YFM250 Moto 4 - Breathing new life.....help?

[pokolbinguy 4]

Hi All,

Following on from the brief interlude in the "introducing myself" thread....

 

In a nutshell, I acquired a YFM250 Moto 4 (1991) for cheap recently with the previous owner citing "no spark, needs a new magneto coil and I don't have time to fix it"... anyway I am dubious that the magneto/generator is the issue and thinking more along the line of ignition coil as after a clean up of the magneto I was able to get a rather decent voltage reading off the magneto with pull start and resistence readings seem to check out that the magneto is all ok (all 3 x phases = 1.2 ohms and no run to ground)

None the less I ordered a new Ignition coil and Magneto/generator coil and am waiting for them to arrive.

 

In the mean time I cleaned up the current Magneto, popped in a new battery and sparkplug, checked out all the wiring harness, all seemed good except I came across the "neutral switch" wire was broken.

 

After wiring up a new neutral switch wire, the neutral light now comes on  (small win) and the starter relay (attached to rectifier) now clicks. If I hit the starter switch on handle bar the starter motor spins and if I  pull the cord starter I get a spark on pull....YAY!! I'll try and attach a video below if possible.

 

So onto the starter motor. Starter solenoid seems to work A-ok, even if it looks crappy and starter motor spins as it should when I hit the start switch....but here is my issue.

 

When the starter motor runs it turns Cog #1 and Cog #2 (see photo below)....but the chain in the back of the starter which I assume is the timing chain, does not move and there is no apparent movement of the piston in the cylinder.

 

If I turn it by hand (per photo) or with the pull starter however the chain moves and the engine turns. However cog #2 rotates but not fluidly with the "Crank" (part I turn by hand) for the lack of a better word to use if that makes sense?

 

 

Is there a grub screw or similar on Cog #2 that fixes it to the center shaft to make it all turn when the starter motor is run? Could there be a part missing? Previous owner had the starter apart so could be possible?

 

The outer/front part seems to be on a key-way so not sure how to remove this easily to check how Cog #2 is attached.

 

What am I missing here?

 

 

 

 

 

Edited January 9 by pokolbinguy

[pokolbinguy 4]

Spark

 

Video if interested.

Edited January 9 by pokolbinguy

[wanrep 37]

You need a starter clutch.  It bolts to the back of the flywheel.  It's a one way clutch that locks up cog 2 when cranking.  You'll need a flywheel puller if you don't have one already.  Be sure to loctite the screws that hold the starter clutch to the flywheel.

Edited January 9 by wanrep

[pokolbinguy 4]

Looking at these links;

 

https://www.partzilla.com/catalog/yamaha/atv/1991/moto-4-yfm250b/generator

 

https://www.partzilla.com/catalog/yamaha/atv/1991/moto-4-yfm250b/starter-clutch

 

I assume the 'starter clutch' sits behind the generator rotor assembly?

 

Surely the original clutch is still in position and just needs freeing up?

 

 

[wanrep 37]

Yes, the starter clutch bolts to the back of the rotor/flywheel.  It has 3 rollers in it that grab the big gear when turned in one direction but freewheels in the other direction.  Usually the rollers and/or springs go bad, allowing it to slip instead of grabbing that big gear.

[pokolbinguy 4]

1 hour ago, wanrep said:

Usually the rollers and/or springs go bad, allowing it to slip instead of grabbing that big gear.

 

 

Thanks for the point in the right direction. Sounds like I need to the rotor/flywheel off. Any tips?

Surely the rollers / springs can be cleaned up instead of replacing the whole clutch?

[pokolbinguy 4]

Rightio so I got the fly wheel off behind the generator and removed the starter clutch......

 

Ummmm....See photo.

 

Where at the internals of the clutch? Springs etc?

 

Seems someone must have had issues with the clutch in the past so has removed the workings of it. Damn...Now I have to replace them / it.

 

In the mean time, is anyone able to explain in layman's terms how this clutch works? there doesn't seem to be anything to physically engage the cog (aka Cog #2 in previous post) when the starter motor runs?

 

How does the magic happen?

 

Cheers, Pok

[wanrep 37]

Someone would have to remove them.  Not like they can fall out.  Here's a pic of what it should look like.  When the sleeve part of that gear is in the clutch, it'll spin free in one direction but lock up in the other direction.

[pokolbinguy 4]

So I had a partial win after a dig around in the 'bucket of parts' (mainly bolts etc) that came with the Quad.

 

I found most of the parts for the starter clutch, well I think so anyway, (photo below)....but missing one part (Grrrr!!!) - 1 x 'CAP, STARTER CLUTCH SPRING' (part 1J7-15583-01-00). Hopefully I can get my hand on this. Partzilla shows it as available so hopefully available in Australia as I am sure it will be cheaper than replacing the whole clutch assembly if I can get away from it.

 

What I didn't come across, and not sure if I need them or not are the unknown parts that are shown on the exploded parts diagram (see below as "What is this?) - When I have looked at photos of the Starter clutch on line, replacement parts etc there doesn't seem to be any other parts?

 

Also, am I correct that the dowel pins are out of scale in the exploded view? I assume they are the the parts I have marked in my photo below and not another part that I require???

 

Cheers, Pok

 

Link to Partzilla with parts diagram as per below - https://www.partzilla.com/catalog/yamaha/atv/1991/moto-4-yfm250b/starter-clutch

 

 

[wanrep 37]

I think the mystery part in the diagram is still inside the clutch.  If it came out easily, there'd be a part # for it.  The dowel pin, in the diagram, is the big roller that you have.  They didn't draw it to scale.  Looks like all you need is one of those spring caps.

[pokolbinguy 4]

8 hours ago, wanrep said:

  Looks like all you need is one of those spring caps.

Nice ! if I can get them I may as well replace the springs while I am at it. I figure they are really the only parts that can fail?

[pokolbinguy 4]

So I got a new Starter cap today (part #9 on diagram), but still waiting on the new springs (part 8), I have the original three springs but figured they were the weak link in the chain so worth replacing....BUT they are coming from Japan and I won't have them until next week at least and I was hoping I might be able to get the old girl running sooner than that, so I thought I would put the starter clutch back together using the old springs. 

For the sake of it some photos attached to show the Starter clutch fitted back to the fly wheel to show it all ready to roll.

However, when I attempt to install the fly wheel  / starter clutch on the bike one of the little dowels keeps falling out.  VERY frustrating.

Am I right to think the springs need replacing and they are "lazy" ? Therefore they don't apply enough pressure on the dowel pin within the clutch plate to hold it into position as the flywheel/clutch is installed? Or am I just not doing it right...is there a trick?

Any suggestions?

 

Cheers, Pok

 

 

 

Edited 17 hours ago by pokolbinguy
grammar

[wanrep 37]

If the springs are too weak to hold the rollers in, it's good you ordered new ones.  They are probably too weak for the clutch to work properly even if you got everything together.  I'd wait until you get the new springs.

When you're ready to install it, put the gear into the starter clutch first.  Then slide it on the crank as a unit.  Before you slide it all the way on, you'll have to fit that small gear (cog #1 in your picture) into place.