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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => Project Classic Motobricks => Topic started by: johnclaude on October 14, 2018, 06:35:20 PM
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Hi guys,
Just picked up my first BMW, a 1988 K75C, with 55xxx miles (fun discovery-the odometer turns over verrryyyy slowwwwlllyyy). Will follow the gauge rebuild guides and check out the gears/connections. It has been down on the right side, needs a new seat, new headlight or glass, new RH front turn signal assembly, and a thorough cleaning. Any suggestions on that front? Wire brush and simple green?
Found the original toolkit under the seat, and what looks like a homemade tool kit in the rear cowl. Does anyone know what that mystery BMW light is??Look forward to changing the fluids, plugs, and checking the spline conditions!
(http://www.motobrick.com/gallery/1/6107-141018182543-17762466.jpeg)
(http://www.motobrick.com/gallery/1/6107-141018182442.jpeg)
(http://www.motobrick.com/gallery/1/6107-141018182351.jpeg)
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From Aurora myself, years ago.
Good luck with your build. I've got some S parts I'm not going to use, Fairings and the like. If you need something let me know, shipping is not that great from Phx to Den.
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Does your bike have hazard lights? Does the mystery light flash? If you don't have hazards and it flashes it is a roadside hazard light. I believe some BMW cars had them, or could be a after purchase accessory.
Regards Martin.
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The mystery thickens....into a delicious stew. I can't get it to light up, mainly because I have no idea what kind of power port that is. We tried it in a cigarette lighter, but it was too small. I hit it with 12v, but nothing. I did figure out that the lighting mechanism turns and exposes what looks like a flashlight. Also, the yellow part has a little knob that allows you to turn the lens. Interesting....also, I'm not sure if my bike has hazards or not. I'm guessing not.
(http://www.motobrick.com/gallery/1/6107-141018212521.jpeg)
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The mystery thickens....into a delicious stew. I can't get it to light up, mainly because I have no idea what kind of power port that is. We tried it in a cigarette lighter, but it was too small.
If your moto has an accessory socket that will accept that plug, it will likely be under a small, round hinge lid mounted on the plastic coil cover where indicated by the arrow on the attached image.
(http://www.motobrick.com/gallery/1/1601-141018214306.jpeg)
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I can't tell from the photos, but in the top of the coil cover there may be an outlet that matches the plug on the mystery light. That outlet isn't switched and is for auxiliary stuff like that light and for trickle chargers.
The outlet, BTW, is a BMW cigarette lighter plug, they were first used in German military equipment during WWII.
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The plug is called a Merit plug. There should be a socket located on the black plastic coil cover on your bike, it has a lift up cover. Merit sockets and plugs can be bought from some automotive shops or electronic stores. They should also sell an adaptor cable that goes from a Merit plug to a cigarette lighter socket. This allows you to plug in common accessories. My battery charger has a Merit plug installed to make charging easier, just plug it in to the fitted socket.
Regards Martin.
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You guys are a wealth of information! I'll do some exploring, and report back. Thanks, everybody!
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johnclaude,
For your first BMW you got IMO one of the their best, just a great bike to ride on two lane mountain roads!
The black and polished aluminum look really sharp when cleaned up but a wire brush may be to harsh, try a tooth brush first. The bike looks like it will clean up nice, Purple Power is also good for removing dirt and stains.
Good luck getting it sorted out and keep us posted.
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Congrats on your Brick, it'll detail up nicely. I had one of those lights as part of the required "Breakdown" kit in a 1997 318i when living overseas. If I recall, mine had a very long lead wire, spending it's entire life bundled up next to the first-aid kit and road triangles. I've had good luck with Rustoleum High-Heat brush on paint for the cases and forks. It takes a few coats, but doesn't seem to get dinged by pebbles/bugs. Good luck with the refresh!
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Today, I held my breath and removed the rear wheel to inspect the final drive and driveshaft. I was pretty nervous, since I bought this bike for $500 from a guy who I'm pretty sure jumped the title and may have bought it from an impound lot. For some reason, a decent amount of gross what smelled like gear oil came out of either the final drive or driveshaft, which was a surprise. Any ideas? What do you think of the DS/FD?
(http://www.motobrick.com/gallery/1/6107-130119225314.jpeg)
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Driveshaft looks ok to me. Post pics after removing the gunk for a better look.
Final drive is splines are great but the input shaft seal is probably toast. You may have just discovered a rare, prototype auto-lubing spline set up. ;-)
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Today, I held my breath and removed the rear wheel to inspect the final drive and driveshaft. I was pretty nervous, since I bought this bike for $500 from a guy who I'm pretty sure jumped the title and may have bought it from an impound lot. For some reason, a decent amount of gross what smelled like gear oil came out of either the final drive or driveshaft, which was a surprise. Any ideas? What do you think of the DS/FD?
