Bent Exhaust Valve

Rode home recently on a sick bike, sounded like a single (i would like a single but not like this). One plug out at a time and no comp on the right cylinder. Head off and the right exhaust valve is slightly bent and not seating. The only other apparent damage is pitted seats for both exhaust valves - but....
The stem on the bent valve doesn't have the same shiny appearance of the other three, but not scored, and having pulled things apart the rocker spindles on the right intake and right exhaust have been bored completely through (and have a few grind marks on) whereas both on the left are dead end, there are no seals on the intake valves and no obvious recess for the seals on those valve guides. Also found a couple of rough looking shims instead of the rocker thrust washer in one case. All on an engine the was "professionally" rebuilt a few years back. This time its me and a friend doing the work, i'm the assistant.
So a few queries,
Rocker Spindles - dead end type is what we had expected - correct?, if so any thoughts on why the straight through ones??
Valve Seals - lack of seals doesn't seem to have caused any drama to date so tempted to stay as is.

Bike details, modified pre mkIII 850, head planed (pistons have valve pockets), cam - don't know, may try to measure push rod lift to get a clue?

Any feedback appreciated.

sounds like you had a valve stick in the guide and hit by the piston. it the guide is to loose and allows to much oil past it can carbon up and stick. Norton NEVER put seals on the exhaust side as that will also cause a valve to stick cue to lack on lube.The intake should have seals, looks like you will need to replace all the valve guides
The drilled through rocker spindles should both on the intake side. that mod is so you DON'T need the crossover oil line on the head.

windy

If the valve was hit by the piston, you should also check that the piston isn't cracked. You could get a very expensive surpise very shortly if it is.

During early high speed endurance testing of the Commando prototypes, we had a final drive chain fail at about 105 mph on full throttle. The resulting overspeed (the tachometer needle was bent aboout 20 degrees after hitting the stop) caused a piston/valve collision, bending the valve stem. The rider was lucky the chain didn't jam up the back wheel as it departed and that an Aston Martin sharing the track at the time didn't run him over.

In the autopsy, we figured that the piston split down the middle, through the center of the wrist-pin bearings, as the con-rod was on the way down. The piston jammed in the cylinder. The wrist pin then tore through the piston skirt, popped out the bottom of the cylinder and the remains of the connecting rod punched through the crankcase.

Immediately after that, the final drive was changed from a 1/4 inch chain to a 3/8". I was pushing for a shaft drive, but was outvoted on the basis of cost and complexity.

Thanks for the feedback.

We have cleaned down the piston tops and no obvious signs of damage, or even contact. I do remember thinking my keys were jingling a lot, which was now obviously the damage being done - riding with earplugs does mask a few things.

Windy, i have external braided oil lines including the crossover line, any thoughts on whether having the drilled through spindles (once both in the correct place) and the crossover is a bad thing?

<Windy, i have external braided oil lines including the crossover line, any thoughts on whether having the drilled through spindles (once both in the correct place) and the crossover is a bad thing?>

it should not hurt anything to have both. just make sure that the spindles are installed with the flats facing the proper direction ( facing towards the valve )

windy

I had the top end off my bike recently,same thing, very pitted ex seats.Although they are quite hard they are they are more than likely a castiron of some type. Oil burning will cause the seats to pit due to carbon build up,so it would pay to fit the inlet seals.If your guides are worn &still tight in the head get guide liners installed instead of replacing the guides,removing the guides tends to wear the holes out. If the seats are worn, take the opportunity to get some decent inserts fitted,probably cost less than you think,as I dont think that fuel addative does any thing.

Splatt , The valve seats are made from the valve material there is no need to replace them. But I have seen in the last five years many Commando with stuck valves. They all came with one common symptom the combustion chamber was full of a heavy black coating of unburnt fuel and what not. Around here we call it old man's syndrome. Gee I never rev my bike above 5000 RPM I don't what went wrong.... I was going up this long hill in fourth gear and was only turning 3200 RPM and boom.....
Rev freely and regularly is all I can say.

norbsa,valve seat are not made out of 'valve material',at the most the poms would have used something like 'duraloy' which is only a heat treated cast iron alloy. Most british vehicals only use piston ring material,with the occasional one useing a special alloy,but any way something in or fuel is burning nice pits in our valve seats,the seats are not receasing or burning valves,just deep pits when refacing the seats & i agree with you keep it buzzing, side question, how many 850 have you seen with broken top rings and no apparant loss of performance.

In alloy heads Brit bikes use Austenitic iron for their valve steel, which is alloyed & heat treated to give hard properties.

http://en.wikipedia.org/wiki/Austenite

Yes ,but they are still cast iron based,extremely hard, but only just coping with unleaded fuels,modern inserts have higher nickle&chrome-moly content which withstands corrsion better

Norbsa - you are correct about the revs not getting too high of late, combined with a pair of FCR's which are still over rich won't have helped.
Valve seats recut (if there is an ongoing issue may look at hardened inserts), new valve, gasket and ready to assemble. Looked properly since the first post, with glasses on this time, and inlet valve seals were there

bill said:

The drilled through rocker spindles should both be on the intake side. that mod is so you DON'T need the crossover oil line on the head.
windy

Click to expand...

Got me curious on the drilled spindles, would be interested to know why it needs to be the intake side?

hi iain they need to be on the inlet side because its the only way for all four rockers to recieve oil when being fed by one banjo on the head,i heard of the mod some years ago ,the guy that did it wanted to do away with the little crossover pipe on the head

Thanks Chris,
a bit bleeding obvious now i stop and think - given the closeness of the intakes they must link and the splay on the exhausts means they can't.