Chang Jiang 750 Restoration

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Korto
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Re: Chang Jiang 750 Restoration

Post by Korto » 2018-08-04 10:37am

All right, I've got to remove the cylinder, and replace the gasket right at the back, where you can see it's all wet and oily.
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I'll see if I can do this today. I've been busy for a chunk of the day so there's only a few hours of daylight left. Well, maybe it'll only take half an hour, or maybe it'll take two days. I have no idea, I've never done this before. I don't particularly want to do it now, but as I said, no real choice. It's not going to pass inspection leaking oil like it is.

I do at least have gaskets for it, and if there turns out to be a problem, I have gasket goo. Not actually the real name of the product I've got, but just generically what we called all the brands back in Car Maintainence in high school.

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Now, first I've got to remove the rocker cover here, which we do by undoing this allen key bolt. Since the bike has been running, there should be oil in there, so I've grabbed myself a nice clean...clean it out, there we go...tin to go under and catch the oil. Hey, if it's clean enough, I might even be able to put it back again. Who knows.

Is there such a thing as an M7 Allen key? Because M6 is too small, and M8 does not fit well at all. Wonder if the fucking thing's Imperial? If it is, it's being replaced. Not having another bit of Imperial on this bike, sick of it. And the bolt was very loose, too.

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Cover's off. Compared to more modern vehicles, it's very simple inside with just the single inlet and exhaust valves. The oil, which is quite new, could afford to be emptied and replaced from its colour to be honest, which might well happen soon after a bit more running--change the oil for some fresh stuff, rinse and repeat, clean the old gunk out.
You know, what I'm dreading is having to remove the rockers. I have this tiny hope though I might be able to remove the head in one piece, which would be pleasant, but first I need to detach the exhaust pipe.
Here's a surprise, I'm able to unscrew the big nut thing by hand. (no picture, but you can just see it in the picture of the rocker cover. On the left of the cylinder, in the shadow). OK, sure, I sprayed some WD40 on it a couple of days ago in anticipation, but I didn't expect it to work this well.
To remove the head, you've got to undo the four nuts recessed down deep in the head, which you can just see down those two deep wells. They're a bit tight, too, which wasn't unexpected. Now try and pull the head off...it seems happy to come off as one unit, except it's a bit unhappy that I haven't really removed the exhaust pipe, just undid the big nut in the hope that would be enough, and the pipe is still sticking in its little hole, which is probably going the hold the head there. Might have to actually remove the exhaust pipe, which I was preferring to avoid because, you know, more work, but I don't think I have any choice. Well, there only seems to be one other bolt holding it, so I suppose I shouldn't complain about that too much. I will, but I suppose I shouldn't.
And now let's see if the head will come off...
...
...Well, there's the head off.
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Came off reasonably easily, actually, which is good. There's probably like, useful shit things I could do while this thing's off... I have no idea what they are... you know, clean something or other or something... ummm... I suppose I could have asked my brother. He's a mechanic.
Anyway, the cylinder head doesn't seem to have a gasket, which is interesting. It really does not, just metal on metal. This isn't where it's leaking, this is where the compression shit is. Why doesn't this have a gasket? Seems a bit naughty.
I also should have considered somewhere clean to put these parts before I pulled them apart. That would have been a good idea. Maybe I'll do that now.

Now to take the actual cylinder off. It doesn't look to me like there's anything more restraining it than the bolts that passed through the head and I've already removed the nuts from, and I've just found a small nut hiding in the cooling fins of the cylinder from somewhere else that I lost a few months ago. So that's where it went. Cool. Mine now.
Anyway, with only those bolts, already undone restraining the cylinder, it should hopefully just pull off nicely, too.
...
And it did pull off quite easily.
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Right, well, this does have a gasket, which has been leaking, and I've just found another little nut, another one I've lost at some point in the fins and I would then have replaced from my stock. Thanks to these bikes I've bought a decent selection of nuts and bolts.
I've scaped the old gasket with my knife I've found today, after being lost for months (it's been a good day for finding things), it feels pretty smooth now, and I'll just read the instructions on this gasket goo. I'm thinking I'll run a bead either side of the paper, and try to make a really good seal. I don't feel like doing this again in a hurry.
"Clean the surface with white spirit or mineral turps" I wonder what white spirit is. Metho? Might be, can't remember. Have I got any turps hanging around? Maybe. Not sure. "And scrape if necessary" Well, it was necessary. "Coat the surfaces with paste so no metal shows, and then bring surfaces together". OK, that's if you're using the goo just by itself. I reckon coat this around the paper gasket and put it all together will make a good seal.

