So Do Ya think Maybe possibly ........
- Thread starter DrFarkoff
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Decster
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perhaps this is the reason for the replacement Boxer engine in the GS /RT i.e. DOHC, different valves etc.
In a high gear crack open throttle, engine mixture explodes force can't go anywhere because of wrong gear, pressure applied to valve heads instead.
what planet you on
,think about what you said and how people drive in the real world
In a high gear crack open throttle, engine mixture explodes force can't go anywhere because of wrong gear, pressure applied to valve heads instead.
Stick to computers
In a high gear crack open throttle, engine mixture explodes force can't go anywhere because of wrong gear, pressure applied to valve heads instead.
That's how engines work! And when that explosion happens, both valves are fully seated and supported.
D6
Registered user
In a high gear crack open throttle, engine mixture explodes force can't go anywhere because of wrong gear, pressure applied to valve heads instead.
you want some pressure applyin to your own head
soft valves, they stretch,
kawasakis sometimes had the same problem in the 80s/90.s though not so severe
The failure method always seems to be that the head fails at the junction to the valve stem with evidence of brittle fracture.
I believe the heads are friction welded to the stems as they are sodium filled stems for cooling. It could be this weld zone that fails either through cyclic metal fatigue or by the carbon structure changing through the heat affected zone of the weld.
I would suspect some metallurgical reason, the only surefire way to tell is if someone could get the fracture surface examined under a scanning electron microscope by a metallurgist for evidence of inclusions within the metal or the grain structure of the material.
I don't think that mechanical sympathy has much to do with the failure other than running the correct valve clearances and not over-revving eg missed gears or sustained full throttle.
I believe the heads are friction welded to the stems as they are sodium filled stems for cooling. It could be this weld zone that fails either through cyclic metal fatigue or by the carbon structure changing through the heat affected zone of the weld.
I would suspect some metallurgical reason, the only surefire way to tell is if someone could get the fracture surface examined under a scanning electron microscope by a metallurgist for evidence of inclusions within the metal or the grain structure of the material.
I don't think that mechanical sympathy has much to do with the failure other than running the correct valve clearances and not over-revving eg missed gears or sustained full throttle.
What he sez, It's common on airhead engines over 40K miles as well..
But with oilys it seems to be at any mileage
I blame the Quality control in valve component {IIRC is in China} factory ....
mechcanico lee
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Sounds good that, in the picture you can see the valve stem has broke away pretty clean, not very good design really ,are they still making them that way ?
jpooch00
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When you see a plug like that, AFU and FUBAR immediately come to mind. No happy ending - ever.
GSband
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As far as I understand this seems to be the cause :
the valves are pushed by rockers, which means there's always a slight sideway motion being exerted on the valve stem. Possible consequences are overheated stems because of friction in the guidance, and stem guidance wearing out leading to too much play in the guidance. And this leads to the valve not closing properly in it's seat, and breaking off at the weakest spot.
It would seem that the exhaust valve (or stem) is more at risk because of the already present heat from exhaust gasses. The RHS problems are most common, but there have been some LHS problems too, and it's always an exhaust valve.
A chap with an R12 on belgian BMW forum heard a rattle on the RHS, and had the RHS cylinder head checked. It was diagnosed that the valve guidance had too much play. A completely new RHS cylinderhead was installed under warranty.
I suspect there's a relationship with the following :
- lean mixture leads to high temperatures
- 'popping sounds in exhaust pipe' actually meaning fuel mixture being burnt in exhaust : not good for exhaust valves (pressure at the wrong side of the valve)
- BMW does not favour oil radiator grilles : interferes with cooling (do a search 'oil cooler covers')
- BMW recommendation for oil changed from 20W-50 to 10W-50 (better for cold starts, and starts in cold T°)(and no I don't want to start an oil thread
)
- new cylinder heads (model 2010) : no rockers
But these are just personal hunches.
the valves are pushed by rockers, which means there's always a slight sideway motion being exerted on the valve stem. Possible consequences are overheated stems because of friction in the guidance, and stem guidance wearing out leading to too much play in the guidance. And this leads to the valve not closing properly in it's seat, and breaking off at the weakest spot.
