Power Valve Adjustability

[jefgil123]

Was looking over "there" and the KTM 2 Strokes have optional power valve
springs and preload, that people have been experimenting with. Many seem to favor the "red" spring with little preload, which I think is the softest.

This should allow the power valve to open sooner. I would think this would
be harder to ride with my "lugg-it" style, as the power valve opening sooner
would theoretically put the "hit" down at a lower RPM. And thats what the
KTM manual says....

But the riders that have tried it, said the power just comes on sooner, and
is real smooth and controllable and more abundant down low. Just what I want !

Has anyone experimented with a lighter spring, or tried heavier tungsten
balls in the mechanism ? What are your results ??


Jeff in Lake Tahoe, riding paridise. 2001 EC300

[J D]

Someone on one of my local forums, (Aus) ,has mentioned a Gas Gas Dealer sugests to use shims to mimmick the same thing. I have searched but as yet have been unable to find out any info.

Has anyone used shims to preload the powervalve rod? How is it done?

[jostby]

I'm unsure how you could "shim" the powervalve actuating rod. Possibly bend it to allow earlier or later opening maybe.
As for the KTM adjustable PV cover there was at one time one available for GasGas in Europe, see this thread.. http://www.gasgasrider.org/forum/sho...ighlight=valve
I couldn't find it on their website any more though and as the thread mentions it was around 300 euros
Like the KTM cover it used "helper" springs that attached to a differant PV shaft on the left side behind the cover. It was the helper spring that then kept preload on the PV and you used the dial to change it. Seems like a unique idea and if the price where right I would try it.
Maybe someone else on this forum knows if it is still being made and can supply a link to it.

[reiterrider]

Trial Enduro Direct Sells them http://www.trialendurodirect.com ---->Adjustable Power Valve

Here's what it looks like.

[PEB]

Howie, How is the seat?

[jostby]

Dang I wish I could get my hands on one of those! (ugh, for less than that though!)

[Cruiser]

Wow!! 259.99 pounds + $422.95 US dollars.. thats one pricey cover..

[J D]

Originally Posted by jostby

I'm unsure how you could "shim" the powervalve actuating rod. Possibly bend it to allow earlier or later opening maybe.

Supposedly it's the lower end of the Power Valve actuator rod in behind the water pump that gets shimmed.

Anyone?????? Surely some of you GG gurus wold have some knowledge on this.

[rpduc]

Supposedly it's the lower end of the Power Valve actuator rod in behind the water pump that gets shimmed.

I don't see how shimming that connection could do anything to alter the operation of the PV. It's just a hoop of wire and a bolt. No place to "shim" that I can envision. The only "adjustable" bit is the "cam" that rides against the spring and washer in the centrifugal clutch. Set screw #3 in the pic below. That can be adjusted until the preload is pretty heavy or the opposite. If you open up the case it will be obvious.

[GMP]

You would have to remove and disassemble the governer assembly, and then add shims to the spring. There are already some shims in there, I assume to set a standard preload. Shims of this size could possibly be obtained from an industrial supplier, I would have to measure them. Springs also possibly, but the rate would need to be measured.

The difference between increasing preload and increasing rate is as follows: When you increase preload you increase the point (RPM in the case of a PV governer spring) at which the system starts to move. When you increase the rate you decrease the rate at which it moves. This is basic physics of springs.