139qbm roller weights

[abansb]

I was wondering if anyone could tell me if they know the difference between these roller weights I know the holes in the middle are different but I don't know how to tell what size they are or anything the ones on the left are from my old engine and the one on the right are from another engine I was going to replace them with and how can I tell what size they are ?



Thanks

[stepthrutuner]

Measure the outside diameters and lengths. This is the usual order roller size is stated in ads for rollers - diam. x length. They must also be weighed with a scale that weighs in grams.

[90GTVert]

It kinda looks like the one on the right is larger, but it's hard to tell really. A 16x13mm and a 15x12mm are so close you're best off to measure like Reggie said. If they're both from a stock GY6 50, they should both be the same 16x13mm. The weight being different can make a big difference in performance. Have to weigh them each to know what's working and what's not.

[abansb]

which is best larger or smaller for performance

[90GTVert]

The correct size is best. Larger won't fit. Smaller will rattle and not open the vari as far and is at a greater risk for getting turned about improperly.

[abansb]

gotcha they are the same roundness what got me was the size of the hole in the middle

the ones to the left are worn when I broke the belt it trashed the variator ripped the nubs that stick up off and the sleeve that is on there looks like it is made on there not for sure If I can get it off or not

[lackthereof]

Weight is what you need to worry about. Size, so long as they're pretty close to the same and fit properly in the variator slots, won't have an impact on performance. 16mmx13mm is the typical size for a 50cc GY6. Depending on the construction of the weight, the center hole may be different. Unless you are absolutely sure they have the exact same metal composition, you can't compare weights by the center hole.

The weight of the roller is what has a big impact on performance. Heavier weights will cause low RPM shifts, light weights will cause high RPM shifts. I'm running 5g weights right now, which gives me a steady acceleration/hill-climb RPM of about 6000. Peak HP on these engines (stock) is supposed to be somewhere around 7500. I experimented with lighter weights to get it governed right on that 7500 RPM peak, but in the end my performance gains in those last 1500 RPM were trivial, and the fuel economy losses huge. It seems like the HP curve on these engines is really flat between 6000 and 8500 rpm.

My top speed on a particular steep hill I use for benchmarking was 25 MPH with the 6000 rpm weights, and 26 MPH at 7500 rpm. By contrast, my observed "absolutely flogging it" commute MPG went from the low 70s to around 50. With the stock weights, it couldn't break 15 MPH on that same hill.

You can use a little digital scale to check your weights - you can pick them up on ebay straight from China for around $5 like this, or if you're in a rush you can get one at any local smoke shop at retail prices. You can get cheap inductive tachometers off of ebay, too. Little digital ones like this will get the job done, if you're not too concerned with quick display response.

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That center sleeve shouldn't be attached to anything. The rear slide plate should be trapped behind it, if you just yank on it the whole mess should come flying off.

[abansb]

looks like some of the teeth on the gear is a little messed up and wont budge I think if I get a wheel puller on it will come off