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    1966 Dnepr K750

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  1. Hi Guys. I'm really sorry for the delay in replying to this after you all left such good responses. Thanks for that. Others stuff took over but I did have a look at this a couple of times. I checked the ring gaps and they seemed a little tight so I opened them up. However, it was still getting hot. To cut a long story short, I took the barrels and pistons to a local machine shop. When cold, all measuremnts seem to work and tolerences for the barrels and pistons seemd fine but... the machine shop guy poured boiling water on the piston (100 deg C, obviously : ) and the piston expanded so much it was larger than the bore. I'm also pretty sure it gets much hotter than 100 deg c when running!! Here are his measurements: Orig Bore size: 78.50mm = 3.0905" Actual Bore: 3.0905" / 3.0910" Piston: 78.43mm = 3.088" After boiling water: 3.0916" (bigger than the bore size) These seem to be original pistons. On page 1 I posted a picture of the piston top. They have the P2 size stamped on the top then below what looks like 'OTK 2' What's going on here? The expansion seems huge and obviously is my problem. Are the pistons too big initally for the bore? Are these cheaper pistons where the metal isn't good, expansion wise. When I bought the bike, I'd be told the engine had been rebuilt and the oil was crystal clear so don't think it had ever been run. I don't undertand how these pistons would ever work with that much change under heat, unless the cold tolerance was really, really loose? Luckily the machine shop guy says the barrels are in good condition. It's just the pistons that aren't great. Any suggestions? Different (smaller) size pistons needed or same size but better quality / lower expansion? Thanks in advance if you have the time to reply.
  2. Thanks for the info on the piston markings. Is P2 the max repair size before affecting the integrity of the cylinder? Also, the second part of your info, are you talking about the ring gap? I think you are. Are all 4 rings set with the same gap? So, my gaps are potentially a bit tight? I think I also read somewhere that sidecar bikes have bigger gaps than solo bikes? Although I don’t think this will have any effect initially in this case since I’m not riding it either way : ) Thanks again
  3. The last two photos are from the first time i removed the barrels. The marks on the piston are odd becuse they are around the circumference, so couldn't have been caused by the stroke. My thought is that someone has done something manually to this at some time in their life. It's also odd that these makes are within the lateral marks I mention above, almost like someone has marked the piston then worked within this area. It's also confined to the area below the top oil ring and above the lower oil ring. I don't understand what has happened or why there marks are there?
  4. Hi there. Hope you all head a good xmas day. Had a bit of time this morning so took another look at the bike. Checking the fuel mixture is what I've been trying to do at idle and am pretty confident it's not this as a turn of the mixture screw either way affects the idle. Also, there's no oil pressure indicator that i can find. This is a mid 60s bike but I also think oil is circulating OK since it travels to the valve springs and is behind the pistons I've now taken the heads and barrels off a couple of times. The very first time, I found the top oil ring was tight in it's groove. The top and bottom of the piston, at maybe 10 o'clock to 2 o'clock and underneath from 4 - 8 o'clock, had scuffs on it that had burred the groove the oil ring was in, stopping it move freely. The odd thing is, both pistons had this issues - almost identical. However, the bores don't seem to reflect these marks or damage?? So, I freed the oil ring both sides and cleaned / polished the burr so it all moved / rotated easily. I was pretty happy about this discovery as I though it must be my issue. I put it all back together but there still seems to be an issue with overheating. So, I took it apart again as I wanted to check the ring gaps They all seem to be 0.25mm, which seems to be in tolerance. I found this below - sorry, I forget who posetd it: So, my gap is maybe on the lower end of this. Both top rings and oil rings have similar gap. Do these look OK for a sidecar bike? Is this likely to get tight if idled for too long? Pistons look a bit rough but, and seem to have been scuffed in the past but since it's the rings that contact witht the bore, can't see too much here that might be an issue, but I'm not expert. I found figures of 0.15 - 0.23mm for this. The bore does seem to have honing marks on it. Piston to bore gap also seemed within tolerance, I found figures of 0.15 - 0.23mm for this - 0.2mm feeler went around the entire gap. Does all this seem OK or would a larger ring gap be better? Also, piston face has writing on it. Is this the piston size? It's a bit difficult to make it all out. Thanks again in advance for any input. Cheers : )
  5. Hi. Sorry for delayed reply. Thanks for all your suggestions. I really appreciate you taking the time.I'm going to have another look at it this weekend. I'll report back with what i find. Cheers
  6. Thanks for the replies. I spoke to someone earlier who suggested crank endfloat; ie not enough, could cause a mild heat expansion. Also, another suggestion was back to carbs being too lean. I need to do some more investigating but have little experience with engine internals. It's frustrating as the mention of the engine having rebuilt should be a positive thing but I'm just wondering if something was put together wrong. I really don't want to have to tear the engine down. I just want to ride it!!
