TTR Starter Rebuild.
Although this article is specific to a Yamaha TTR, much of the advice and tips refer to many a bike and workshop task.


Nice when new but 11 years can take its toll on the electric starter!

The Yamaha TTR250 was a very well built trailbike when it was first introduced in the UK back in 1994. Mind you at nearly 5 grand (back then) it was expected to be good.

However after 11 years of off-road use and in some cases abuse, many are now suffering from expensive failures due to the electric start mechanism wearing and causing big money damage.

The typical cost of replacing all the faulty bits with new would be around 600, so its worth taking a serious look at the problem. But many have tried bodging and taking short cuts during the repair, which nearly always results in it blowing up again very soon and costing twice as much.  

So What Goes Wrong?

An small electric starter motor drives the TTR flywheel via two sets of idler gears and a one way 'sprag' clutch. Its a very ingenious design, but after thousands of miles the sprag clutch wears slightly causing it to not work properly. Two things happen. 1) When stopping the engine a clunk is heard due to the small amount of freeplay. This puts a severe shock load back through all the starter gears. 2) When the engine fires up, the sprag clutch doesn't release quick enough, so it spins the starter motor and idler gears up at horrendously high speed. Together these two effects shatter the idler gears and grind the teeth off the starter motor.

As the sprag clutch is over 90 and never appears damaged it usually gets left in the bike when all the other broken bits are replaced - and guess what? Its not long before it all happens again. 

Its easy to see why people don't replace a hopefully okay part at 90, when you realise how much the other parts cost. Idler gears 55 each. Starter motor 360. Then there is the gaskets, oil, filter and labour, etc.

I learned the hard way as it happened to me twice, and it appears I was lucky. When it also happened to a close friend it wiped out his engine cases as well - mega bucks!

In all these cases if the sprag clutch had been replaced as soon as it started clunking it would have saved MAJOR money - and a break down in the middle of nowhere.

So we have blown our starter money and don't want to fork out 360. Is there anything we can do?  

YES, YES, YES and here is the official 'Biker' way of doing the repair and saving a few hundred quid -

In this article we are going to look at how to: Replace a sprag clutch and fix a damaged starter cheaply.

Start by taking off the flywheel generator cover. NOTE: One of the cover screws is inside a small 3 screw plate which holds and idler bearing and is located up by the starter motor. 

Picture Right:
1) Starter motor location.
2) Flywheel generator cover.
3) Flywheel (sprag clutch is bolted behind)

When this is off you will see how much damage is done. Check the teeth on the starter for wear or breakages.

Picture Below:
1)
Worn and damaged teeth on starter motor shaft. 


It is a good idea to punch the case screws through a piece of 
cardboard to keep them in the correct order.

When removing the idler gears be careful not to misplace any of the thin shim washers. Lay all parts out carefully and in order. 


The small idler gear with its 2 shim washers.

Check the teeth on both idlers for wear or breakages.


The big idler being removed. You can just see the small idler in behind it.

   

To remove the flywheel a puller and holder of some sort is needed. 

If you don't happen to have either one handy (like I didn't), you can often use the bikes rear axle as a puller and fashion a flywheel holder from an old allen key or right angled screwdriver (see pictures left and below).

Picture Left: Place a suitable sized allen key into a flywheel balance hole and brace against the bikes frame.

  


Bike rear axles often make good flywheel pullers.

  
Use a rag to stop teeth damage on the starter ring. 

Always undo tough screws like these (which here hold the flywheel/sprag-clutch/starter-ring assembly together) by placing the ratchet on the farthest screw head from you. By levering across the flywheel centre as shown in the photo, you gain a mechanical advantage over the forces which are trying to rip the whole lot out of the vice.  
This means you do not have to tighten the vice so much and reduces the risk of teeth damage.
  


Keep the flywheel sprag clutch screws safe and wrap the flywheel in a poly bag top keep any metal swarf away from tis strongly magnetised part.


Photo Above: The flywheel (1) is finally off, leaving the 
sprag clutch (3) resting in the starter ring (2).


Photo Above: The sprag clutch (1) just lifts out of the starter ring (2).

If you have had a serious blow up involving any parts connected with the electric starter. It is nearly always the sprag clutch which starts the problem. SO LOOK FOR WEAR VERY CAREFULLY. If in doubt use a magnifying glass to make sure. But if it 'clonks' loudly when the engine stops, replace it anyway. It will be 90 well spent.


It is not always easy to see the wear on a sprag 
clutch but here it is quite apparent.