(http://www.motobrick.com/gallery/1/6107-130119225314.jpeg)
(http://www.motobrick.com/gallery/1/6107-130119225256.jpeg)
(http://www.motobrick.com/gallery/1/6107-130119225236.jpeg)
(http://www.motobrick.com/gallery/1/6107-130119225213.jpeg)
john, I am sure, the more knowledgeable will chime in, but the ds seems quite nice to me. Compare it to mine, that was still driving the bike (but God only knows, how long that would have been the case) http://www.motobrick.com/index.php/topic,11767.0.html
Sulfuric smell is gear oil leaking from either the input seal on the fd or the output shaft seal on the transmission. If you are lucky, like I was, it is both :) Easiest to tell if you remove the driveshaft, if it is oily on it's body too it is output shaft (too), if dry only input shaft. From the pics however it looks to my untrained eyes an input shaft failure
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http://www.motobrick.com/index.php/topic,11767.0.html
yikes, those were shot. Good example, though.
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When photographing splines, clean them off and get the light to reflect off the top of the spline. What you're looking for is a nice wide flat at the top of the spline. That flat gets narrower as the spline wears.
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That tool roll looks amazing for being 30 years old! The CO2 & patch kit was included when the bike was new. Those splines alone are probably worth what you paid, I'd say you got a deal.
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Thanks for the replies, everyone! Sorry about the poor picture quality, that gear oil was nasty stuff. Should have cleaned it up better prior to photographing. Looks like I have some more disassembling to do to determine if it's the input/output shaft seals, or both! Super relieved that the DS/FD are in decent nick.
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I hear the FD input seal is a major job.
Mine weeps a bit (less than yours it appears), so I just keep an eye on on the level via the speedo sensor hole. Mine set for a several years before I picked up and leaks like this have lessened with regular riding. yay me!
Long shot, but there are oil additives that advertise that they swell seals a bit. Ie for transmissions and leaky engines. Clearly mixings some of that to new FD oil may put the whole drive at risk.
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I hear the FD input seal is a major job.
You've heard about it; now you can read about it here (http://www.motobrick.com/index.php/topic,7029.msg48428.html#msg48428).
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Thanks, Laitch! Now that’s service!
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After cleaning the fuel tank and fuel pump and replacing the fuel level sending unit, I am not getting power to the fuel pump. Cleaned and replaced the #6 fuse, cleaned the 4 pin connector, verified that the pump runs when hit with 12 volts, and verified power to the female (harness side) of the connector...leaving the connector itself. Ordered some 4 pin waterproof connectors. Ugh. Should have just replaced the connector before replacing the fuel sender!
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Congrats on the '85, but it looks like a naked and not a 'C' - the C had a fairing and windscreen mounted to the handlebars I always thought
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Every " Standard " or " T " that I have owned was titled as a " C. " I was told by a dealer that they all were in the USA.
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Every " Standard " or " T " that I have owned was titled as a " C. " I was told by a dealer that they all were in the USA.
Yeah the VIN/title comes up as C, but it definitely appears to be a "Standard" model.
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Yeah the VIN/title comes up as C, but it definitely appears to be a "Standard" model.
The model C has a drum rear brake; the others don't.
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Last night I put +12v on the green pin of the male tank connector, and -12V on the brown pin, and of course the fuel pump works. So, to recap: power at the female end of the 4 pin when engine turning over, when 12V applied to the male end pump runs = bad 4 pin :( Luckily have some waterproof connectors arriving today. The dreaded 4 pin connector strikes again!
Also, K75C it is! Drum brake isn't so bad after all.
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Hello Flying Brick Friends,
Since we're in a bit of a warm patch here in CO, I've been spiritedly riding my K75 the last couple of days. Today, about halfway through a 10 mile ride the bike started surging/sputtering around 6k RPM. It does it in gears 1-3, but it seems more pronounced in gears 2-3. I thought it was maybe a fuel starvation/clogged vent line issue since I can hear some faint bubbling coming from within the gas cap after I'm done riding, so I turned the bike off and unlatched the cap. That worked for a couple minutes but then the sputtering came back. Also the idle is higher once the bike is warmed up (goes from ~1000 to around 1500 rpm). Any suggestions? The bike runs great up to right around 6k rpm.
I've replaced:
z hose
throttle body caps
air filter
battery
all outside fuel lines
vacuum line to FPR
fuel pump
fuel sender
4 pin connector
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I spose you replaced the fuel filter. Was the tank full before you went on the ride, and was it the first ride of the day. Maybe the vent is blocked or the fuel filter.
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Yeah I’ve replaced the fuel filter as well. Tank is over 3/4 full. It was the first ride of the day. Seems odd for it to start out of the blue in the middle of a ride.
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Does the exhaust have a hissing sound at idle or revs like maybe it's blocked? Maybe check to see if removing the cap consistently fixes the problem, if so it might be time to check fuel pressure if there is nothing conspicuous in the tank or fuel pressure regulator.
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If you have a non OEM fuel return line they can crimp where they go into the tank this can cause running problems. It's hard to detect because as you lift the tank and pull it back it can uncrimp. Look for signs of crimping and collapsing. If it has collapsed you can remedy the problem by fitting a Unicoil.
Regards Martin.
