Just bought my first BMW! (K75C)

[ikirven]

Hello all!
I'm new here - I just bought a 1986 K75C. What a cool bike! It has ~80k miles on it, but I got lucky as the previous owner was very diligent about recommended / dealer service and babied the machine. I've been going through it for the last few days and have found:
-Nasty Injectors
-Exhaust leak (at the header / muffler joint, no gasket)
-Intake leak (probably the first of a good few, at the crankcase breather)
-Not one, but TWO (2) ant colonies taking up residence in the airbox and the toolkit storage box thingy
-A certain strange noise. It's like a knocking / rattling that comes from the front of the motor, loudest just above idle with little / no load. I know the manual reads piston slap here, but given how the bike isn't running too well, it sounds / feels more like bad timing and dieseling to me.


Anyway, I've fixed the exhaust by wrapping a 1.5x15" strip of 0.01" aluminum sheet on the header at the joint, have soaked the fuel injectors in cleaner, rigged the breather hose to work (better), and am headed to recondition the intake manifold and all it's ancillaries later today.
I've read a lot about modifications and things to check for on these bikes, and so far I've gathered that I ought to:
-Check / Grease the final drive splines (done)
-Change all fluids (in progress)
-Check the timing chain / valve shims / chain guides and tensioner (I figure it can all be one job, maybe tomorrow).
So this last part leads into that noise. I got this bike in semi-running condition, but it was just checked out by a BMW mech who told me it really needed nothing but some new intake rubbers and a fluid change. I suppose he thought that the noise was nothing - however, I don't. I'd hate to pass up due diligence just to have the bike slip timing and drop a valve or worse.
So, my question: what do you think that rattle / knock could be, and what should I check first / why?
Pictures will come when I get back to town.
Thank you all in advance!

[Laitch]

-Not one, but TWO (2) ant colonies taking up residence in the airbox and the toolkit storage box thingy
-A certain strange noise. It's like a knocking / rattling that comes from the front of the motor, loudest just above idle with little / no load. I know the manual reads piston slap here, but given how the bike isn't running too well, it sounds / feels more like bad timing and dieseling to me.
Thank you all in advance!

Welcome, ikirven! BMW is well-known for not using enough insecticide on their bikes during routine service. :giggles

What's needed now are some photos of your bike as soon as you return and a recording of the troublesome sound uploaded to this site or YouTube. K-bikes will rattle if ridden at low revs in a gear that's too high for the speed. There are several other conditions that cause rattles. It's too early for that diagnosis.

If the injectors were nasty, it doesn't seem to me like the dealer was too diligent in servicing this bike. Based on that, new spark plugs, new spark plug leads, new high pressure submersible fuel lines in the tank and maybe a new fuel filter might be needed. Do you have records that any of those items have been installed?  What's the interior of the fuel tank look like when it's empty?

Check the intake rubbers for leaks using the propane or carb cleaner test. Once their condition is proven ok, finish with the valve clearance/timing chain/throttle body balance. After that, there might be more indication of where the problem lies. 

I don't accept thanks in advance.  :yes

[The Mighty Gryphon]

That noise is normal.  It's caused by a lot of clearance between the slots in the output gear and the dogs on the balancer shaft.  It's designed in and the only fix I have been able to do is to clean the faces of the clutch basket and the balancer shaft and torque the clutch nut to the top of it's spec.  You have to pull the transmission and disassemble the clutch to do the job, and then who knows how long the noise will stay away.  Mine has been 12K miles and I can hear it starting to come back.

Personally having done it once, I would live with the clank.  It doesn't hurt anything.  Balancing the throttle bodies helps and keep the revs up once you're out of first gear.

[Martin]

Welcome to the asylum from the land of OZ.
Regards Martin.

[Christopherguzzi]

Welcome and congrats on your "new" K75C.  They are among the best of the k bikes imho.  Enjoy!
 

[ikirven]

Good Evening All,
Thanks for the warm welcome and info. Over the last day, I took down the intake entirely, soaked the injectors in cleaner for 24 hours, and scrubbed everything down clean, with new fuel lines installed and all electrical connections cleaned and greased. As promised, here are some pics I took today during my intake-side refurbishment / rebuild, and a few of the bike all back together (minus fairings). To answer some questions in order:

Laitch
The injectors cleaned up pretty nicely - not perfect, but definitely worth the trade of 98 cents of fuel injector cleaner + 24 hours over the $75 + 20 minutes for new injectors. I haven't looked at the ignition system, but it works so far so I'll leave my hands off it for now. I didn't get the sound to come through on a video, so no evidence of the tapping, but it did (mostly) go away after the intake cleaning. The tank looks good and so did all the intake rubbers, so I reinstalled as I could. I have some experience troubleshooting Bosch MAF units from this era, so I popped this bike's open to be pleasantly surprised that it looked great.

