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/showthread.php?t=321&highlight=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]

Here's the site that sells them in Europe

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]

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.

 

[webmaster]

I remember a discussion from long ago talking about using different springs from different models to modify the engagement - e.g. 200 is different from 250, etc...

jeff

 

[101racing]

Seems as though the springs all have the same part number. 200,250,300. The 300s have different amount shims from 06 and earlier to 07 . We have an 06 300 and an 08 300. They have identical port timing and compression. The 06 has better off idle torque than the 08 . From stock parts manual the 08 has fewer shims behind the the PV spring than the 06. We know that on our 06 PV opens sooner than the 08 but ideally it shouldn't because of the shims. The 06 was bought used so someone could have changed some things.

I am confused about this adjustment screw that supposedly sets the preload on the governor spring. Why is there preload shims if there is a screw to adjust the preload ? We would like to know if anyone has adjusted this screw with any power results ? I would love to duplicate the power of our 06 onto the 08.

 

[PEB]

I have adjusted the preload on all three of my GG bikes to allieviate some power valve slop. I have never noticed any power change.

 

[J D]

I would love to duplicate the power of our 06 onto the 08.

Mines a 07 300 & this is what I'm trying to achieve.

 

[rpduc]

I am confused about this adjustment screw that supposedly sets the preload on the governor spring.

I think you're mixing up your preloads...

Screw #3 is just a set screw on a shaft that holds a finger that pokes into the governor assembly. It does not set preload on the governor spring. One can set it to remove slop in the system, i.e. if the plate at the top of the actuator rod is not held against the stop with a slight amount of "preload." That pork chop shaped plate on my MC 250 was barely touching the stop. I tweaked it just a tad so there was a "slight" pressure against the stop. I didn't notice any power change.

Conversely it's also possible to adjust that setscrew so the plate is nowhere near that stop with the engine off. I would imagine it could rattle in that scenario and it seems those who have adjusted in that manner were looking to alleviate rattle, not affect PV operation.

I would say that is different from adding shims to the governor. As Glenn explained:

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.

The "finger" pokes into the governor and transmits the movement of the governor to the actuator rod but one would have to shim or change springs to affect a significant change in when and at what rate the governor moves.

 

[GMP]

Ross is correct. When I said "preload" in my description of the adjustment, I simply meant just enough force to keep the actuator plate against the stop. it is not intended as a power delivery adjustment.

As far as power differences between an '06 and '08, I would think ignition maps have a lot to do with it. Also, I would suspect some variation in PV spring tolerance, and the possibility of the part actually being different with the same # in the manual. It wouldn't be the first time.

 

[101racing]

Ross is correct. When I said "preload" in my description of the adjustment, I simply meant just enough force to keep the actuator plate against the stop. it is not intended as a power delivery adjustment.

As far as power differences between an '06 and '08, I would think ignition maps have a lot to do with it. Also, I would suspect some variation in PV spring tolerance, and the possibility of the part actually being different with the same # in the manual. It wouldn't be the first time.

We have changed the CDI around with no difference. We are going to pull the clutch sides off to take a look at the difference in shims ,spring etc. There is a difference some where and we have covered everything with confidence other than this subject. The 06 pulls like a mild 500 and the 08 is a good 250 but i know of 250's that are stronger.

The Trusty's power valve adjuster would be a real nice add on but if it wouldn't give the same power delivery as the 06 I'm not spending the cash to find out. Just by the seat off my pants I would think it would limit the opening of the PV more than boost it. JMHO.

Ross, the adjuster screw 3 is for what I suspected in the linkage position . Thanks for clarifying. The shims and spring is what I would be looking at to adjust on rate and timing of the PV.

 

[jefgil123]

101 Racing - We want to know what you find about how the '06 is set up ! Mild 500 - WOW !

 

[101racing]

101 Racing - We want to know what you find about how the '06 is set up ! Mild 500 - WOW !

We ordered the gaskets today and it won't be till after labor day sometime. We also know that our compression is down on both. We are at 150lbs on both at 4000 ft alt. 2 different compression guages and both are identical. We had an RB head on the 08 for awhile and when we pulled a base gasket out the quinch got down to .028 so we swaped heads with the 06 stock head because it had .042 quinch with the RB head. The 08 now has about .072 quinch with the stock head. Don't know if we should pull more base gasket out of the 08. It has a .3mm and a .5mm in it . Running less base will cover the transfers up more but lower port timing and raise compression. Hard to say which way to go before sending in the head to RB. Some on here are pulling base gaskets to a minimum and others are adding to uncover the transfers. Seems to be allot of different opinions. I would like to talk with someone that knows allot more about this subject than me.

 

[jefgil123]

All I know is the squish and compression have a LOT of difference in the
way it pulls off the bottom.
I have had a .045" squish head on mine, and it pulled great !
I then tried a little less with a different head, .060", and it wasn't as good.
(Both heads done by RB Designs, the .060" at my request)
A noticible difference.....

I am going to reduce base gasket soon and get the squish back down there to about .050", which will lower
the transfers a bit , too.....

That , and the CR250 reed block (6 petal) with light Boyesen glass reeds....
Tried the above Reeds and didn't really feel much difference. Oh well..... 11-12-09