O.K. this is not an LBC, but the technology is just as old. I have a
2002 Harley Davidson Heritage Springer. The Heritage Springer has the
1450cc (now 1550 on mine) Twin Cam counterbalanced motor. For the old
school hard tail look that us old farts want, but our backs can't take
anymore, HD bolted the motor directly to the frame on Softail models
just like the old days, thus requiring a counterbalance system to offset
the two piston long stroke mass. There are two steel rollers about 3.5
inches in diameter that are chain driven off the drive shaft that are
timed to offset the pistons. There is a slice taken lengthwise off the
cylindrical stock which is calculated to offset the weight of the
rotational mass above them. A great system that makes the bike almost
as smooth as (dare I say it) a Japanese bike such as the Gold Wing. The
problem is that this system does not like high RPM and the manual states
not to exceed 5600 RPM. Well, sometime during one of the dyno runs I
have made to fine tune the bike, one of the technicians set the rev
limiter in the crane ignition module to 6200 RPM! It had the undesired
effect of shelling out the counterbalance shaft end bearings and the
motor had to be opened up to replace them. My mechanic had an inspired
idea to remove the counterbalance shafts completely and replace the
counterbalance system with a product called "Active Balance" It
consists of a groove machined into the outer edge of the flywheels and a
continuous Teflon tube epoxied into it. The Teflon tube is partially
filled with Mercury. This is supposed to act as a counter balance,
They used something similar in WWII by filling copper tubes with oil and
some ball bearings to counterbalance aircraft engines. Not a new
technology. Well, it did not work as we had hoped. At 60 MPH on the
freeway, the bike was fairly smooth. As soon as I rolled on the
throttle it started to vibrate. At 70 MPH my hands and feet were numb
within 5 minutes. So this "Active Balance" system is not the panacea we
had hoped for. The counterbalancers are going back in. If you have
stuck with me this far, I am coming to the brain teaser part of this.
If I put the counterbalancers back in and leave the "Active Balance"
system in the flywheels, will the two systems fight each other at
certain RPM? Will one system cancel out the other at certain RPM? My
idea is to take the "active Balance system out put the counterbalancers
back in and limit the RPM to 5600 and hope for the best with the
bearings. It is a lot of work to remove the epoxy from the flywheel,
but we will do it if we have to.
Mike MacLean
60 Sprite
56 BN2
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