M16 Balance Gear Removal

[Bill D 2,062]

I have an M16 that had what I assumed was a balance gear rattle.  I opened it up to remove the gears and found them to be loose, with excessive endplay.  After I removed the gears, I checked the motor over and was struck by what I consider some design flaws on the part of Kohler engineers.  The gears add unneeded complexity and machining costs to the motor.  Adding some thickness to the counterweight on the PTO side of the crankshaft (exactly what the David Kirk Balance Plate does) coupled with drilling out less material on the flywheel side counter weight would have totally eliminated the need for the balance gears in the first place.  Weighting a crankshaft specifically for the M16, instead of using the same crankshaft for the M14 and M16 would have made more sense to me.  Am I wrong?  The only design I consider dumber than this crankshaft design is the open web connecting rod design used by Onan.

 

I put the engine back together and ran it.  It vibrates more than before, but the rattle is gone.  I am going to reinstall it and see what happens.  At some point I will consider rebuilding this engine and adding the balance plate to the crankshaft.  Thanks for letting me vent.  Bill  

[Achto 28,275]

Many guys have removed the balance gears. In fact when I rebuild a Kohler, the balance gears will not be reinstalled.

[roadapples 6,983]

31 minutes ago, Achto said:

Many guys have removed the balance gears. In fact when I rebuild a Kohler, the balance gears will not be reinstalled.

Does that include magnums?

[Achto 28,275]

5 minutes ago, roadapples said:

Does that include magnums?

 

Good question, come to think of it I have not rebuilt a magnum.

[bds1984 1,463]

Six years ago I rebuilt my C165's K341 and removed the balance gears.  I didn't notice any more vibration than before after reinstalling and running the engine for the last six years.  Since then, every time I open up a K-series or Magnum engine, I remove them if they have them, and lose no sleep.  

[953 nut 56,867]

Here is the collective wisdom and/or opinions of many of our members on this subject.

 

[oilwell1415 563]

The only reason I can think of to do the balance gears instead of just adding weight to the crankshaft would be the possibility of some kind of second order vibration.  This is reinforced by several people saying that vibration is increased at low rpm and goes away at high rpm without the gears installed.  Simply adding weight to the crankshaft wouldn't fix that, but adding weight that is rotating in a smaller circle in the opposite direction could.  This is why many automotive engines have balance shafts.  Some engines have combinations of components that just don't play well together and a balance shaft is the answer.  Sometimes the vibrations aren't even anything you can feel, but they cause problems 1% of the time and have to be addressed.

[Handy Don 13,131]

3 minutes ago, oilwell1415 said:

The only reason I can think of to do the balance gears instead of just adding weight to the crankshaft would be the possibility of some kind of second order vibration.  This is reinforced by several people saying that vibration is increased at low rpm and goes away at high rpm without the gears installed.  Simply adding weight to the crankshaft wouldn't fix that, but adding weight that is rotating in a smaller circle in the opposite direction could.  This is why many automotive engines have balance shafts.  Some engines have combinations of components that just don't play well together and a balance shaft is the answer.  Sometimes the vibrations aren't even anything you can feel, but they cause problems 1% of the time and have to be addressed.

Resonant vibrations are a burr under the saddle of automotive (and other) engineers since they have the potential of causing failures that compromise safety and are devilishly hard to find. With the advances in sensor and digital storage technologies there are now fantastic machines used to test individual components and complete cars/trucks that let them detect and isolate vibrations (including noise) so they can be addressed. The complexity of this task is one reason that automakers (and engine builders) are wedded to the "platform" concept--when they have one that works there has to be a pretty good reason to start over or make major modifications.

[Bill D 2,062]

I plan to leave the balance gears out.  The shafts were no longer smooth and the gears were rocking on the shafts.  The end play was closer to .30 than .03.  I pulled the upper gear by driving the pin into the block rather than breaking the gear.  If I ever rebuild this engine I will probably try the David Kirk balance plate and have the crank precision balanced.  I'm also thinking about using the Zack Kerber rod and piston in it for a bullet proof lower end.  I saw the

@Greentored K321 build and would like to know more about how he balanced his crankshaft.  Bill

[Searcher60 209]

M12 is a much smoother engine with the balance gears than without. My understanding is that the balance gears are for side to side vibration, not the up and down vibration. The crank counterweight and rod/piston can easily be balanced. But not the side to side. You just cannot balance out the side to side vibration without some type of balance gear assembly. Engines where the balance gear assembly is worn out as you state yours is, assuming this engine has never been rebuilt, are surely long overdue for a complete rebuild.  People, me included, sometimes expect to much out of these engines, and put off the uber expensive Kohler parts rebuild. I can’t see me using  Chinesium parts on a regular worker engine. Why not? One big reason is that the piston assembly and con rod are nowhere near the same weight as genuine one Kohler parts which match the original counterweight balance.(aftermarket is heavier)  So, the engine is going to be out of balance big time using Chinesium rod and pistons vs. real Kohler. Unless you have them balanced. 

 

You first have have to understand that the Kohler engineers were not stupid. 