  7. Hello I want to start by thanking you for indulging me with my other questions. I really appreicate your input. I've had this Dnepr K750 for a couple of months (supposed to be 1966 but plate on the headstock says 1962? I realise that these can be changed but looks original but mightr not refer to the manufacture date anyway??) But I digress. It was bought as a non runner. It wouldn't start so I cleaned the carbs, checked the points, plugs and valve clearances, bought a new battery. Could get it running on occasion but, even when it seemed to be running OK, it would suddenly stop, always after maybe 2-3 mins. So, new: battery, electronic ignition, coil, leads, plugs. Now starts with one or two kicks, which is great. However, carbs need setting up. I've been trying to do this but, when idling and seemingly running ok as I adjust, it will suddenly stop, as above after maybe 2-3mins. It does seem to get really hot on the pots - they smoke. Now, when I bought this, I was told the engine had been rebuilt but not run. I bought it as a trade-in from a dealer, so he wasn't the one who rebuilt but, looking at how clean it is and the fact it has all new mounting bolts, this is possible. Also the oil is crystal clear So, my thought is that, at idle, it's getting really hot and doing a light seize of the piston (perhaps because of new rings?) - if there is such a thing. What I mean is, it's not a high rev overheat and isn't pushed futher once in this state. I've removed both heads and it looks OK to my untrained eye. When cool, it turns over easily. When it's hot and stalls, it's not as easy. So, questions: 1.Does this sound likely? 2. If this is the case, might it just be that a new, tight piston might just need higher revs to run in and idling is not a good idea? 3. I'm worried both idle and higher revs might be damaging the engine. 4. Is there something else or better to check? 5. Might something just be damaged or wrong? I'm in a bit off a viscious circle - I want to test ride it for the first time but need to get the carbs setup properly but might not be able to do that by letting it idle and also don't want to do it at higher revs in case this makes it worse. Any insight or advice very gratefully received. Cheers
  8. Thanks, Vance. They also say 'the proof is in the pudding' I'll be truely happy when I'm able to finally ride it and it's running well and reliable : ) I'll get there. Cheers
  9. Hello. Sorry for the delay in replying. I appreciate all your responses. I managed to work this out and am really happy that it worked. Basically I looked at the cams on the rotor drive shaft. There are two opposite each other. You can see these on the video linked to above. With the original, mechanical points in place, I rotated the engine with the kickstart until the points were just touching the start of one of the cams (I took both plugs out to make this easier) This left the slot on the rotor shaft in about the same postion as in the video above. Obviously it could have also been 180 degs reversed with the slot on the opposite side. I then removed the old mechanical points system without moving / rotating the engine so the rotor shaft stayed in the same position. If I did lose this position, I'd just have to put the old points back on and find the same point again. I then fitted the new electronic ignition in place, similar to the video above, with the sensor to the bottom left, as seem from the front of the bike and loosly tightened the bolts to the mid point, between +10 and -10. As mentioned in my first post, I then fitted the shaft adaptor to the shaft. This can only go in one position since it's locking screw has to fit into the shaft slot. So, with that fitted, I placed the new rotor (photo above) onto the adaptor and loosly tightened this up so it could be rotated but not bee too loose. So, with the rotor shaft still in the same position as when i had the mechanical points in place and just ready to open, I rotated the new rotor to the point that one of the cutouts - there are two opposite each other, so it doesn't matter which one - ligned up with the sensor. To be exact, since the rotor shaft rotates anticlockwise, I turned the new rotor until the start of the cutout was just lining up with the sensor. As such, a small turn of the engine would therefore pass the rotor gap past the sensor. I then connected the wiring; two wires to the new coil (I understand it doesn't matter which way round) and the other wire to live. I then earthed the actual coil; just with a piece of wire from the coil mounts to the engine block. I'd also bought a new length of silicone HT lead, so also made up two new leads. With this all done, I kicked the bike over. I did try to fire but not too well, so I rotated the body of the new EI towards the +10 and then towards the -10 (had to fiddle a few times and obviously kick it over in between each try) I forget which improved it (+ or -) but when it did improve, I set the base back to it's centre position and then loosened the rotor and rotated it a simialr amount to the previsous base setting and tightened it back up. I had to do this a couple of times until the bike started with pretty much a single kick, which I'm happy to say it does. Once ticking over, I just adjusted the base again (+or -) until it sounded the best and tightened it up. So now it starts with just one or two kicks, which is great. Having a kickstart bike that won't start is tedious. However, it still doesn't run well for very long. It has a pair of PZ28 carbs on it. I now have to sort these out but at least I'm pretty confident it's not an igniton probelm now. I hope all that makes sense. Cheers again for all your input.