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OK, entertainment time. The gaskets I have do not match. I was pretty confident they would, but I was aware there was a chance they wouldn't, since these gaskets were for the Chinese bike, and there are some differences. OK, one of those differences is apparently the gaskets. OK, then we're going to use just straight gasket goo, aren't we? And we're going to do this by the book, a complete layer so I can't see metal, and on both sides, wasn't it? "Coat the surfaces", yes, surfaces, plural.
It turns out I've got nearly a few bottle of turps--there we go--cleaned--a generous bead of goo and use my finger to smear it around...what's this say on the back? "Warning! Do not allow contact with skin! Causes skin cancer, bone degeneration, ulcers, blood poisoning, appendicitis, and your dick will fall off!"
OK, that sounds negative. (*)
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I'm having trouble getting the damned piston back in the cylinder--there, got the bastard. Now put the head back on--the rubbers are being a bit stubborn, I've replaced the old rubbers with fresh ones, and I've just managed to spill half the bottle of my goddamned turpentine. Maybe I should have put the lid back on. And I'm still trying to put the head back on.
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I'm going to try some brute force by putting the nuts back on and screwing them down. I don't actually recommend this method, I'm going to try and be careful and sensitive to how much force I'm applying so I don't damage anything or shear a damned bolt.

That's seems as far as they're wanting to go on, and it looks pretty good. A good line of goo has been squeezed out all around the joint. I'm happy with that.

Interesting detail, the exhaust pipe and muffler seems to be held on entirely by one bolt at the back, and happy thoughts, because this bit nut at the front comes straight off the pipe. So, as far as I can tell, it's doing absolutely nothing. Oh yeah, new way of putting this on. Just screw the big nut on, then stick the pipe in. That nut does absolutely nothing. I am thinking of replacing these pipes. I'm wanting to get something to quieten the bike down a bit, while keeping the power. I don't know how to do that, but there's muffler specialists. They'll hopefully work something out.


I've also now got the reset the clearances on the rockers and push-rods, because they've definitely been mucked up. I've done this before, and it went just fine, but I couldn't remember the correct clearances, so I looked it up in the manual. I forgot the English translation manual was a Soviet joke perpetrated against the Evil Imperialistic West. Honestly, I have no fucking idea what they're talking about. Fortunately, I've managed to find someone on-line who reckons it should be between 0.05 and 0.1mm, which sounds good, and I've done this before, so should be fine.
Anyway, what you've got to do is turn the engine until one spring is completely compressed and about to come back up, and then check the clearance on the rocker arm for the other spring (which is completely uncompressed). The clearances are adjusted by loosening that top lock nut, and then screwing the bolt which the spanner is currently attached to in or out, depending on what you need. The push-rod goes into the head of the bolt there, so screwing the bolt in and out adjusts the height.
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I tell you now, the thing's way too tight. I can't get a 0.05 in there. It's going to have to be loosened.
There we go, 0.05 will slip in there easily, but 0.1 won't go in. Perfect. Now just rinse and repeat for the other spring, double-check both, and done. That should be adjusted correctly again.

