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Inquiry on K-750 wiring and gearbox, plus damper.


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I'm going to start with the gearbox since it's a smaller question.

In some engine testing videos of these flatheads, you see people changing gears with the engine running and NO clutch. 

 How is this even possible without grinding? You can see the clutch lever doesn't even budge.

Wiring questions

This is my 1966 KMZ K-750. Solo, no sidecar. https://ibb.co/LxJvv0Q 

Wiring by the headlamp: https://ibb.co/6gxX2mM

Grounding on frame: https://ibb.co/PNRcxRs

Previous owner has done the ignition electrics, but I have 7 coloured wires coming from the headlight. One which I assume is a red wire, but it's discoloured to the point I don't know if it's red or orange, and the other one is completely missing. According to the folks on Soviet Steeds, there should be a yellow wire, which I do not have. Other than the ignition wires, everything else has been cut off, so I might just have to strip out everything and buy a new harness.

This is where things get even more confusing... Harnesses online have 6 colours while soviet steeds and diagrams have 8 colours, so it's driving me insane and I have no idea which one to follow for my KMZ. I'm horrible with electrics but everything mechanical is completely fine.

In short, I need some advice on how many wires I need, what colours (if colours hold any true meaning), and some correct diagrams to follow as I'm totally lost right now. It would really suck if I'm unable to restore this solely because my lack of knowledge in terms of electrics. Currently the electrics are the only thing holding me back from completely renovating this bike in 2 years or less. Yes, I will be replacing that front fender too.

Steering Damper

Out of curiousity I adjusted the steering damper knob. Bit thick, I know, so the entire assembly came tumbling. Now I can't find any good pictures on how to put the thing back on, so if anyone is able to tell me what order to put it back on, angle and all, that will help alot.

That's all for now, thanks guys.

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Some Dnepr Gear boxes have a semi automatic function. When you press down on the toe or heal pad a pin below the clutch throw out bearing arm presses the clutch arm disengaging the clutch for you. You can not use it in first gear with the bike stopped! In that case you must use the handlebar clutch lever to get the bike rolling. It does not work for the reverse gear as well. To use the semi automatic clutch function when up or down shifting and the bike is moving simply let off the throttle completely, press down firmly on the toe or heal shifting lever, then gently and slowly take pressure off the shifting lever as you add throttle just as you would do using the hand clutch lever. It's typically used when a firm grip on the handlebars is required. You can up or down shift without needing to remove a "Death Grip" on the left handlebar grip. Remember that Dnepr Motorcycles were originally built for military service and so the Driver may be operating the motorcycle at fearful speed on poor or no roads and loosening the grip on the handlebar could be dangerous under those conditions. There is an adjustment bolt and locking nut that needs to be adjusted properly if you intend to use the semi automatic clutch function. On the end of the clutch lever part #KM3-8.15503611 (Throwout bearing clutch arm) is a bolt and locking nut. The head of the bolt should be touching a pin sticking out of the gear box. Pressing this pin in with a long screw driver should indicate a necessary small gap. A small spring keeps pressure on that pin. The gap should be about the thickness of two credit or bank cards. You must check this clearance regularly! As the clutch wears from use that gap is reduced unlike the handlebar lever where the cable slack increases. If the gap disappears completely the clutch can slip and be burned up. If you do not intend to  use the semi-automatic function simply run the adjustment bolt into the clutch lever so the gap is very wide. To test for proper function simply press the toe pad down into 1st gear with your foot while you are standing beside the bike and push it forward. The clutch should be pressed in allowing you to push the bike forward without the clutch dragging at all as if the gear box is in neutral. When you take your foot off the toe pad the clutch should engage with the gear box remaining in 1st gear. When parked with the engine off with the bike in first gear you will need to pull in the hand clutch lever in order to find neutral for starting the bike running. It's very difficult to find neutral on bikes with semi-automatic Dnepr gear boxes without pulling in the hand clutch lever to defeat it's operation when not desired.    

