Dropped valve?

[Deleted account 200502001]

My 09 GSA ended up at a mechanics yesterday as its been sounding rough as though only firing on 3 cylinders, but yesterday on idle revs often dropped to a stall. It just didn't sound good at all.

Report from mechanic...

Spark plugs are ok and timing just half tooth out. Unable to get vacuum result so it's getting a compression test, possibly a dropped valve.

So if its a dropped valve, what's the best & worst outcome from here? Could the head need removing?

 

[MattW]

My 09 GSA ended up at a mechanics yesterday as its been sounding rough as though only firing on 3 cylinders, but yesterday on idle revs often dropped to a stall. It just didn't sound good at all.

Report from mechanic...

Spark plugs are ok and timing just half tooth out. Unable to get vacuum result so it's getting a compression test, possibly a dropped valve.

So if its a dropped valve, what's the best & worst outcome from here? Could the head need removing?

Not wishing to kick you when you're down but if it's actually dropped a valve, it's pretty catastrophic.

The head will definitely need removing.

Worst case: the valve head has detached and the loose valve head has been rattling around and has trashed the cylinder head, piston and bore (very occasionally bending the con rod slightly too).

Best case: it's just burned the valve and you might get away with a new valve and seat.

It'll all depend on what your mechanic finds when he pulls the head but actual dropped valves are very rare, it's usually a burned valve. If it didn't die with a 'death rattle' and stop, it points to a burned valve.

 

[DrFarkoff]

It'll all depend on what your mechanic finds when he pulls the head but actual dropped valves are pretty rare, it's usually a burned valve. If it didn't die with a 'death rattle' and stop, it points to a burned valve.

No Rattle is good

Hearing a Rattle just before it quits is Very Very BAD

 

[Delboy777]

Three cylinders ???????

 

[socket086]

if when the head is pulled and you find a hole in the piston then the engine will have to be split in two to get all the metal out cheaper to get a second hand one at that stage.
if the piston is not holed then it can be fixed in the frame but make sure the conrod is not bent.
the thing I don't get is you say a half tooth out on timeing there is a bit of play when at top dead centre if this is not the case then the pip on the cog has moved a mill [had this happen on a piston blow up.

 

[Deleted account 200502001]

Three cylinders ???????

I likening it to a car firing on just 3, the last time I experienced that was back in the 80's when I was driving a Ford Cortina

the thing I don't get is you say a half tooth out on timeing there is a bit of play when at top dead centre if this is not the case then the pip on the cog has moved a mill [had this happen on a piston blow up.

Im going on the message the mechanic left me. When the problem occured I was about to go on a group ride out with friends of friends, having all met up at a bike workshop one of them owned. So I ended up pushing my bike into their workshop for initial inspection. But others that have used them say they are good set up. Had it happened anywhere else id have towed it to a certain member on here, but it didn't work that way.

 

[ragerover]

Borrow a borascope saves pulling the head off

 

[Pukmeister]

Get it checked.
If necessary get it fixed.
Then get it remapped.

Is it the right cylinder? For some reason they seem more prone than the left. Obviously get both checked.

 

[Deleted account 200502001]

Yes it's tbe right (off side) cylinder

What normally causes it? Mine was fine until I stalled when pulling out of a junction on 3rd gear, that's when it started to sound rough.

 

[(RIP) Miff]

Yes it's tbe right (off side) cylinder

What normally causes it? Mine was fine until I stalled when pulling out of a junction on 3rd gear, that's when it started to sound rough.

There's various theories. The favourite seems to be over lean fuelling. The valves are made out of 2 separate pieces.

 

[JohnnyBoxer]

Yes it's tbe right (off side) cylinder

What normally causes it? Mine was fine until I stalled when pulling out of a junction on 3rd gear, that's when it started to sound rough.

It's always the right side generally

Pulling out in 3rd?

Never good, couldn't you read the gear indicator on the dash?

That probably did it

 

[Pukmeister]

The exhaust valve spindles are hollow and filled with sodium to cope with the heat of the exhaust gasses flowing over them. This 'tube' is normally friction welded onto the head of the valve. Any weld has a weak area where the structure of the welded metal goes brittle (called the heat-affected zone).

With me so far?

BMW (actually most manufacturers) set their fuel maps to run lean by design to meet ever-tightening modern emissions requirements. Lean combustion takes place at much higher temperatures than richer air/fuel mixtures. This can lead to overheating and weakening of the exhaust valve heads as the hot escaping gasses pass over them. A small valve size also doesn't allow much heat to escape into the head casting when the valve is closed. Coupled with the thin walled sodium filled valve stems, it's a recipe for problems such as valves burning and losing compression, or the heads breaking off and causing damage.

A remap to increase the fuelling will reduce the lean effects mentioned above giving smoother throttle response with better power and reliability. The same can also be achieved by bolting on a power commander ( a less elegant solution).

 

[Deleted account 200502001]

That's a great explanation Adam, thanks.

 

[Bendy toy]

Strangely enough NOx emissions are a bigger issue these days than hydrocarbons. Running an engine lean increases NOx so having it chipped could be better for the environment.

Cars went to 16 valves to allow better heat transfer from the valve heads to the valve seats. Two smaller valves have a longer total circumference and therefore more heat transfer area than one larger valve. In many cars the actual performance of early 16V engines was not improved over 8 valves though the potential was there. Over time they'll have used it to advantage.

Bikes use 16 valves to maximise valve area and allow higher revs. Large twins dont really rev enough to benefit but larger valves area is usually a good thing and there is always the heat issue.

 

[Deleted account 200502001]

So it sounds like a natural weak spot was being created which manifested itself when I sett off in 3rd gear?

 

[cookie]

if it was going to happen, it would have happened anyway. nothing to do with gear choice.

 

[MattW]

Sodium filled valves are mature technology (Rolls Royce Merlins used them). As are two part valves (without the sodium filling). Performance cars and bikes have used them for years. Of course they *can* fail due to manufacturing defects or abuse but it's pretty rare.

In the OP's case it sounds very like the burned valve issue rather than the valve dropping its head - the problem manifested over a while with progressively more rough running until it lost so much compression that one cylinder refused to run - pretty much a classic burned valve scenario. A dropped valve head is usually sudden and catastrophic, often occurs at high revs and makes for a pretty dramatic event (huge rattle and usually plenty of smoke and oil from the exhaust as the contents of the sump make a bid for freedom through a holed piston). I've been there (although not with a bike - a twincam Lotus motor in a Mark1 Escort).

As posted by others, with the 1200 motor the burned valve issue is usually attributed to an over-lean emission focused mixture and this may well be the case although there can be other causes such as over tight valve clearances (causing hot exhaust gases to bypass a section of the valve and start erosion) or failure of the valve to rotate in service leading to a buildup of deposits on the seat (causing hot gas bypass as above).

I'd say the setting off in third gear issue is a red herring - purely coincidental.

If it's *just* a burned valve (which it sounds like it is) then it should be fixable relatively easily / cheaply but for the price of a head gasket and a bit more labour, it would be good practice to check both sides.

 

[Deleted account 200502001]

Some detailed replies there, many thanks for taking the time to post them. I'll read them in more detail during my lunch break

 

[JohnnyBoxer]

if it was going to happen, it would have happened anyway. nothing to do with gear choice.

Damn...............that's my 'office chair' theory, blown out of the water

 

[cookie]

Damn...............that's my 'office chair' theory, blown out of the water

i didn't read that.

i should have said that the pulling away in 3rd will won't hurt the valves, but shag the clutch.