Importance of balancing for a limited use engine?

[bugnut68]

what's the verdict on balancing the internal components on a STF or extremely limited use engine?  I'm talking about an engine that won't even be driven on the highway let along to the outskirts of town... I've got the basics to build a very tame 1776 and am debating whether to balance the components if I build it as is.

[louisb]

Is it a performance engine or just an engine to push your car around? If you don't care about performance and just want a pusher it is not necessary. VW engines were not balanced from the factory.

--louis

[Jim Ratto]

Personally, I'd do the flywheel and clutch. At least...

then next in hierarchy would be rods and pistons

I re did my Vanagon waterboxer motor @ 105K because the jacket gaskets were seeping, and while in there I slapped in a set of new cyl and pistons. Didn't balance them. Let me tell you... even sitting way up in front of that Vanagon... I felt the difference. At high 3000rpm region, I sensed the vibration. Shortly after that I had a few issues that came up, that I felt stemmed from not balancing them
1. alternator bracket and bolt broke
2. plastic H-shaped water manifold in front of cyl 3 broke (common)
3. coil wire eroded and fell out of coil... I think it worked itself free, and was arcing, killing the wire.

then again, I drove that Vanagon 10K a month.

[bugnut68]

It's basically an engine to keep the car mobile whilst I start building up the existing engine... and I live in a town of 2,500, so I definitely won't be wracking up the miles on it.   I was just curious.  I'm still figuring out where I"m at in terms of building up a bigger beast, so I think I'll keep balancing on the table as a possibility, if at least the clutch and flywheel only.

[SlingShot]

Slap it Together !!!
My 1600 STFM didn't get any of its parts balanced as a complete assembly , and it see's a lot of highway miles and even revs up to 6K fairly quick with no problems.
I would suggest using a counter weighted crank if you got one, better main bearing life.  

[John Maher]

Is it a performance engine or just an engine to push your car around? If you don't care about performance and just want a pusher it is not necessary. VW engines were not balanced from the factory.

--louis

VW engines WERE balanced from the factory!
Maybe not to high spec race tolerance but pistons and rods were within 5gms of eachother- sufficient for a stock low rpm motor
Crank assemblies were also dynamically balanced

Picking up 4 miscellaneous rods off the floor you could have as much as 50 gms difference between lightest and heaviest
A cheap set of kitchen scales will get you close enough for a low rpm moderate performance motor

I've seen an engine pound itself so bad due to massive unbalance the brand new case needed a 1mm line bore to clean up the main bearing saddles after only 600 miles

Brand new Mahle piston/cylinder kits rarely have pistons within 5gms of eachother

As for dynamic balance - if you're using the original crank and flywheel you probably won't be too far off for a basic build
Lightening the factory flywheel removes the original balance correction (drillings on perimeter)
Result: runs way off spec compared to the unmodified version

KEP clutches come with instructions advising against further balancing
Not sure what tolerance KEP work to but it's obviously a million miles off what I use 

Your choice...

[javabug]

Here's something to think about:

It's basically an engine to keep the car mobile whilst I start building up the existing engine

It will be in your car longer than you expect or want it to be.  I have one of these.  I call it my "interim" engine.

[louisb]

Is it a performance engine or just an engine to push your car around? If you don't care about performance and just want a pusher it is not necessary. VW engines were not balanced from the factory.

--louis

VW engines WERE balanced from the factory!
Maybe not to high spec race tolerance but pistons and rods were within 5gms of eachother- sufficient for a stock low rpm motor
Crank assemblies were also dynamically balanced

Picking up 4 miscellaneous rods off the floor you could have as much as 50 gms difference between lightest and heaviest
A cheap set of kitchen scales will get you close enough for a low rpm moderate performance motor

I've seen an engine pound itself so bad due to massive unbalance the brand new case needed a 1mm line bore to clean up the main bearing saddles after only 600 miles

Brand new Mahle piston/cylinder kits rarely have pistons within 5gms of eachother

As for dynamic balance - if you're using the original crank and flywheel you probably won't be too far off for a basic build
Lightening the factory flywheel removes the original balance correction (drillings on perimeter)
Result: runs way off spec compared to the unmodified version

KEP clutches come with instructions advising against further balancing
Not sure what tolerance KEP work to but it's obviously a million miles off what I use 

Your choice...

Obviously you don't want to use parts that are outside of factory tolerances. But just meeting some minimum standard is not balancing an engine. At least not in my book anyway. A lot of motors have been built without any more balancing than meeting factory tolerances and have been driven for thousands of miles. I would say save the money for your big motor.

--louis

[Bruce]

...just meeting some minimum standard is not balancing an engine. ...

Sure it is.
The whole purpose of balancing an engine's parts isn't to meet some arbitrary number, it is to produce an engine that doesn't vibrate.  If you use the loose factory tolerances, it won't vibrate when the rpms are kept at stock levels.  Obviously, a higher reving engine needs a different spec to achieve no vibrations.
If you just throw in a set of P & Cs, they most likely will not meet VW's stock spec, since they don't even mix the pistons around to create sets of closely matched pistons.

[Jim Ratto]

Is it a performance engine or just an engine to push your car around? If you don't care about performance and just want a pusher it is not necessary. VW engines were not balanced from the factory.

--louis

VW engines WERE balanced from the factory!
Maybe not to high spec race tolerance but pistons and rods were within 5gms of eachother- sufficient for a stock low rpm motor
Crank assemblies were also dynamically balanced

Picking up 4 miscellaneous rods off the floor you could have as much as 50 gms difference between lightest and heaviest
A cheap set of kitchen scales will get you close enough for a low rpm moderate performance motor

I've seen an engine pound itself so bad due to massive unbalance the brand new case needed a 1mm line bore to clean up the main bearing saddles after only 600 miles

Brand new Mahle piston/cylinder kits rarely have pistons within 5gms of eachother

As for dynamic balance - if you're using the original crank and flywheel you probably won't be too far off for a basic build
Lightening the factory flywheel removes the original balance correction (drillings on perimeter)
Result: runs way off spec compared to the unmodified version

KEP clutches come with instructions advising against further balancing
Not sure what tolerance KEP work to but it's obviously a million miles off what I use 

Your choice...

yes, VW did balance engine parts. Look at drllings in stock cranks and flywheels. Open any Workshop Manual....check instructions on matching rods and pistons.

Why invest time in building a motor if you're going to know in the back of your head, something isn't right? You know how they say if you wash your car, how it seems to run better? Imagine knowing that parts in the motor are shaking themselves to death. Then imagine experience of the evidence.... a rough, noisy, shakey idle...you'll be upset. Run a traction bar or stiffer mounts? It will be worse. Dual carbs with air cleaners? Imagine how disheartening it will be listening to the air filter rattle against the body.... or when you get the shears out and start cutting because you've had it.