Big clunk when going into gear the no go!

[thomaskwscott]

Hi guys,

I was just about to pull of the drive this morning on my etz251 when I put it in gear and the was a large crack! It's was followed by a recurring clunking that scared me so much I turned it off. After that it appeared that the even in neutral the bike was seized so I checked the chain had not snapped and indeed it was ok. A little rocking back and forth freed up the seizure but there is still clunky noises coming from the clutch/gearbox area.

These are pronounced even when pushing so starting up is out of the question, I've heard stories about the backing plate to the clutch cracking and wondered if anyone had any tips for diagnosis. I need the bike everyday for commuting so could really do with fixing it this weekend.

Any help much appreciated.

[DAVID THOMPSON]

sounds like the clutch basket may have lost some fingers ( the tabs that rub against the clutch plates)
dave
after looking this is different than i am used to seeing

item 17 the studs hold it together along with i think item 7 a nut
if one of those studs cames loose
you have a problem as it compresses the springs

it appears to be a simple engine and clutch
a fast strip down may give you time to get parts saturday
dave

[mr_luke]

Definitely worth draining the gearbox oil and taking the primary drive cover off. The clutch is a taper fit on the end of the crankshaft, and it's not unknown for it to come loose on its taper, particularly if the nut on the end of the crank isn't tight enough. Once the clutch is spinning on the taper it can make quite a mess and make it difficult to get it to grip again. Luckily yours had the good grace to go wrong at home, so hopefully this shouldn't be too much of an issue. Although it might be worth lapping the tapers together with a bit of grinding paste - just make sure you get rid of it all afterwards!

It would be a good idea to buy yourself a clutch puller, if you haven't got one already. A normal puller with legs just isn't up to the job here. Obviously if the clutch has come off its taper you won't need it for disassembly, but ideally you want to get the taper good enough that it will grip even when you just push the clutch on by hand. If the problem is something else and you need to remove the clutch you'll definitely need the puller!

I suppose another possibility is that something could have come adrift and been 'eaten' by the primary heard? The crank seal circlip or perhaps the spring for the gearchange detent come to mind...

Either way, I'd take the cover off and have a look. Have you been in there before? Do you have a manual?

[therealche]

I would second Mr Luke and say my first guess is the crank has come off the taper. Quick check is to take the small cover off at the from of the clutch cover and see if you can rotate the nut without feeling compression.

[breakwellmz]

I had the clutch come off it`s taper on a newish Supa 5 i had years ago,as a result of a piston seizure doing 80 two up,in the outside lane on the M4!

Managed to sort it on the hard shoulder and complete our journey though.

[thomaskwscott]

Hi guys thanks for the help. The taper issue sounds plausible and could be quite easy to fix. I already bought a clutch puller to investigate previous issues so shouldn't have too much trouble investigating this weekend. I'll let you know how it goes.

[DAVID THOMPSON]

that taper needs to be smooth and clean ..no grease or oil
its a safety thing if your engine locks up at speed..
the rear coupling on a bmw most or all driveshafts are like that

TQ IT TO SPECIFICATIONS as that is part of it working like it should

so hard downshifting on both bikes is something you should do only
when the brakes are not getting the job done

and bump starting is not a good idea either...

[thomaskwscott]

Hi Guys,

I've got bad news i'm afraid. It turns out that the big clunk i heard was actually one of the chain adjusters at the back saying goodbye in dramatic fashion. This is good news as it means the clutch is fine (this is confirmed this weekend). However when taking the left hand clutch cover off, some idiot (me) may have chipped a bit of aluminium off the inside casing. It's not a large piece and as far as i can see not structural. Is there any way these can be patched/mended?

[MichaelTorre]

just so I know that I am NOT reading into the post. Am I correct in the assumption that the taper on
the crankshaft and theclutch act as a safety to disconnect the rear wheel from a seized engine?
Thank you Michael

[DAVID THOMPSON]

seem to me thats what it does
the rear output flange on a bmw transmission and the rear coupling on the drive shaft are done that way

i had a transmission lock up at about 30 mph one time and
it slipped at the transmission output flange letting the rear wheel run free
the engine stopped in a few seconds but the clutch screamed really loud till i pulled in the lever
and the motor stopped

it should be clean no oil and the nut tightened to Specification

[mr_luke]

If the MZ clutch taper occasionally serves that purpose, then I'm afraid I'm pretty sure it's purely a coincidence! A good, well fitting taper is one of the strongest ways possible to attach something to a shaft, and as far as I can tell the only times it will give up are when the nut isn't correctly torqued up (the factory manual instructs you to do it up incredibly tightly!), the taper wasn't perfectly free of oil or grease upon the last reassembly, or it has been damaged in the past by the clutch spinning due to one of the above reasons!

a previous owner was unable to remove the clutch from my crankshaft to replace the crank seals, and eventually resorted to releasing it with an angle grinder(!), so there is now a flat cut into one side of the taper, about 3/4" wide. Even so, I can confirm that when I siezed it a few weeks ago, while doing 60mph along the motorway with a heavily overloaded sidecar, the clutch stayed rock solid and the back wheel locked up for a good distance before I pulled the clutch in. I was carrying a dismantled motorcycle, a garden strimmer, and a load of tools in and around the sidecar, so I think that was probably one of the harshest siezures you could expect the clutch to be exposed to!

With regards to the OP's 251, assuming it's not a massive chunk missing, and it's only a part of the sealing surface, you should be able to bodge something up with araldite, superglue, or even just an extra blob of silicon gasket goo! My own crankcase has a small triangular chunk missing from the flange for the clutch cover, just under 1cm across and 1cm deep. The gap had previously been filled with araldite, filed flat where the gasket seals, but I used silicon gasket goo on the cover, and upon removal it took the small lump of glue with it! I just stuck an extra squirt of silicon in the gap and it's been fine since! If the damage was any worse I think I'd be trying to glue the original chunk back in, and obviously the ideal solution would be to find a friendly aluminium welder to weld it back in!

[therealche]

Ive filled in broken bits of cases with araldite before now with no problems. In fact we rebuilt the water jacket on a GL1000 with Devcon aluminium putty! A well meaning friend had decided he could get a broken engine mounting bolt out with the application of some heat and brute force and ended up snapping the lug off. He tig'ed it back together but when we stuck the head back on we found the jacket had shrunk back, so roughed the edge up, slapped some Devcon on, and once it was hard sanded it down using wet and dry on a glass plate to get a good surface. Saw the bike 10 years later and was still running the same repair

[MichaelTorre]

BMW has approved usage of the product JB Weld to fix eroded heads from
long term head gasket weepage on their lovely 318i four bangers.
I've done a few. Never came back.
(25 years labour in BMW car dealership) finally escaped, and changed hats.
M

[DAVID THOMPSON]

My stepson would not be able to fix anything if they stopped making
JB Weld and DUCK TAPE and bailing wire
dave