thickness rear sprockets

Dragon · 04-30-2009, 10:57 PM

Is the 520 JTF rear sprocket the same thickness as the stock 428 ones? If not, do I need some kind of spacers/washer? I see a snap ring, and if the 520 sprocket is thinner than the 428's, there would be a gap between the snap ring and the sprocket. Would this gap be a problem?

forchetto · 05-01-2009, 01:47 AM

520 sprocket width is 0.227" against the 428's 0.284", about 0.057" difference. The correct thing would be to insert a shim to make up that difference between the sprocket and the circlip, the problem is finding a suitable one. It might be OK as it is, a case of suck it and see.

warrior91 · 05-01-2009, 02:07 AM

.060 shimstock @ machine shop or motor/mech shop.

czowner · 05-01-2009, 04:20 AM

Quote:

Originally Posted by forchetto

520 sprocket width is 0.227" against the 428's 0.284", about 0.057" difference. The correct thing would be to insert a shim to make up that difference between the sprocket and the circlip, the problem is finding a suitable one. It might be OK as it is, a case of suck it and see.

I think you've got that the wrong way round mate. I don't have my vernier to hand but my spare KLR250 sprocket (520) is thicker than my spare Hongdou sprocket (428).

Jonathan.

forchetto · 05-01-2009, 05:07 AM

I've got the data from this site:
http://www.gizmology.net/sprockets.htm

I was surprised by this when I tried (unsuccessfully...) to convert to a 520 pitch my Qingqi's transmission. The new sprockets were something like 1.27 mm thinner that the standard 428. The thickness of 428 sprockets is 7.2 mm.

I've have seen this confirmed in other sites and charts but find that the real-life measurements can be a bit vague. For example there's a difference in the measurements if the sprocket is painted or plated, if it's machined all over or just cut from stock plate, etc.

By the way, do you really own a CZ?...what model?. I had a JAWA-CZ 350 in the 90's. Great no-nonsense bike and smooth as a dynamo. Awful gearbox and silly multipurpose gear lever that worked the Kickstarter, gearchange and also the clutch at the same time. It was quite a challenge to work it and prevented the bike from being stolen by the common rabble.

czowner · 05-01-2009, 02:30 PM

Forchetto,
Appologies for jumping the gun without checking, you are correct, now I've scraped the muck off thew KLR sprocket it is indeed thinner.
I have a home made CZ trail bike, there's a picture in my Gallery (my gallery's on the 4th page).

Jonathan.

Dragon · 05-02-2009, 11:17 PM

Quote:

Originally Posted by warrior91

.060 shimstock @ machine shop or motor/mech shop.

I don't know of any local machine shop. But I'll ask around. Do I ask 'em to cut to shape?

Dragon · 05-05-2009, 10:17 AM

I managed to make shims out of galvanized sheet metal and with a dremel. Then, I installed both the rear and front 520 sprockets. This is what I used.

Front: jtf-328.13
Rear: jtr-279.35

Gear ratio: 2.692 (originally 2.875)

I can definitely feel a difference, but I wish I could go even lower on the gear ratio. A 14-teeth front sprocket would give a nice 2.5 ratio, but would also be way too big for the casing. A lot of metal would have to be grinded away, and I'm just not brave enough.

katoranger · 05-05-2009, 10:27 AM

Another option for taller gearing to swap the tire to a slightly larger one too.

A 110/100-18 tire will be taller than the stock and would be like dropping a couple teeth on the rear.

Allen

FastDoc · 05-05-2009, 11:28 AM

Quote:

Originally Posted by katoranger

Another option for taller gearing to swap the tire to a slightly larger one too.

A 110/100-18 tire will be taller than the stock and would be like dropping a couple teeth on the rear.

Allen

Good point. As we have recently discovered a fat knobby will gear it taller with the same setup otherwise.

