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The TTR250 FAQ web pages -> TTR250 -> Repairs and maintenance -> Replacing the starter "idler gears" - beware!
Post Info TOPIC: Replacing the starter "idler gears" - beware!
TTRfan


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Replacing the starter "idler gears" - beware!
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Some of the older models such as the 4GY1 ran different teeth combinations to later engines.

There was a 72T/20T (#4GY-15512-00-00) large idler gear which ran with a 16T/15T (part #4GY-15517-00-00) small idler gear. The large idler gear is no longer available from a Yamaha parts dealer in the UK although, oddly enough, the smaller gear is still available so if you have a damaged 72T/20T large gear you might have to buy both so that they mesh properly. confuse

The most common and readily available gears are now 72T/19T (part #4GY-15512-01-00) and 16T/14T (part #4GY-15517-01-00) and seem to have been used in all engines.

The parts fiche for the 4GY1 lists both combinations.

If you are buying used or new parts please check you are buying the right gear(s).

The reason for posting this information is that I came across my first 72T/20T gear this morning and have done a bit of research to find out about it wink

I hope that may help someone!

Brian

 



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TTRfan


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I am not sure why but in the last week there has been a spurt of orders for starter motors and sprag clutch assemblies.

I am sure most owner don't need reminding not to leave a worn sprag clutch as it can easily strip the teeth of the starter pinion and also damage the idler gears.

I was working on an engine this morning which needs a new sprag, starter motor and large idler gear and that adds up to quite a lot of £p. I took a pic of the idler gear to show the sort of damage that a worn sprag can cause. It also means that, as well as replacing the parts, I need to try and track down the shards of that gear tooth no

Large idler gear damage 1.jpg

Large idler gear damage 2.jpg



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Cubber


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Gulp. bleh

It's a good job someone with a head for numbers and details is on this job. confusehmm

Things like this only become apparent when the job is to be done. Thankfully it's not a job the average TTR owner has to do every few months.

Thanks for being on the ball, Brian. It's this sort of dedication to detail that instils confidence. biggrin

Martyn



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TTRfan


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Wow - wasn't expecting that!

Tidying up my used stock and found that I have a pair of the rare idler gears! It seems that the smaller gear is now no longer available from Yamaha.

See here

If you need both then it makes more sense to buy new 72/19 and 16/14 but, if you only need one or the other of  these rare beasties then here's your chance wink

Brian



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hanzo


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I have a 16 /15 if it helps anyone i do not have the shims but the gear is ok changed mine a while back to readily availble gearing caused me and Brian a head scratching moment i seem to remember lol well my counting did at the time 😂

 



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devon_rich


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Thankfully it's not a job the average TTR owner has to do every few months.biggrin

 You can tell it's not a KTM forum....



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TTRfan


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devon_rich wrote:
Thankfully it's not a job the average TTR owner has to do every few months.biggrin

 You can tell it's not a KTM forum....

biggrinbiggrinbiggrinbiggrin 



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