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Variable valve timing for CRF230

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I roadraced a Yoshimura powered CB590 Honda with my own version of variable valve timing in 1978 and prepared but never followed through with a patent application on a second system. Because of this interest I have been trying to follow progress over the years. Most systems have too much complication in either the hardware or the control systems but they do always provide some benefits. Even though I was changing the phasing of a single cam and moving both intake and exhaust lobes together it worked pretty well. It is best to be able to change phasing separately in both cams but it turns out that with a single cam the intake closing event sort of dominates the powerband the most.

Imagine you take any cam and advance it to boost low end, then retard it to boost top end,.. then allow it to shift phasing as rpm increases. 

The 2017 GSXR 1000 uses a simple centrifugal system like the old Revloc auto clutches. This bypasses the moto GP ban on hydraulic or electric systems. The cool part is that its all fitted into the intake cam sprocket. You can see it here http://www.sportrider.com/unveiled-2017-suzuki-gsx-r-1000-and-gsx-r-1000r#page-4 There are also youtube videos showing it in operation.

I have enough projects going so I thought I would throw this out there for others to digest too. The GSXR sprocket appears to have 34 teeth and so does the 230. I don't know if its the same chain pitch or width? It may only take a custom cam to make a drop in VVT kit for our bikes. Possibly even a bolt on sprocket using the CRF cam???

The end result would be retaining all of our beloved low end power but being able to boost top end power as well. A simple RPM based cam timing shift with no electronics or outside controllers would be cool.

Greenhuman,.. Terry Miller,.. this is right up your alley. I get the first one though  : )

 

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GM recently started doing this with their single-cam pushrod engines.  The problem is that if we want to close the intake valve sooner to boost low-speed VE we also end up opening the exhaust valve sooner, which has the opposite affect.  However, very generally speaking advancing the cam boosts low-speed VE and retarding it boosts high-speed VE.  Agreed the intake side tends to dictate overall power delivery characteristics.

Way back in the old days there were some gimicky cam advancer/retarder mechanisms in the back of Hot Rod magazines.  I am 100% sure my father could find one in his large collection of Hot Rod mags.

Mike Coe did some work on the Kawi KLR by changing one of the cams by one tooth.  One tooth sounds crazy but it worked well.

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I roadraced a Yoshimura powered CB590 Honda with my own version of variable valve timing in 1978 and prepared but never followed through with a patent application on a second system. Because of this interest I have been trying to follow progress over the years. Most systems have too much complication in either the hardware or the control systems but they do always provide some benefits. Even though I was changing the phasing of a single cam and moving both intake and exhaust lobes together it worked pretty well. It is best to be able to change phasing separately in both cams but it turns out that with a single cam the intake closing event sort of dominates the powerband the most.
Imagine you take any cam and advance it to boost low end, then retard it to boost top end,.. then allow it to shift phasing as rpm increases. 
The 2017 GSXR 1000 uses a simple centrifugal system like the old Revloc auto clutches. This bypasses the moto GP ban on hydraulic or electric systems. The cool part is that its all fitted into the intake cam sprocket. You can see it here http://www.sportrider.com/unveiled-2017-suzuki-gsx-r-1000-and-gsx-r-1000r#page-4 There are also youtube videos showing it in operation.
I have enough projects going so I thought I would throw this out there for others to digest too. The GSXR sprocket appears to have 34 teeth and so does the 230. I don't know if its the same chain pitch or width? It may only take a custom cam to make a drop in VVT kit for our bikes. Possibly even a bolt on sprocket using the CRF cam???
The end result would be retaining all of our beloved low end power but being able to boost top end power as well. A simple RPM based cam timing shift with no electronics or outside controllers would be cool.
Greenhuman,.. Terry Miller,.. this is right up your alley. I get the first one though  : )
 


Or Frank at EO....

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The other huge benefit to systems like Honda's is that by reducing overall lift and duration we are also increasing low-speed port velocity.  Lots of variables in such a system.  This is also why so many auto engines today have not only tuned-length but also variable-length intake runners.  Terry told me one time he built an engine with tuned intake and tuned exhaust and when it all started working together he thought he blew the pipe off the engine because it started making a bunch of noise.  My slow-turning SRX600 gained a bunch of power right in the middle with tuned intake runners.

My guess is a small engine like ours with tuned intake and tuned exhaust and variable valve timing could find all sorts of extra area under the TQ curve.

However...  More parts and pieces and complexity...

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My CRF230F is simple. That's why I bought it. That's why I still own. Yes it's been modified to make it better, but never at the expense of simple. I have the opportunity to work on Yamaha 300hp outboards at work. The latest and greatest of everything. They are not simple.

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What provides the resistance to the ball movement in the track? Are there some springs on the ball missing from this pic?

 

gsx-r1000_al7_variable_valve_timing_system.jpg

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You know I wouldn't suggest something that's not simple. That's the beauty of this system,... two main parts, some ball bearings and disc springs. Tune the advance curve with the spring. Any failure at all leaves you with cam timing that is within the limits of its design. 

E-start adds about 50 parts 12 lbs. and many failure points while adding no power,... so much for simple.

Could be an easy bolt on part without major disassembly and one gasket,.. maybe 15 minutes. No cables, hydraulics or electronics. Its self contained.

I just checked the price but I think its a mistake, entire GSXR cam with magic sprocket attached $381.00 Sprocket assembly only $491.00 They must have it backwards?

I wonder if its a bolt on upgrade to last years GSXR's?

 

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The two disc shaped washers are actually conical. They are called belleville springs. They push the halves together and the grooves are ramped. One set of grooves is curved so it twists as the balls move. 

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20 minutes ago, woodsryder said:

The two disc shaped washers are actually conical. They are called belleville springs. They push the halves together and the grooves are ramped. One set of grooves is curved so it twists as the balls move. 

Ahhhh..... :thumbsup:

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Some consideration in a single vs multi cylinder machines...

The strobe studies of the cam drive system show a tremendous amount of "snap and slack" conditions on the the chain in a single cylinder...  The comparatively  long time between combustion pulses has sub harmonics introduced from valvetrain loading...

Heavier crank assemblies and milder valvetrain action will moderate some of the snap and slack of a single cylinder...

I'm not sure what the added flywheel like weight would mean as part of the cam sprocket assembly... It could potentially make the valvetrain action smoother via inertia... Or the action of advancing and retarding the cam could induce extra stress... Making a stronger cam chain necessary... The RPM range of the 230 is relatively mild... But the valvetrain also is dealing with the weight of rocker arms in its inertia ...

Very interesting idea though....  

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