CVT test run

[thebuggyman1]

Tuning the CVT clutches seems to be more of an art form than science.
When I built the Bigfoot http://www.6x6world.com/forums/max-a...-tall-tub.html I ordered clutches from Recreatives, hoping to get a matched set and not need to tune. I also mounted the 40 horse Kohler on the original motor plate with rubber mounts. I knew there was a lot of movement in the mounts, so I added a couple extra stabilizing springs to help out. The problem I had was the clutch upshift seemed to happen too fast. When I would start out Everything seemed to engage properly, but the machine would take a giant leap forward in speed making trail riding tough...it really wanted to run over the person in front of me.Over the Christmas break I pulled the motor and replaced the rubber mounts with solid ones. That change really improved how the clutches worked.Now I feel I just need a slight amount of fine tuning. My thought is the engagement is a touch too high...like 1900-2000 rpms, but the normal driving range is correct at 2500-3500 rpms.I'm looking for opinions here, so please let me know what you think.

[micmac]

Jim,

What kind of solid mounts did you use? How much increase in vibration did you notice if any?

[thebuggyman1]

The original rubber mounts were 1" tall. so I replaced them with a piece of 1" square tube layed on top of the frame rail. 3/8" holes drilled through it (them, X2) and nuts welded to the underside of the frame. I adjust the motor by sliding it on the motor mount plate, not by the original slots in the motor plate.
Vibration is not an issue...if it were out of balance that bad, it would shake itself apart at high rpms.

[Noel Woods]

I noticed there was no engine shudder, I believe there is a calibration issue between the two clutch assemblies. Otherwise engagement wouldn't come at such high rpm.

[Bazooo guy]

Did you have it on blocks for the video or were you driving on level ground.
I dont think the clutches react the same if the wheels are spinning free.
My understanding is the secondary spring determines the shift point and the primary
determines the engagement point based on rpm.

[thebuggyman1]

I was driving around the yard. It's mostly flat ground, but at about 4 1/2 minutes in I stopped at the base of a small hill (dirt pile). That is where I was able to get a realistic engagement RPM. On flat ground it rolls too easy...like with a good breeze. I tried to keep the machine at normal driving speeds. One thing I did fail to mention is belt tension.
I have 1" to 1 1/8" of deflection, perhaps I should loosen it a little.
What little info I could find on the powerbloc clutches ...... the spring in the primary determines the engagement RPM, the weights determine the upshift. The secondary is more downshift. Of course there is interaction between all three.

[Bazooo guy]

Did you set the correct offset for the clutches?
In the video the belt seems to be on an angle in high gear.
Or is it just the angle of the camera?
This video shows how easy it is to tune the primary.

http://m.youtube.com/#/watch?v=sIYXGRaEb_Y&desktop_uri=%2Fwatch%3Fv%3DsIYXGRaEb_Y

[Tomo]

hi,
I will refer how to tune a comet 780 drive /driven although i do think the cvtech clutches tune differently because there design is different ..

First are u using the centre to centre distance [eng to trans] supplied by recreatives .This determines the belt length. This influences engaugement rpm.

Assuming the belt is for these clutches eg wrong belt width and the side angle ""v"" of the belt sides gives improper drive and enguagement etc

Has the gear ratios been changed eg more so for high speed ????
Or are they stock
There may be no difference between the bigfoot and the standard gears installed ..
The bigfoot has bigger tyres
The bigfoot will there fore have higher speed gearing.

The clutches need to be setup so it places a very small load on engine engine rpm increases at a moderate speed and not to max rpm straight away as soon as the throttle is touched

The fact of having a 40hp motor will pull thru taller gear ratios very easy and this includes the clutches set up for lesser hp

1 maxium speed faster or slower change sprockets as needed
2 change clutches to influence changing
in a 780 driven u would first change the "ramp angle " the flatter the angle the more acceleration is slowed or resisted ,then u fine tune with springs

This happened in my ssfox previous owner had a black spring 41 degree clutch very fast acceleration . This set up had no pulling power in the low end range as the clutch changed into "4th gear"" very very quickly

hope this helps , clutch set up is very much to each style of machine and to confuse u the application .

tomo

[thebuggyman1]

Bazooo guy: Clutch offset is correct, camera was mounted on the rollbar brace at a complex angle. I have the powerbloc 80 clutch, and it's different than the one in your posted video. I have fixed weights @ 275 g each, I wish I had the adjustable puck ones, that would be too easy to try different weights.

Tomo: There is nothing even close to original with the belt/clutches/motor. It originally came with a Briggs 16hp comet clutches and 45" belt. Both clutches were changed along with the engine, and it now has a 49" belt. Most CVT setups recommend 1 1/4" belt deflection, so I should try a little more than I have now.
Gear ratios are stock MaxII, but it does have the larger heavier tires....everything I've read says to ignore the tire diameter, it's the weight (rotating mass) of the larger tires that matters. Either way, there is no formula for the changes.
You may be on the right track with gear ratio changes though. It would be easy to try some different gears on the jackshafts and see what happens. I have plenty of speed,but better low end creep would be nice.

