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Old 03-26-2012, 06:07 PM   #91
mark883
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Oh you poor idiot / nut / sucker.

I own a K750 as well. But I bought mine running. Then took it apart, in a bout of stupidity.



Let me know how the pistons work. I need to bore out as well, and I don't want the hubcab & vodka bottle cap Russian ones, or worse yet, CJ chinese crap.

I'll be watching intently. Maybe even pointing and laughing at times. But what's a little schadenfruede amoungst fellow Commie Bike owners.

I'd say you definitely have an older M72.

Good looking machine work...
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Old 03-26-2012, 07:12 PM   #92
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Originally Posted by MotoJ View Post
Nice crack there, huh? What a kick in the gut. Hopefully that will be OK. There's a video on YouTube that shows an M72 running with much worse damage:
Lol, it must be the Ford 300-6 of the motorcycle world. :P

Shove some JBweld in there and it'll be fine. ;3
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Old 03-27-2012, 01:31 AM   #93
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Hmm...I can't seem to see the crack. Where is it?

This thread rocks! Keep it up! I'm especially impressed that you are tackling this without previous engine rebuilds under your belt.

You make me feel better about rebuilding my japanese engine. I've done this before and I have available parts!
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Old 03-27-2012, 04:38 AM   #94
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Originally Posted by lstzephyr View Post
Hmm...I can't seem to see the crack. Where is it?

This thread rocks! Keep it up! I'm especially impressed that you are tackling this without previous engine rebuilds under your belt.

You make me feel better about rebuilding my japanese engine. I've done this before and I have available parts!
Thanks for the compliment and encouragement. It's been a learning experience, no doubt...

The crack is at the right of the cylinder bore at a threaded hole. It goes from the outside of the hole out to the fins. I think it will be OK if I don't go nuts with the torque wrench, or drop it on the floor!
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Old 03-27-2012, 04:45 AM   #95
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Originally Posted by mark883 View Post
Oh you poor idiot / nut / sucker.

I own a K750 as well. But I bought mine running. Then took it apart, in a bout of stupidity.



Let me know how the pistons work. I need to bore out as well, and I don't want the hubcab & vodka bottle cap Russian ones, or worse yet, CJ chinese crap.

I'll be watching intently. Maybe even pointing and laughing at times. But what's a little schadenfruede amoungst fellow Commie Bike owners.

I'd say you definitely have an older M72.

Good looking machine work...
I like the K750s- I think mine has a K750 tank, actually. It's a real hodgepodge of parts. I'm dealing with brake and hub issues in real time right now and it seems I have '70s or '80s Ural bottlecap wheels and maybe a Dnepr front hub....
the front had two different width brake shoes, and one was binding in the brake plate and only contacting the drum on one edge.....that will all come later....

Pointing and laughing I can deal with- a couple pals stopped by the other day and just kind of silently shook their heads. That's worse!

Anyway, put up some pics- the more the merrier!
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Old 03-27-2012, 05:49 AM   #96
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Hmm...I can't seem to see the crack. Where is it?
Here?



I think it'll be fine if it's filled with something so the structural integrity remains and it doesn't crack somewhere else and have a piece flake off.

We've fixed transmission cases with jbweld before. I think it'd do fine. :3
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Old 03-27-2012, 10:01 AM   #97
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Back on the bench

OK, motor case back on the bench like it never left. A little cleaner now.



Inside there's a little mesh floor that covers the sump. There's a tube that is the main oil passageway. When everything is turning the pump pressurizes that tube, drawing oil up and through to the fore and aft crank bearings. There's a channel around each bearing retainer that the oil passes through.



See the little hole in the bearing retainer?



The casting is top-notch, eh? Looks like it was modeled out of concrete.
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Old 03-27-2012, 10:22 AM   #98
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And away we go....

I had everything at hand, so nothing to do but take a deep breath and patiently assemble it all with care and finesse, classical music softly playing in the background..

Nah, most of it got bashed together with a lot of four letter words, a BFD, and MotorHead on the IPOD. Still, it got put together.

Started with the ol' crank flip. It went back in easier than it came out. There's one of the infamous oil slingers there. Incidently, cleaning those oil slingers was one of the reasons I initially tore this thing apart. I had read they were supposed to be cleaned periodically, and if they weren't, contaminants would gum up the crank bearings or rod bearings and seize the motor. So were they dirty? 'Course not- clean as a whistle. It did need to be torn down though- the bearings were on the way out..



So, crank is in there, lying like a dead fish on the mesh floor. I had ordered SKF bearings all around. Everyone told me they were some of the best (Timkens didn't make all the ones I needed), better than any crap Chinese bearings or what-have-you. So of course, the main crank bearings came in with a big Made in Malaysia on the side of the box. They went in anyhow.



They went in the retainer by hand, so I used a little Loctite bearing cement. A little assembly goop and ready to go...



In the front the the bearing was nice and tight. It took a little punishment with the BFD and a block of walnut, but it went in the retainer and on the crank nice and straight and flushed up in front the way it was supposed to..



Then the bearing retainer plate goes on, securing the bearings and eliminating end play in the front. It's hard to see, but there's a little macaroni shaped tube on the left that directs oil onto the bearing and the crank timing gear, which will go on in due time.



