1200 exhaust valve burnout

[Schtum]

If the bikes were all the same, then you could try and work it out.

The bikes could be the same but it's unlikely that they would have been ridden in the same way, subjected to the same conditions or the same level of maintenance. Tight valve clearances in combination with one or more other factors might well be a contributing factor.

However, I think the comments about fuelling are probably very relevant. You said the bike didn't have an aftermarket system on it but could it have done at some point in its life? BMW have got the engines to run very lean by using knock sensors but that hasn't done the exhaust gas temperatures any favours even with a catalysed system. Remove that and the engine runs even leaner and hotter.... I think that BMW have perhaps got quite close to the margins, even in stock form, before people start modding the bikes.

 

[Humbug]

I've just striped my friend's Kawasaki VN800 engine down and found this. Nothing to do with oil starvation. The piston wasn't even seized and there is no damage to the bore.

The cause was fitting an after market exhaust system without rejetting. I also discovered the valves hadn't been shimmed for quite a while and this had obviously contributed to the problem. The remains of one of the valves was found in the front downpipe!

 

[Pauly S]

oooh...

that hurt...poor kwaka.
afaik the exhaust was standard,both knock sensors are fitted, cat is still present.
Talking of debris we found spoonfuls of dead engine in the exhaust and in the air filter box , sitting in a pool of oil.
The engine build is coming on nicely, i'm stuck now waiting on a sheckle of bits from bmw,particularly the valve stem oil seals.
The valve seats are now lovely and lapped in, the valves are shiny as new,
its all getting prepped slowly, before the whole lots gets a trip the the degreasing bath to get all the grit and shyte out,before the final build up.
I must say i'm proper enjoying this, and i'm looking forward to reuniting the 1000 odd bits again and making them sing together in harmony.woohoo.

 

[cookie]

the valves are shiny as new

properly new exhausts though?

 

[Pauly S]

shiny as new mate.

properly new exhausts though?

I even polished the piston crowns for the hell of it.

 

[Pukmeister]

Paul, the only way you can be 100% sure is to get a rolling road dyno run with exhaust gas analysis once the rebuilt engine is run in. Only then will you see the true air/fuel ratio across the whole rev range whilst under load. The only thing you won't know is how much altitude compensation factor they run.

 

[Pauly S]

what about

Paul, the only way you can be 100% sure is to get a rolling road dyno run with exhaust gas analysis once the rebuilt engine is run in. Only then will you see the true air/fuel ratio across the whole rev range whilst under load. The only thing you won't know is how much altitude compensation factor they run.

The fact the exhausts run two into one,you cant monitor each cylinder directly, although there are 2 lambda probes and two injectors etc,one cylinder could mask the other,see the problem?
i need to know if the injection pulse is the same either side, i can prob get this measured, in theory it should be the same,but also i wonder if the modded software runs a richer right cylinder to stop this burn out scenario.

 

[Pukmeister]

The fact the exhausts run two into one, you can't monitor each cylinder directly, although there are 2 lambda probes and two injectors etc, one cylinder could mask the other, see the problem?

I do now.

 

[Pauly S]

hand grenade with the pin out

there you go..After the grenade went off.

And after, Just add some instant cylinder head..

The Valve..

 

[Deleted account 190920001]

Looking at the last pic it looks to me like it is melted off as opposed to sized, hit and snapped. I would also expect the cam follower to be snapped if it was a stuck valve. The sodium has had enough heat to melt on to the stem and theory would say the stem was holed first for this to happen. As soon as the head broke off there wouldn't be any combustion heat any more so the sodium wouldn't melt afterwords. The other exhaust valve looks like a typical burnt valve as well but without seeing it out it might simply be that a bit broke off with contact. Lean mixture and or poor valve clearance would be my guess. That's my theory anyway simply going by the pictures but it is difficult to tell due to the amount of damage that is cause with a valve head bouncing around.

 

[davegs]

Valves

Are these sodium filled? this was done on Manx Nortons (racing machines) , and these valves were a fortune many years ago hence the £67 each that was quoted. mo of thwe old bikes I had in the sixties (now classics then crap!!) only cost £50.!!.
Dave GS.

 

[Deleted account 190920001]

yes they are sodium filled, probably the only way they could take the heat.

 

[Smug]

I'm not surprised the valve heads drop off when you see how small the stems are and hollow as well.

I thought that BMW blamed the problem of the 06 bikes on a batch of faulty valves.

 

[Pauly S]

How do you know this?

I'm not surprised the valve heads drop off when you see how small the stems are and hollow as well.

I thought that BMW blamed the problem of the 06 bikes on a batch of faulty valves.

where did you find this out?

 

[Smug]

A mechanic at the local BMW dealer was repairing a GS where a valve head had dropped off. He was showing me the bits and I was amazed at how small the valve stems were especially when he said that they were hollow and contained sodium to help keep them cool. It seemed to be common knowledge in the workshop that a lot of the 2006 bikes had suffered a similar problem because of a batch of faulty valves.

He said that the fault was eventually traced to a problem with the friction welding of the stems to the heads.

 

[Pauly S]

Thanks for that

top stuff.well done.

 

[DrFarkoff]

It doesn't only happen to 2006!

My 2004 did it but I suspect the lean airfuel mixture is a contributing factor (along with tight valve clearances and skinny valve stems!) hence I have an accelerator module fitted now