[Bazooo guy]

I would set the deflection at 1 1/2" and see how much of a difference it makes.
If the belt is too short it will try to creep at low rpm and shift too soon.

[2gnospam]

Sorry I can't help with the clutch tuning, but would want to know where did you get that tach. Been looking for a low cost one compatible with a Vanguard twin.

Thanks

[wfo]

you can get different weights for that primary, i used a 150 gram weight and it seemed to work better

[JohnF]

Totally science. Insanely complex.

get ready >>

Olav Aaen's "Clutch Tuning Handbook" if you want to know the theory of operation.

Sheave angle
ramp angle
spring preload
belt
flyweight
yada yada yada...

I assume that : you've found what you consider the proper belt, that we must tune the CVT you have now, this CVT has fixed sheave angle/secondary helical angle/primary flyweight ramp angle, that the only variable we can adjust are flyweight mass, primary pressure spring, secondary spring preload - like any of the CVTech Powerbloc series CVTs, and that we are pretty close with the CVT we are starting with.

Changing any one of those variables will change all output parameters of the CVT to some extent, as you have mentioned, but each variable has a much bigger effect on one particular output than the others.

. flyweight mass - running RPM
. primary pressure spring - engagement RPM
. secondary spring preload - gearing selection (upshift/downshift)

First tune the primary

The drive pulley (primary clutch) is an RPM sensitive device and we use it to dial in the power output of the engine. I can't tell very much about the tuning of the primary from your video because it doesn't look like you ever ask for max HP.

Keep in mind that your engine performance is subject to the effects of density altitude and that your primary clutch tune is subject to the performance of your engine.

First goal is to get the flyweight mass right. For this we need to see what RPM the CVT runs at as it shifts through gears so you need to create a situation where you can go WOT and have the CVT shift through gearing slow enough to see it. Since we are watching tachometer and not having a computer doing the watching I would try WOT speed run either on a slope or towing a heavy trailer. We want to see: engagement - quickly go to target RPM - then gear up shifting. If RPM is too high you heavier flyweight mass - RPM too low use lighter flyweight mass.

Next we'll tweek the pressure spring. It has two variables that we really look at and that is preload and rate. Preload will change the engagement RPM and rate has a small effect on running RPM. Shimming a spring like Rock Doctor does changes the preload but do so with caution because you can coil bind the pressure spring and limit the movement of the drive pulley sheaves. Engagement at an RPM (and therefore engine HP) too low and you'll just kill the engine, just like when you learned to drive a standard transmission pickup truck. Engagement RPM too high and you'll endure violent launches. Too high/too low depend completely on the what is necessary to get the vehicle mass moving which is completely dependent on the vehicle mass/terrain slope at the time. If you always run light on flat ground you'll prefer a lighter preload and engagement RPM. If you carry the materials for a small house in a single trip... well, you get the idea.

If your CVT is one of the new Powerblocs with the little mass disks then I might cycle at this point a bit to tweek the flyweight mass around the pressure spring weight assuming I am at some middle of the road density altitude. If one of the older Powerblocs, like on the conquest, then I'm done.

And now shifting

The driven pulley (secondary clutch) is a torque device and it is how the CVT chooses a gear. If this were grossly off then everything I told you so far is wrong and you've wasted your time.

Grossly off secondary

The drive and driven parts of the CVT communicate through the squeeze pressure on the belt and the spring preload in the secondary dials in what that pressure needs to be. If the preload is too high (imagine so high it is like the secondary is welded) then there will be gobs of heat generated by the pulleys overcoming the giant squeeze just to turn and the CVT won't shift up. WOT but won't shift out even on a flat (assuming proper HP) would be a clue to this. If the preload is too low then the CVT will be lugging the engine by trying to be in too high a gear for the situation and if grossly off then there will be a gob of heat created in the secondary sheaves and belt squeal because the belt will slip. The "right" rate of upshift/downshift is dependent on use - again, light -vs- loaded.

So, if you are lugging then increase preload; if you are waiting forever to get speed then decrease preload; if you are generating lots of belt/sheave heat/squealing and/or the shifting was grossly off then adjust the preload towards improvement and start the tuning process all over.

Anyway, that's just my opinion. Put some WOT runs on video and post those.

Oh, and totally science, right?

[Bazooo guy]

Great info John.
So many variables ...
I think a big part of tuning is testing until it works best for the driver and conditions.

[thebuggyman1]

Wow, Great info John. I did hit WOT a couple times in that video, but only for 2 or 3 seconds...I was trying to keep the RPMs low, and in the "normal range".
Adding the load, Hmmm, I never thought of towing something heavy. I don't have any large hills, but they really don't bog that motor anyway. I guess I could tow the 1200# Avenger around the yard with the hand brake on. That might bog it down. lol
I think I'm pretty close to where I need to be, maybe a slight decrease in spring rate in the primary.....and maybe the same in the secondary.
Do you have any info on the primary springs? Colors/rates etc.
Do you have any info on how to adjust the Invance secondary? Are the springs replacable/adjustable? Info on rates if they are? The ramps work differently in the Invance secondarys, so I think the only adjustment would be in the spring.