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One thing leads to another...my '67 K-750


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After posting now and again as things have come up, but after seeing the new forum I decided to make this a running thing.

 

So, to catch up to where I am now...

 

I got my 1967 K-750 (mostly, who knows what it started out as) a few years ago. Things started off great. I had some friends with similar bikes and we made good use of them.

 

 

 

 

 

I had to do the usual:

- Wheel Bearings

- Changed the 301 carbs for K68s

 

12578054974_08db70213d_c.jpg

 

- Cleaned up the PP302

 

12577705583_55b03d50e4_c.jpg

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- Cleaned the commutator and replaced the brushes in the 414

 

- Found this AGM battery which has worked out nicely

 

- Fixed the gearbox (broken reverse, and leaky dnepr-glide)

 

 

- Tore apart the final drive (without actually fixing anything after all...)

 

 

Then this happened:

 

I was getting a lot of blow by in the right cylinder. Lots of smoke, oil soaking my boot; it was a mess.

 

So, obviously I investigated. Nothing too terrible. You can see the 77.95 stamp on the piston

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Well, I cleaned up the cylinders a bit, and slapped on some "new rings" to get it back on the road.

 

12577719223_2c425b7fc8_c.jpg

 

This, however, did not last. After about 700Km or so the oil leak was back with a vengeance. Now, my friend and I did the last ring replacement in a rush to go on a ride and we basically did nothing to set the rings or their end gap. Not surprised I ended up with this:

 

This time I was determined to fix it right.

 

Left Side

Right Side

 

 

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I got the cylinders honed locally and the results were disappointing

 

 

Well, it was out with the engine and time for a full tear down to see what I was working with. This came from me finding a bit of play in the crank and I wanted to see the internals.

 

With some photo-magic the engine found its way onto my workbench fully reassembled.

 

Front cover off, gives a good look at the points. They look a bit misaligned.

12446971715_3debd2015a_c.jpg

 

With the friction packs removed, it was time to take off the fly wheel. That was a pain in the ass. I hate buying new sockets for one use.

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After buying another tool, a 2-post puller, I attacked the rear cover.

 

This thing was stubborn. Whoever was in there last time had used some serious gasket adhesive on it

 

Front covers removed

 

12447097823_3beda2415e_c.jpg

 

Out came the cam. I can't tell whether this is worn or just poor metallurgy. I will try to find some cam specs to see if I need to replace this thing.

12446957185_3c670f86c8_c.jpg

 

This cam seal retainer will need to be replaced

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After watching some YouTube videos, the crank came out with no problems

 

 

Doesn't look too bad after a bath in the parts washer and some scrubbing

 

Look at that quality casting. Its definitely got character.

 

With the engine apart, the plan is

1. New pistons and bore match cylinders

2. Find some specs on the crank and cam to see if those need to get replaced. Hopefully not.

3. New bearings and seals

4. Blast aluminum and clean/paint the cylinders

 

Hopefully, this will set me up with a descent running engine for at least a few miles. I am looking forward to hearing everyone's input.

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  • 1 month later...

Does anyone have a source on some new over-sized pistons? They're currently 77.95, so what do you all suggest for the next suitable size? I have seen a lot of variety on uralzentrale and oldtimer for a 21mm piston pin.

 

Ural-zentrale shows 1st oversize as 78.91 (which is what I have heard before)

Oldtimer shows 78.93 as the closest.

 

Any recommendations?

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Does anyone have a source on some new over-sized pistons? They're currently 77.95, so what do you all suggest for the next suitable size? I have seen a lot of variety on uralzentrale and oldtimer for a 21mm piston pin.

 

Ural-zentrale shows 1st oversize as 78.91 (which is what I have heard before)

Oldtimer shows 78.93 as the closest.

 

Any recommendations?

Jörg Warnke, www.ural.de got german oversized pistons (79.00) for K750. I don't have any experience with the side valve, but Warnke is a honest man.

 

You have taken some really nice pictures!

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  • 2 months later...

Time to make some headway. I am looking at buying the following:

- Piston SV-Engines 1st Oversize 78.91 mm EU quality / Product No.: S317-7891

- Piston ring sv engines Schoettle 79 mm / Product No.: S28-S-7900

- Oil control ring Schoettle 79 mm / Product No.: S29-7900

- Piston pin circlip / Product No.: S27

 

- Crankshaft M72, K750, R71 / Product No.: S335

- Crankshaft felt seal ring / Product No.: S338

- Lock washer for flywheel centre bolt / Product No.: S42-Si

 

- Gasket sealing ring bracket camshaft 4 holes / Product No.: S4255

- Oil pump gasket, Ural, improved / Product No.: S367

- Rear engine cover gasket Ural and sv engines, improved / Product No.: S362

 

I am considering saving the camshaft. The lobes have some pitting, but otherwise it still looks good. There’s a picture of it above. If I change my mind, I’ll buy one from ural zentrale - Camshaft / Product No.: S350

 

Hopefully, I can salvage the following parts:

- Piston Pins

- Valve Springs

- Valves

- Tappets

 

They all look ok, but if anyone has advice from past rebuilds please let me know. If I need to I’d rather just replace it now that tear the motor down again in a few months.

 

Finally, does anyone know where to find the K750 crankshaft endplay limits? I want to make sure I use the right Crankshaft Spacer Washers; and I don’t really trust the current setup.

 

This will be the first time I’ve tried to rebuild a Dnepr motor. Any advise is greatly appreciated. I’d love to send it off for a proper rebuild by a specialist, but I don’t have that kind of money. I just want to get this done right, but for the best price so I can get back on the road and enjoy this thing!

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  • 4 weeks later...

There are smaller oversizes available. 78,13, 78,35, 78,43 mm. Basically nothing will happen with 79 mm, just good practice to not bore more than you need. 78.13 is the russian 1st oversize, not very useful, bores are mostly worn beyond that. 78,35 is the chinese 2nd oversize, but as they have about 0,15 mm play already from new, pistons are about 78,35 mm and bores should be about 78,43 mm according to russian specs. NOS chinese pistons are very good quality. 78,43 = the russian 2nd oversize.

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  • 6 months later...

could I ask what it does cost for a company or someone to rebuild a full engine for you, I would rather hand it over to some one that has worked on these engines rather than me guessing lol.

I live in Sheffield, England and would not mind dropping the engine off to the right people, I recycle waste oil for my diesel fuel so the travelling costs me peanuts driving my van I'm working on a diesel bike but that will take a bit more time.

ALAN

Sheffield S25

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Alan, thanks for your offer. I've been quoted around $1700 which is, unfortunately,, too much for me to swing.

 

There's also something about the challenge of doing it myself. These bikes are fun to ride, but I prefer the tinkering. Right now I'm trying to save up for crank/clutch plates.

 

If I ever find myself in Sheffield I'll look you up!

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