Dnepr-MT-Clutch-Release-Lever-Gearbox-Dn

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47 minutes ago, Scott E said:

Some Dnepr Gear boxes have a semi automatic function. When you press down on the toe or heal pad a pin below the clutch throw out bearing arm presses the clutch arm disengaging the clutch for you. You can not use it in first gear with the bike stopped! In that case you must use the handlebar clutch lever to get the bike rolling. It does not work for the reverse gear as well. To use the semi automatic clutch function when up or down shifting and the bike is moving simply let off the throttle completely, press down firmly on the toe or heal shifting lever, then gently and slowly take pressure off the shifting lever as you add throttle just as you would do using the hand clutch lever. It's typically used when a firm grip on the handlebars is required. You can up or down shift without needing to remove a "Death Grip" on the left handlebar grip. Remember that Dnepr Motorcycles were originally built for military service and so the Driver may be operating the motorcycle at fearful speed on poor or no roads and loosening the grip on the handlebar could be dangerous under those conditions. There is an adjustment bolt and locking nut that needs to be adjusted properly if you intend to use the semi automatic clutch function. On the end of the clutch lever part #KM3-8.15503611 (Throwout bearing clutch arm) is a bolt and locking nut. The head of the bolt should be touching a pin sticking out of the gear box. Pressing this pin in with a long screw driver should indicate a necessary small gap. A small spring keeps pressure on that pin. The gap should be about the thickness of two credit or bank cards. You must check this clearance regularly! As the clutch wears from use that gap is reduced unlike the handlebar lever where the cable slack increases. If the gap disappears completely the clutch can slip and be burned up. If you do not intend to  use the semi-automatic function simply run the adjustment bolt into the clutch lever so the gap is very wide. To test for proper function simply press the toe pad down into 1st gear with your foot while you are standing beside the bike and push it forward. The clutch should be pressed in allowing you to push the bike forward without the clutch dragging at all as if the gear box is in neutral. When you take your foot off the toe pad the clutch should engage with the gear box remaining in 1st gear. When parked with the engine off with the bike in first gear you will need to pull in the hand clutch lever in order to find neutral for starting the bike running. It's very difficult to find neutral on bikes with semi-automatic Dnepr gear boxes without pulling in the hand clutch lever to defeat it's operation when not desired.    

Dnepr-MT-Clutch-Release-Lever-Gearbox-Dn

I appreciate the explanation. 

Since you seem to know an incredible amount about these transmissions, perhaps you could explain for me, a newbie, why my clutch arm will not budge? You can see here https://ibb.co/9trzntq mine has been zip tied to what seems to be a mount for the cable to connect to the arm, but when I try pushing the arm in to disengage the clutch, no matter how hard I pushed it wouldn't move. Now, I didn't try a hammer or anything in fear that I was maybe doing something wrong, and I wouldn't want to cause damage doing something wrong. Could it be that maybe it's already pulled in? It's just that even when it's in gear and I turn the engine via the kickstarter (electrics and fuel have all been cut by the previous owner) the rear wheel turns on the kickstand, so I really don't know what to think.

 

Edit: P.S, you see in this video that his output shaft turns even in neutral but seems to be on a bearing of some sort, as his hand is able to stop its turning. 

 

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servus,

if the engine / gearbox stood for a long time, the coupling plates can be rusted together. Sounds worse than it is, afaik mostly they are still usable, but it might need some force to unlock them. Or better - remove the gearbox and have a look. The gearbox is fixed with 4(?) bolts and can be removed while the engine stays in the frame.

I'd remove the clutch lever and pull the rod and bearing off out of the hole, and then remove the bolts and finally the gearbox. The pushrod can be hard to remove because its hard to get a grip, so you can remove the gearbox bolts and fiddle with the pushrod to get it out. It's actually a pretty simple system, you'll understand by looking at it. And imo sooner or later you will have to remove it anyways, so why not now? It's fun 😉

Imo it's not like the modern stuff where a hundreth inch can make everything fail and fall apart (:-)), and there are really good manuals with explosion drawings available. Well, inside the engine and gearbox it's becoming a bit more difficult, but everything else is manageable, I'd say.

