flywheel key broke

[arnaud]

Hi, i experimented witrh the other-no warranty. engine and samemflywheel.. the key broke in half(i supposed weak iron) and when i managed to remove the half uot of the crankshaft i replaced it with the key from my older engien which has run over 60.000km.. and this one also broke in 2??
so.. how come??

[coachgeo]

Key is acting like the Sacraficial Lamb to some other issue that exist. Something out of balance? One is getting some kind of shock load the other is not? Key slot size just slightly different (larger) in one that keeps breaking?

Try the flywheel on the engine that never broke a key and see if it breaks the key? Then you know it is a flywheel issue?

[arnaud]

i did use the older flywheel with that key! i balanced that flywheel before i built in in..

[coachgeo]

i did use the older flywheel with that key! i balanced that flywheel before i built in in..

was refering to using the flywheel which was in use when keys broke on the engine that in the past did had not broke any keys with it's orginal flywheel.... I am assuming you have two flywheels..... one from past no key breaker engine and one from engine that is breaking keys. Of course I may be remembering wrong that we are discussing two different engines....

[arnaud]

No, it is not any more elaborate as i have written;
2 engines, one flywheel..

[penybryn]

Key is acting like the Sacraficial Lamb to some other issue that exist.

There should not be any great force acting on the key, the close fit of the tapers should taking the forces. So I agree with Coach geo that there is some other problem. I wonder if there is a mismatch between the tapers of the crank (replacement engine) and flywheel (old engine)? Could be slightly differences dimensionally or some damage to the taper of one or the other? I think it likely that the tapers are not mating correctly.

[arnaud]

Since this whole engien broke down within seconds, i took the head off(the only part i needed for the old engine) and the fuel pump and installed tehse on my old-ohtherwse fine engine.. but, as my other topic states.. it won't start..

[skoleskibe]

Since the engine timing is done by the camshaft, there is no real reason for having a keyway to hold the flywheel, the flywheel should be tightned enough to stay put, with or without the flywheel key.
This also means that the mounting surfaces has to be absolute clean from dirt, ironfilings, oil, dead flies and what have you.

[coachgeo]

Since this whole engien broke down within seconds, i took the head off(the only part i needed for the old engine) and the fuel pump and installed tehse on my old-ohtherwse fine engine.. but, as my other topic states.. it won't start..

ahhhhhh.... good point...... Hopefully the switch to the other engine will solve this issue at same time.

[arnaud]

Considering the many starting attempos the key seems to stay intact..
now wondering, really don't know why it won't start.., see my other desparate topic..
ah, back on the jawa again..

[dethmachinefab]

On this topic of the original engine, i would suspect timing to far advanced. Try lapping the flywheel and crank. You could also try heating the flywheel before install say in a toaster oven to get it seated further up the taper.

[snoopy]

Don't worry it did it on mine too. I posted a thread last year about it.

Reason - the chinese are spot welding the key onto the shaft. Guaranteed failure.

Easy fix, simply groove a proper key yourself then stick a wedge of metal in it of appropriate size.