Cracked Gear-Case ETZ 250

[nice2day]

Just when I thought everything was going nicely I spotted a nasty crack in my cases just above the output shaft bearing

The crack is right through to the inside. It looks like at some time the chain has risen up and hit the case with a massive blow....maybe the spring link came adrift and allowed the chain to bunch up and jam against the casing?...You can see the chain has cut the case during the impact.

If you think about it, it must have occurred on the over-run where the chain is driving the engine otherwise the engine should have pulled through all the remaining slack cleanly. Fortunately (?) the position is relatively only slightly stressed but I will take it to a local TIG welder to have it welded both sides (pics to follow).

I was wondering if anyone had seen or had this happen to their machines? I would be interested to find out and hear any comments.

Click on photos below for more detail.

Les

[Blurredman]

That is indeed very nasty, and I do wonder if the gearbox barings align properly? I wouldn't really worry about that though. It'll work out.


I've not personally seen this, but it's very possible- It may have happened at quite a speed- or downhill (if you're thinking it happened at throttle off moment).


Also- Looks like you might need to punch the 10mm 'core' plug back in (adjacent to the Neutral switch). After taking the engine apart, they move after the selector assembly is re-installed. On both my re-built engines I have had to re-seal and seat these plugs, when before rebuild they never leaked.. Just for you to know if the future.

[nice2day]

Hi Blurred man...Thanks for pointing that out regarding the selector shaft plug...I hadn't noticed that it was not in correctly....yes it's so maddening as the engine has only done 9000 miles which I can say is completely accurate as there is zero wear on any moving part but I'm doing a full strip down anyway mainly for the seals but will replace every bearing just for the perfection of it all...now the casing is cracked it's galling, but as said, the position does not affect any bearing alignment or stress point...Les

[nice2day]

Just for reference to the chains proximity to the case (from the video):

It wouldn't take much for it to hit...but the marks on my case are quite a length and high up which seems to indicate a bunching up of the chain at this pinch point. The only way this could occur is that for some reason, (see further explanation) a couple of links had moved off the sprocket teeth and folded back onto the chain now sitting in those same teeth so had no where to fit back into. Perhaps this might occur with an extremely loose chain or, as suggested before, the spring-link had broken. The rear wheel sprocket could have fed the loose end of the chain shooting forwards through the rubber guard tunnels into the sprocket area of the case. The drive sprocket (still spinning) could have picked up the mass of folded loose chain and crashed it into the case wall...the engine was likely to have stopped instantly at that moment....

Les

[DAVID THOMPSON]

seen this from winter riding i always used BMW in cold weather. with drive shaft

but others here used many brands
They forgot to clean the sloppy snow and slushy left overs
from this area when parking it would freeze and break the case near the output sprocket
what a mess to repair

but we were lucky to have a fellow that was VERY GOOD at welding them and getting it all corrected
Dave

i got the front disk brakes froze to the rotors on the R90S once and had to haul it home to thaw out
in the work shop so went to using one of the bikes with a drum when it was very slpppy

[Puffs]

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[nice2day]

Hi Puffs, a very nice visual description of the breaking strains on a roller chain. This must have happened at some time but I wonder if the owner knew the case had been damaged as much as it was?....he certainly never told me which is not surprising...

Many years ago I owned a Norton 750 Commando. They were quite a powerful machine and produced lots of torque and in first gear could lift the front wheel off the ground if you were heavy handed on the gas and clutch in first gear. After replacing the rear chain it wasn't long before the spring link failed when I did a fast launch to impress some friends causing the chain to smash a big hole in the inner section of the alloy primary chain case. Within a few weeks a friend who also had a Commando and similarly had bought a new chain, had the very same thing happen. We put it down to a bad batch of spring links as we know the links were fitted correctly. We both had to buy new cases as they were beyond repair.

I will be taking the case to a nearby chopper builder...he is extremely good at TIG welding. What worries me though is if he asks me to leave it there as I'm paranoid about anyone doing work on my motorcycle parts fearing that somehow it'll all go wrong if I'm not around to safeguard their existence …although in this case the weld is as much to do with sealing the case from oil leaking out to the chain side as it is with regaining any lost rigidity so is not super critical. I will, however, emphasise with him really strongly that the inner joint faces don't use a gasket so he must be extremely careful that he doesn't damage the faces as the cases will be ruined very easily. As said, when I get it done I'll put on some pics here of the repair.

All the best.
Les

PS...You might be interested in this tragic story of a land speed record attempt when the chain broke and sliced the poor mans brain in two: https://www.carthrottle.com/post/x7yjy3o/

[Puffs]

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[breakwellmz]

Personally i would look for another case or use something like JB weld (epoxy) to repair the crack after first drilling to stop it extending.
Not sure how`weldable`this alloy would be and then you have the problem of potential distortion.

[nice2day]

Hi Puffs and breakwellmz....all this talk on distortion is starting my day off with a big dose of fear, worry and depression
Ultimately, the proof will be in the eating to coin a phrase. I did consider using JB weld maybe just on the inside but then again it does seem a bodge so I'll give the welding man his chance to impress me or if that fails I'll be looking for a set of new crankcases.....

Les

[Puffs]

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[Blurredman]

I agree with puffs. I was thinking you could assembled the two halves, maybe even with the gearbox in too for extra bracing inside and alignment holding (?) whilst the outside is welded up. ?

[AlanJ]

Hi Guys,
Sorry about the crack, I was about to post the same thing with putting the cases together but the other thing if I remember rightly, It's such a long time
ago, that there are different levels of alloy weld ie. if it's not structural, a weld rod with more silicon in it is softer but easier to fill a crack. I hope that's not a load of rubbish. if that is still relevant it might be worth mentioning it to the welder. Hope it all goes well Les. Alan.

[nice2day]

Thanks Blurredman and Alan. I'll take the complete crankcases and see what the welder thinks...I'll also mention the low silicon filler rods. much appreciate all your good advise...I think I'll take them down tomorrow...I know he likes wine so I'll buy him a bottle as a little present and hopefully he won't swig it all before doing the welding...
Pics to follow as soon as I have them....All the best chaps....Les

[AlanJ]

Hi LES,
The sort of thing I was referring to is, SIFALUMIN NO 15 4043
SIFALUMIN NO 15 4043
An Aluminium alloy with 5% silicon giving excellent flow characteristics and penetration. Suitable for welding: • Duralumin • Cast (LM25) and wrought alloys 6063 (H9) • 6061 (H20) • 6082 (H30) • Weld will discolour if anodised.
Good luck with the weld guy tomorrow. Alan