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The TTR250 FAQ web pages -> TTR250 -> Repairs and maintenance -> Another sprag and idler gears
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een705


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Another sprag and idler gears
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I have read loads about sprag and didnt want to hijack the one below. My bike makes a clunk its not very loud but its there so I did some reading on here and looked behing the cover near the starter. The idler gear is damaged but the starter should be okay. I have added a picture of gears but what do you people recommend I do now? Do they need replacing straight away or can I run the bike without doing more damaged

 

 



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mossproof


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I can't make out the damage on the idler, but I would change the starter and the idler before something locks up and goes bang. In my opinion this is the only weak area on the TTR and it can get expensive if things go too far.
The bits of starter teeth are likely to have made their way down to the flywheel magnets so I would definitely take the cover off, have a good clean out and inspect all the other teeth for damage. Sorry to sound negative, but you have done the right thing in looking into it now. If a bit of tooth goes through the gears when they mesh, it could crack the starter motor mount. Don't risk it.
Good luck,
Simon.

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TTRfan


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I agree with Simon that you need to replace both the starter and idler gears - sorry cry

It looks to me that the starter pinion is toast and at least one tooth has been chipped off the idler gear.

The usual cause of this sort of damage is a worn sprag clutch. Do you know the history of yours? It would be an expensive shame to replace the starter and idler gears only for it to happen again because of a worn sprag.

Brian

PS Try and find a genuine TTR starter even though cost will probably dictate that to be a used one. Steve doesn't usually have them in stock but you are lucky coz he has one in at the moment - see here. Else look at the starter megathread and see what alternative Yam starters can be made to fit wink



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een705


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Thanks ttrfan Bought the one of Steve will strip down probably tomorrow and see what other damage as been caused. I dont know the history of the bike but its certainly got loads of new parts now. I suspect the spag is worn and hope there is no more expense after that.

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een705


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I have stripped down the sprag clutch can I just put the new sprag in even though there is wear on other parts?



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mossproof


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Wow, that sprag is knackered! None of the clunkers I've changed have had such obvious wear (although TTRFan will doubtless have come across it!)
The boss that it spins on (pic 2) should be a smooth surface. It looks to me like it has been roughed up by the coarse surface of the sprag "teeth", in which case I would advise changing this too, sorry When the engine stops, I think it's this bit which "bites", sending a shock wave through the gear set and making that sickening bang.

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TTRfan


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mossproof wrote:

Wow, that sprag is knackered! None of the clunkers I've changed have had such obvious wear (although TTRFan will doubtless have come across it!)

I've not come across a worn sprag with such rough looking wear marks Simon confuse 

It looks like a metal shard or splinters have been grinding away in there.

I agree that the boss on Gear 3 is suspect and best fit a new one or good second-hand. 

Sorry to bear bad (more expense!) news but, once done properly, you shouldn't need to touch the e-start side of things for the rest of your ownership - hopefully biggrin

Brian



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een705


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All parts ordered from Steve/Lisa thanks for posting opinions this has cost a small fortune :( but should be okay for the future. Im glad there is a forum like this

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een705


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New chain and sprockets fitted, that 30mm bolt was tight and took ages to get off, new starter fitted and now waiting for sprag to arrive, battery went flat so will need to check charging or could be the battery isnt that good. Hopefully Im getting there. Does anyone know what tensile strength screw to use if not I am going to buy 12.9 these are the 6 for the sprag...

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TTRfan


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No idea of the sprag bolts' tensile strength but I have always re-used the originals with no problems. Best to use some thread locker on them if you got it wink



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JOHNYBOY


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I THINK NORMAL BOLTS ARE 8.8 SO YOU SHOULD BE OK WITH 10.9 OR 12.9 AS BRIAN SAYS USE LOCKTITE

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een705


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Local engineering shop charged 35p for 6 12.9 all sorted. I couldn't use the originals due to thread not looking right

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