Harmonic damper balancing

[Spider]

A static balance on a part like this, will possibly be better than not balancing it at all, just be sure to compensate when setting it up for the material removed for the keyway and to also mark all the bolts & washers so they are always fitted back in the same holes.

The reason for a dynamic balance over a static one (and where a static one can come unstuck) is that the mass throughout the item being balanced may not be equal throughout the item from it's centre - this is in fact why an item, like this, needs to be balanced in the first place.

What results from this is that while it maybe balanced at one speed it will not be at another. At some certain speeds, the effect accumulates and results in the item being further out of balance than prior to it being static balanced. When dynamically balanced, usually the item is checked for it's out of balance at a few speeds, then material is removed (or added) not just from it's outer circumference, but 'the right place' to compensate for where the out of balance mass is within the item. This is why balancing odd shaped item, like crankshafts, can be quite tricky. It's often, though not always, a sure sign of a possible 'lazy' balance when all you see is material removed from it's outer circumference and no where else.

[Gary Schulz]

Except of course if the item being balanced (in the limit, to use a mathematics term) is infinitely thin in section. I strongly suspect that in this case there is a great deal of correlation between the points of static and dynamic balance given the geometry of this particular item. Wheels and tires are completely different largely because they are "thick" and can depart from homogeneity far more dramatically. The true balance point for a wheel/tire may in fact lie somewhere inside the surface where the tire is mounted.

I will test my hypothesis once I figure out if I am going to true this thing up or not.

I sent an email to MS early this morning but so far no response from them...

Yes, this is the junk HF bench grinder. I originally was using it to grind Tungsten electrodes for my TIG but it would serve pretty well in this application I think.

Gary

[Kiwi Craig]

I was going to get the Harmonic Balancer on my Cooper S refurbished by a company here in NZ.
I then found Mini Spares had new ones for a third of the price.
Are there any more people that have M S ones that have had issues with not running true/out of balance?

[mk1]

I have used new MS ones on about a dozen engines (upto over 150 hhp & 8,500rpm) over recent years. I have had them all balanced with the rest of the rotating components & have only once ever had any sort of issue. That was when The rubber wasn't bonded correctly & it was replaced instantly.

Wouldn't hesitate to recommend them. Great value!

[ChrisM]

if you are going to have that 2 part damper balanced, and it is a nice tight fit on the pulley boss, to be honest, you could just leave it. It will come back with a few holes in it, but who cares? If you trim the OD of the damper true, the ID will still be running eccentric, where it is bonded to the inner part. So it will still have a heavy and light side. It won't be as bad as doing nothing, but should really still be balanced on a machine afterwards.

If you are not going to have it balanced, and lets say it was mine, and I couldn't get it done, I think I would open out the centre bore just enough to be able to clock the OD of the heavy part true. Then bolt it up, or as Spider says - pin it.

You will get unbalance from the thin inner part running out of true, but nowhere near as much as if you left the much heavier part running out 14 thou.

Don't get too hung up on it though, its two bits bonded together with rubber, so they are going to move when its rotating at speed. If you look at the earlier thread mentioned in this one, I ran up a pretty loose 2 part damper, taking a few readings, and it wasn't really that bad.

I do think you should do something with it though. Not just bolt it on with the 14 thou run out.

Regards: Chris.

[CooperTune]

I also have been using MS two part balancers on all builds 850 to 1400. The little paper says you must balance the parts. I'm sorry to say some are a little loose on the pulley shoulder. Index and pin the parts if that's so. My first choice machine shop balances the crank first making a mandrel for balancing the rest of the parts. Adding the pulley he checks it then with the outer ring with four mounting options he can mount the ring for best correction and torque it and pin. This is done with the rear sensor locked and only the front sensor reading. Corrections are made drilling the ring, lock front sensor and begin adding on flywheel followed by the back plate and spring. It works best for me if every part is zero balanced. I have made it a habit to keep a crank that has been balanced on hand. Someone needed a crank real bad and I let it go last fall. I have had people send me balancers and flywheel assemblies for balance. I have no fear of the MS two part balancer. I have turned them to over 8000 in a 850 and over 9000 in a 1330. I need to check my supply of balancers I want to build a 998 and two 1071s.Steve (CTR)

Since my first Cooper S build late 60s early 70s I have balanced every engine I build. I'm currently studying balance for 90 degree V6s. Before ordering any parts I want to understand how and why. The beginning of this build will start with the best balancer I can buy and a new ring gear and flywheel surface. I even plan the buy a after market light rod set made for a V8 which I'll machine to give me the side clearance I want. Sorry got a little off topic.

[850man]

I have used new MS ones on about a dozen engines (upto over 150 hhp & 8,500rpm) over recent years. I have had them all balanced with the rest of the rotating components & have only once ever had any sort of issue. That was when The rubber wasn't bonded correctly & it was replaced instantly.

Wouldn't hesitate to recommend them. Great value!

I second that notion.
I use them on all the S engines we build, and on our supercharger conversions, with a Multi V pulley Never had an issue with any of them.
For the race car engines, I use an MED damper.

Always dynamically balanced.

[Kiwi Craig]

Thanks guys for the advice. That has reassured me, so will order one with my other parts.
Its just that its a long way to NZ if it had to be returned if not fit for purpose.
Craig

[Kiwi Craig]

I have received my Mini Spares damper and it has been balanced along with the other usual parts.
Apart from a small amount ground off in one place so that it runs true, it was actually spot on.
No complaints from me, maybe the other guys were just unlucky and got a dud one.