A forum for owners of Yamaha TTR250 trail and enduro bikes!

Dan-in-a-Van · Veteran Member

Sprag clutch or starter?

TTRfan · Super Guru

I am sorry to say that doesn't sound at all good cry

When you took the starter cover off was the starter pinion in good condition with no worn or chipped teeth?

Brian

ttr steve · Super Guru

Made me grimace, sounds like the starter pinion has been stripped. Hope I am wrong 😬

Dan-in-a-Van · Veteran Member

I'll take it all apart at the weekend and post up some photos of the starter & idler gears. I only had a quick look earlier. The pinion and gear still engaged when I turned them by hand but they looked a bit slack :(

Dan-in-a-Van · Veteran Member

A closer look wasn't pretty :(

I am surprised the pinion & idler gear went from working fine to knackered it just a couple of presses of the starter. Hey ho. Replacement ordered.

TTRfan · Super Guru

Bad luck Dan cry

OOI, was the starter OEM or after market?

Brian

PS I am sure you realise that the most likely cause of that damage is a worn or damaged sprag clutch so it is likely to also need replacing at the same time as the starter and gears.

PPS Steve has some genuine Yamaha used starters in stock - see here . It's just not worth buying an after-market starter - tempting though it is because of their low price.

ttr steve · Super Guru

Good advice, and Don't buy aftermarket sprag clutch, they will explode and ruing everything again

Only use genuine yamaha parts inside your engine

Dan-in-a-Van · Veteran Member

Ok. I tried to jump start the bike to ride it back to where my tools live and is just wouldn't fire up. It was a sunny day so I decided to push it the mile or so (unfortunately mainly up hill) to my garage.

What I found when I got the tools out has got me scratching my head as to what has happen. The first surprise was a crack in the casing just by the idle gear shaft.

I guess this happened when the idle gears locked up and shocked the casing?

The next surprise was when I put a socket on the fly-wheel. The bolt was loose and the fly-wheel just pulled off by hand. :0

With the flywheel off, the reason the bike wouldn't bump start became obvious. The woodruff key had sheared in half. Never seen that before.

Luckily both halves of the key came out easily with a poke with a screwdriver. Having never seen a sprag clutch before I'll have to ask for opinions on whether it looks ok? Everything seems to turn pretty freely, and the teeth on the cogs look ok, and apart from some minor brindling clutch teeth look ok.

So what do people think? New starter, new idler gear and a new casing, and leave the clutch for another day?

domski1 · Senior Member

The sprag clutch will more than likely have caused the engine to kick back and caused the damage you have. It is hard to tell a worn out sprag from a good one but I certainly would be replacing it at the same time as the rest.

mossproof · Super Guru

Definitely change the clutch and big gear as well if I were you. That brindling (good description!) is what causes the binding of the sprag - stops it releasing properly.
Sorry, more expense!
Could be worse - I have a Honda XR400 with an electric leg conversion (TRX400 quad parts) Genuine parts repair costs £400! Incidentally, the woodruff key has mashed on that job too

-- Edited by mossproof on Monday 3rd of May 2021 09:52:13 AM

ttr steve · Super Guru

I wouldn't be using that sprag or boss gear again, best to do the job fully and not be in the same position again.

Not trying to sell stuff, just a bit of advice.

iran ttr250 · Member

hi man i repair it

-- Edited by iran ttr250 on Wednesday 12th of May 2021 09:54:51 PM

mossproof · Super Guru

Nice bit of aluminium rescue Iran ttr! The sprag clutch and gear would still need replacing because the smoothness of the surface of the boss and the "teeth" of the sprag is critical to allow the lock-up release when the engine fires, or prevent kickback when switching off.

iran ttr250 · Member

mossproof wrote:
Nice bit of aluminium rescue Iran ttr! The sprag clutch and gear would still need replacing because the smoothness of the surface of the boss and the "teeth" of the sprag is critical to allow the lock-up release when the engine fires, or prevent kickback when switching off.

very tanks

for guidance

iran ttr250 · Member

Dan-in-a-Van wrote:
Ok. I tried to jump start the bike to ride it back to where my tools live and is just wouldn't fire up. It was a sunny day so I decided to push it the mile or so (unfortunately mainly up hill) to my garage.
What I found when I got the tools out has got me scratching my head as to what has happen. The first surprise was a crack in the casing just by the idle gear shaft.
I guess this happened when the idle gears locked up and shocked the casing?
The next surprise was when I put a socket on the fly-wheel. The bolt was loose and the fly-wheel just pulled off by hand. :0
With the flywheel off, the reason the bike wouldn't bump start became obvious. The woodruff key had sheared in half. Never seen that before.
Luckily both halves of the key came out easily with a poke with a screwdriver. Having never seen a sprag clutch before I'll have to ask for opinions on whether it looks ok? Everything seems to turn pretty freely, and the teeth on the cogs look ok, and apart from some minor brindling clutch teeth look ok.
So what do people think? New starter, new idler gear and a new casing, and leave the clutch for another day?