CBR250 starter issue (locking up)

[HRT]

Hey people, got a 1986 CBR250 MC14 here with a bit of a problem.

If I crank it over in the morning it will kick over a couple of times then then there is a clunk like someone has just jammed something in the engine. The bike doesn't try to move away like its in gear or anything, just a sudden clunk and everything locks up. Tap the starter motor button a few times and you can hear its like its jammed on something, but if you keep doing that for a bit it eventually kicks over and starts (sometimes) or just cranks over and locks up again.

Once the bike it running then everything is fine. And it seems to start properly without doing this once its been started too.

I've got the starter off, seems to spin fine without catching anything inside. Powers up alright and spins freely. Some in/out play which I would have expected.

Popped the cover off and nothing looks out of place inside there, though I've never had a bike in pieces before so thought it would be time to start asking if its a common thing, or if anyone else has struck this issue before?

Help

[davereid]

Next time it does it, put the bike in 3rd or 4th if you can get there. Rock the bike back and forward, with the ear-ometer ON. If you hear a "CLUNK" and the problem has cleared, then the starter motor is binding. I have never seen a bike do this, but it used to be common on pommy cars when the bearings got tired in the starter.

We used to belt the starter motor with a mallet, (unkind, but all you could do if you were alone), or rock it back and forward as described to fix it.

[HRT]

Will give it a go when its back together. You can hear the clunk each time you tap the starter when it does it too. Seems very strange.

What exactly binds in the starter?

[davereid]

The starter has no mechanical connection to the engine until you press the start button. As the starter starts to spin, the torque produced causes a gear to "climb" up a shaft and engage with the engine.

If either of the gears is worn you often hear them clash with a hell of a scream.

But sometimes they just jam.

More commonly, if the bearings in the starter motor are worn, the massive torque of the starter motor will soon lock everything up, it generally happens just after the starter motor engages with the engine, and the real load comes on. On the bench, the starter motor will spin fine.

Check the free play in the bearings, and check there is plenty of meat on the brushes.

(This all assumes the fault IS the starter motor locking up.)

[prvoke]

i had to replace the starter on my CBR and was surprised to see that it doesnt flick out at all its constantly out and engaged. i wired it to battery to test and it jst plain spun didnt move out.

[davereid]

Yep, the design I described is very common but its not the only way its done.
On your bike the starter clutch will still be there, it just doesn't come out when you remove the starter motor.

[vagrant]

I would guess that the starter clutch, which is part of your gearbox, is playing up.
Have a look here for the CBR250 manual.
http://bayonetwork.com/cbr/CBR250ServiceManual.pdf

[HRT]

Its always engaged there davereid

Hey vagrant, yeah I thought about the clutch on it, but if it was locking up I cant see how it would be an issue as the starter is trying to turn it in that direction anyway. Are just just a sprag type clutch in them?

Pulled the starter off, everything looks normal inside (from my limited knowlegde). Might just give it to the bike shop, maybe they have struck this issue before

[davereid]

Its always engaged there davereid

hehe bet its not.. does your starter really do 10,000 rpm !

[HRT]

Alright then, its not like a typical car starter then (as best as I can tell). One way clutch which I would assume all the drive goes through and the starter just stays engaged with that. Still cant quite work out what the issue would be

[HDTboy]

The starter is always engaged with the starter clutch being fixed to the end of the crankshaft.
My money would be on your bike having a leaky fuel tap, and probably leaky float needles in the carbs too.

Next time you park the bike for any length of time, manually turn the fuel off. Turn the fuel on before starting it again, if that fixes it, you know where to start looking.

[HRT]

So more of a hydraulic thing? Suppose its a small space to fill up, not a bad idea
Will have a check

[HDTboy]

It wouldn't be the first time it's happened

[HRT]

The funny thing is it only started doing it since it came back from the shop to get the carbs cleaned out...

[davereid]

I'll be interested in what you find.

Your description that it turns over, then stops as if jammed still points IMHO to a mechanical failure of the starter.

As HDTboy points out, your bike engages the starter motor via a clutch rather than a gear, so you have to add the gears that drive the clutch to the list of possible faults.

Its not correct to say the starter is always engaged, but it certainly has an idler gear train between it and the engine proper.

So, you haven't eliminated the starter motor, you have just added a couple of extra gears and a clutch !

Of course it may not be the starter, we only assume that because I think it's what your description points at, as well as our newly discovered gear train and clutch.

So if the engine is jamming, what could it be ?

Well, it seems to run once going, so its not seized. That also tends to suggest that its not slipping into gear and stalling while cranking, as it would blast off down the road.

Leaking carbs can cause an engine to seize if it is a two stroke. This is because the carbs are higher than the inlet port, so a leaking carb can fill the crankcase up with fuel. But I have never heard of it on a four stroke - I would suggest that you would need a great deal of good luck for fuel to leak out of the carb, and go uphill to the inlet valves.

But it is possible that poor timing or bad fuel mix could cause a backfire that feels like a jammed engine - except that you would think it would crank OK next time.

Given :

"If I crank it over in the morning it will kick over a couple of times then then there is a clunk like someone has just jammed something in the engine. The bike doesn't try to move away like its in gear or anything, just a sudden clunk and everything locks up. Tap the starter motor button a few times and you can hear its like its jammed on something, but if you keep doing that for a bit it eventually kicks over and starts (sometimes) or just cranks over and locks up again.

Once the bike it running then everything is fine."

Then free beer for you and your pals here at my place if it turns out that either
- the starter IS always engaged to the engine
- its not starter train related

Keep me in touch !