Anyhow, my insights come only from my own experience with my own rig which I rebuilt, so there are many guys out there who know much more than me. Listen to them if they say I'm writing sh$t 😉

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On 3/19/2021 at 7:03 PM, stahlsau said:

servus,

if the engine / gearbox stood for a long time, the coupling plates can be rusted together. Sounds worse than it is, afaik mostly they are still usable, but it might need some force to unlock them. Or better - remove the gearbox and have a look. The gearbox is fixed with 4(?) bolts and can be removed while the engine stays in the frame.

I'd remove the clutch lever and pull the rod and bearing off out of the hole, and then remove the bolts and finally the gearbox. The pushrod can be hard to remove because its hard to get a grip, so you can remove the gearbox bolts and fiddle with the pushrod to get it out. It's actually a pretty simple system, you'll understand by looking at it. And imo sooner or later you will have to remove it anyways, so why not now? It's fun 😉

Imo it's not like the modern stuff where a hundreth inch can make everything fail and fall apart (:-)), and there are really good manuals with explosion drawings available. Well, inside the engine and gearbox it's becoming a bit more difficult, but everything else is manageable, I'd say.

Anyhow, my insights come only from my own experience with my own rig which I rebuilt, so there are many guys out there who know much more than me. Listen to them if they say I'm writing sh$t 😉

Maybe you could provide some of these diagrams? I'm a bit sh!t with them though to be honest, I've learned alot of stuff throughout the years through 3d models and other sorts of things, but never exploded drawings. Either way, I'm sure I can learn.

I'm going to be honest, I'm a bit worried about opening up the gearbox because this is going to be my first EVER project vehicle, ever. The previous owner rebuilt the engine and gearbox, I'll probably call him tomorrow ask him a few questions but yeah, I'll do that. I understand the principles of a gearbox but I've never really been able to find proper resources for a KMZ gearbox, but as you said, I'll learn by looking at it. All I'll really have to do is probably document what I've done to dismantle it, then do the opposite when... Re-mantling? Forgot the word.

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Do not be worried about going into the gear box. It's very simple in there. You will more than likely need new gaskets and seals if the bike has been sitting a long time. I have no idea why they have a zip tie on the clutch lever unless they thought it would spring apart when they removed the clutch cable.

You need to pull out the clutch throwout bearing assembly and inspect it. Simply remove the Carter or split pin holding the axle for the clutch arm. Then remove the axle and then the clutch arm. Then pull out the plug the clutch arm pushes in and below that you will find a ring of ball bearings captured in a plastic or brass ring between two flat bearing plates the balls ride on when the handlebar clutch lever is pulled in. Don't be surprised if it's damaged. This is one of those assembly’s you keep as ready spare parts. The problem is mostly with the operator sitting stopped with the gear box in first gear and the engine idling. The throw out bearing assembly is located above the gear box oil level and receives oil only when the input or output gears are rotating. When you come to a stop for a red light or stuck in non moving situations you should always find neutral and release the handlebar clutch lever. This will allow the input gears to spin with the engine slinging oil inside the gear box to lubricate everything including the clutch throw out bearing assembly so it will have oil in it ready for you to pull the clutch lever in and start the bike rolling again.

The out put shaft turns when the gear box is in neutral without being connected to the final drive from the viscosity of the oil in the gear box. It creates a sloppy sort of fluid drive between the gears in the gearbox.

If the bike has been sitting then as others have commented the clutch plates could be stuck together or the throw out bearing could be damaged.

Here is a drawing of the clutch throw out bearing assembly.

Clutch_Release.jpg

 

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On 3/22/2021 at 1:37 AM, Scott E said:

Do not be worried about going into the gear box. It's very simple in there. You will more than likely need new gaskets and seals if the bike has been sitting a long time. I have no idea why they have a zip tie on the clutch lever unless they thought it would spring apart when they removed the clutch cable.

