Counterbalancer Removal

[Brass]

A question for the 4T mechanical tech heads that I know are out there.

Has anyone removed the counterbalancer from their motor and field tested the bike for tractability?

Before everyone jumps up and down on this, yes removal is generally a safe thing to do. I say this based on previous experience with street bikes and many years of abusing them. The mechanics of a motorcycle counterbalancer has more to do with creating inertial mass and therefore increased momentum than with engine life or even rider comfort.

I’m about to reassemble my motor and am thinking of leaving the balancer on the work bench. The reason is to decrease the mass and by doing so increase the speed that the engine will pick up revs. Essentially making it rev more like a 2T.

My question has more to do with traction and the local terrain. Trying to take the rider out of the equation do slower revving bikes work better on the local trails or do riders here look for more “snap” like a 2T motor has?

Yes, I really do have way too much free time at work.

[dirtyboy]

I have a power aggressive/soft switch on my bike that changes the CDI mapping. I often run this on soft as the bike tracks better on slippery roots and rocks.

I'm sure others will tell you that they like to run the aggressive power valve spring and the power switch on aggressive. Most of the guys the I see running this combo are breaking their rear tire loose often. The more technical the trail, the more smooth you need to be. The more open and fast the trail is (closer to moto track) the more the aggressive (to a point) engine tuning will be an advantage. It's a personal thing.

Can't wait to see the other opinions on this.

[350scott]

Don't listen to dirtyboy. He's almost annoying to ride with because he gives you a false sense of security. He never spins his tire, leaving the poor schlub following him to think there actually is traction.

Generally I don't think you want a fast revving bike on our trails. Particularly, because most of the better trails in the area are somewhat tight and therefore run in lower gears with enough rear wheel torque on hand to break the rear wheel loose if needed.

[Brass]

You're right, it is a personal thing, it's also very bike specific. Without secondary CDI mapping, to make a change that dramatic in the power delivery, there are very few options, even fewer are as cheap as pulling out the balancer while the engine is apart.

I still have yet to get a tire dirty in this part of the country and that's the reason for the question. Where I’m from, there was either mud that needed to be cleared from the tires or rock that gave great traction. Many local 4T guys out there pulled the counter balancers for the faster rev. But that is there, not here.

It’s much easier to ask the question now and make a decision while the motor is apart, than to put it together either with or without the balancer, and then have to pull it apart again to change it back.

As always, I appreciate input from everyone.

[Wangchung]

I don't know what bike you have. But on the KTM RFS motors, oil is pumped thru the middle of the Counterbalancer.

I rode with a guy on the ice last year. He took his out of his DRZ 400 and it his seemed to rev pretty quite, but the engine viberated like crazy when you going down 5th gear straights.

[cedric]

The counter balancer's main purpose is to quell vibrations from the piston going up and down. It uses an offset weight that moves in an opposite (counter) direction to the piston.

If you remove this, you will feel a lot more vibrations through the bars/seat/footpegs and this will tire you on a long ride. You will lose more bolts and maybe break more parts.

If you want a freer revving engine, wouldn't it make more sense to keep the counterbalancer and use a lighter flywheel? Obviously this costs more than just omitting the balancing shaft, but I think you'd be happier in the long run. If you had two different flywheels, you could tune your engine to suit the conditions for the day's ride.

The cost of all the gaskets and time to tear your engine down again to put it back in would probably cost almost as much.

[dirtyboy]

Based on Cedric's point ( a good one I might add ) did you want to end up with a combination device? The new Yamaha off road massage chair motorcycle!

[WR_Dave]

I think you will find that the "modern" high performance 4 strokes , when jetted correctly will rev much quicker than the DR350 that you are putting back together. WR Dave

[Brass]

The counter balancer's main purpose is to quell vibrations from the piston going up and down. It uses an offset weight that moves in an opposite (counter) direction to the piston.

If you remove this, you will feel a lot more vibrations through the bars/seat/footpegs and this will tire you on a long ride. You will lose more bolts and maybe break more parts.

If you want a freer revving engine, wouldn't it make more sense to keep the counterbalancer and use a lighter flywheel? Obviously this costs more than just omitting the balancing shaft, but I think you'd be happier in the long run. If you had two different flywheels, you could tune your engine to suit the conditions for the day's ride.

The cost of all the gaskets and time to tear your engine down again to put it back in would probably cost almost as much.

