| Author | Message | ||
     Rokoneer |
  This happened about two miles in on my first ride of a BMW I recently bought. Opinions on the cause of this would be appreciated...Too lean? foreign object sneak into the cylinder? | ||
| M1combat |
Looks to me like maybe a cam was installed incorrectly and was constantly bashing the valve into the piston? Was the engine rebuilt recently? Maybe there was something foreign in there, but I can't imagine how a person could get 2 miles w/o hearing something like that... Maybe just a bad piston if it was just rebuilt. Maybe detonation? Did it happen at low or high RPM's? Were you just letting the clutch out when it grenaded? | ||
| Rokoneer |
Non rebuilt engine with 45K on it, supposedly. The heads had been swapped on it a couple years ago. The cutouts for the valves look good and the valves themselves, while covered in slag, do not appear to be bent or have been hammered on by the piston although there was contact due to a valve being stuck open by piston parts that got trapped between it and the seat. The machine started up fine and ran and revved apparently as it should. the exhaust consists of straight pipes with a SuperTrapp on the end of each with about 10 disks, so the exhaust note is rather, um, burly, but still no oddball noises were heard at any time. Happened at high RPM's while at constant speed. Engine acted like it started running out of fuel and coasted for a bit with no power and then the motor stopped spinning completely when a chunk of piston got under a valve and wouldn't allow the piston to complete it's stroke due to valve interference. | ||
| Rocketman |
That's detonation by the looks of it. It could have started out as pre-ignition but what limited info you provide, and the pic's, suggest detonation. Rocket | ||
| S1eric |
Yep I have to agree with rocket, Detonation. You might want to check the timing, or look for a possible intake leak S1Eric | ||
| Budo |
I have one of those from my 1998 S1W. Exact circumstances. I was motoring along about 120 and biiiffff, loss of power. Big hole in piston. I had a intake seal leake. Caused detonation. A normal hearing person might have picked up on it but not only am I pretty deaf I wear ear plugs to save what hearing I have left. Check your intake seals. I bet you have a bad one. | ||
| Oz666 |
Ditto the detonation and probable intake leak. If there was sufficient contact to cause that amount of damage, I doubt it would have started let alone got up to speed. BMW boxer motors (at least when I was at a BMW shop) had solid lifters and a fair bit of piston to valve clearance. So check I would the cam timing also. May the roundel be with you.   Oz | ||
| Bomber |
damnbetcha detonation and/or intake leak -- at least the beemer is easily worked on with the jugs hangin out in the air and all S1Eric -- hey! long time no hear! | ||
| Outrider |
Still don't overlook your idea about loose metal in the engine getting in there and causing an explosion. Happened to a good friend about 1998 with a new BMW with only around 5,000 miles on the clock. Turned out to be some excess just floating around the system that finally got its way into the combustion chamber. BMW did cover it after a lengthy debate. The dealer was the one that discovered the cause and forced BMW to honor the warranty. Then again, posting a pic of a Honda ST1100 towing the BMW helped as well. | ||
| Kano832003 |
i also heard from a friend of mine that if you run any kind of like splitfire type spark plugs in a bike they will burn a hole through a piston. don't know for sure but maybe something to look at. | ||
| Oz666 |
Take a look at the Buell race plugs - had 'em in my bike for over 30K, no holes so far... Oz | ||
| Budo |
"Turned out to be some excess just floating around the system that finally got its way into the combustion chamber." How is that possible. The only thing in the air/fuel system is either air or fuel. Oh, there has been a incident of a screw on the butterfly assembly working out and getting sucked into the combuston chamber but other than that. As long as you are using a air cleaner there shouldn't be anything 'floating around'. That looks like detonation from a very lean condition, ie intake seal leak. |
