Moving Matter - No Vibration Exemption

The Question - I noticed that you redid your Glamis page, specifically the setup spec's on your ride and once again I noticed that you have lightened another component. The balancer shaft. To make sure we're on the same page, are you referring to the counterbalancer, and the shaft that runs from each side of the case to the weights on each side respectively??? I hadn't thought of removing material from there to lighten it, I suspect that any change in balance would be minimal that close to centerline, and not affecting the weighted portions at all if my presumptions are correct. I'm trying to lighten up my motor as much as I can to free up it's ability or "tendency" to want to rev quicker, and it's also not power wasted spinning mass.

The Response - Yes it's the counter balancer that I machined about 1 pound (think about that!) of weight from in an attempt to get the motor to rev more quickly (this goes back to 1987). It accomplished that but the vibration was terrible. I couldn't stand it - and things were loosening up real fast on the frame (not good). I wouldn't recommend it unless you're running a VERY light piston and racing only. For dune rides and play riding it's just to much to tolerate. I ran it with a 66mm (1986 CR250) piston. The stock Honda cast CR piston/rings/clips and a (Pro-X) taper wall wrist pin made the lightest piston/rings/pin/clips combination that I could get at the time - it came out to about 24 grams lighter than stock and a couple grams lighter than that when the top is cut. Wiseco made a piston for the TRX, but at the time Wiseco made crummy 2 stroke pistons and the domes would collapse if they got very hot so I wouldn't run them. Now the Wiseco ProTrue forged pistons are very light and durable - about the same weight as the CR piece. I usually favor a cast piston when ever I can get one because they can be set up to tighter tolerances, but it's not always possible.

You have to be very careful not to damage the bearing when machining the shaft. It's a real pain to get the bearing off the shaft without damaging it (almost impossible to do) and Honda doesn't sell the bearing separately - you have to go to a bearing house and match it up or buy a complete balancer assembly to replace it. When I did mine I filled the bearing up with wax so I wouldn't get any chips of metal in it. I cleaned the shaft real well and heated the balancer in the oven to about 120 degrees then poured the wax on both sides of the bearing and let it cool down. It can get real hot when machining because it's made of cast iron so you have to keep an eye on the temperature of the piece or the wax will melt out. When it's done just clean it real well again and desolve the wax with solvent. The wax worked out pretty well for this.

I would have removed it all together but you need to keep something in there to turn the water pump. I thought about running an electric water pump instead and adding a battery or rectifier to run it but didn't go that route. The way the shaft comes from Honda it is balanced to counter about half of the weight of the crank/piston assembly and works well. If the motor is using the larger 69 mm, 72 mm or 76 mm piston the vibration would even be worse because the piston weight is quite a bit heavier - about 60 to 90 grams (depending on the piston) and would be a nightmare in my opinion. Actually weight should be added to the balancer to counter the effect of the heavier parts, but it is tolerable running it without adding any and the frames don't crack very easily.

Rick - [I understand the bearings for the balance shaft are now available at bearing houses. It may now be easier to pull the bearings and replace them after machining the part.]

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