The Mighty Gryphon
I'm glad to hear that (most likely) it's not hurting anything. I'll do some further investigation when I get the valve cover off next weekend to take a look at the chain, cams, valve clearance, and chain guides. On inspection, I found that the throttle bodies were damn near balanced already, so again, I cleaned them and left them be.

Martin / Christopherguzzi
Thank you gentlemen!

So now I have another, more pressing problem. Before the intake job, the bike would always start, but it really only liked to idle - it would take the gas, but only if you were EXTREMELY careful and slow about applying it: even then, it would bog / stall before revving up. Not really driveable. Now, after the intake job, it revs up beautifully and sounds great, but... it's random. I give it the throttle, it bogs a little, and then I let off, and THEN it revs up. Usually, it goes to ~3000 RPM and stays there, before either climbing more or dropping back down. If I manually depress the throttle follower connected to the throttle bodies, the revs drop back to a healthy idle of ~950 RPM. Even if I don't use the throttle, the 'resting' RPM of the engine will pseudo-randomly climb and fall. On a potentially related note, the grip throttle does NOT return to 0 without turning it back - give it the throttle, and the grip will stuck until you twist it back. To clarify, I'm aware of the thumbscrew right there - that's not engaged. To recap:

-Valves looked good, #2 running rich before service, #1,3 running lean before service
-Fuel injectors cleaned and working.
-The engine starts and runs every time.
-Engine runs just fine now that intake was cleaned.
-3 cylinders getting fuel, 3 cylinders firing
-Initial knocking noise has diminished, bike runs quieter.

What in the world could be the problem? I reason that it has something to do with the throttle or the throttle position sensor. Of course, it's possible that there's a vacuum leak, but I did my best to search for potential leaks and ensure that it, well, wasn't leaking.
Let me know if there's any more information I can volunteer! Pictures are below. They were too big to attach, so they're on dropbox via link.

Thanks,

Ian


https://www.dropbox.com/s/g282qw4wwmrunm7/IMG_3678.JPG?dl=0
https://www.dropbox.com/s/g7emd2rujkftp3a/IMG_3679.JPG?dl=0
https://www.dropbox.com/s/cavs4xjqlfv2c9t/IMG_3680.JPG?dl=0
https://www.dropbox.com/s/evtgvaqj8bderfb/IMG_3681.JPG?dl=0
https://www.dropbox.com/s/becqgs64z2x50bt/IMG_3682.JPG?dl=0
https://www.dropbox.com/s/nqgk8e7vt8epafo/IMG_3683.JPG?dl=0
https://www.dropbox.com/s/y45mhkzmdd3fqe7/IMG_3684.JPG?dl=0
https://www.dropbox.com/s/juatfs23sx251jp/IMG_3685.JPG?dl=0
https://www.dropbox.com/s/a1rmwjfimp9zi8c/IMG_3686.JPG?dl=0
https://www.dropbox.com/s/osxqefgba4dfpuc/IMG_3687.JPG?dl=0
https://www.dropbox.com/s/ukojvakp7556k8b/IMG_3688.JPG?dl=0
https://www.dropbox.com/s/fpd4f64aonm7tsw/IMG_3689.JPG?dl=0

[Martin]

Check to see if the grip is pushed on to far and binding. Remove the large phillips head screw that holds the cover over the throttle mechanism. With the cover removed see if the two lines on the gear assembly line up. Check that the grease has not gone hard, BMW does not recommend lubing the cable as some lubricants can effect the Teflon liner. However a PTFE based lubricant called Tri Flow can be beneficial to easy throttle movement. It is available from bicycle shops, do not use WD40.
Regards Martin.

[Laitch]

As promised, here are some pics I took today during my intake-side refurbishment / rebuild, and a few of the bike all back together (minus fairings).
The tank looks good and so did all the intake rubbers, so I reinstalled as I could.
On inspection, I found that the throttle bodies were damn near balanced already, so again, I cleaned them and left them be.
What in the world could be the problem? I reason that it has something to do with the throttle or the throttle position sensor. Of

It is widely considered that looking at manifold rubbers isn't as effective in judging their condition as doing the propane/carb cleaner test to find leaks that may occur during intake. A throttle body balance is usually done by using a manometer assembly of some type—Carbtune or Snapple bottle. :giggles Is that the inspection you did? If it isn't, can you describe your inspection?

If Martin's suggestions don't remedy the situation, you might have the #3 throttle body manifold clamp out of its correct position. You could always post a picture on the site of the clamp arrangement once you take the time to resize it.

[The Mighty Gryphon]

+1 on Martin's suggestion that the right grip is pushed down too far.  This will not only cause a sticky throttle, but if you have heated grips the wire can rub on the end of the bars and wear off the insulation causing the #1 fuse to blow when you turn on the heaters and killing the charging system and a bunch of other stuff. 

Another source of vacuum leaks is the crankcase breather between the rear of the case and the air box.  it's a zig-zag hose located behind the throttle body switch.  These are notorious for cracking at the clamps.  Fortunately, it is one of the few reasonably priced parts sold by BMW.  A lot of guys just replace it when they get a "new" bike just to be sure.