That plate also keeps the crank in place in the front while I'll be bashing the rear bearing onto the crank from behind. Note the holes in the bolts. That's for safety wire. No Loctite in them days..
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Old 03-27-2012, 10:38 AM   #99
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Are those cases sand-cast? O_o Or is it just age pitting?

Man, I hope that thing runs. The feeling of anticipation is indescribable. =:O
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Old 03-27-2012, 11:10 AM   #100
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Are those cases sand-cast? O_o Or is it just age pitting?

Man, I hope that thing runs. The feeling of anticipation is indescribable. =:O
Yeah, I think it's sand-cast. There's also pitting, rock dents, battery acid damage, cat urine stains, you name it...
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Old 03-27-2012, 11:27 AM   #101
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Moving right along

Inside a machined trough in the rear bearing retainer lives a felt seal, like the mainseal in a BMW. If I had been slick I would have asked Jerry the machinist to mill one side out so I could use a Nitrile seal or something, but I forgot. This felt seal is new, all the way from Estonia. I primed it with 90 wgt and squished it in with my fingers.





I had the bearing in the retainer and hammered onto the crank and some bolts started, and was feeling pretty proud of myself when I looked down and saw the bearing cover washer and the evil "wavy-washer", bane of all Russian motor-rebuilders, lying on the bench. F**K!
So, had to get the puller out and try again.

The "wavy-washer" is the theme of a few web-threads that I read. No one is 100% certain where it goes on each model bike, it seems to me. It doesn't show up on some of the parts explosions, even. It's meant to serve as a spacer to keep the bearing off the slinger, or as an end-play eliminator, just before the flywheel. That's where mine was when I took it apart, so that's where I put it when reassembling...

You can just see it in there....


Next, a poor safety wire job. I have to get some of those cool pliers...



Last bearing is the cam bearing. It has its own retainer plate the keeps it snug in the case..



Finally the timing gears get pounded back on. The lower one was a challenge. I finally ended up putting it in the oven and carrying it down cellar with welders gloves. It went right on, heated up. the bearing plate bolts will get a crummy safety wire job with the needlenoses, too.

Starting to look like a motor again!

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Old 03-27-2012, 12:39 PM   #102
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Next up, Jugs 'n' Slugs

I tried to shang-hai my neighbor to help me with this next bit, but he couldn't make it, so I forged on by myself. It was a little hairy, but luckily I seemed to have some extra coordination that day, rather than stumbling around and tripping over big parts, or dropping things because I had two or three tools in one hand at once, which is the case a lot of the time.

It was a nice day- (not much winter this year), so I masked up the cylinders and got out the BBQ paint..

While I was masking I noticed a big chunk of fin missing. I hadn't noticed that previously, and at first I was ready to blame poor Jerry the machinist, but after scrolling through all my hundreds of pics of this project, I saw where it was busted to begin with, probably long ago. Not much to do about it now. I was ashamed to have jumped to conclusions, too.





I gave the cylinders a few light coats and brought them in for fitment.

I squeezed the rings together by hand, set the gaps 180 dgrs apart, and tapped the pistons into the upside down cylinders. I used a little transmission fluid for lube, since it was handy. Lube is never inappropriate! I put a circlip in one side only. Then, I took each jug with (piston skirt sticking out) to the motor, stood on a piece of 4x4, balanced the cylinder on my knee with the conrod in the end of the skirt, got the piston started in the bore, and fit the second circlip with my left hand (i'm a righty). Then I started a couple nuts on the top two studs, to hold it there so I could let go. Somehow I did this twice without incident (confession- 3 times- first time I forgot the base gasket).

Roma Dakota weighed his cylinders and I think they were 14lbs apiece..





That's one of my dogs, a potential hack monkey. Looks like she got into the BBQ paint. Eh, she'll be fine....

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Old 03-27-2012, 12:49 PM   #103
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Very entertaining build. Makes me want to go find an old soviet hack for me and my dog.
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Old 03-27-2012, 07:04 PM   #104
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Last bit is the flywheel. I'm leaving the valve covers off until the motor is in the frame. I posted pics of the flywheel earlier. it was pretty rough and needed a good cleaning and de-rustification.



Finally I got it looking fairly presentable, but after all the rust on the clutch carrier studs was gone, I could see they were cashed- big grooves where the plates had worn them away.



Luckily I had a new set in the parts cache. Normally these would be pressed in and out with a hydraulic press, but I don't have one, and I was feeling like I was on a roll, so out came the BFH again, and a soft metal drift. I put the new ones in the freezer while I bashed the old ones out from the back side of the flywheel.


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Old 03-27-2012, 07:13 PM   #105
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I pounded the new ones in with the drift and the hammer. They had contracted a bit, so they went in without too much trouble. Only one felt like it went in too easily, but they all got some leftover bearing Loctite. I touched up the ends with the Dremel just to keep things neat. They all measured the same from face of flywheel to ends, so I think I'm OK.



With the carrier studs in, I could install the flywheel, and seal off the innards for good. Hope they are all in there correctly!



The big bolt holding the flywheel on the crank has another folding lock washer.

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