22 replies to this topic

[Chris.Williams]

Hello all,
My question today is about engine balancing, and it's pros and, if any, cons.
I've had a browse through the forum and not really found an answer.

I can understand doing so in a race engine, not building one of those haha.
Road going pocket rocket ......yes.

A little info on my build project.
1275 metro block std
9.75 piston set
Evo 1 mini spares cam
Evolution performance dizzy
Ported head, std valves reshaped stems
Double valve springs
Hif44 on mini spares manifold
Lcb with rc40 twin muffler system
Lightened flywheel
3.44 final drive

Would you or wouldn't you if it was yours.
Cost is not an issue, as I have permission from my wife......very important hahaha

[Cooperman]

If you are intending to rev it to over around 6000 rpm on a regular basis then a full dynamic balancing is worthwhile. It makes the engine much smoother, although for a 1275 Mini the terms 'engine' and 'smoothness' don't ever really go together.

It's your choice really and not vitally important.

That looks a nice engine spec for a road engine and not over-cammed like so many are where owners have been reading and taking inspiration from the two 'comics'.

[Chris.Williams]

If you are intending to rev it to over around 6000 rpm on a regular basis then a full dynamic balancing is worthwhile. It makes the engine much smoother, although for a 1275 Mini the terms 'engine' and 'smoothness' don't ever really go together.
It's your choice really and not vitally important.
That looks a nice engine spec for a road engine and not over-cammed like so many are where owners have been reading and taking inspiration from the two 'comics'.

Yes I agree, to big a cam in a road car is more of an ego stroke then a stroke of genius.
I want to be able to drive it haha.
I have driven both balanced and unbalanced, yes there is a difference in the higher rpm range for sure.
Not to sure I'll be stretching her legs into the 6000+ range to often, I like building engines, but not over and over.
Torque rather then revs for me thanks.

[icklemini]

Yup to getting it balanced... especially the flywheel assembly...

(Fit an out of balance assembly and you'll certainly feel it).

Makes the whole engine far smoother.. and reduces stresses on engine internals.. and fixings in the car...

[Chris.Williams]

Yup to getting it balanced... especially the flywheel assembly...
(Fit an out of balance assembly and you'll certainly feel it).
Makes the whole engine far smoother.. and reduces stresses on engine internals.. and fixings in the car...

So really I should consider this http://www.minispare...sic/22A598.aspx to go with my lightened flywheel?
I've been looking and wondering if it's worth doing.

[nicklouse]

If you are doing a fresh build I would have it ballanced as a matter of course.

[Chris.Williams]

If you are doing a fresh build I would have it ballanced as a matter of course.

What components do you have balanced when doing it? Crank rods pistons flywheel etc, down to bearings???

[nicklouse]

Ok there are two sets of things that can be ballanced

The first is the rotating parts so fly/clutch Assy, crank and crank damper.

Then when assembling the rods and Pistons it is good to get them matched so they are of a similar weight per set.

[Midas Mk1]

Balancing makes all the difference imo from my engine builds..

[Steve220]

It will make the engine smoother throughout the rev range.

[Spider]

My take based on experience with balancing.

 

Pros;-

 

If it spins, balance it

 

Cons:-

 

If it goes up and down, it's a total waste of time and effort

 

As far as making any engine 'smoother' balancing won't help though may change it ever so slightly. Vibrations from an healthy engine have zero to do with balance, they come from harmonics and resonances of those harmonics.

 

In regards to what's I've mentioned here about 'if it spins', it's not a bad idea to include the Big Ends of the Con Rods.

 

In regards to what I've mentioned about 'Cons', think about it. The reciprocating parts of the engine can and never ever will run in any kind of 'balance' If they did, then there'd be no energy what so ever to make it spin in the first place. Balancing here is a total wast of time, however, lightening components can pay dividends.

[icklemini]

"
As far as making any engine 'smoother' balancing won't help though may change it ever so slightly. Vibrations from an healthy engine have zero to do with balance, they come from harmonics and resonances of those harmonics."

A real world example...
I did a clutch job on a mini van... this was a bog standard a+ 998 engine in it..
Verto clutch... all replaced using branded parts from main supplier... engine became very rough.. very lumpy when revved... horrible to drive... as un-smooth as you could imagine...

All because of the clutch and flywheel now being out of balance with the new clutch bits...

Flywheel assembly removed and all balanced... refitted.. owner delighted as the engine is 'smoother' than it was before the clutch change!

[icklemini]

Yup to getting it balanced... especially the flywheel assembly...
(Fit an out of balance assembly and you'll certainly feel it).
Makes the whole engine far smoother.. and reduces stresses on engine internals.. and fixings in the car...

So really I should consider this http://www.minispare...sic/22A598.aspx to go with my lightened flywheel?
I've been looking and wondering if it's worth doing.

Yeah thats a lightened backplate... doesnt necessarily mean its balanced!..

You may find some setting up and machining of the backplate is needed to get the clutch setup correctly..

[Chris.Williams]

Yup to getting it balanced... especially the flywheel assembly...
(Fit an out of balance assembly and you'll certainly feel it).
Makes the whole engine far smoother.. and reduces stresses on engine internals.. and fixings in the car...

So really I should consider this http://www.minispare...sic/22A598.aspx to go with my lightened flywheel?
I've been looking and wondering if it's worth doing.

Yeah thats a lightened backplate... doesnt necessarily mean its balanced!..
You may find some setting up and machining of the backplate is needed to get the clutch setup correctly..

I realise it's probably not balanced, but the mod would be worth it, and I will amass all parts before handing over to machine shop.

[ACDodd]

Balancing engine components maximises smoothness. Some clutches produced now typically the verto type have horrendous in balance when new. Simply balancing the flywheel and clutch on ita own will give the biggest improvement in engine smoothness, noticeable from idle speed upwards. This is because it is the single biggest rotating inertia.

Balancing other components will all help, fully balanced engines run smoother than those that have not.

Its up to you really where you want to spend your budget. Balancing is a nice to have. Shown below are just 2 typical verto flywheels that have been lightened then balanced by myself.

Attached Files

•  WP_20161222_16_06_34_Pro.jpg   61.1K   29 downloads

Edited by ACDodd, 15 January 2017 - 11:09 AM.