cooked a valve

[grownup]

Happy new year,

Looks like I cooked my valve on my old RT the last ride for the year on 12.31.2013.



The good one looks like this.



Can I bring this to Tech Day and will someone fix the bad valve for me ?

[vacommuter]

I destroyed an exhaust valve on my KLR. I'd keep them in spec but at the tight end. Lesson learned. It went to zero in between checks. Had to get the head machined for oversized valves. While it was apart I had a big bore kit done so now its a 685 vice 650. These days I keep my valves at the loose end of the spectrum. Other than watching with a beer in my hand and making off-color comments I would be pretty useless.

VAC

[Rick F.]

Ted,

If I'm reading your compression gauge right, it looks like you're getting only 40 psi on the bad cylinder--that's a really low reading that suggests something other than "just" a burnt valve.

I'm wondering if you might have a rocker clearance problem, i.e., a valve that is not actually closing all the way? It's easy to check whether the clearances are okay, and it's possible that the problem isn't as bad as you fear. On the other hand, an open valve would generally burn pretty quickly. Was it running really badly on your last ride?

Good luck tracking this down, and let us know what you find.

Rick

[grownup]

Ted,

If I'm reading your compression gauge right, it looks like you're getting only 40 psi on the bad cylinder--that's a really low reading that suggests something other than "just" a burnt valve.

I'm wondering if you might have a rocker clearance problem, i.e., a valve that is not actually closing all the way? It's easy to check whether the clearances are okay, and it's possible that the problem isn't as bad as you fear. On the other hand, an open valve would generally burn pretty quickly. Was it running really badly on your last ride?

Good luck tracking this down, and let us know what you find.

Rick

I thought if it had a cooked valve the fuel would still burn and create heat. However, the fuel was not burning on the left side despite having a spark and fuel. Maybe I should adjust the valves and see if the compression returns. I might get lucky.

[Rick F.]

Ted,

If I'm reading your compression gauge right, it looks like you're getting only 40 psi on the bad cylinder--that's a really low reading that suggests something other than "just" a burnt valve.

I'm wondering if you might have a rocker clearance problem, i.e., a valve that is not actually closing all the way? It's easy to check whether the clearances are okay, and it's possible that the problem isn't as bad as you fear. On the other hand, an open valve would generally burn pretty quickly. Was it running really badly on your last ride?

Good luck tracking this down, and let us know what you find.

Rick

I thought if it had a cooked valve the fuel would still burn and create heat. However, the fuel was not burning on the left side despite having a spark and fuel. Maybe I should adjust the valves and see if the compression returns. I might get lucky.

Ted,

I think checking the valve clearances is definitely the right place to start. If one of them has zero clearance throughout the engine's cycle, then you've got an open valve, which would kill your compression down to the sort of level you're measuring. A hole in the piston would also cause very low compression, but you'd generally get some serious noise as well. A very badly burned valve would also cause a large enough air leak, but something like that would presumably have been giving you a misfire that became progressively worse over time as the valve burned. A broken valve would cause obvious noise.

If an intake valve is not closing, then the net airflow into the engine would be minimal--i.e., the piston would blow out about as much air as it sucks in. The fuel injection system would measure something close to zero airflow and inject little or no fuel. That scenario could lead to your non-firing cylinder, I suppose. Similarly, if neither intake valve is opening, then you'd get zero airflow--but it would presumably be less common for a problem to affect both valves simultaneously. A broken rocker could do it but would probably cause a fair amount of noise in the process.

Anyway, a look inside the valve cover would confirm or rule out some of these possibilities. Good luck!

Rick

[henwin]

Ted,
If I'm reading your compression gauge right, it looks like you're getting only 40 psi on the bad cylinder--that's a really low reading that suggests something other than "just" a burnt valve.
I'm wondering if you might have a rocker clearance problem, i.e., a valve that is not actually closing all the way? It's easy to check whether the clearances are okay, and it's possible that the problem isn't as bad as you fear. On the other hand, an open valve would generally burn pretty quickly. Was it running really badly on your last ride?
Good luck tracking this down, and let us know what you find.
Rick

I thought if it had a cooked valve the fuel would still burn and create heat. However, the fuel was not burning on the left side despite having a spark and fuel. Maybe I should adjust the valves and see if the compression returns. I might get lucky.

Ted,
I think checking the valve clearances is definitely the right place to start. If one of them has zero clearance throughout the engine's cycle, then you've got an open valve, which would kill your compression down to the sort of level you're measuring. A hole in the piston would also cause very low compression, but you'd generally get some serious noise as well. A very badly burned valve would also cause a large enough air leak, but something like that would presumably have been giving you a misfire that became progressively worse over time as the valve burned. A broken valve would cause obvious noise.
If an intake valve is not closing, then the net airflow into the engine would be minimal--i.e., the piston would blow out about as much air as it sucks in. The fuel injection system would measure something close to zero airflow and inject little or no fuel. That scenario could lead to your non-firing cylinder, I suppose. Similarly, if neither intake valve is opening, then you'd get zero airflow--but it would presumably be less common for a problem to affect both valves simultaneously. A broken rocker could do it but would probably cause a fair amount of noise in the process.
Anyway, a look inside the valve cover would confirm or rule out some of these possibilities. Good luck!
Rick

I have a question...if the valve is stuck open--for whatever reason--doesn't that mean that it is sticking down into the cylinder bore and if that's the case, how come the piston hasn't closed it by pressing the valve back into its seat?

[Georgeinva]

The R1150 burns exhaust valves, even when properly adjusted, more than most BMWs. I would be shocked if it were anything other than a burned valves.
With the bike in gear pull the valve cover off, put the engine to TDC, hold the rear brake and find a way to put air in the spark plug hole. Blowing into you pressure tester or just a piece of hose will work. If you like to buy tools then buy a leak down tester. Listen for the leak. Exhaust pipe = burned exhaust valve, air box = burned intake valve, engine breather =rings, valve guides or a hole in the piston.

Henry, "Piston assisted valve closure" is very bad. On most modern engines the valves are at angles to the piston. Contact usually bends the valve prior to closure. The piston also has a few thousands of an inch clearance between the crown and head so it would not close all the way. If you have weak valve springs that allow the valves to float you will hear the piston hit them. If the valve clearance is too tight and causes the piston to hit the valve things are going to break.

[henwin]

Henry, "Piston assisted valve closure" is very bad. On most modern engines the valves are at angles to the piston. Contact usually bends the valve prior to closure. The piston also has a few thousands of an inch clearance between the crown and head so it would not close all the way. If you have weak valve springs that allow the valves to float you will hear the piston hit them. If the valve clearance is too tight and causes the piston to hit the valve things are going to break.

Hi George.

Thanks for the explanation. I assumed that if the piston ran into the valve there would be Hell to pay, and that things would get damaged, but I wasn't quite sure, based on the discussion.

[Anton]

... A very badly burned valve would also cause a large enough air leak, but...

Any burned valve is a massive air leak. I've posted pictures on this forum before of some BMWBMW member's burned valve. There is usually a substantial amount of missing metal. It might have been this one:

[Chiba]

HI ANTON!!!!