* Note - I'm kidding! Honest!
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Korto
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Re: Chang Jiang 750 Restoration

Post by Korto » 2018-08-09 09:27am

OK, so what we need to do here is take about 10mm off the length of this cable. First I need to take the little cap off, which isn't willing to just pop off, so I'll have to cut it off, and then you have the coating and the outer sheaf-- and I just learnt how to make close-up photos with my camera--cool.
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The outer sheaf is made of a single steel wire, wrapped in a coil, and the cable runs along inside. The way I found to cut this is to use a wire-stripper first to separate out the bit of sheaf I'm targeting (the wire-stripper allows you to part the outer sheaf, while the inner cable is safe in the centre),
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and then I use a dremel to cut a deep gash (more than half way down) along the length on one side, and then cut all the way through on the opposite side. The sheaf will come off in little rings around the inner cable, which you can then bend away off the inner cable since it's weakened by the deep gash you cut in the opposite side.
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You did do that, right?
New caps can then be obtained and put on the ends, which I'll get around to, but this is done well enough to hook back up for now.





Well, the bike is almost ready to get its first test-ride, and in order to delay that moment of truth, I've decided I better fix up the headlight, which is currently in pieces.
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To replace the old 12v bulb, which of course won't work now since I've reverted it to a 6v system, I bought an LED headlight on-line, which has come with a number of fittings. After staring at it for a while, to figure it out, I discovered that the fitting slipped down over the shaft, and then screwed down in place. So you just picked your correct fitting, and off you go! There was even a spring included, in case you needed that.
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So, I went to put it in place, at which point I discovered two things.
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1) It actually doesn't quite fit. It's so close it's obviously meant to fit, but it doesn't. A bit of adjusting with a file would be in order.

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2) This isn't a push-and-twist bayonet fitting. It's a spring-clip fitting, put it in place and it's held there by a clip. The problem is, there's no clip, and I have no memory of ever seeing a spring-clip. I suspect the spring-clip disappeared a long time ago.
Sigh
So, I've picked up a little strip of steel, and the idea is I bend it into shape and make my own clip. Because, Goddamnit, I can.

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OK, the clip works, but there's too much space between the clip and bulb, allowing the bulb to bounce around. I need to tighten it up somehow.
I've got some single-sided foam tape. A couple of slivers of that between the clip and bulb might just work...
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And there we go, it works! Held firm, and in the right place, beautiful!
I'm running out of excuses to not give this thing a test drive.

Bad news. The LED bulb is rubbish; it doesn't work at 6v, despite being sold to me as a 6v bulb. It's too late now to chase up a complaint on ebay, and the bulb was cheap enough to take the gamble on (about $8), but it does mean the work fitting it was a waste of time. And now I've got to get another bulb. This time from a real supplier at a real address. At 10x the price.
Believe me, this one had better work, or there will be complaining.

PS - The bad LED isn't a total loss. It works well at 12v, and the postie's 12v...


Time to gird my loins, and give this bike a test ride. I spent some time yesterday re-adjusting the carbs, since I realised it was only running on one cylinder, then put some more petrol in.
God, it takes a lot of petrol. It swallowed my whole fuel can, and it's maybe only a quater full. How big is it? 20 litres? 25?
Oh yeah, I should probably mention I've been riding a postie bike for more than a decade. It has a fuel tank size of a large tea pot.

Anyway, the bike starts easy enough, although I'm concerned with how the choke no longer seems to have any effect on the running of the motorcycle, hot or cold.
It slips into 1st so gently I don't even realise it did. I then ride it gently in 1st for about 20 metres, put it back into neutral, and then back into 1st...
Horrible grinding noise, like it's not in gear correctly! Stomp on gear-change hard! No effect! Change back to neutral!
Noise goes away.
Change back to 1st...Horrible grinding noise! Change back to neutral!
Noise goes away.
Change up to 2nd...Horrible grinding noise! Change back to neutral!
Switch bike off and push back. Time to think.

Extra data - from later experiment, it also makes that horrible noise when in reverse, including when the clutch is actually released.

Hmmm....
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InsaneTD
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Re: Chang Jiang 750 Restoration

Post by InsaneTD » 2018-08-10 02:25am

Could the gears not be syncing speed correctly?

