B****r....Dropped valve

[gammakeith]

The NC30 I rebuilt for my daughter has been running lovely until last night when she got some nasty rattles followed by loss of power. It started fine and ticked over OK with no nasty noises when it was recovered to home but the back right exhaust was cold. I quickly pulled the rear cam cover to confirm my suspicion and, sure enough, one valve has made a bid for freedom. I recovered both springs, valve seal, seat washer and half a rocker arm but the shim, the other half of the rocker and the collets are no where to be seen The valve stem is visible and clearly bent. I'll pull the head to tonight and see if piston and valve guide have survived and drop the sump to see if I can find all the bits. If the piston and bore are OK then I will try and patch it up. What I don't know is if the shell bearings can normally survive such an incident? I am concerned the impact will have damaged that particular big end?

I'm baffled why it has happened as it was the front cylinder head I replaced. All I did with the rear head was reshim a few valves. Hopefully the PM will reveal the cause.....

Keith

[VtypeV4]

Gutted for you, let us know how you get on..

[Morespeedvicar]

That's a shame, its always the parts you don't look at that go wrong! Hope the rebuild goes ok.

[gammakeith]

Looks like I have been very lucky and stupid in equal measure :-) When I replaced the front cylinder head I left the rear alone but did re shim some valves. I had forgotten I dropped a shim so ended up pulling the cams and gear drive from the rear cylinder to retrieve it. Obviously, I didn't notice that one of the rocker shafts had moved slightly when putting it all back together so it was not locked correctly by the cam carrier bolt. Thus it gradually backed itself out until the far rocker arm flew off and took out the valve collects as it went. Fortunately, the springs jammed around the valve stem so it didn't drop completely and toast the piston/bore. I was able to find all the bits with the cams off and when I pulled the head I was delighted to find an intact valve guide and only some mild rub marks on the piston. I still have a load of bits from my old cylinder head so had valve, collects, springs etc to replace the damaged parts. After some minor dressing the head is now ready to go back when the new gasket arrives....phew! Lesson now learnt :-) I'll see if I can put some pics up in a day or so.

Keith

[leef82]

good to hear it aint done too much damage. I did the same, hadn't realised the little pin on the rocker had slid to the left, fortunately for me the valve jammed up and didn't hit the piston and also i was able to find the shim and the collets with an extendable magnet..

[lukemillar]

Those rocker arm shafts are all staked on the inner lug on my current set of heads to prevent that from happening. Wasn't sure if it was a previous owner or that they are RVF400 heads and done by the factory. Either way - seemed a good idea!

[gammakeith]

All fixed and running well again :-) I'm certainly getting good at taking the carbs on/off! Katie scared me earlier in the week though. She said the engine is sounding loud and making a horrid noise. Turned out to be blowing exhaust....phew!

Staking the shafts certainly seems like a good idea. Its odd as the manual says to remove the screwed plug on the outside of the head to withdraw the rocker shafts but they come out very easily from the inside (as I found out ha ha). While I was at it I checked the front head and I turns out I had only made the mistake on the one rocker.

Keith