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Post by golfmech on Jul 18, 2018 20:02:07 GMT -5
So I bought a 2.88 / 49-17 tooth gear set for my 07 50cc rokita scooter. the large gear that came in the set fits right on my axle shaft but the small 17 tooth gear that is supposed to press on to my old final drive gear doesn't fit, the part of the gear that presses into my original gear is about 3-4mm too large. Has anyone else had this problem is my gearbox some oddball that has weird gear sizes?
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Post by golfmech on Jul 18, 2018 20:36:26 GMT -5
The original small gear is 13 tooth. I can't seem to find anything online about anyone else having this problem. I could probably have the new gear turned down to fit but I'd rather find the correct parts
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Post by golfmech on Jul 19, 2018 14:39:52 GMT -5
So I milled the 17t down to fit and it works great my top speed on flat grade is now 41 vs 35 I do have a 72cc bbk installed with the a9 cam. I feel like I'm not quite getting the rpm I used to. Is the big valve head a decent upgrade? Will it help me get more rpm on the top end?
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Post by humanshield on Jul 19, 2018 15:03:32 GMT -5
Did you mill the gear down yourself?
How much difference in take off from a stop do you notice? Going up hills?
You could try lighter weights in the variator but overall, you've reduced your final drive ratio and so you need torque to overcome it.
Yes, a big valve head can increase torque by allowing more charge into the chamber at a time and faster loading and unloading. (Bigger pop). Just be careful because many BVH's also come with increased volume and that can lower compression. If you lower compression at the same time you go with a BVH you might gain horsepower but lose torque.
Problem with a GY6 motor is they're not really all that happy with high rpms where you'd get that extra HP.
I have a 50mm BBK and have been considering a gear change so I'll be following your results.
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Post by golfmech on Jul 19, 2018 20:27:45 GMT -5
Yes I milled it myself the gear that came with the new set had a .750 press fit gear. My stock press in gear was about .675 so I milled the new gear to .673 heated and pressed it together. My acceleration hasn't really suffered too much I still have plenty of power to move my 210lb self around in soft sand. But it does up shift slightly to fast I feel like I am just under the power band once I get to about 34 then it creeps up to 40-41 GPS I'm going to try lighter weighs to hold higher rpms. Hopefully I can get higher rpms and still get maximum belt travel at the top end
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Post by golfmech on Jul 19, 2018 20:44:44 GMT -5
Still pulls up hills good stays above 30 on seep hills I forgot to mention the gears I got are not straight cut the are angled like the stock gears so I haven't noticed any gear noise. You can find them for 24.99 free shipping right now it's a pretty good deal if they drop right in or if you have my issue have access to a mill. My scoot is an 07 and had a Factory 13 tooth pressed gear so I think it's an odd ball for gearing. The fact they are angle cut made doing the millwork worth it in my opinion as all other 17-49t gear sets I have seen have been straight cut. So they are louder weaker and more prone to failure than this set
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Post by humanshield on Jul 21, 2018 15:33:59 GMT -5
Can you give me a link to where you got yours?
I'mma go ahead and do this because with my 50mm BBK with cam, it winds up to max rpm pretty easily and just howls there.
It REALLY feels that a taller set of gears would help it. If I could cruise along at around 40mph without winding it out I'd be happy. Right now if I go over about 37mph, she gets to howling. Launch is stellar. I can hang with the cars up to about 30mph then they're gone. Top speed I ever hit is 47.5 I believe (flat ground NO WIND, tucked) But man was she wound up tight.
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Post by golfmech on Jul 21, 2018 17:43:53 GMT -5
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Post by humanshield on Jul 25, 2018 18:13:58 GMT -5
My 2.88 set arrived today. Looks good. My original set was 3.71 (14/52) and I was easily pulling over 8,000 and she just wouldn't go any more. Hoping this set will let her walk out top end better without sacrificing too much acceleration or hill climbing torque. Will see. I measured my gear with a caliper and they seem to match my Bentelli Scorch within a couple tenths of a millimeter. But definitely not off by even 1 full millimeter. So I should be good. Looking forward to the results. Hope to have it back together tomorrow.
