Dead Cylinder Help

[lukeman]

Well after a ride around town the bike ran like shit, huge thumping noise coming from the engine area.  It sounded like one of the cylinders wasn't working correctly.  After my bike's idle continued to deteriorate I finally bought a set of vacuum gauges which got here today.  I hooked it up the intake and the result is found in this video.  The first three cylinders showing up on the meter at a reasonable level.  The last has nothing!  I adjusted the screw in and out and no change (the one you're allowed to change, not the blue painted one).  I pulled out the spark plug and there is a spark.  The cylinder is getting gas as I checked the injector. The exhaust pipe is hot out of that cylinder after a time. I believe the intake manifold is working correctly.  So that leave's compression?  Is my line of reasoning correct?  I imagine the next step should be to check the cylinder compression.  If that shows bad compression, whats the next step?



Thanks!

[sh00ter]

(edit) run the compression test on all the cyls first - try this on any that look completely suspect->  what i used to do with cars and I don't know if it would work since you're getting NO reading is put some oil in the cylinder via the plug hole, then run compression test, ideally you do this on a cold engine and turn it over manually a couple time to get the excess oil out before your run your test.  If you get better compression, you know it's likely a ring issue; if it's the same probably one or more valves...  YMMV

[Scott_]

I had the same issue with my '97 in '08. Exception being I had 2 cylinders not working.......

End result, 2 bad valves at the same time for 2 adjacent cylinders... what are the odds....

[lukeman]

These symptoms would point to the exhaust valve or the intake valve.  I'm fairly mechanical, but don't have any experience dealing with the valves so any input would be helpful. 

[TimTyler]

Have a look at this http://bavarianmotorcycleworkshop.com/tech-articles/valve-adjustment-seminar-bmw-k75-through-k1200lt

[lukeman]

Ok thanks everyone for the help!  I'm going to check the valve clearances soon to see what they look like.  Is there a way to tell that a valve is bad without taking off the head?

[Scott_]

Ok thanks everyone for the help!  I'm going to check the valve clearances soon to see what they look like.  Is there a way to tell that a valve is bad without taking off the head?

Well, if you removed the exhaust header, you can possibly see up in to the exhaust ports.
Same for the intake, remove the throttle bodies, and the injector tubes, you can then possibly see in to the intake ports.

Other than that, the head will need to come off.

[CubPilot]

Remove spark plugs, remove the oil fill plug, Run the piston to the bottom of the Power Stroke thread a compression test fitting in that plug hole and apply air pressure.   What ever valve is leaking you will hear, respectively, at the muffler or the air cleaner.

[lukeman]

Took a look at everything more closely last night.  A friend let me his compression gauge which didn't fit,  but in the process I noticed that the screw on the intake manifold that shouldn't be moved on the right side had vibrated loose.  It was so far out that it cut most of the air getting to the cylinder.  I'm not sure how those screws work but I tightened it back to normal and the engine ran as it should.  I put the vacuum sync gauges back on and it was reading about 25% less vacuum from the 4th cylinder.  I adjusted the regular adjusted but wasn't able to get it synced with the other ones.  I'm going to mess around with it some more, but at least the engine is actually running now.

[sh00ter]

Took a look at everything more closely last night.  A friend let me his compression gauge which didn't fit,  but in the process I noticed that the screw on the intake manifold that shouldn't be moved on the right side had vibrated loose.  It was so far out that it cut most of the air getting to the cylinder.  I'm not sure how those screws work but I tightened it back to normal and the engine ran as it should.  I put the vacuum sync gauges back on and it was reading about 25% less vacuum from the 4th cylinder.  I adjusted the regular adjusted but wasn't able to get it synced with the other ones.  I'm going to mess around with it some more, but at least the engine is actually running now.

Check this post

http://www.motobrick.com/index.php/topic,364.msg2044.html#msg2044

[lukeman]

I thought i remembered seeing a guide about doing this, thanks!  Evidently the previous owner fiddled with them, so I could probably do no more harm and improve the situation.  The vacuum gauges seems to be pretty accurate so hopefully I can nail it down pretty close, or at least closer than it currently is.

[lukeman]

I've replaced all the rubber around the engine now.  I checked all the valves and the clearances are spot on.  I still can't get the carbs to sync.  I've even switched the throttle body with a lightly used one I got off ebay.  I might just end up biting the bullet and have someone do a leakdown and see what the result is.

I'm trying to think of a list of things that would affect the vacuum reading.  Obviously vacuum leaks, valves. I imagine rings, and head gasket.  What about things like the ignition, good spark and leads?  I don't think they would change the vacuum...?

Also when I remove the oil cap it expels a lot of air.  Should the crankcase be pressurized?


One interesting thing is if I remove the injector wire from one of the first two cylinders the engine characteristics don't change that much.  If I pull it off either cylinder 3 or 4, then the engine barely runs.  This seems odd to me and maybe could help figure out what the hell is wrong.  Its also the same if I pull a lead from a plug, on 1 or  2 not much change. But if 3 or 4 is off then it runs like shit.  Just trying to wrap my head around why this would be the case. 



Thanks

[sh00ter]

I've replaced all the rubber around the engine now.  I checked all the valves and the clearances are spot on.  I still can't get the carbs to sync.  I've even switched the throttle body with a lightly used one I got off ebay.  I might just end up biting the bullet and have someone do a leakdown and see what the result is.

I'm trying to think of a list of things that would affect the vacuum reading.  Obviously vacuum leaks, valves. I imagine rings, and head gasket.  What about things like the ignition, good spark and leads?  I don't think they would change the vacuum...?

One interesting thing is if I remove the injector wire from one of the first two cylinders the engine characteristics don't change that much.  If I pull it off either cylinder 3 or 4, then the engine barely runs.  This seems odd to me and maybe could help figure out what the hell is wrong.  Its also the same if I pull a lead from a plug, on 1 or  2 not much change. But if 3 or 4 is off then it runs like shit.  Just trying to wrap my head around why this would be the case. 

Thanks

Have you tried moving the injectors around?  - move 1 to 4 and retry, if it does the same thing, could be the injector wiring.

[frankenduck]

If you can't get the carbs to sync that usually means a leaking boot between the TBs and the cylinder head.