Limting CVT to achieve lower max ratio

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alexanderfoti
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Limting CVT to achieve lower max ratio

Post by alexanderfoti »

So my bike rides the cvt up to 3+ rpm until 20 mph where it drops to 2500 rpms and stays there.

The front pulleys and rear pulleys are still going through their ratio. This means on the flat land (motorways) the bike is held at 2500 rpm at approximately 60mph. I struggle to get past this unless downhill, and uphils drop this to mid 50's.

I theorised that if I can get the engine revs up, I should get more power, and retain that speed.

I used an laser tachometer and reflective tape on the rear wheel to measure its RPM.

at redline with the bike on the stand I had 1580 rpm which was roughly translated to 110mph ground speed. Obviously no good, bike hasn't got the power to achieve this, so I set about blocking the movement of the CVT pulleys to lower the "top" gear.

A 3d printed collar on the rear pulley, that looks like this:

Image

This serves to limit the amount the rear pulley opens.

It goes here:

Image

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That is half done, After this we move the attention to the front pulley. With the setup as it is now, the front pulley will burn the belt out as it wants to go through its full range of movement, to solve that, we run the engine up to top rpm and mark on the pulley with a marker the belt position.

Then we print another shim to go on the stub axle and prevent the pulley from moving in all the way, therefore saving belt life!

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I did 125 miles yesterday and initial results seem good. Bike can now do 70mph on flat at redline, and hills only slow this to 62-63. Fuel economy SHOULD be improved as well, as the governor is not overfueling the whole time, but I' on the fence on that one.

The rear one is plenty thick enough, but the front blocker is very thin and I do worry that it wont last, so will keep a close eye on it.
gilburton
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Re: Limting CVT to achieve lower max ratio

Post by gilburton »

There should be a thin bearing on the front pulley to prevent wear like this
http://www.grays-aixam.co.uk/index.php? ... uct_id=308
The belt sits on it at rest.
This is the bearing number/size so possibly a slightly wider one would do the trick or shim it?
61806 30 X 42 x 7
alexanderfoti
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Re: Limting CVT to achieve lower max ratio

Post by alexanderfoti »

gilburton wrote:There should be a thin bearing on the front pulley to prevent wear like this
http://www.grays-aixam.co.uk/index.php? ... uct_id=308
The belt sits on it at rest.
This is the bearing number/size so possibly a slightly wider one would do the trick or shim it?
61806 30 X 42 x 7
The wear in the last picture?
It was a used pulley so I'm sure its from dragging at idle. My belt drags very slightly at idle but I cant get the idle any lower than around 800 rpm or the engine stalls ....

I did think either the shim on the shaft, or a shim in the middle to stop the pulleys closing but it would have to be quite wide to be wider than the opening.
gilburton
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Re: Limting CVT to achieve lower max ratio

Post by gilburton »

Aixam recommend changing the belt at 11000 mls but that is on a car capable of carrying 4 or 2+2 people so on a bike the belt should last a lot longer.
I thought you meant belt wear on the front pulley that's why I mentioned the bearing. If it's not turning it's seized and will cause wear when the belt is idling.
Any wear/ridges on any pulley will increase wear and make it "snatchy" all the pulleys should be smooth.
In France these cars are treated fairly gently basically as mopeds around town. In the UK we had gearboxes exploding as we treated it as a car and thrashed them around.
Another fault was that drivers would select reverse/forward before the car had fully stopped. This would cause wear on ALL the components. In France they never got the gearbox problems we got.
I know you are not using the gearbox but it explains the heavy wear you seem to have.
alexanderfoti
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Re: Limting CVT to achieve lower max ratio

Post by alexanderfoti »

The pictures make it seem like that, but the reality is the pulleys are completely smooth.

The rear one has no visible marks on it, probably because its sheltered from the elements. Belt is all good.

Front idler bearing turns freely and is in good condition.
alexanderfoti
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Re: Limting CVT to achieve lower max ratio

Post by alexanderfoti »

So am now geared to 75mph at top rpm.

The obvious downside to this method of limiting RPM is that you loose the whole range of the CVT. If your speed drops too far down (below 66-67mph) then the rpms drop back down to around 2500 and you loose "power" again. This is mainly an issue on hills with headwinds etc, but you still end up going faster than lorries so I am happy.
alexanderfoti
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Re: Limting CVT to achieve lower max ratio

Post by alexanderfoti »

So I just discovered an additional 800rpm by fiddling with my goverener, so I re-geared for 81mph and I should be able to get there quicker.

2 issues.

1. The vibrations from the higher rpm running has broken my "epoxy repaired" thermostat housing, so now I need to remove the head to change the housing (argh kubota!!!)
2. I have little puffs of white smoke at 3900 rpm accompanied by misfires.... wonder if my timing is too far off for this rpm, or if my nozzles have bad spray patterns.
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