YB100 help please!

[russeleoin]

Hello all. On my way to work this morning the love of my life died. wow is me!
I ride up a very steep hill, 2nd gear type hill. Just as I changed from 2nd to 3rd at the top of the revs the engine started a serious knock. I stopped immediatly but I suspected the damage was done. The knock sounded like a bearing, the same sort of sound that you would get with a car and a damaged bearing. So I loaded the bike in a truck and brought it home. I have now taken the head, and barrel off and all looks okay. The little end bearing looks fine, the gudgeon pin is not marked at all and the piston also okay. Rotating the engine using the conrod feels fine too so I dont know what the problem could be.

I suppose I should have restarted the old thing once I got home and it cooled down but I did think it was the bearing and worried about more damage caused by running it. I checked the oil and it is full.

Any ideas?

Thanks

Russ
____________________
I love classic merc's but bikes take up less space.
Current ride is a Yamaha YB 100 and I love it! Oooow and now a running GPZ400R!
Next stop, Direct Access hopefully by the end of summer.

[stinkwheel]

Any up and down movement on the conrod?

Could it be coming from the transmission? (half broken chain link, stiff link etc.)

Could the points have moved or the flywheel spun up* causing the engine to detonate?

* Was it you having trouble with mangled Woodruff keys on the flywheel a while back?
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[cb1rocket]

could be a simple timing issue, and the points have buggered themselves.

[Amreet]

If the knock only 'appeared' after changing gear, check the transmission, could have broken a tooth on a sprocket, or mangled something else.

If you can, have a look in there. If nothing is obvious, start the bike up again, try and find what causes the knock. If its there from startup in neutral, then it's probably engine but if its not there, find the gear(s) where it is knocking then try and identify if the knocking is in sync with engine revs or rear wheel speed if you can (to work out which 'end' of the transmission the knock is coming from)


Good luck! My Dad had a YB100, his favourite out of the bikes he owned back in the day.

[russeleoin]

Aggh gents, you are dream come true. Well may be not, but you know what I mean. Stink, you sowed the seed, I was fiddlin wit the stator etc about this time last year, trying to improve the lights. So I popped the side cover off and low and behold the nut was loose and the magnet thingy was flappin around like a dogs dick in a marble bag!
So I have tightened it up with some thread loc on the threads. Hopefully it wont happen again. And whilst I have the head, cylinder and piston all out, I am de-coking.

Thanks again guys sometimes fresh minds makes all the difference.
Russ
____________________
I love classic merc's but bikes take up less space.
Current ride is a Yamaha YB 100 and I love it! Oooow and now a running GPZ400R!
Next stop, Direct Access hopefully by the end of summer.