Because the crank is already balanced to the piston, pin and rod assembly with the weight on the crank, the only vibration that is not canceled is from the loading on the power stroke. In a nutshell you aren’t dealing with an unbalanced rotating assembly, you are dealing with an unbalanced intake vs. power stroke. Obviously, the bigger the bang in the cylinder the more pronounced the vibration. The counter balancer is the product of the engineers best guess at where in the rpm range the rider will ride the bike, and his attempts to dull the vibs in that rpm range. It’s actually much more complicated than that but that is the shortest possible description I can give. You wouldn’t want to read the long version that I went through when I first discussed this 15 years ago.

Look at a 2 stroke, they don’t have balancers because they have a power stroke during each rotation of the crank. They are relatively easy to balance.

Smaller 4 stroke motors don’t have balancers because the power stroke doesn’t cause that much load (vibration). Any vibration that does pop up is often dampened with the use of heavy flywheels. Look at the CRF230, no balancer.

If keeping the balancer, a lighter one would of course result in the same effect on the motor’s ability to rev. That isn’t always an option though for a number of reasons, cost, availability, and interference with other parts can come into play here.

As for the vibration that does come through to the bars, pegs and seat, they are subject to harmonics, again in a nutshell, there will be points in the rpm range where the motor will shake and points where the motor will actually be smoother.

The cost of removing and reinstalling the balancer if needed, in my case, is only a matter of $35 for the one gasket needed, the head gasket, and 3-4 hours of alone time with the bike. Tuning for the day’s ride wouldn’t be an option though.

I think you will find that the "modern" high performance 4 strokes , when jetted correctly will rev much quicker than the DR350 that you are putting back together. WR Dave

You’re right Dave, a modern 4T will rev much faster than the old tank I’m working on, due to, along with other things, lighter flywheels and counter balancers. Which is pretty much what generated the question in the first place.

[cedric]

I'm no engineer. Sounds like you already know way more about this topic than anyone else here. Feel free to leave it out man. It's not going to affect me in any way...

When it comes to the newer engines, I think you'll find that they have shorter strokes and bigger bores than the older 4T bikes. This is one reason they rev faster. They also have much better carbs (or EFI), shorter (lighter) pistons, titanium valves, DOHC, etc. You will spend a lot of money and get frustrated trying to make a DR350 run with one of the newer bikes. Luckily, for most the trails we ride, more power is not the answer, and an older bike ridden well will be just fine.

I had a DR350 about 15 years ago. It will need stiffer springs to ride it at any sort of fast pace. Beware the exposed part of the engine cases behind the coverage of the stock skid plate. I landed on a rock and busted my cases. When you push the bike hard, you will feel the frame flexing like a noodle. Otherwise, it is comfortable, reliable and fun.

[Brass]

I have no delusions about the DR running with the new bikes or even the desire to try. It’s a model T compared to the bikes of today.

If a little time spent “tweaking” it makes it a bit better suited to the trails then I don’t mind doing that, up to a point. It is a model T, no matter what is done to it, it will always be what it is.

Thanks for the tip about the engine guard, that’s an area of the bike I haven’t spent much time looking at yet but will now.

[cedric]

After busting my cases, I ended up having a piece of aluminum welded to the end of the skid plate, extending back to the edge of the frame where the linkage attaches. A full aftermarket skid plate would probably be better, but this arrangement worked for me and was cheaper at the time.

It's an older bike, but it will get you out there exploring and should require minimal maintenance time and $$$.

What year is yours? I had a 1990, not much changed over the years, I think they upgraded the forks a bit in the later years (1996+?).

Have fun!

[Dude]

Your DR 350 will never keep up in the tight trees. It might be fun in the parking lot.

[Brass]

The suspension is off a ’99 but is pretty beat up and needs a lot of attention. Luckily because it was never a front line bike and now is very out dated, the parts to rebuild it are so cheap they are almost given away.

The bike was purchased as a means of getting my tuning skills back on par as well as getting me back in the dirt. Also, because my riding skills have rusted away to nothing, an old slow scooter like this one will also keep me from running into a tree at too high of a speed.

Going out and buying a new bike would have been easier and cheaper in the long run but going about it this way will ease me back into things. I’m also not as likely to end up missing work because I did something stupid.

Since this is such a low value bike, I’m not interested in upgrading it all. It is getting treated to a full freshening but it ends there, if along the way there are “free” upgrades that can be done, then I’ll go ahead with them.

[Dude]

I hope your bike works out good for you.