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Author Topic: Chain run on RM-T  (Read 2247 times)

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Offline Graeme M

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Chain run on RM-T
« on: August 23, 2012, 08:00:13 pm »
Question to the suzi gurus. I have recently bought an RM250T for riding at CD9. I replaced a few odds and ends but on the whole it seems a fairly original bike. My question is about the drive chain run. With the wheel adjusted correctly, and running a 130/80 tyre, the chain runs within a couple of mil of the tyre. To my mind this will lead to the tyre giving the chain a nudge and possibly derailing it.

Is this how they are normally? Any suggestions for fixing it?
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Offline Nobby25

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Re: Chain run on RM-T
« Reply #1 on: August 24, 2012, 03:24:08 pm »
Graeme, I just checked my N with a 120/100 its about 10mm from the chain and has old scars from hitting the chain which I hadn't taken any noticed of before, Its only a recent resto and only done a few K's so I'm not sure if its going to be a problem. the only thing is check the spacers, as in the post below but in the end you can't change the sprocket/hub offset.
Cheers Nob

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Offline Graeme M

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Re: Chain run on RM-T
« Reply #2 on: August 24, 2012, 03:36:11 pm »
Hmmm... I've fiddled around with spacers and can get the sprocket in a direct line with the front sprocket, but then I've got maybe 2mm clearance. I did a little research and as far as I could see the 130/80 tyre was the same as originally specified but it looks to me like a narrower tyre would be the better option. 120/100 sounds more like it in that case. My other thought was to add a 5mm spacer behind the sprocket - cheaper than a new tyre at least...
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Offline asasin

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Re: Chain run on RM-T
« Reply #3 on: August 24, 2012, 03:50:16 pm »
Is the back wheel spoked up correctly? it can get 10mm out at times if not right . check centre of tyre is running in centre of bike.
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Offline bazza

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Re: Chain run on RM-T
« Reply #4 on: August 24, 2012, 05:14:56 pm »
assasin is on to it (must have stoped raining in katikati)
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Offline steve7406

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Re: Chain run on RM-T
« Reply #5 on: August 24, 2012, 05:29:44 pm »
I'm runing a donlop 110/100 on mine with no problems
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2000 Yamaha WR400f
1980 Suzuki RM250t
1977 Suzuki RM125b                                         
1975 Yamaha MX250b
1973 Yamaha mx360 (on the rebuild table)                                                               
1972 Yamaha dt1 250
1976 Suzuki ts 185

Offline PEZBerq

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Re: Chain run on RM-T
« Reply #6 on: August 24, 2012, 05:34:53 pm »
A 110/100 sounds like a much better tyre for a 250 to me. Would be much better for chain clearance I would think. Why the 130/80?
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Offline Graeme M

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Re: Chain run on RM-T
« Reply #7 on: August 24, 2012, 05:34:53 pm »
I thought of that. The wheel was respoked at some stage, but it does appear to line up OK. I did do a little adjustment and moved it right by a few mil but that hasn't helped a lot. I don't really want to pull it apart and respoke it. I reckon the spacer idea is the best bet, I'll use the centre ring of an old sprocket.
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Offline Davey Crocket

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Re: Chain run on RM-T
« Reply #8 on: August 24, 2012, 06:05:03 pm »
110/100 is all you need.
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Offline vmx42

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Re: Chain run on RM-T
« Reply #9 on: August 24, 2012, 06:19:42 pm »
Quote from: Graeme M on August 24, 2012, 05:34:53 pm
I thought of that. The wheel was respoked at some stage, but it does appear to line up OK. I did do a little adjustment and moved it right by a few mil but that hasn't helped a lot. I don't really want to pull it apart and respoke it. I reckon the spacer idea is the best bet, I'll use the centre ring of an old sprocket.

Are you sure?

If the chain line is correct and it is only a tire that is too wide causing the problem, then why complicate it by messing with the sprocket alignment? You will end up fouling the chain guide by spacing it out 5mm.

If the wheel you are using has the correct spacers [in the correct places] it shouldn't be anywhere even close to 5mm out of line. If the tire is still too close, then I think that the rim is not centred correctly and the offset is wrong. It is easy to make a mistake as the RM swingarm is assymetrical.

If somebody with an RM250 could measure the rim offset - [as it is on the bike, a straight edge on the outside of the sprocket - and then measure the distance from the straight edge to the lip of the rim]. That would give you a good idea if your wheel is laced correctly.

I would do this before messing around spacing sprockets.

But Graeme, you really should have known that you would have a problem or two after announcing that you were ready for CD9 3 weeks early. That is Mr Murphy Bitch-slapping you for your over confidence. Doh!!!  :D
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oldfart

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Re: Chain run on RM-T
« Reply #10 on: August 24, 2012, 06:22:28 pm »
Ok ... just come back from man cave  ;)  you should have 45mm from out most  edge of rim to centre of chain which will give you 10mm tyre clearance running 110/100.
 
« Last Edit: August 24, 2012, 07:30:01 pm by oldfart »
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Offline Graeme M

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Re: Chain run on RM-T
« Reply #11 on: August 24, 2012, 08:44:51 pm »
Thanks for the numbers, I'll check in the morning. As has been said, whoever spoked it may have got the offset wrong. Tyre size wise, the specs say stock is 5.10x18, and I read that the equivalent is 130/80x18. Which is what I bought. I agree that it is probably a bit large just from eyeballing it. I guess I could buy a smaller tyre and bring the big one to CD9 to sell it. Interestingly enough, I didn't notice when I bought the bike but checking the old tyre I removed from the rim - and all the side knobs have been cut back!!

And yes - I was testing things by saying all was set to go so early in the piece, wasn't I?   ;D
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