04-30-2009, 10:57 PM	#1
Dragon Join Date: Nov 2007 Location: Tejas Posts: 834	thickness rear sprockets Is the 520 JTF rear sprocket the same thickness as the stock 428 ones? If not, do I need some kind of spacers/washer? I see a snap ring, and if the 520 sprocket is thinner than the 428's, there would be a gap between the snap ring and the sprocket. Would this gap be a problem? __________________ Chinabikeless
	0

05-01-2009, 01:47 AM	#2
forchetto Join Date: Jul 2008 Location: Gijon, Asturias,Northern Spain Posts: 396	520 sprocket width is 0.227" against the 428's 0.284", about 0.057" difference. The correct thing would be to insert a shim to make up that difference between the sprocket and the circlip, the problem is finding a suitable one. It might be OK as it is, a case of suck it and see. __________________ Jincheng Monkey JC50Q-7 (two of them) Skyteam Dax replica ST110-6 (two of them) Zongshen ZS125-43 Qingqi QM200GY-BA Super Motard Yamaha Virago XV1100 Triumph Bonneville SE Qingqi QM110GY PGO Bug rider 250 Buggy
	0

05-01-2009, 02:07 AM	#3
warrior91 Join Date: Nov 2007 Location: N.E. Saskatchewan, Canada Posts: 679	.060 shimstock @ machine shop or motor/mech shop. __________________ '91 Yamaha Warrior- stage 2 '83 Honda ATC 70 '08 Yongjiang 125cc mx (Loncin) '08 Yongjiang 150cc atv (Jinlong)
	0

05-01-2009, 05:07 AM	#5
forchetto Join Date: Jul 2008 Location: Gijon, Asturias,Northern Spain Posts: 396	I've got the data from this site: http://www.gizmology.net/sprockets.htm I was surprised by this when I tried (unsuccessfully...) to convert to a 520 pitch my Qingqi's transmission. The new sprockets were something like 1.27 mm thinner that the standard 428. The thickness of 428 sprockets is 7.2 mm. I've have seen this confirmed in other sites and charts but find that the real-life measurements can be a bit vague. For example there's a difference in the measurements if the sprocket is painted or plated, if it's machined all over or just cut from stock plate, etc. By the way, do you really own a CZ?...what model?. I had a JAWA-CZ 350 in the 90's. Great no-nonsense bike and smooth as a dynamo. Awful gearbox and silly multipurpose gear lever that worked the Kickstarter, gearchange and also the clutch at the same time. It was quite a challenge to work it and prevented the bike from being stolen by the common rabble. __________________ Jincheng Monkey JC50Q-7 (two of them) Skyteam Dax replica ST110-6 (two of them) Zongshen ZS125-43 Qingqi QM200GY-BA Super Motard Yamaha Virago XV1100 Triumph Bonneville SE Qingqi QM110GY PGO Bug rider 250 Buggy
	0

05-05-2009, 10:17 AM	#8
Dragon Join Date: Nov 2007 Location: Tejas Posts: 834	I managed to make shims out of galvanized sheet metal and with a dremel. Then, I installed both the rear and front 520 sprockets. This is what I used. Front: jtf-328.13 Rear: jtr-279.35 Gear ratio: 2.692 (originally 2.875) I can definitely feel a difference, but I wish I could go even lower on the gear ratio. A 14-teeth front sprocket would give a nice 2.5 ratio, but would also be way too big for the casing. A lot of metal would have to be grinded away, and I'm just not brave enough. __________________ Chinabikeless
	0

05-01-2009, 02:30 PM	#6
czowner Join Date: Sep 2006 Location: North East England Posts: 313	Forchetto, Appologies for jumping the gun without checking, you are correct, now I've scraped the muck off thew KLR sprocket it is indeed thinner. I have a home made CZ trail bike, there's a picture in my Gallery (my gallery's on the 4th page). Jonathan.
	0

05-05-2009, 10:27 AM	#9
katoranger Join Date: May 2007 Location: Altamont, Kansas Posts: 15,103	Another option for taller gearing to swap the tire to a slightly larger one too. A 110/100-18 tire will be taller than the stock and would be like dropping a couple teeth on the rear. Allen __________________ You meet the nicest people on a Honda Clone.
	0