One of my rockers perforated the cylinder head cover!
 

Guys, today I am an unhappy man:

Yesterday I was doing an evening session at BH (with simon748 - ciao simon) when I heard a noise from the engine and the bike shut down.

Today I stripped everything down and had an ugly surprise:

One of the valve rockers in the horizontal cylinder snapped and, after causing all sorts of damage inside the desmodromic distribution system, actually perforated the cylinder head cover!

I just do not know if the stuck valve (because of the broken rocker) also damaged the piston and the rings...

Three questions:

I had the timing belts replaced less than two months ago and when I saw them today, the tension seemed a bit too loose (approx. 10mm belt swing, measured between the two front/head timing rollers). Is the gap/swing too much? Could that have caused one of the rollers' teeth to "slip" and therefore throw everything off?

Can a rocker brake for no apparent reason?

Can you comment on Pro Team (or Twin?) as the potential workshop to do this work?

Any other comments are obviously welcome...

Ciao, Mario

[Edited on 23-6-2005 by MarioP]

[Edited on 23-6-2005 by MarioP]

Mario,
that sucks the big one - really feeling for you mate.

Pete at PRO-Twins is the man. He is the one to talk to. They are the only people that touch my bike.

Doogalman

Ditto Doogalman.

My guess would be that the broken rocker is a symptom of whats gone wrong, not the cause of it. What might make a rocker break? Well a piston hitting an open valve would do it. Broken belt or belt too loose and jumping a few teeth. Get it back to whoever did the belt change and threaten them!

Pete at pro-twins is a top man and so is the setup. I have had my last two services completed at pro-twins without any problems at all. You might have to wait a few weeks though so book as early as possible.

Guys,

Thanks for all your comments and nice words!

Paul (rockhopper), could the opposite be true: could a stress fracture of one of the rockers cause the belt tension to loosen up a bit?

Just try to understand what could have happened...

Ciao

P.S.: Your avatar keeps reminding me of that damn rocker!!!:mad:

That's seriously bad news, Mario. :o I don't think that a hairline crack in a rocker would significantly affect belt tension, since the pulley don't move in relation to each other. Only the belt tensioner and the belt itself affect its tension. Either it was too loose to begin with or the tensioner pulley has moved somehow.

Most likely scenario is that the cam pullet jumped a few teeth, piston kisses open valve. Even so, it's not usually the rocker that breaks.

Hope the damage is not any more serious than you already know.

Well if the valve is open and the piston smacks it one then something has to give. I have seen rockers break on engines that have been seriously over revved but i'm not sure if the desmo would fail like that. I dont think the broken rocker would affect the belt tension. The head needs to come off really or you might be able to find someone with an endoscope to have a shuftie down the spark plug hole to check for damage to the piston crown.

Wot we need is pictures!