If you have the time reading the manual that comes with a balance machine will bring you up to speed on engine balance. The info you link to raises more questions than it answers. It also touches on internal balance. Yes there are internal as well as external balanced engines. I mentioned spinning a complete rotating assembly fully assembled, crank, flywheel, pressure plate, timing gear, pulley and damper all bolted together. The externally balanced engines are done this way due to the crank counter weights being just to small to balance the shaft. They carry a damper with a large off set weight as well as a flywheel with a big offset weight. This adds two more counter weights to the shaft just located out side the engine. In the event of a bad damper or flywheel needing replaced the entire assembly would have to be removed and rebalanced.

Like I mentioned earlier I have balanced 1000s of engines over the years. Something I have noticed on English engines, it is quite normal for very large corrections to be made on the rods and rotating assembly. I have never been able to correct the balance by even a single gram on a German engine.  Steve (CTR) 

Yep. That's what I suspected—not sexy. Still, it seems pretty important. I've read further and I now realize that harmonic dampers aren't designed to correct rotational imbalance, but torsional imbalance resulting from the pulsating nature of internal combustion engines. [link1]  Our host has a nice explanation on balancers as well. [link2] Interesting reading, both.

Sorry Steve, I did not notice you mentioned ROMAC in your post. ROMAC has two versions of their A-series balancer. Maybe one is better suited for racing? While I don't baby my 1275 on the street I'm not stressing like it a dedicated racecar would. At the time of my engine build I felt to ROMAC was a better option than an old and tired BMC balancer. And in my case it is holding up great (of course I wouldnt know otherwise unless it blew up). Maybe I have been lucky?

Still this is a great topic and one I feel gets overlooked because a harmonic balancer just isn't sexy. For sure twin SU's and oil coolers are great to look at but you need to start with a solid foundation for a quality and long lasting engine build.

John 

They were fine and I'd still run them on street engines. It was when turning high 8000 s that issues appeared. I did say racers had issues. Steve (CTR)

I run a ROMAC harmonic balancer in my AA based 1275 for over ten years and have not had any issues. 

//www.romac.com.au/balancers_US.html

Thanks Steve, for an excellent description of how an engine is balanced.

850 s and a lot of 998 s came from factory with sheet metal front pulleys ( no damper ) with the Cooper line came the two part damper. This was followed by the 1 pc. damper with the 1275/1300 range. In spite of having to change the front engine mount and radiator lower half I add the two piece damper to all engines I rebuild.

Like so many things, I have a bucket of old dampers both 1 and 2 part with cracked or parting rubber. If the outer ring begins to move balance will change.

The balance process ( and I must have done a couple 1000 in my 25 years at the machine shop ) all pistons with rings and pins are made the same weight ( by removing weight from the piston or cutting the pin bore. Next the rods are balanced first by supporting the small end and weighing the big end using a special fixture that holds the rod level and centers it over the scale. Once the big ends are all the same the rods are weighed and the total weight made the same by correcting the small ends. This is what they mean when saying rods balanced end for end. Next the crank shaft by it's self is placed in rollers and spin balanced. The rollers are such that each end can be locked and readings taken from one end at a time. Once the crank is balanced parts are added the crank sprocket and damper to the front and corrections made on the weighted part of the damper. Once that is balanced the flywheel is added and corrections made followed by the back plate and spring are corrected also. Then the complete assembly is spun and checked. I realize there could be some who assemble everything and spin making corrections at the easiest point. The problem with that approach is say a flywheel or a damper gets damaged, to replace the part and hope for that well balanced unit is lost. I keep a balance crank which I use if a part needs balanced alone. Spin and check the crank then add the new part to balance it, remove and add to an already balanced assembly. If getting used parts balanced be sure all machine work is done first. Such as surfacing the flywheel and back plate or installing a new ring gear. I believe we are paying $225 for a balance job here now.

Side note my first mini was a 850 with a fully balanced and blue printed engine. I traded it and $350. for a 67 Cooper S with a so called rebuilt 1275. First time I cranked it up I didn't even drive it. I stripped the unit which had been rebuilt but not balanced. New rings a balance job and mirrors went from fuzzy at 1750 to clear though out rev range. Decided right then balance would be part of all my engine work.

Not sure if this is the info you were looking for. But there it is. Steve (CTR)

Edit: I do tend to get off topic, a damper is a very important part of any performance engine. I have taken to using only the two part S type damper. I have seen reconditioned dampers and don't use them for a number of reasons. I also don't think much of the so called fluid dampers. I have also seen some of the racing dampers and pulley kits offered. I don't know if Romac in OZ still offers dampers. Racers started having issues with them maybe 10 years ago. 

Damper should be balanced with the rest of the rotating assembly 

It surprises me that high performance engine builders put a great deal of time and effort into assuring that the engine is perfectly balanced; a gram or two ground off the crank and flywheel, .25 grams off the con-rods, pistons, etc., then the whole assembly is dynamically balanced. Yet I get the impression that little attention is paid to the harmonic damper. In fact, a search on this forum returns zero (0) threads on the subject. After all the effort that goes into balancing an engine, it would appear that the engine builder simply slaps on any old damper they may have on the shelf, or even reuses the old damper. Seems to me that the harmonic damper is kind of like the "gate keeper" for all that balancing. Yes?

Could it be that harmonic dampers don't really have much of an effect? After all, they're pretty small and don't have much mass considering the mass of all the engine internals they're required to dampen. Just wondering...


See? I told you.