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Korto
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Re: Chang Jiang 750 Restoration

Post by Korto » 2018-08-10 06:39am

About an hour ago, when I first saw your post, my answer was "I don't know, and I'm going to have to pull the frigging gearbox apart, aren't I?", but then, during the kids' quiet time before bed, I suddenly realised that if the bike is in gear, the clutch is pulled in and the bike is stationery, then the gears are locked to the wheel and nothing in the gearbox is moving. It can't be the gearbox. Can't be the engine, either, or it would always be making the noise. It's got to be something with the clutch.

And then ten minutes ago I checked a russian motorcycle site I joined last night just to ask this question, and someone's suggested it's the thrust bearing on the clutch. I hope he's right, because I might be able to replace that without removing the gearbox, and therefore without disassembling the entire rear-end of the fucking bike.
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InsaneTD
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Re: Chang Jiang 750 Restoration

Post by InsaneTD » 2018-08-10 11:24pm

Here's hoping.

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Sea Skimmer
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Re: Chang Jiang 750 Restoration

Post by Sea Skimmer » 2018-08-11 12:19pm

Thrust bearings love to rust up and die on stuff that doesn't move, so that wouldn't be surprising. But great progress I see since I last checked this thread!
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Korto
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Re: Chang Jiang 750 Restoration

Post by Korto » 2018-08-14 09:19am

I removed the thrust bearing, and it seemed to be OK, I think. More literally, after finally managing to extract the bloody thing, I then promptly dropped it in the dirt :roll: , so I washed it in petrol and sprayed it with WD40, and then it was a bit sticky at first (which could have been from being dropped in the frigging dirt), but soon freed up and all the balls weere rolling nicely.
I was then going to stick the one from the CJ750 in, but a couple of its balls had seized right up, so in the absence of any alternative I greased the original up and stuck it back in.
I did actually first go to a local bearing place to see if I could replace it with something high-quality Western-made, instead of by Yuri and Boris inbetween slugs of vodka, but apparently it's a special snowflake and there's nothing standard in that size. Of course.

The noise is still there. It only happens when the bike is in-gear AND the clutch is pulled. When in neutral, or the cluch is released, there's no noise. I've got to think about this.

When the bike is in gear, and the clutch is pulled, the two separate parts of the clutch, the part connected to the engine and the part connected to the gearbox, are moving at different speeds to each other. That's not true when the clutch is released, obviously, and it may not even be true when the clutch is pulled but in neutral, as there may be sufficient drag, and lack of resistance in the gearbox, to allow the clutch plates to spin together. This might have something to do with it. It's got to be the clutch.

Other funny news--I stuck the sidecar back on to work out where to put the mirror, and noticed another thing about my new gearbox. It has the kickstarter further to the left, so it now hits the sidecar when you try to use it. As it is, I won't be able to start the bike with the sidecar attached. I'm going to have to cut 30mm off the kickstart lever to make it fit.
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Re: Chang Jiang 750 Restoration

Post by Korto » 2018-08-15 09:12am

Update.
Uncovered the clutch; which involved taking off the rear wheel, differential, shaft, and gearbox. Getting surprisingly good at it. Must be all the bloody practise. Also helps that by now I've learnt, through painful experience, that trying to "save time" by leaving parts on and just trying to work around them only means everything takes longer and is more frustrating. If it looks like it's in the way, remove it!

Anyway, while the gearbox shaft and pushrod look fine (it's a bit blurry. I hadn't noticed my camera had focused on the wrong part)
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The teeth on the second, inside, clutch plate there is oddly shiny, and feels very sharp and jagged to the touch.
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It's been suggested that the shaft isn't engaging the plate correctly, which is apparently something that happens. The teeth looked fucked to me, but I'll talk to my supplier about it.
Someone else on the bike site reckons the plates look like they've been put in backwards. I am going to kill whoever it was who worked on this bike before me. :kill:
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InsaneTD
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Re: Chang Jiang 750 Restoration

Post by InsaneTD » 2018-08-15 10:18pm

Probably some backyard mechanic who figured such an old bike would be easy and, didn't have a clue and gave the previous owner a good price to do it. Then did a shoddy and rushed job when he found out how difficult it would be.

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