  10. Hello. I've looked through many threads, video s and topics on this but can't find anything definitive to guide me. I'm trying to install an electronic ignition system on my bike. From what I can tell from the standard points setup, the only adjustment of anything seems to be the points gap. The actual timing seems to be fixed - no adjustment or slots on the bolts to advance / retard the timing other than the cable from the handlebar. Is this correct? Anyway, as such, my new EI kit has slotted bolt holes for +10 to -10 degrees, which is pretty straight forward. So, if my timing can't be set, other than by using these new slotted holes, I just fit it, set it central in the slots and that should be OK to then adjust + or - to get the smoothest running. Is that correct? So, the kit has a small adaptor that just fits over the ignition drive shaft and has a small screw and block to lock it in place but it can only go in one place, so this is also straighforward enough However, my main issue is the main rotating sensor which bolts to the top of this adaptor. It's just a rotor 'pot' with two slots cut into it - this has nothing to align it with the small adaptor on the drive shaft.; it can spin 360 degs. So where to lock it into place? I does have a shaped cutout on the underside which would align to the top of a newer drive shaft, which is this shape. In that scenario, is can only be in one of two positions. However, my ignition drive shaft is round with a slot. Is there any correspondence with the newer shaped shaft and the slot in my shaft? So, the most crucial question is, how to I align this rotor with no obvious way to find TDC. Where are the slots in the rotor are supposed to align with the sensor and at which point in rotation of the shaft? Here's what i have (images attached) This video is the same system as mine but I can't easily see the corresponance of the shaft slot, the sensor or the slots in the rotor. I see where he has the shaft slot but don't understand how he's found the point to draw that line on the rotor Thanks very much if you are able to help with this. I'm trying to get this running but not having much luck : (
  11. Hi. Propwash. Thanks for the info on the step. Scott E - I'll give it a go. Cheers
  12. Hello. Thanks for the replies. I appreciate it. Regarding the front brake; it's not the cable I'm trying to adjust but the length of the rod between the cams to make sure they are balanced the same. I'm just not sure of the correct procedure. It would be easier if the threads on the bar were opposed so turning lengthened / shortend it, like a track rod, but this isn't the case. Regarding the sidecar step, do you mean the small cross plate part that you'd actually place your foot on rather than the actual frame? I'm not sure as I've had to store the sidecar elsewhere at the moment while I work on the actual bike. So it's not here to check. Why would this matter? Thanks again : )
  13. Hello. I've just joined this wonderful forum after searching for some technical info on a 1966 K750 I've just bought. I've been looking at these bike for several years but didn't intend to buy just yet but this came up locally for a good price so was too good to turn down. It's not registered yet in the UK but I've started this process. It was also sold as a non runner so I've got to fix a few things. It's also unfortunately missing some parts. I'd be really interested in some feedback on it's original condition. If anything is glaringly wrong Also, what main rear light should it have, based on the sidecar light? Is it the one I've included in the pictures? Or the same as the one on the sidecar? I'm also stuggling to work out how to accuratley set up the front drum brake as it seems this can only be done by hand with the adusting rod being taken off, adjusted, then put back on but I'm still not happy that the balance will be ok. Finally, for now, I found the m72 pdf english manual on here somewhere. Is this mostly applicable to this bike? Great if it is as it answers a lot of questions. I look forward to contibuting (but probably mainly asking lots of questions : ) Cheers
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