You need to pull out the clutch throwout bearing assembly and inspect it. Simply remove the Carter or split pin holding the axle for the clutch arm. Then remove the axle and then the clutch arm. Then pull out the plug the clutch arm pushes in and below that you will find a ring of ball bearings captured in a plastic or brass ring between two flat bearing plates the balls ride on when the handlebar clutch lever is pulled in. Don't be surprised if it's damaged. This is one of those assembly’s you keep as ready spare parts. The problem is mostly with the operator sitting stopped with the gear box in first gear and the engine idling. The throw out bearing assembly is located above the gear box oil level and receives oil only when the input or output gears are rotating. When you come to a stop for a red light or stuck in non moving situations you should always find neutral and release the handlebar clutch lever. This will allow the input gears to spin with the engine slinging oil inside the gear box to lubricate everything including the clutch throw out bearing assembly so it will have oil in it ready for you to pull the clutch lever in and start the bike rolling again.

The out put shaft turns when the gear box is in neutral without being connected to the final drive from the viscosity of the oil in the gear box. It creates a sloppy sort of fluid drive between the gears in the gearbox.

If the bike has been sitting then as others have commented the clutch plates could be stuck together or the throw out bearing could be damaged.

Here is a drawing of the clutch throw out bearing assembly.

Clutch_Release.jpg

 

It's been a mere few days and already I've learned a huge amount more specifically about the older models than a while on Soviet Steeds. Wish I had the proper vocabulary range to thank you. What I'll do is drain the oil from the transmission and engine, pull the transmission out and un stick the clutch plates. 

Instead of riding around in traffic since I'm not old enough to ride, and it's currently SORN (off the road, so not being taxed and not allowed on the road) alongside rusty wheels, a faulty unscrewing steering damper and no proper wiring, do you suggest that I just put the kickstand up and rev/run it in gears on the spot, and in neutral?

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If you can't drive it on the road you could put the stand down and run it through the gears with the tire off the ground. That could give you an indication of proper shifting and clutch operation as well as checking the engine oil pressure and if the carburetors are setup correctly. The speedometer will function with the tire off the ground so you can watch it so you don't over speed the engine. If you hook up the alternator with a battery and regulator you can test it as well when it's running. Just connect a volt meter to the battery and if the voltage is around 14 VDC above idle the alternator and it's regulator is working. I hope you can get it running and driving and have it ready to go when you can start driving and register your Motorcycle. You will always remember your first motorcycle the rest of your life. Be sure and take a picture of you and the motorcycle together because you will find joy in it when you get old like me. Working on and getting that first motorcycle going makes it even better. I had to fix my first motorcycle too. It was about to be taken to a scrap metal yard when I asked if I could take it, and he let me.

Soviet Steeds forum is filled with rich people that only know how to pay others to work on their motorcycles. It's also useless to try to help them because their mechanic shop fixes their motorcycles for them and no one else can do it as well in their opinion.   

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On 3/24/2021 at 1:26 AM, Scott E said:

If you can't drive it on the road you could put the stand down and run it through the gears with the tire off the ground. That could give you an indication of proper shifting and clutch operation as well as checking the engine oil pressure and if the carburetors are setup correctly. The speedometer will function with the tire off the ground so you can watch it so you don't over speed the engine. If you hook up the alternator with a battery and regulator you can test it as well when it's running. Just connect a volt meter to the battery and if the voltage is around 14 VDC above idle the alternator and it's regulator is working. I hope you can get it running and driving and have it ready to go when you can start driving and register your Motorcycle. You will always remember your first motorcycle the rest of your life. Be sure and take a picture of you and the motorcycle together because you will find joy in it when you get old like me. Working on and getting that first motorcycle going makes it even better. I had to fix my first motorcycle too. It was about to be taken to a scrap metal yard when I asked if I could take it, and he let me.

Soviet Steeds forum is filled with rich people that only know how to pay others to work on their motorcycles. It's also useless to try to help them because their mechanic shop fixes their motorcycles for them and no one else can do it as well in their opinion.   

