My 1986 K100RT engine has always been very smooth, with just a very slight tingle around 3700 to 3800 revs. In the last week it has become very rough, vibrating enough to rattle the side stand against the exhaust, and even causing the fairing to vibrate when you rev it in neutral and close the throttle, and also on the overrun. The vibration seems worse around 2500 revs, but is there through the rev range, or at least up to 4500 revs ( I didn't feel like pushing it any harder in case something went bang ). Power doesn't seem to be affected, and there is no problem with starting, and it idles around 1100 revs which it has always done. Investigations are ongoing.

I would give it the inlet leak test first then a compression test. Does it increase with engine speed or road speed?

Engine speed, road speed doesn't make any difference.

Checked so far;

Leak test on throttle body rubbers etc, OK.

Compression, 160psi on Nos. 1,2,3 cylinders, 170 on No 4.

Plug leads, plugs, coils, OK.

Valve clearances, OK.

The only thing I have found not right is No 4 inlet cam lobe. The leading edge (side ?) of the tip of the lobe is worn, leaving a distinct ridge just as it goes over the top. Could this be causing the vibes?? Time to crack open the rocker cover on the spares bike and see what's in there. :-c:

That's not a very good thing to see on a cam lobe. I would replace the cam and don't use the shim again. Replace the spring as it could be where the problem startes with a bit of chatter.
I would not say for sure that is where the vibes are comming from but it could well be

yep sounds like a stuck lifter ,,,could some thing like dirt - sand have gotten in the lifter bore preventing it from rotating ? or a blocked oil path out one of the camshaft saddles ?

Only got back to this today. Removed the cam cover on the spares bike to find that the very part I need ( the inlet camshaft ) is broken between numbers 1 & 2 cam lobes, so I have a single cylinder K bike. No wonder the thing made a racket for the couple of seconds that I ran it. The cam lobes look blue, as if they have been run without oil. My guess is that the shaft seized in the bearings and sheared under the 2nd bearing cap. Now I have to hunt down an inlet cam.

bugga !!!

hope you find one soon gt ...

ill bet that most folks want sell the whole motor though ...i wonder if motorworks ot the bins have wrecks that might contain what you need ?

Motorworks list used camshafts for £29, so I will call them tomorrow and see what they have.

Avenger sorry to hear your problem. Hope you get it sorted soon. Motorworks excellent. Got my ICU from them, ordered on Wednesday arrived following Monday and was as expected.

I think 88KE might be interested in a run sometime, if we can have all 3 Ks running at the same time! Any more takers out there,? Any thoughts on somewhere to meet up? South east? Waterford? Lobster Pot in Carne [Wexford] is a really nice run and the lunch is excellent. Some nice places in Cashel too.