It would seem that the exhaust valve (or stem) is more at risk because of the already present heat from exhaust gasses. The RHS problems are most common, but there have been some LHS problems too, and it's always an exhaust valve.
A chap with an R12 on belgian BMW forum heard a rattle on the RHS, and had the RHS cylinder head checked. It was diagnosed that the valve guidance had too much play. A completely new RHS cylinderhead was installed under warranty.
I suspect there's a relationship with the following :
- lean mixture leads to high temperatures
- 'popping sounds in exhaust pipe' actually meaning fuel mixture being burnt in exhaust : not good for exhaust valves (pressure at the wrong side of the valve)
- BMW does not favour oil radiator grilles : interferes with cooling (do a search 'oil cooler covers')
- BMW recommendation for oil changed from 20W-50 to 10W-50 (better for cold starts, and starts in cold T°)(and no I don't want to start an oil thread
)- new cylinder heads (model 2010) : no rockers
But these are just personal hunches.
jpooch00
Registered user
As far as I understand this seems to be the cause :
the valves are pushed by rockers, which means there's always a slight sideway motion being exerted on the valve stem. Possible consequences are overheated stems because of friction in the guidance, and stem guidance wearing out leading to too much play in the guidance. And this leads to the valve not closing properly in it's seat, and breaking off at the weakest spot.
It would seem that the exhaust valve (or stem) is more at risk because of the already present heat from exhaust gasses. The RHS problems are most common, but there have been some LHS problems too, and it's always an exhaust valve.
A chap with an R12 on belgian BMW forum heard a rattle on the RHS, and had the RHS cylinder head checked. It was diagnosed that the valve guidance had too much play. A completely new RHS cylinderhead was installed under warranty.
I suspect there's a relationship with the following :
- lean mixture leads to high temperatures
- 'popping sounds in exhaust pipe' actually meaning fuel mixture being burnt in exhaust : not good for exhaust valves (pressure at the wrong side of the valve)
- BMW does not favour oil radiator grilles : interferes with cooling (do a search 'oil cooler covers')
- BMW recommendation for oil changed from 20W-50 to 10W-50 (better for cold starts, and starts in cold T°)(and no I don't want to start an oil thread
- new cylinder heads (model 2010) : no rockers
But these are just personal hunches.
My theory is: Cheaply produced, under-engineered, defective valves.
GSband
Registered user
Okay, but then why only exhaust valves, and why mostly on RHS ?
jpooch00
Registered user
Because exh valves run far hotter and therefore have more heat related failures when poorly engineered. Generally, if a valve failure happens in any engine, it'll be an exhaust valve regardless of how well made they are.
No clue on the RHS issue, other than some other engineering/design defect that causes that side to run hotter for some reason.
wully
Registered user
No clue on the RHS issue, other than some other engineering/design defect that causes that side to run hotter for some reason.
Maybe something to do with parking the bike on the side stand and draining the oil from the RHS cylinder head
jpooch00
Registered user
Maybe something to do with parking the bike on the side stand and draining the oil from the RHS cylinder head
I don't see how that could do it, but who the hell knows.
There's no evidence from the pics I've seen that the valves are sticking open and getting hit by the piston.
It appears that the valve heads just fall off at the bottom of the taper where the stem is attached. I'm still thinking the right side just runs a little hotter and pushes defectively designed/made valves over the edge.
It's truly incredible to me that BMW is willing to take the financial and reputation hits from this long running and well documented problem rather than just figuring out what's wrong and fixing it.
Decster
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jpooch00
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maybe they have with the DOHC
I guess time will tell. I don't see how changing the cam arrangement could help, but since they made some very slight changes to the valve sizes, who knows?
Hopefully, this will fix the problem though.
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