Come to think of it there's actually a reasonable amount of truth to that. I cannot find anyone else with a side valve Ural or Dnepr or KMZ on there, but as soon as I came here the first 4 other members I see have a side valve. And yeah, I'll put the stand down and run it like that.

I have 2 more questions, if you don't mind.

1, is that I can't tell if I have a K-750 or K-750M anymore. I saw this image (dark blue new looking bike, not mine) where the static arm is very long and goes to a hole in the frame,

where my damper is a short arm, which sticks onto a little prong that comes out the frame, but it also has the hole you see below. Here's my picture. https://ibb.co/NVtjYL5

And 2, how many wires are there meant to be for wiring a solo bike? Some people say 8, harnesses online have 6, and I have 7. So I'm a bit confused right now 😐DAMPER ASSEMBLY.jpg

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  • 2 weeks later...

@Scott E Don't want to create a whole new thread for this, so hopefully you're fine with me tagging you.

 

file.php?id=9008&sid=c92751269975b33b5fef2261ca3281ed&mode=view

I want to do the wiring, I've bought a harness. There's six colours to the new harness, White, Black, Green, Red, Blue and Brown. Currently the wiring has the positive grounded and the negative connected to the positive terminal (despite it being a negative ground system) along with other serious issues, like the generator wires connecting to the battery directly. However, the wires dangling out the headlight currently, have 7 colours. All the ones listed above, with grey. 

Since the harness has come with pre measured bits of wire, and I can't seem to find a diagram online with only 6 colours, perhaps you have some advice for the wiring? Thanks

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After so many years and so many people working on the bike I'd say the colors mean nothing. Worse it may have a new main switch that is nothing like the original and was replaced with a new switch from another model motorcycle. You just don't know until you start tracing it all out, which you will need to do. The easiest way to go about it is buy or make a simple test light connected to a 6 volt battery if you are keeping the motorcycle 6 volts or a 12 volt battery if you plan on upgrading to a 12 volt system. You can use one of the warning lights in the headlight as your test lamp. Start with the main switch in off position and check all connections making sure that none turn on your test light. Then switch it to ignition on and find the terminals that light up and mark them. Some main switches have a parking lights on position.  That position turns off the ignition power and turns on the tail lights and front clearance lights and allows the key switch to be removed. The other electrical devices in the headlight bucket are warning lights, the headlight, fuse, and the small clearance or parking light in the head light reflector. It's all shown in the electrical schematic you posted so once you figure out the terminals using your test light setup then you can see what colors they used. You could then keep whatever is there or change them to match what colors are shown. Here is a drawing of the test light setup with the switch being whatever switches are closed or open for the chosen position.

9x1a8q9tmr.jpg

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27 minutes ago, Scott E said:

After so many years and so many people working on the bike I'd say the colors mean nothing. Worse it may have a new main switch that is nothing like the original and was replaced with a new switch from another model motorcycle. You just don't know until you start tracing it all out, which you will need to do. The easiest way to go about it is buy or make a simple test light connected to a 6 volt battery if you are keeping the motorcycle 6 volts or a 12 volt battery if you plan on upgrading to a 12 volt system. You can use one of the warning lights in the headlight as your test lamp. Start with the main switch in off position and check all connections making sure that none turn on your test light. Then switch it to ignition on and find the terminals that light up and mark them. Some main switches have a parking lights on position.  That position turns off the ignition power and turns on the tail lights and front clearance lights and allows the key switch to be removed. The other electrical devices in the headlight bucket are warning lights, the headlight, fuse, and the small clearance or parking light in the head light reflector. It's all shown in the electrical schematic you posted so once you figure out the terminals using your test light setup then you can see what colors they used. You could then keep whatever is there or change them to match what colors are shown. Here is a drawing of the test light setup with the switch being whatever switches are closed or open for the chosen position.

9x1a8q9tmr.jpg

Just to ensure I've read correctly, start off by only completing one main circuit, like the secondary or primary headlamp light, to see if the electrics are faulty, and go from there?

