Chain thrown off - head intact, engine less so

moolfreet · Post by **moolfreet** » 08 Nov 2009 17:00

Evening all,

Just spent a couple of hours looking at the bike after the chain came off about 2 weeks back. The nut for the front sprocket had slackened off, so I guess there was enough sideways movement for the master link to split open.

Anyway, the chain wrapped itself around the front sprocket inside the engine case and stoped the motor. Luckily I was in town and I wasn't going too fast and was able to coast into a handy parking space (it doesn't happen often in downtown Brussels).

I can start the bike ok but there's a distinct clang-clang-clang from the engine, which doesn't sound too good.

Since the fins on the back of the rotor are all now broken and much shorter as a result of contact with the chain after it had wrapped itself round the front sprocket, I thought (wishful thinking) it might be bits of metal from the fins rattling around inside it but I've removed it and had a look and there don't seem to be any problems with the rotor and the stator plate. So no good news there...

The clang-clang-clang is difficult to pin down to any part of the engine just by listening to it.

What would have happened inside the engine when it locked up? I was doing about 20-30 mph maybe, having just pulled away from a junction and there was a marked clank before the engine just died.

Any ideas and suggestions about further diagnosis gratefully received

Best,

Nick

mgill · Post by **mgill** » 08 Nov 2009 21:07

Does the noise change or go away when you pull in the clutch?
What if its in gear (not neutral)?

Mathew

moolfreet · Post by **moolfreet** » 08 Nov 2009 23:27

Hi Mathew,

Thanks for the reply-
It makes no difference if I pull in the clutch or shift into gear. The noise gets faster if I rev the engine, though I didn't want to take that too far.

nick

Post by **morini_tom** » 09 Nov 2009 11:58

Hmm sounds like that rules out clutch or gearbox.

Hate to say it but I'd be suspicious of bottom end damage. Try holding the flywheel in your hand and rocking it up and down and side to side- if you can see the belt flexing or feel any movement then chances are you've done a main bearing. If you've thrown a big end then you may be able to feel the play by rotating each cylinder to tdc and listening/observing what happens as you come up against compression.

Bear in mind that it's relatively cheap and straightforward to rebuild an engine with minor bottom end damage- you could just get away with new shells but the more you run the engine the more likely you are to score the crank or damage a rod- and this us when it gets more expensive and complicated.

mgill · Post by **mgill** » 09 Nov 2009 13:37

Start by measuring valve clearance when you take it down,
you may have bent a push rod or two as well.

Mathew

moolfreet · Post by **moolfreet** » 12 Nov 2009 20:33

Thanks for the advice - sorry I haven' t got back to you before now. It's been a busy week.

Doesn't seem to be any movement on the flywheel.

If one (or more) of the pushrods had got bent, what kind of effect would this have had on the valve clearance? There would now be more clearance since they're no longer straight, is that right?

Stripping the whole engine sounds a bit daunting - I can see it taking years before I get it back all together again

. I was planning on doing it sooner or later ... but preferably later

Nick

EVguru · Post by **EVguru** » 13 Nov 2009 10:40

It sounds like you've got quite a lot of crankcase damage if the chain flailed far enough to damage the alternator.

I think you really should strip the engine down and check for damage. The cases can probably be repaired, but are fairly common and cheap to replace.

It's one of the simplest engines ever made and only takes an hour or so to strip or build if you've done it before.

Just take it in stages, watch out for the hidden bolts and ask if you're not sure of anything.

mgill · Post by **mgill** » 13 Nov 2009 19:19

If one (or more) of the pushrods had got bent, what kind of effect would this have had on the valve clearance? There would now be more clearance since they're no longer straight, is that right?

That's right. If you remove them and role them on a flat surface you should be able to tell if they are bent.

I agree with Paul, loud noises from the engine are a perfect excuse for a tear down. It's really not that difficult.

3potjohn · Post by **3potjohn** » 14 Nov 2009 06:53

I had to strip my motor after I got the bike,my first Morini. I haven't had a bike crankcase apart since 1978, apart from gearbox rebuilds and the odd head swaps now and again on my BMW's.
I can confirm it is indeed a simple engine to work on.Compared to the aforementioned Beemers it's light too. I did open the plugs in the crank and cleaned out the sludge traps whilst at it.Just make sure that when you pull the generator rotor off the puller is properly screwed into the threads,after removing the nut and washer within. Is the end of the crank with the generator running true?Any obvious metal in the oil?
I didn't get a good seal with the 2 hidden bolts the first time which was a nuisance as it meant disturbing the left hand kickstart/oil pump seal/gasket side again.
Just take your time and when its done you can sit back with a nice glass of Straffe Hendrik or similar and wait for the windy season to end!

moolfreet · Post by **moolfreet** » 16 Nov 2009 14:32

Thanks to everyone for their tips and encouragement - I've decided to have a go. It'll certainly be more satisfying doing it myself than trying to find someone to do it for me!
The fact that it's winter will help, and then there's plenty of West Vleteren beer down in the cellar to keep me company - just in case I need a little consolation.

... and it'll give me something other than the decorating to get on with.

I'll be back in touch to let you know how I get on... or if I run into any problems,

Cheers,

Nick

Brubru · Post by **Brubru** » 17 Nov 2009 12:21

Any help needed?

Even if I would be better at opening the Westvleteren than the engine, I could at least bring some Floreffe and good will... and the Blue Book if you don't have it.

Bruno

moolfreet · Post by **moolfreet** » 20 Nov 2009 09:18

That's a very kind offer, Bruno! (The help, I mean, not the Floreffe )

I am kind of busy at the moment, and need to organise the space in the cellar to work on the engine - and get it off the bike - but I'll certainly get back in touch with you once I get down to the nitty gritty!

Hope you're taking advantage of the mild Belgian weather so far this winter to get some extra kms in.

Best,

Nick