Help - only running on one cylinder

[davegooch]

Can anyone come up with any ideas.
My bike (04 BCR) and I recently parted company at about 70mph - braked whilst travelling in straight line and the front end went away - don't ask!!
Anyway, for various reasons I decided not to involve the insurance company (a decision I'm starting to regret), and purchased two new rocker covers, indicator pods etc.
These have all been fitted, but on trying to start the bike, it initially didn't want to go, and then when it did it was only running on one cylinder - the left hand one. There is a good spark and fuel appears to be getting through - took the throttle body off to make sure. Have swapped injectors over, and spark plugs - this has made no difference. It runs like a pig. Unplugging the electrical feed to the right injector makes no difference, unplug the left and the bike stops. The throttle cable is in the correct position and is operating the throttle mechanism. Will be trying a compression test, probably tomorrow, but does anyone have any ideas why this might be happening and what can be done to rectify it????

[gus]

Hi
Check you havent dislogded the right hand side cable which goes into the throttle body.Also make sure both black nipples are in place.If you have a spark and fuel, as long as they in the right place at the right time it should fire.
gus

[davegooch]

Thanks
Both the Left & Right cables going to the Throttle bodies are connected and appear to be operating correctly!
By manually operating the LH cable, the engine revs rise, by operating the RH cable the engine Backfires!
Black Nipples? are these the vacuum balance points? if so, they are in place as should be.

[Jason M]

Dave - purely speculative suggestions. but could it be an air leak into the inlet. Like the rubber ring on the throttle body where the airbox joins, a split somewhere or just bad alignment. I had one split on my GTI golf and it ran like a complete bastard till I swapped it. It must be setting fuel as you say and maybe too much air (like when there is a hole in the exhaust) could make it backfire.

[davegooch]

Please speculate away, but using the further data that a compression test shows zero compression on the right hand cylinder. We know the tester's not faulty as it worked on the left hand pot. Visibly there's no obvious damage on the right hand side, other than to the rocker cover, which was basically intact but needed replacing (and has been)
If anyone has any ideas as to what could cause zero compression, please post here
Thanks

[Jason M]

Dave - thats a weird one. I would guess that you can't hear anthing amiss like metal touching metal, and that you've removed the rocker cover and rotated the wheel in gear to check the valve gear is even moving and timed correctly. Could the accident have caused the valve chain adjuster to fail and allow it to jump a cog, though that might make metal meet metal - I once saw a bimmer whose valve sheared accross the face and spat the bit out which obviously lost compression. Could try dropping the exhaust manifold off the front to see if it's coming out there I guess. To get absolutely no compression it sounds like the valves aren't moving

[davegooch]

The valves certainly appear to be moving properly. There are no obvious metal on metal sounds. I'm not particularly technical, but my mate is, so we've done all the obvious checks we can think of, however he doesn't have a lot of practise on BMWs so any idea, however possibly stupid, are welcome cos we might not have thought of it!!

[nab 301]

Dave when you say it backfires do you mean backfire through the throttle body or do you mean unburnt fuel igniting in the hot exhaust?.
Did you do the compression test with or without the throttle open?
How badly did you damage the r/c cover could the head be cracked?
Nigel B

[Skint]

Try this as an off the wall suggestion.
Had a bit of a violent off, which caused the handlebars to fly everywhere snapping the lugs off the front frame. After picking it up and welding foot pegs, i tried the bike before the front frame dismantle. It too ran very odd indeed, the left cylinder was running fast or normally, but the right was running light a right pig when it ran. Could tell it ran bat as petrol was comming out the exhaust and the rocker cover was just warm on a longish run. What it turned out to be was the bowden cable box. The bars turned so violently it disturbed the cables, the left cylinder was running full on and the right had full slack so ran leaner than lean. So lift off the petrol tank and dismantle the bowden box and check the cables are free and easy.

[Jason M]

I still can't understand this If the valves are operating and aren't buggered buy you get absolutely no compression then maybe the piston rings have broken, the head is cracked, the head gasget has blown or there is a hole in the piston. If the rings or the piston was the fault then there would presumably be blue smoke everywhere and if the head gasget was gone or the head cracked enough to leak all the compression then I presume there there would be a chuffing noise unless the timing is completely out on that side -

Have you checked the timing using the TDC mark under the little 10p sized plastic cover? When the TDC mark is visible then the valves should all be closed and you should be able to get the feeler guages under the rockers. Maybe the valves are open slightly - sounds unlikely though

[davegooch]

Thanks for all the suggestions.
Work commitments, both mine & my mate's, somewhat limit when he can come over for further checks, but we will be having another (quick) look this evening, so will check as much as we have time for, give results, and await further feedback!!
Dave

[mdouglas]

If there's no reading on the comression gauge, you can rule out any issue related to throttle cables, throttle bodies and the like.

There can only be a few reasons for no compression:

1) The valves are not closing properly (visual inspection with rocker cover removed)
2) The piston is not moving (test with a long screwdriver down the plug hole - you an also check that all 4 valves are closed when the piston is at bottom dead centre and that they stay this way until just after TDC which will eliminate issues to do with valve timing)
3) The cylinder is not gas tight (rings have broken, crack in barrell/head, major failing of cylinder head gasket, holed piston) - you'll only be able to tell by progressively stripping it down (which isn't a particularly big job)

[davegooch]

Thanks for all the help - problem is resolved. The pushrod for the exhaust valve had become dislodged and was partially out of its cup, thus preventing proper operation of the valve and stopping it running!! Fortunately an easy, and cheap, fix as there appears to be no further damage in that the engine seemed to be running fine afterwards, although I have not yet had a chance to actually ride it.