But...my gasket did split so I either have to repair it or hope I have a spare on hand. If not, it could set me back a week waiting on one.
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Post by golfmech on Jul 25, 2018 19:00:56 GMT -5
Ah goop it back together with some silicone for now and run it. I have changed my gear oil twice since I changed gears I am still getting a little metal probably put on 80 miles so far. honestly I just wacked the old gear out with a hammer then used a vice to get the new gear started and a hammer again to drive it home. I tried out some 4.5 gram rollers took off like a bat out of hell but lost about 2mph on the top end so I went with a mix of my factory 8G rollers and the 4.5's. pulls nice off the line to about 34 then kinda creeps into topgear for 41-42 mph. after playing with weights I have to say gearing wont kill your acceleration if you tune your cvt
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Post by humanshield on Jul 26, 2018 6:14:15 GMT -5
Sounds good. since I'm running the 50mm BBK I'm expecting it to keep pretty good power to push the gears. If it doesn't I'll just do some more mods to up the power enough to push them.
I was able to max at 47.5 with the 3.71 gears.....so hopefully I'll hilt 50 now. But more important (to me) is that I can cruise at about 40 without winding the motor out. I just don't like the poor little 4T buzzing at 8500rmp to do 44mph
35 @ 7000RPM is just too slow but 40 @ 7000RPM would make it comfortable. Small difference....but big difference.
If I can't get access to a press today I guess I'll change the gear like you did.
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Post by GrumpyUnk on Jul 26, 2018 9:21:55 GMT -5
I think there is a video or link, or at least several pictures on a site posting.
I ordered a full set of gears to replace a set that had been run with failing bearings. Replaced all the bearings also. BUT. The one of the gears would not fit into the gearbox. Had multiple emails with the vendor and their China technician. I ended up taking pictures of the original and the replacement with a micrometer indicating the gear diameter indicated. They finally believed me. I suggested they check their stock.. and note the measurements of the individual gears in the images on their site. They must have done the former as that item was gone(maybe still) from their web site, and all the pictures sprouted measurements. They were very nice about it, but were consternated that their product could be so far off. I would want the vendor to send me a new set if the diameter was off rather than trying to machine the teeth to a lower profile. I would think lighter weights in the variator would be a reasonable step with a 'long legged' final drive set. That would allow higher rpm on takeoff, but better cruise when the variator finally got to where it was going. If the variator was not strong enough to upshift all the way, perhaps a lighter contra spring would help. tom
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Post by golfmech on Jul 26, 2018 13:52:53 GMT -5
I didn't machine any teeth just the surface of the small gear that presses onto the larger gear. But my setup seemed rare as my original small gear only had 13 teeth. Also you need lighter weights for higher rpm at takeoff but too light and the belt won't ride all the way up on the primary. It's a a balancing act
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Post by humanshield on Jul 26, 2018 18:45:22 GMT -5
Welp, the gears are all in but I'm not happy. when I spin the rear tire it sounds like there are rocks in the housing. Now, this could just be the new gears needed to be worn in to each other. Or, it could be something else. Pretty sure I got everything in there right. But man it sounds awful. And it trembles as it rotates. Again, it could just need a few miles....or ....
Did yours spin smooth and quiet after you installed the new gears?
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Post by GrumpyUnk on Jul 27, 2018 13:38:45 GMT -5
Did you remember to install the plastic washer? The gears with spiral cut teeth will tend to move in one direction, thrusted against the wall/bearing as the teeth mesh under pressure. If you left out the thrust washer or put it on the other side of the gear, you might get some noise. Did you turn the input shaft manually, or the clutch bell, to see how smooth it felt? If it is rough, take it apart again as it will not get better. I think if you look at the teeth as delivered you will not find they have rough spots that need to 'wear in' to become as quiet as before. If the teeth have damaged surfaces, they will not heal themself. They will always make noise. Compare teeth on the new gears to the teeth of the previous set. tom
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