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TOPIC: DT100 Rear Sprocket Size

DT100 Rear Sprocket Size 11 Aug 2017 17:02 #1

  • Ship_faced
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Im in the process of bringing my '75 DT100 back to life and my driveline is in poor shape. Before I spend $75 on another NOS rear 49t sprocket, I figured Id get some opinions from the gurus! Has anyone put a larger (or smaller for that matter) sprocket on and been happy with the results? There are other sizes (45t, 47t an 55t) available for half the price, but I wasn't sure how much it would affect this particular bike? Just looking for some real world results/opinions to weigh my options before I pull the trigger.

Any advice appreciated!

Cheers!

**I tried a search before posting this

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Last Edit: by Ship_faced. Reason: Typos/Long-winded

DT100 Rear Sprocket Size 12 Aug 2017 08:59 #2

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What do you plan to do for riding? Around town or woods riding? It's quicker and easier to change out the front sprocket. I can't give you a solid answer without knowing your intentions. The stock gearing is great and you can easily go up or down one tooth.

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DT100 Rear Sprocket Size 12 Aug 2017 09:21 #3

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Yeah your right and I agree! Fronts are nice and easy to change and I keep a couple different ones around for some of my bikes to change the gearing for certain riding. I was just trying so save a little money if one of the other options have been good for people since the 49t is more than double the price. Your absolutely right though, without knowing what type or riding ill be doing, its hard to say, so sorry for leaving that out!

This will mostly be around town and maybe some mild woods riding here and there but just dirt roads and putting around if off road. I have other dirtbikes to beat on. No long rides either.

Im thinking of maybe going 16/55? keep it kind of close to stock with a little more low end (about 2.5t up from stock). any experience or advice with that?

Thanks for the reply!!

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Last Edit: by Ship_faced. Reason: Wrong tone

DT100 Rear Sprocket Size 13 Aug 2017 13:54 #4

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Are there any aftermarket sprockets that you guys recommend? I read somewhere that someone bought a JT sprocket that didn't fit, but maybe they ordered the incorrect one? I really haven't found any other than the JT838..

I love the look of the stock sprockets, but the NOS aren't cheap. After giving it some thought however, I think I would like to keep the stock gearing.. so im looking for a 49T.

Thanks in advance! You all have been really helpful thus far!

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Last Edit: by Ship_faced.

DT100 Rear Sprocket Size 13 Aug 2017 14:18 #5

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Do you know what size chain you have? 420 or 428?

The 1990's RT100 are extremely similar to the DT100... RT100 rear sprocket is a 48 tooth with 4 bolt holes. Sprocket lock tabs are the same part as DT100 so bolt spacing should be the same. Rubber hub dampers are the same as DT100.

One tooth on the rear is not much... RT100 sprocket is available from Yamaha (partzilla) for $17.44

www.partzilla.com/parts/detail/yamaha/YP-2U2-25448-10-00.html

I think the RT100 used a 420 chain and you might have a 428 chain? But again there is a good chance the FRONT sprocket from the RT100 would also work perfectly on your DT100.... in other words you'd use the chain and both sprockets from the RT100? Might be worth looking into?

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1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

DT100 Rear Sprocket Size 13 Aug 2017 18:30 #6

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Thanks a lot MarkT!! Great info there! I do indeed have a 428 chain, and I just ordered a new one... BUT, I am going to look into that right now as there is still time to cancel my order.. Thanks a lot, and good call!

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DT100 Rear Sprocket Size 13 Aug 2017 18:50 #7

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Just to be clear... I've never actually tried the RT100 sprockets on the DT100... but from the parts lists it looks like it should work fine.

Let us know how it works out if you decide to try it.

:Buds

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1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

DT100 Rear Sprocket Size 14 Aug 2017 07:26 #8

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MarkT wrote: Just to be clear... I've never actually tried the RT100 sprockets on the DT100... but from the parts lists it looks like it should work fine.

Let us know how it works out if you decide to try it.

:Buds


I did some research and it does indeed look like it should work! based off what you said and my cross referencing for the front sprocket, it should all bolt up fine! I just need to make sure I get the right length chain (not sure if they are different). But even the chain is drastically less expensive even for OEM. Id like to order the chain form partzilla at the same time, but its a 104L vs a 112L. Does anyone know if the a 104L 420 chain is close to a 112L 428?


Cant thank you enough MarkT! Beers on me next time I see you ;)

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DT100 Rear Sprocket Size 14 Aug 2017 07:48 #9

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You should order longer and cut it to length. Chain breakers are not overly expensive, and a good tool to have in the stash.

For 420/428 the difference is in how thick the sprocket is, not the distance between the pins:
  • 420 sprockets are 5.70mm Wide

    428 sprockets are 7.14mm Wide

This chart will show you the differences between the more common motorcycle chain sizing.



I.E. if the sprocket sizing (# of teeth) are the same, the same number of links will be required.

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No Good Story ever started with a Salad . . .

DT100 Rear Sprocket Size 14 Aug 2017 07:57 #10

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While we're on the topic of chains, here is a neat little graphic showing the way to remove and install a master link, without tweaking it . . .



And another on one way to test for chain wear . . .

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No Good Story ever started with a Salad . . .
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