Vibration and noise

Got my st70 properly on the road now and have been riding around for a few weeks, which is brilliant fun. My only minor issue, and to be honest I can live with it, is that when I am going full throttle, mainlty in 3rd but sometimes a little in second, I get a vibration and noise that appears to be coming from the left casing area. Is this the cam chain? Any ideas?

Yeah, you should check the cam chain (timing and tension) as well as the flywheel (mounted correctly, undamaged?), the tension on the bolts that hold the engine in the frame and the chain tension / condition of chain and sprockets.

Went to adjust the tension and upon removing the sealing bolt found that I have a part missing, part 12 int the diagram below:

http://images.cmsnl.com/img/partslists/ ... 4_d829.gif

Have ordered the part from www.cmsnl.com along with new springs etc for the tensioner (mainly to get the order up to the minimum of 10 euros). Now I just have to wait for its arrival and hope with the correct adjustment the problem will be fixed. I am not going to ride the bike until I have the tension correctly adjusted as I don't want to risk any damage.

Are you sure you've got the arliest type of engine, with the manual chain tensioner?
If so, it's VERY wise not to ride the bike before you mount the missing part.
It's impossible to keep the right tension on the cam chain without that nut.

The later version (starting mid '70s) have an automatic tension system, which uses the motor oil pressure to put tension on the cam chain.
I prefer the manual version myself because I found it more reliable.
Also, check if the rubber top on the tension rod is still there, and in good condition.
(nr 14 for manual, nr 13 for automatic version)

My bike is a 1979 model. How would I know it is this type of engine. I was basing it on the fact that it had all of the parts in this lower left box on the diagram other than this one nut. I havent checked the rubber top but have ordered a new one anyway, so if missing or in pore condition I can replace it.

Is there a spring in the hole above the bolt on the bottom of the engine?
(next to the oil drain plug)
If yes, it's an automatic tensioner.

Parts came and i now how a lovel quiet cam chain, however i still have this noise and vibration as i described before. I haven't checked the flywheel and everything suggested as of yet, mainly as I am a little intimidated to delve this far with regards to the engine, however I may give it a go.

One thing I have noticed is that if i lean to the right/turn right when the noise and vibration is taking place it disappears

Will checking the flywheel etc damage any gaskets?

Just take of the ignition cover.
Give the flywheel a turn, and check if the distance between the flywheel and the left crank case remains the same.
If not, your crank tap is damaged.
Check for chips etc on the flywheel.

You don't need any new gaskets etc, it's a quick test to make sure the flywheel isn't causing this.
You could check the ignition timing as well.
Other things to check: valve clearance (should be checked anyways after replacing the cam chain) and most common: make sure all bolts, washers etc that hold the engine in place are in good condition and tight.
+ the chain tension / condition of the front and rear sprocket / condition of the bearings in your "rear fork" (can't remember the correct English name") and check if it's still fit firmly to your frame.

Took the cover off and checked the flywheel and all seems to be fine with it regards to its condition. There are no scratches on it, chips or anything like that. I also rotated it a number of times and as far as i can tell the distance between itself and the crack case alwatys remains constant.

Checked the sprockets and chain and all was good here.

I also took it for a quick test up and down the road with the cover off to see if it would make any difference and it didn't the noise and vibration are still there.

It does seem to feel as it it is coming from the flywheel tho, or this area. Could something be mounted incorrectly behind it? Can you mount then too tightly or loosely, not that it feels loose in any way?

It is frustrating as the noice and vibration is hard to explain, probaby the king of thing that someone would recognise straight away if taken for a ride.

It seems that once the flywheel gets up to a certain speed it happens, be it in first, second or third gear.

So you get the virbation and noise as well when you're revving the engine while standing still?
(in neutral gear)
That would eleminate a lot of possibilities.

Oh, and what brand is the flywheel?
Is it the flat Hitachi?