[Bill D 2,062]

15 minutes ago, Searcher60 said:

You first have have to understand that the Kohler engineers were not stupid.

Still, it seems to me that a different crank design would have eliminated the need for balance gears in the first place.  I was looking at the billet steel cranks the pullers use and noticed that the counterweights are the same size on either side of the crank pin.  To my untrained eye, a crankshaft design that had even size weights on either side of the crank pin would run smoother than Kohlers original design.   

[Searcher60 209]

You cannot balance out the side to side imbalance without a counterbalance of some type such as the weighted gears. It would be physically impossible for a Kohler engine without balance gears to be as smooth as one with the gears, assuming correct assembly.  When the crankpin and counterweight are not in line at opposite ends, the crankpin side is to lite due to it not having the piston/rod inline with the counterweight to offset the added weight of the counterweight. This imbalance cannot be offset on a single cylinder engine by crankshaft design alone. 

 

Balance gears were/are the affordable engineering compromise. 

[Greentored 3,217]

8 hours ago, Bill D said:

 

@Greentored K321 build and would like to know more about how he balanced his crankshaft.  Bill

Basically, I weighed the big end of the rod, plus half the weight of the small end, piston, pin, rings and clips and matching the counterweights. This is a ‘50% reciprocating’ factor, which is much higher than the factory used, or so I understand. I needed to add tungsten slugs to the counterweights, which was done by drilling crossways through them and pressing slugs in.
The guys here are correct, there is no way to perfectly balance a single cylinder engine. If the counterweights equalled the entire piston and rod assembly, they would cancel each other out at top and bottom dead center, but at 90 degrees, the counterweights would need to equal the bottom half (big end) of the rod to cancel out- a much much lower weight. Basically, you either have an engine that’s balanced well on a vertical plane and far out horizontally, or vice versa. To confuse things even more, as the engine rotates, the counterweight would have to change its weight incrementally to cancel ‘piston and rod’ at TDC to ‘big end rod’ at 90, back to ‘piston and rod’ at BDC and so on. Hence the 50% factor, which is somewhat of an industry standard- a compromise of slight imbalance in all directions versus extreme on one plane and smoothe on another. 
My humble opinion is that Kohler perhaps found operators or parts more sensitive to horizontal vibration, so they reduced this 50% number, meaning less counterweight, therefore less side to side vibration, at the cost of more up-down. I can tell you my 321 most definitely ‘feels’ smoother than my other big blocks, but it still shakes. 
There’s a ton more that comes into play, hopefully this rambling makes some sense at least on the basic level 👍
 

[Bill D 2,062]

That makes sense and explains a lot, thank you.  I wonder how the engine would feel balanced at 50 percent and having the balance gears installed.  If Kohler had made them out of steel and used larger shafts and bearings, maybe they wouldn't have the reputation they have.  I have a 320000 series Briggs.  I am going to have to look at its synchro balance system to see how the designs compare.  Thanks for all the info.  Bill

[Greentored 3,217]

5 hours ago, Bill D said:

That makes sense and explains a lot, thank you.  I wonder how the engine would feel balanced at 50 percent and having the balance gears installed.  If Kohler had made them out of steel and used larger shafts and bearings, maybe they wouldn't have the reputation they have.  I have a 320000 series Briggs.  I am going to have to look at its synchro balance system to see how the designs compare.  Thanks for all the info.  Bill

I've never checked to compare a non counterbalanced engine crank versus one designed to run with them and wouldn't know if taking one to 50% would help or hurt, as the counterbalancers might be weighted to correspond with a different number. Maybe someone else will chime in on this.

FWIW- my 321 was originally equipped with them, and they went in the dumpster. It would be interesting to do a side by side comparison of an engine with counterbalancers, one without, and one at 50%

Gotta wonder just how critical this stuff is- with guys just tossing the counterbalancers out on rebuilds and going for it, adding or removing weight from the cranks, installing heavier/lighter aftermarket parts, etc.... all on an engine thats going to be out of whack on one plane or the other regardless. There is one factory counterbalanced engine that will supposedly vibrate terribly if they are removed and the crank not rebalanced, I think its the 12hp magnums but not sure.....

Again, I think the best thing anyone can do is shoot for having the imbalance on horizontal and vertical planes as close to equal as possible, and the 50% is pretty close.

[oilwell1415 563]

5 hours ago, Greentored said:

Maybe someone else will chime in on this.

 

I agree with everything you've said, but after thinking about this for a few days I think Kohler really screwed up the design.  If the rotating assembly itself is balanced vertically, installing the balance gears to fix the horizontal imbalance as they did would unbalance it vertically.  What they should have done is put them in so that the crank drove one of them directly and the second one was drive from the first.  This would spin the two gears in opposite directions and allow the counterweights on the gears to work in the same direction horizontally to "fix" the horizontal imbalance while cancelling each other out vertically.

[Bill D 2,062]

Does anyone here happen to know if the crankshafts used in John Deere Kohlers were balanced differently?  I have seen several blocks on eBay and noticed that none of them have balance gears, nor provisions for them.  Bill