NOW FOR THE STARTER ITSELF - OUCH!!!
What really got to me was the fact that the Japanese bike manufacturers only sell a complete starter - not the part that wears, and at 360 a time its no laughing matter. So here is how we got around it.

Second hand TTR250 starter motors are as rare as rocking horse manure in the UK. But a trip around a friendly bike breakers revealed that a cheap FZ600 starter motor - although looking different and is longer hence it will not fit a TTR - has the same size diameter motor shaft and gear teeth. 

Now unfortunately the shaft itself and whole armature is just too long to to come out and go inside a TTR casing. But we can still use it and save lots of cash! 

As FZ600's (and other fast road bikes in general) seem to crash a lot, it is very easy to find a second hand starter in mint condition quite cheaply.

All we really need is a replacement shaft with good gear teeth. So basically we take the starter apart and remove the shaft from the armature itself. Get it machined a little shorter and insert it into the TTR starter armature.

Here is how to do it in pictures -

Undo the 2 starter front case screws and ease it off the engine leaving the rear part of the starter motor case with brushes still on the engine (this saves hours of stripping the bike apart to remove the whole unit).

Picture Right: Main body of starter motor removed leaving rear of starter case with brushes still in place.

  

Take the starter apart and lay out all the parts and shims carefully in the correct assembly order.

  

 All starter internal parts in order.

  

 

Remove the starter shaft from the newly aquired second hand unit by grabbing the armature tightly and bashing it against a strong vice. Doing it this way is good practice for removing the TTR one next - without damaging the windings etc, which we need in good order.

 

Picture Right: Here I am bashing the newly machined shaft back into the old TTR armature and taking care not to damage the gear teeth. The same process was used to knock it apart in the first place.

It may be a good idea to put a thin piece of soft aluminium on top of the vice (if you have any at hand) to make prevent tooth damage.

  

  

When you get both shafts out you will see that the FZ600 shaft is longer than the TTR's and will need a simple machining job done by a local machine shop.

    
Picture Above:
1) The end that wears out - the gear teeth !!!
2) The measurement from the front of the collar (5) to the gear end of the shaft should be the same on all FZ600 shafts.
3) This end of the FZ600 shaft was cut back to match the TTR's, this is a critical measurement.
4) Some FZ600 shafts have a long spline like this one. If so this needs to be trimmed back too. This length is not critical but needs to be short enough.
5) Shaft positioning collar. Some FZ collars look the same as the TTR's.

NOTE: Some FZ600 shafts have more splines, this repair still works but it is much harder to get the shaft out, and even harder to bash it back into the TTR armature. 

   
Picture Above:
A) The FZ spline has now been machined back to match the TTR.
B) The armature must be bashed back into exactly the same position - that is up against the collar or where the green laquer starts.
C) the gear teeth damage on the old TTR shaft can clearly be seen.

       
Picture Above:
It was so difficult to get the armature off one of the FZ600 starter motors that we had to hacksaw it and then wedge a chisel into the cut to loosen it enough to get it moving (this was a newer motor with extra splines, the trouble is you can not tell which is which until you get them apart!). Be careful you do not cut into the shaft. 
DONT cut the TTR armature off - WE NEED IT, it is a special short one and I have not found an equivalent - so take good care of it.

Yes it hurts bashing the armature back in (old bones you know). Wear a good strong glove, it helps.

The front needle bearing on the TTR starter is also possible worn through being over-reved. Some FZ600 starters have an identical end case with a much newer bearing in - use the whole end cap if you can.

Done properly this job isn't a bodge and therefore it should last another 10 years. It may have taken a few hours but it saved over 250. The second hand starter cost me 50 and another 25 for machining - AND if I had replaced the sprag clutch in the first place I would have saved over 500 altogether as I wouldn't have had to replace all the gears and starter twice on the same bike !!! 

When reasembling take care to shim all the starter and idler gear parts up correctly. Flush all broken gear teeth out off the engine. And change the oil and oil filter as it will be full of metal swarf if any teeth have been damaged.

Finally best of luck and as its now 2005 -
DISCLAIMER: Biker's website and the Author are only offering this article for readers interest and are not suggesting that anyone should follow these what may to some look like instructions and therefore we are not responsible for anyone who attempts this work and certainly not if they are not skillful enough to do it properly!

   
(NB: This article is offered as an item of interest only and Biker's Website, DirtyBiking and the author take no responsibility for any misinterpretation by any reader resulting harm or damage to either themselves or any equipment.)

Article Copyright   Adrian Harris - Not to be reproduced without prior permission.