[ikirven]

Thank you all!

Laitch,
Thanks for the heads-up on forum practices and intake testing. I'll be sure to resize and properly attach my pictures from now on. This is my first BMW and second motorcycle (myself being 20 years old) and I've only ever had to troubleshoot carbureted engines, so forgive me that this my training in diagnosing a more complex fuel injected machine. I did a sight-and-manual-operation test off the bike, and the butterfly valves were all lined up and ports cleared. I suppose this needs more attention than that. I'll put together a rig to test it all together on the bike the next chance I get. Do you have a preferred method for doing this?

Martin and The Mighty Gryphon,
Taking apart the throttle assembly is probably next on my list. I've ordered the crankcase breather hose, because the original is not looking so good - I've made it work in the interim, but a new hose might just do the trick.

[Laitch]

I did a sight-and-manual-operation test off the bike, and the butterfly valves were all lined up and ports cleared.
Taking apart the throttle assembly is probably next on my list.

Did you check the position of that #3 manifold  clamp?

[Martin]

Checking the throttle mechanism is not a hard job, cleaning and lubing takes a maximum of 20 min. When changing the grease I use  the light white lithium spray grease, you don't need anything heavy. The idea is to do it at least once a year. With the PTFE cable lube I run the lube in until it runs clear and do it at the same time as throttle greasing.
Regards Martin.

[ikirven]

Hello All,

I'll have to be away from the bike until the weekend, but I did some more diagnostics.
I figured out what you meant by balancing throttle bodies, Laitch  :2thumbup: will do when I actually get the thing running more consistently. I'll get you a picture of that manifold clamp when I can.

I played around with it yesterday and found that I have good fuel pressure, properly,  working injectors, functioning spark plugs (though I replaced those anyway because they weren't looking great), but the alarming bit was that the plugs were WET, even after the bike had been running. I have confirmed spark and confirmed fuel, so I suppose the next logical thing to eliminate would be compression. The bike sounds fine and there's exhaust pressure when it runs, so I think I have compression. That said, I'll be doing that and pulling the valve cover off to take a look at clearances / timing chain guides on Saturday.

Those bits aside, I cleaned up the throttle assembly and freed it up a little, and adjusted the TPS to click when the throttle bottoms out.

Before I can get a video, allow me to try to describe what's going on:
Hit the starter, it ALWAYS fires, but doesn't always start. When it does start, it hunts for idle between 600-1300 RPM and doesn't run for longer than a few seconds UNLESS I give it a very slow throttle advance (too much throttle will bog it down). Instead of dying off, it'll catch after about a second or two and rev up to 2500-3500 RPM and stay there as long as I hold it. The bike hasn't been properly run in several months, so I see some light black smoke from the exhaust when it revs up. If I c, but it sounds OK at higher RPM. If I can hold the RPM around 1400, I can work the clutch to get it rolling, but then it wants to stay at 1200-1300 RPM and responds to throttle by bogging down. In my post-run inspection, it seems the #1 header is not as hot as the rest. I'm thinking that something is wrong with the fuel mixture, somewhere, or that the valves are badly out of whack. I'm waiting on a new crankcase breather and 90 degree airbox hose to install, so I'll be back in the thick of the intake before too long to do further diagnostics if you all have some further ideas.

Thanks all,
Ian

[The Mighty Gryphon]

Sure sounds like an air leak to me.  The symptoms make me think of a lean idle mixture. 

My money is on the crankcase breather Z-tube, but it could also be in the MAF sensor, possibly someone has been messing with the MAF idle air adjustment.

When you say you have working injectors do you mean they cycle and FLOW THE PROPER AMOUNT OF FUEL?  Have they been serviced and bench tested?

[ikirven]

I thought about a lean fuel mixture as well, but that doesn't explain wet plugs as far as I know. After soaking the injectors and cleaning them up, I tested the injectors individually with 40psi and a momentary switch, as well as all together on the fuel rail with the fuel pump and starter running - they do work. By MAF idle air adjustment, how is that adjusted?

[ikirven]

Update!

I got some time to swap the crankcase breather hose, the 90 degree intake hose, and adjust the valves with some new shims. I dragged an aluminum rod across the bottom of the tank where I couldn't see, and found quite a bit of gel / dirt / general crap down there. After removing the fuel filter and pump, I could see that things were not looking good. I cleaned all of that out, put it all back together, lubed / rerouted the throttle cable, and readjusted the TPS, and now the bike runs like a top  next thing on the list (now that I have a stable idle) will be throttle body balancing, fluid drain / swap and a trip to the inspector and plate office to get this machine back on the road. Thanks for all the help! I'm looking forward to getting to know my K bike better in a non-wrench-turning sort of way. Pics to come when I get it road-ready!

[Martin]

Make sure the fuel hose in the tank is rated submersible.
Regards Martin.