancer and flywheel if the shop is good. That $300 is pretty small compared to what you're talking:

- $800, forged crank
- $700, forged pistons
- $800, forged rods

Those are minimums, you can feel free to spend more there. :p Now how about:

- $120, block cleaned/magnafluxed
- $200, cylinders bored/honed
- $200, new bearings
- $350, OEM upper/lower gasket kit
- $50, new oil squirters
- $50, new freeze plugs and oil gallery plugs
- $250, heads cleaned/pressure tested/resurfaced
- $100, valve job
- $350, new OEM oil pump, water pump

That's minimum, and I'm sure I'm forgetting some things anyway. In point of fact, if you rebuild an engine you're going to spend a hell of a lot more when you factor in other things like new timing components, pulleys, hoses, nuts, bolts and other miscellaneous stuff that it's a good time to replace. So, no, you don't have to balance if everything is new and from reliable vendors. But when you're building a forced induction high performance engine - and even stock, our engines are high performance - it is a sensible thing to do.
 
  • Like
Reactions: green-lantern

·
Quit while you're ahea
Joined
·
7,917 Posts
+1. What GL said. Balancing will cost about $300, and the entire assembly is balanced together - including the harmonic balancer and flywheel if the shop is good. That $300 is pretty small compared to what you're talking:

- $800, forged crank
- $700, forged pistons
- $800, forged rods

Those are minimums, you can feel free to spend more there. :p Now how about:

- $120, block cleaned/magnafluxed
- $200, cylinders bored/honed
- $200, new bearings
- $350, OEM upper/lower gasket kit
- $50, new oil squirters
- $50, new freeze plugs and oil gallery plugs
- $250, heads cleaned/pressure tested/resurfaced
- $100, valve job
- $350, new OEM oil pump, water pump

That's minimum, and I'm sure I'm forgetting some things anyway. In point of fact, if you rebuild an engine you're going to spend a hell of a lot more when you factor in other things like new timing components, pulleys, hoses, nuts, bolts and other miscellaneous stuff that it's a good time to replace. So, no, you don't have to balance if everything is new and from reliable vendors. But when you're building a forced induction high performance engine - and even stock, our engines are high performance - it is a sensible thing to do.
Nice breakdown :)

I try to keep all that money I spent out of my mind :lol3:
 

·
Minty
Joined
·
3,295 Posts
Discussion Starter · #9 ·
So I would take my crank in with rods and pistons and all, with my harmonic dampener installed and flywheel and have them balance it like that?

Interesting.. I figured the most youd do was an internal balance, not external too
 

·
Minty
Joined
·
3,295 Posts
Discussion Starter · #10 ·

·
'96 VR4
Joined
·
3,290 Posts
Nice breakdown :)

I try to keep all that money I spent out of my mind :lol3:
Yeah, guess what I did this spring? Just don't show it to my wife!


So I would take my crank in with rods and pistons and all, with my harmonic dampener installed and flywheel and have them balance it like that?

Interesting.. I figured the most youd do was an internal balance, not external too
Actually, our engines are "internally" balanced. That is, our crank and pistons are nominally in balance by themselves. Some cars do have balance weights on the flywheel - those really are externally balanced systems, because the crank and pistons, by themselves, are not balanced.

Still, a good shop will take all the rotating masses and balance it as a system. The point, after all, is to reduce the forces that generated by the unbalance. So, ideally, all the rotating pieces are included.


So then, curiousity is lurking again,

the 3SX Forged Shortblock - NEW Block + NEW Crank, 3SX Rods, Ross Pistons*-*Mitsubishi 3000GT*/*Dodge Stealth Parts
forged shortblock, appears never to be balanced, this would be considered un-ideal? Perhaps less longevity?

Factory shortblocks, what do they go thru?
IDK. I would guess, though, that the individual parts all meet a production standard, and that after they're put together you get what you get. Any rotating system is going to have a tolerance on the amount of imbalance allowed, at all planned operating speeds. Generally, in a mass produced system like a car engine, the individual pieces are all going to be produced to a standard that results in the final assembly meeting whatever the standard is for the system as a whole.

On one of a kind systems, you have to check that the final assembly really does meet your standard. I once helped to spin balance a satellite and it's orbital injection rocket... together they weighed about a ton and stood 15 feet high. That was actually done with the satellite and rocket stage in one building, and the controls and instrumentation (with CCTV so you could see what was happening) in a concrete blockhouse a few hundred feet away. Because, you know, if something goes wrong you don't want to be sitting there next to it! But on mass produced systems, the prototype and initial production stages usually iron those issues out.

And, then, in the final analysis, the engine dropped into the car at Nagoya was operating at well under it's maximum possible output, as witness we can run stock blocks, rods and pistons with pretty good results up to nearly twice the designed power output (crank, not wheel). So, taking all that into account, the assemblies leave the factory "good enough."

It's still a good idea to spend the cash when you're doing a custom build; if all we wanted was average performance, we wouldn't be here. And we'd have a hell of a lot more money!
 

·
Minty
Joined
·
3,295 Posts
Discussion Starter · #12 ·
Yeah, guess what I did this spring? Just don't show it to my wife!




Actually, our engines are "internally" balanced. That is, our crank and pistons are nominally in balance by themselves. Some cars do have balance weights on the flywheel - those really are externally balanced systems, because the crank and pistons, by themselves, are not balanced.

Still, a good shop will take all the rotating masses and balance it as a system. The point, after all, is to reduce the forces that generated by the unbalance. So, ideally, all the rotating pieces are included.




IDK. I would guess, though, that the individual parts all meet a production standard, and that after they're put together you get what you get. Any rotating system is going to have a tolerance on the amount of imbalance allowed, at all planned operating speeds. Generally, in a mass produced system like a car engine, the individual pieces are all going to be produced to a standard that results in the final assembly meeting whatever the standard is for the system as a whole.

