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Front Fork Rebuild - 1967 K750


Afcope
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Since I have owned this bike the ride has been very bad. I realize that it is what it is, but I felt like the front may have damage because is it nearly impossible to compress the forks. So, I took apart the forks and found the usual problems. Bad seals and a lot of muck built up from a lack of maintenance.

 

First off, where is the best place to buy a fork rebuild for these? It looks like there's not much to it, but I still need the main seal, an o-ring and the felt seal.

 

Secondly, are there any tricks for cleaning up the years of abuse? The inside of the components are filthy, and I am not sure how smooth the upper and lower shafts have to be to work right.

 

Finally, the springs have in it seem unnecessarily stiff. They look right, but does anyone have any specs on them? Are they all this stiff? It seems like you can only get 2-3 inches of compression travel out of them before they collapse all the way...are they just meant for rebound, with little to no compression?

 

Any tips would be greatly appreciated. Thanks!

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Fork seal kits readily available from the Ukrainian sellers on ebay ( eg. Item 141051451061 ). Clean all the sliding surfaces and polish smooth if needed. Don't worry about the springs and remember to put a new aluminium sealing washer on the m8x1 mm bottom assembly screw. Grease the legs before assembly and finally fill each leg with 130cc of sae10 oil. Work from there.

 

Springs can be tensioned via the screwed rod and locknut, damping is altered by altering the viscocity of the fork oil.

 

Hope that helps

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Grease the fork stanchions ( the long leg that clamps in the yokes ( triple trees?). This will aid assembly and help protect them from rusting under the shrouds. Use normal grease as used for wheel bearings etc. Thinking about it, whilst the wheel is off. If you want to do a full job, get a pair of 30204 taper roller bearings and change them in the wheel. You will then have done almost a full recondition of the front end

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  • 2 weeks later...

Thanks for all of your inputs. I have taken the forks apart and I am getting ready to put on the new gaskets/felts and put it all back together. One thing I noticed is that the inner forks have a lot of scoring and pitting on them. I have heard that you should polish that to make sure the new seals aren't quickly destroyed.

 

How important is that? I have it all apart, so if I should sand/polish them smooth again I had might as well do it now instead of rebuilding it and having to tear it apart in a few months.

 

I have heard of setting up a drill or drill press set-up. Has anyone ever seen anything like that?

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When I was alot younger I had a set of forks that the tubes were badly pitted. Knowing that the seals would be adversely affected, and being relatively poor, I JB welded the pits in, and smoothed the whole mess with sandpaper [go as fine as you have the patience for]. Worked a treat...Hell! I would do it again if new/original parts weren't available...

RP

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What do you mean by 'inner forks' ? The rubber for seals slide on the outside of the fork stanchions. On the bottom of the fork stanchion is a cast iron bush that is fixed. This slides on the inside surface of the fork bottom. If it is this inner sliding surface you are bothered about, don't be. Any polishing in there will only result in introducing wear and sloppyness. Likewise don't polish the inside of the hydraulic cylinder on the end of the spring assembly for the same reasons. Just remove any sharp edges.

The outside sliding surface of the fork stanchion must be smooth so as not to damage the rubber seal but wear on this surface is not as important as the seal has some flexibility

 

All Dnepr forks use the same seal kit and only vary in minor detail. You can download manuals from Charlie Harvins site at. Www.goodkarmaproductions.com and the books covering k750/mt9-10-11-12-16 all cover the same forks.

The mt9/10 parts manual covers all the bike apart from the engine and gearbox.

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What do you mean by 'inner forks' ?

I consider the sliders the outers.....So the tubes the inners...the part the lowers or "sliders", slide on.

If the fork tube surface is Pitted...replacing seals is relatively pointless..But. YMMV.

RP

 

On most bikes, any pitting will indeed ruin seals, especially if the pitting is in chrome plate. Dnepr fork seals are compressed by a screwed collet and pressure on the seals can be varied. They are a lot more forgiving and tolerant than is usually the case, sliding surfaces must be smooth , sharp pits will wreck them , smooth ones won't

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  • 4 months later...

Looks like I've got it all together again with no major issues. As I am getting ready to reinstall them though I have run into some confusing guidance on the nut on the top of the threaded rod that protrudes from the top of the spring. I am reading that it should go above the top of the spring, and "lock" against the large nut that screws into the top of the fork body.

 

Am I supposed to lock the nuts together, or use the smaller nut to keep the spring compressed inside the shock? I've watched the video that has been linked before and I didn't feel like that answered this question.

 

My threaded rod is long enough to allow the Large nut to be tightened down tight with a sizable gap (>2mm) between the smaller nut and the top of the spring.

 

Thoughts?

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  • 4 weeks later...

Here is a wrap up of my fork rebuild so far.

This is how they looked when the first came out

 

The insides looked pretty rough too

 

 

Mine had an o-ring inside, but it looks like it shouldn't have been there. I have read about this on a few forums. Most people say they don't think it needs to go in even though it comes in the rebuilt kits. It is not listed on the parts diagrams. I left the new ones out when I rebuilt them.

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Assembled. You can see the smashed o-ring protruding from below the seal.

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I tried to clean up the fork shaft with a homemade lathe. It did not work well, they would need to be re-chromed. I am just going to reuse them. I tried sand paper and scuffing pads. I even tried polishing compounds. It made it look a little shinier, but not much smoother.

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I also cleaned up the lower, outer portions of the forks. I found this technique on a BMW website. It worked pretty well.

 

This was the final result of the inner shock tubes. Not great...

 

Here is the new assembly. Like I said, I later took out that o-ring since it seemed to serve no purpose

 

The inner spring appears to be off-kilter. I tried to file down the locating pin since that seemed to be pushing the spring rod off. This was as good as I could get it without filing the pin down so far that it no longer engages.

 

Final assembly

 

This is my final problem.

 

I think I need another nut on each of the spring rods. This bike has a lot of hidden surprises.

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I found more nuts for the top and set it up to check the gap

 

Soaked the felts seals in 10wt fork oil

 

Put it together on the bike (don't drop the threaded rod back inside the fork when you take the top nut off to LocTite. That sucked).

 

So, it seems to work. Just missing an engine. I am kinda liking the all black vs the silver lowers.

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