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I've replaced:
z hose
throttle body caps
air filter
battery
all outside fuel lines
vacuum line to FPR
fuel pump
fuel sender
4 pin connector
Check that the fuel lines and their couplings within the tank are tight and in good condition. Consider replacing the fuel filter. OEM filters are dated on the outside. Alternatives are available. Check the site's Alternative Parts section.
How is the tank being vented—into a cup mounted on the frame, or by a hose from the underside of the tank to behind the right foot peg plate? Check that the tank vent pipe within the tank is unobstructed.
Check for tightness and clean all ground connections, battery post connections and the battery ground strap attached to the transmission.
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What's the average elevation of where you regularly ride?
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For reference: Fuel filter=NAPA Gold 3032.
If you don't have the plastic cup under the tank that the vent and filler cap water drain run to, then you may have a pinched tank vent hose where it goes behind the right side footpeg plate. Easy check is to take the bike out for a ride with the cap unlocked. You might want to have about half a tank of fuel or less when you do it to prevent sloshing out.
Another possibility is the Hall Effect Sensors that trigger the ignition and the injectors. When they start to fail they misbehave when the engine warms up, and work properly again when the engine cools down. I'm not sure that is your problem, but it is something to consider when everything else has been checked.
I agree with Laitch that you should check electrical connections, especially the grounds on the engine and frame backbone. Make sure the connector on the ECU is tight while you're at it.
It's also possible that you have a bad spark plug or plug wire. Do you have the terminal nuts on the spark plugs? Bosch has them, but NGK doesn't and you have to get them and install them yourself. They are necessary if you have OEM plug wires.
Last, I have had problems with dirty ignition switches on two bikes. They would cause the engine to quit when running. It's not a likely cause of your problem, but with these bikes getting older, it's something to consider. There are cleaning tutorials here.
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Thanks for all the replies, guys. Forgot to mention in the original post that the fuel filter is new as well (NAPA unit). I do most of my riding around 5280' but don't use the high altitude plug, and can't find where it would go either. I have not balanced the throttle bodies or checked the valves yet. FOR SHAME.
@Daveson- the bike idles well and revs up to around 6k rpm well. No exhaust hissing or anything like that. I'll look running it w/out the cap and see if that makes a difference.
@Martin-is the fuel return line the front left hose? If so, I used a length of non-OEM hose for that. Good call on the unicoil spring device. I will check that as well, as there is a pretty sharp turn into the top of the FPR also.
@Laitch- I will admit I have paid zero attention to the ground points. They could undoubtedly use a cleaning. As for the tank venting, there is a hose that runs from the rearmost tube to the footpeg plate, and a check valve on the other line that runs to the crankcase. I will investigate all the vent lines, and probably just buy the cup.
@Gryphon-I'm hoping it's something as simple as a pinched tank vent hose. I've checked the spark plugs (they're NGK with terminal nuts and in great shape). Ignition switch and HES crossed my mind also. I'll take that under advisement!
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The high altitude plug is just above the coils below the tank, usually behind a frame tube. The jumpers are something like $9 from the dealer. I run with the jumper installed all the time when I'm in your part of the world.
It's not all that critical as far as I can tell. I have forgotten it and been up to 9000 feet without it, and left it in down to almost sea level. I suspect that it's more of an emission thing than performance.
If you haven't seen the plug, you may already have it connected by the previous owner.
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Update:
I've cleaned the spark plugs, ground points, checked the tank vent tube (can blow through it), and replaced the fuel filter again. I also removed the airbox to verify that the fuel return line is unkinked. All of that helped a little, but after awhile the bike would continue to sputter/surge above 6k RPM. Another point: I have the vent stub by the fuel cap, but my fuel pump screen doesn't have the little vent fitting, so I've just removed the vent hose. Then I cleaned the fuel injectors, and while doing so may have stumbled upon a clue.
After removing the fuel line at the most forward part of the rail, gas was continuously pouring out. I remember doing this in the past and having a very small amount of gas come out, but not in a continuous stream. Now I'm thinking that it must be a hole in the submersed fuel line within the tank? Planning on removing both fuel lines and submerging them and blowing into them to see if there are any splits or cracks. What do you guys think? It couldn't be related to the fuel pressure regulator could it? HALP
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Planning on removing both fuel lines and submerging them and blowing into them to see if there are any splits or cracks. What do you guys think?
It couldn't be related to the fuel pressure regulator could it? HALP
Checking those lines was recommended in Reply#31 and I still think it should be done. As far as the fuel pressure regulator is concerned, try starting the moto, shut it off then remove the fpr's vacuum hose from its port at the #3 throttle body. If it smells like fuel or leaks fuel, a new fuel pressure regulator is needed.
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Thanks for the reply, Laitch. The fact that gas pours out of the feed line makes me think that it has to be one of the submerged fuel lines, which would maybe explain why it surges at speed when the fuel pump is working overtime (if gas under pressure is escaping the fuel lines). Does that sound plausible? But I will also check into the FPR vacuum line for gas stank as penance for not checking the lines earlier.