One concern that I have is with the harness having pre lengthened wires. I'll have to try out each wire as I go to see if they can reach where they need to go, e.g make sure the green can reach the positive on the ignition coil, and if it doesn't, swap the headlamp wire with it etc. So I guess I'll do as you said, trace things as I go. 

I've also noticed that the diagram I posted was for a K-650 and has an oil sensor, which mine doesn't have. Perhaps you have a reliable diagram to follow for an early K-750M somewhere? There is a colossal variation of them out there and quite frankly I have no idea which one is the most accurate.

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I don't have any diagrams that are not already available on this site and on the internet via a search. It's really not all that complicated. It looks complicated when you look at all the wires and connections as one big puzzle but if you work on only one circuit at a time it's really simple. It's just several circuits all located in one place with a couple of  them going through the main switch and others just going to light bulbs. The oil pressure switch is just a simple circuit that is connected to the battery through the main switch, then the oil pressure bulb, and ending at the oil pressure switch on the engine that is closed when the oil pressure is low allowing the electrons to flow and stop when the oil pressure is normal because the oil pressure switch has opened. When I was young my Uncle told me to think of electrical circuits like pipes with water flowing through them except for electrical circuits where it's electrons flowing through wires. Think of electric switches as valves to let water through when open and stopped when closed except that's backwards for electron flow. When a switch is open electrons can't go through and when the switch is closed the electrons can pass through it freely. The battery is like a storage tank of water and the alternator pumps electrons like water to refill the tank or battery. Also you can think of a light bulb as a water fall or shower. When the bulb is on it's spraying electrons like water that you can see with your eyes and when it's off there are no electrons or water to spray.   An example using the colors shown in the diagram you posted find the positive post of the battery with the blue wire. On the diagram that wire going into the headlight shell is connected to the key switch (5). If you look at the wire that is connected between the battery post and the key switch and find it a different color then you would need to use tape and an ink pin to label it so you know what it actually connects to. If you step through each wire tracing it to the connections shown in the diagram one at a time labelling them with tape and ink if the wire colors are different before you know it you'll have everything correct. Don't get in a hurry and if you get frustrated just stop, put it away, and sleep on it. Once I was trying to install an engine in a car and simply could not get the transmission shaft through the clutch disc splines. I fought it for hours and walked away to do something else. The next day I took hold of the engine and pushed it a little and the shaft went through the clutch disc splines with almost no effort. It's the same with electrical work. If you get frustrated go do something else and come back when you are not frustrated and you have a clear mind. That's when the magic happens!

 

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Trinidad:

Scott E offers sage advice.

I will add: 

Acquire an electrical multimeter and learn how to use the "Ohm Meter" portion to trace wiring.  In my Electrical Engineering career that tool has been one of the most useful for troubleshooting electronics. This will allow you do "unravel" the wire harness without physically tracing the wires, and then mark those connected wire ends for later use. And considering that I have never found coherent use of wire colors in Russian wire harnesses and diagrams on 4 different motorcycles, this is important to do.

Because you do not know the history of work on your motorcycle, expect it to not follow existing wiring diagrams.

DO expect to think about each circuit, trace wires, and connect them properly to activate each individual item such as a brake light.

DO expect to study and understand each individual simple circuit your bike has.

DO expect to spend time learning what wires the ignition switch assembly connects in each switch position.

'Sounds like a lot of work, but welcome to old machines.  If you give yourself this level of knowledge, riding your machine and keeping it running on the road will become a pleasure and not a hassle.

Been there and still do that.

RussN

 

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Good advice from all. If you are having trouble tracing a wire from one end of the harness to the other, another tool that can help is a cable tracker. It consists of 2 pieces, a signal generator that you clip to the wire, and a receiver that detects the signal and thus the wire. Harbor Freight carries one and they are available at other places too. I would try the other methods listed first as it avoids the expense (about $25 US) but if you aren't having luck this can help. Here's a link to the Harbor Freight one:  https://www.harborfreight.com/cable-tracker-94181.html

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