well, ive bougt another engine for my nc29, theres a few minor problems with it. second gear makes an awefull whirling sound on the revolutions of the engine, though all the other gears are fine, my dad thinks it may be an idle gear gone? and the other is it vibrates! . ive had the head ofrf and had a valve job on it and a new head gasket, and the compression is fine, ive just syncd the carbs and it idles and fuels fine, at first when i tried to sync the carbs, they sounded a bit rough. the pilot screws were set at 1 1/2 turns, cylinder one was stone cold, though there was good compression, spark and fuel. so i wound them out to 2 1/2 and it runs chirpy as a bird. idles perfect :-). Theres one thing that bothers me though is vibration. ive just changed the front wheel bearing 2 days ago so it cant be those. its not alot of vibration but its enough to give u pins and needles after about 30 mins of riding at about 7-8000rpm. all the engine mounting bolts are secure and tight, with the spacers in the correct places. what else can cause vibration?

right well ive just checked and its definatley on the engine, maybe the cranks on its way out or something?
the good news is though, ive got another engine that dropped a valve, but a week or two before it did it, i had the crank re-shelled and the gear box was alot more solid, so i was thinking, if i chop these engines together, with the good top end on one and the good and sound bottom end on the other, will make a good engine. my dad says that its fairly easy changing a gear box but changing the whole bottom end is tricky, what sort of work is involved and is it easy for someone thats pretty ok with spanners etc.

swapping a top end is not a problem mate... Even I did it..lol

Sounds like your vibrations are not too healthy so swap the top end of the rumbly one onto the reshelled and nice gearboxed one...some gaskets, some stella for afters and a few hours sould see you right.

I would probably get dremel crazy on the ports as you have it in bits...and re grindd the valve seats too..

good luck!

Pretty sure you can't touch the gearbox without splitting the crank cases entirely anyway. So just go for the head swap.

Is it vibration while riding or vibration with the engine running? Either way, it is probably a spun bearing on its way out, it's just a matter of whether it's in the gearbox or crank.

Swap the head and engine now before the bearing (if it is that) completely shits itself and ruins the good head.