Bad vibes man!

I'd be suspicious of the cam being worn. It's a known problem. You can probably estimate the lift by watching or measuring the rocker movement as you turn the engine over. Can't help with how far they should move but if there's any difference between the exhaust or inlet pairs that would indicate a problem. If one cylinder is working harder than the other that might explain the extra vibration too.

Ian

Dear Steve,

can't claim to be a learned expert, however you can do a quick check on main bearings to assess free play by removing primary cover and alternator stator. Look closely at inside of stator for signs of rotor rubbing. Also feel for play at rotor any up/down is bad news, there should be a little end float; if you have a dial gauge or can borrow one let us know what it is.

post above re-camshaft is spot on- check the lift is same for both pairs; base circle of cam does not wear so rocker clearance may well be ok.

Finally, when you checked timing - presumably with a strobe was it dancing around at tickover? as this can indicate cam chain /auto advance (if you have points) problems

regards Martin

Do not ride your bike until you have made sure the layshaft bearing is not falling apart.

If your bike has never been apart , there is a good chance the bearing is original, in which case it needs changing now.

You will have to remove the gearbox covers , ratchet, gears etc and layshaft , normally the bearing will come out with the shaft after heating the gearbox case.

Replace it with either a roller, or the one that Mick Hemmings recommends.

sam

You might consider checking the ignition timing with a strobe. Do it with the bike on it's wheels not on the centre stand. This will stop it bouncing all over the garage. Easy starting and good tick over might indicate the timing is a little retarded and that will loose you a little va va voom. Another thing is to check the compression. You don't say what ignition system it has or wether it has a single carb conversion. If it's got a standard head steady a couple of new rubbers might be a cheap fix in that department. An indication that your layshaft bearing is failing is that under acceleration the kickstart will flick back. Let us know how you get on.

Previously steve_adkins wrote:

Thanks Ian,

I believe standard 750 / 850 cam lift is ~ 0.325", so is this a direct reflection of expected rocker movement / depression? Can someone please confirm?

Thanks again all.

Rgds Steve

There is a difference due to one side of the rocker is longer, could be 1.1 times at the valve, you would need to check. The soft camshafts are mainly MK3's but also some late MK2's

Previously steve_adkins wrote:

Thanks Ian,

I believe standard 750 / 850 cam lift is ~ 0.325", so is this a direct reflection of expected rocker movement / depression? Can someone please confirm?

Thanks again all.

Rgds Steve

There is a difference due to one side of the rocker is longer, could be 1.1 times at the valve, you would need to check. The soft camshafts are mainly MK3's but also some late MK2's

Worth checking your primary & secondary chains and sprockets for wear and/or tight spots.

This can contribute to substantial vibration.

Regards,

Chas