On one of a kind systems, you have to check that the final assembly really does meet your standard. I once helped to spin balance a satellite and it's orbital injection rocket... together they weighed about a ton and stood 15 feet high. That was actually done with the satellite and rocket stage in one building, and the controls and instrumentation (with CCTV so you could see what was happening) in a concrete blockhouse a few hundred feet away. Because, you know, if something goes wrong you don't want to be sitting there next to it! But on mass produced systems, the prototype and initial production stages usually iron those issues out.

And, then, in the final analysis, the engine dropped into the car at Nagoya was operating at well under it's maximum possible output, as witness we can run stock blocks, rods and pistons with pretty good results up to nearly twice the designed power output (crank, not wheel). So, taking all that into account, the assemblies leave the factory "good enough."

It's still a good idea to spend the cash when you're doing a custom build; if all we wanted was average performance, we wouldn't be here. And we'd have a hell of a lot more money!
Well that was a very informative post.

Thanks a lot for the information, I'm also interested in others opinions!

I definitely have a better grasp than before.
 

·
Registered
Joined
·
1,552 Posts
You will also need to take a set of rod bearing shells and the piston rings and wrist pins for a full balance.

if you are using all OE Mitsu parts you can just bolt the thing together and run it.

with aftermarket pistons and rods you bob weight totals will be far different.

my current 3.1 with Mahle pistons and Brian Crower rods was around 780 grams lighter than stock, so a re balance was mandatory.

On my new engine I got new damper pulley and I had the pulley "zeroed" and the flywheel the same. As stated earlier the engine is internally balanced, so if the outside parts are balanced individually they can be replaced without effecting the engine itself.
 

·
Lawn Ornament Since '08
Joined
·
2,670 Posts
What about the pampena 3.1L's. I'm looking into getting one of those made for a 16g set up. Would it be smart that after I get the engine back and put on the flywheel (probably stock, Better for drag) and the harmonic balancer to a good shop to balance it? Or should I do that If I go LW Flywheel and balancer?
 

·
Registered
Joined
·
4,515 Posts
The reason for dynamically balancing a rebuild/upgrade is because the component weights can be quite far off from stock.

For instance, the counterweights on the stock crank are built to compensate the mass of stock rods, pistons, wristpins, bearings etc. If you get forged pistons, they'll most likely be lighter. Many forged rods are lighter than stock but there are a couple (IIRC, Pauter) that are heavier than stock.

When you change the weights of the components, you need to change the crank counterweights to match or the crank will be prone to oscillating/vibrating.

A proper dynamic balancing balances EVERYTHING that is attached to the crankshaft and spinning, i.e. the crank, the bearings, rods, pistons, wristpins, wristpin locks, piston rings, flywheel and harmonic damper.

The shop I had do my balancing also blueprinted and matched the pistons and end-to-end balanced the rods to the lightest example (down to some fraction of a gram IIRC. To clarify, the Ross pistons and Crower rods weren't exacting enough for their specs).

Now keep in mind though, that the flywheel and clutch assembly from a good company should be balanced already (they told me my RPS c/c was properly balanced when I sent it in along with all the other parts). The harmonic damper should also be decently balanced, but I guess you never know.


Max
 

·
Ninja Performance
Joined
·
42,336 Posts
While it is a good idea, it is not 100% needed to have a good running engine. My setups are never balanced due to cost and never seeing damage caused by not balancing. Not discounting it as it can help and is good practice in theory. But if parts are well balanced already the rotating assembly won't be way off. Unless you are going to rev to 10K I wouldn't worry about it too much. Get it done if it's in the budget but don't lose sleep over not doing it.

Keep in mind that the clutch is part of the balance and if the clutch is changed out after he engine that was balanced you have lost the balance.

-Chris
 

·
Stealth Like A Ninja
Joined
·
3,267 Posts
So I would take my crank in with rods and pistons and all, with my harmonic dampener installed and flywheel and have them balance it like that?

Interesting.. I figured the most youd do was an internal balance, not external too
I would assume just interals as that is how our engines are balanced from factory. they arent externally balanced. if everything added to the outside is balanced already then its just the internal stuff that matters.
 

·
Minty
Joined
·
3,295 Posts
Discussion Starter · #19 ·
While it is a good idea, it is not 100% needed to have a good running engine. My setups are never balanced due to cost and never seeing damage caused by not balancing. Not discounting it as it can help and is good practice in theory. But if parts are well balanced already the rotating assembly won't be way off. Unless you are going to rev to 10K I wouldn't worry about it too much. Get it done if it's in the budget but don't lose sleep over not doing it.

Keep in mind that the clutch is part of the balance and if the clutch is changed out after he engine that was balanced you have lost the balance.

-Chris

So when you have put together your incredibly high hp builds (great than 8xx awhp) you have not actually machine balanced your engine?

You just made sure that the piston/rod/etc assemblies were close? or what.

This is interesting
 

·
Ninja Performance
Joined
·
42,336 Posts
So when you have put together your incredibly high hp builds (great than 8xx awhp) you have not actually machine balanced your engine?

You just made sure that the piston/rod/etc assemblies were close? or what.

This is interesting
None of the engines I have built for my personal car have been balanced. That was my choice to save that money and test parts. I have never seen unbalance damage due to not balancing. I do make sure rods are VERY close on small and big ends, and the pistons are close. Could it help? sure. But I have not done it on my car.

I did it for T4 on 1 or 2 builds early on. But after that did not.

Then again, I don't put a lot of miles on either. And I use a stock flywheel and OEM dampener.

-Chris
 
1 - 20 of 25 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top