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Service Ur Ural Shocks

A shocking (if not absorbing) treatise on Ural shock absorbers.

With the completion of the Mark II shock compressor (the first model using exhaust clamp U-bolts couldn't reach the required compression), I finally got around to servicing my shocks. 

This was the first time I had ever serviced a Ural shock or any shock, for that matter.   I've serviced and replaced seals on quite a few front forks, but with most of the bikes and all of the cars I've ever owned, I've always just replaced the few shocks that ever leaked.....like many others, I've always seen shocks as something like a BIC lighter or AA battery.....disposable when they leak or quit working.

And with most modern gas charged sealed shocks, that's the only option. 
But Ural shocks are so simple in design (and it's roughly $500.00 to replace all  5 shocks on a LL rig!)  A reliable source convinced me not to buy new ones, that the old shocks would last forever if serviced regularly.   Well,  after hearing other riders' experiences, it's not hard to start to see a new way of thinking about this.

Since I would doing this for the first time, I thought I would share what I found out with other riders.  

What I'm writing here is just my opinion of the mechanical characteristics based on what I learned about the shocks,  both by using them for 4 years and learning to deal with them as they wore out and then, by taking them apart and seeing how they work and if a successful repair and service could be done.

It can. 

The cost of servicing them is just the cost of oil and even the cost of resealing them is like $5.00 per shock?   Safe and frequent service as well as ease of servicing the shocks, demand a good spring compressor and because of the length of dust cover, a traditional type won't work.  

At 85000km, they had never been opened.   I had tried several methods, but couldn't compress the spring! They had needed attention since about 50000km, but I didn't have the right equipment to disassemble them safely and I couldn't afford new ones.   The bike was not unsafe, but it had become uncomfortable on rough roads and I had retuned the alignment for springy shocks.   The shocks were all set on the highest preload setting and they never bottomed out but they would occasionally "top out"......when driving off curbs, over speed bumps or potholes, the shocks would fully extend without resistance and "clunk"! 

In fact, you can use this same "clunk" to test the damping action of your shocks.

Compress the springs by shoving down on the frame or fender -  rear and hack (all models) and front (Tourist/Patrol)......when you release the pressure, snatch up on the frame hard (don't lift it slowly...snatch it!)   If the working cylinder is empty or the viscosity of the fluid is now like that of alcohol, you will hear.... "clunk!"  

The working cylinder "topped out".....the cylinder/piston reached full extension..... metal on metal.  

Time for some fresh oil?

The Ural Shock

If you really like old technology.... like kick starters, drum brakes and points ignition, you will love Ural shocks!

Ural shocks are twin tube, atmospheric vented spring dampers....this is old technology, invented about 100 years ago and very popular until the 60s when sealed, gas assisted shocks became the standard.  Like most things on a Ural, they are a very simple design and completely user serviceable.  

As the name suggests, there are two tubes....the bottom outer part with clevis that you see (which is really just a surplus oil bottle) and the inner "working cylinder" that does all the real work.   These are not sealed shocks.....turn them upside down and compress them (if you can!) and they WILL leak.  Even worse, when tipped over and cycled, they can suck air into the working cylinder and in some cases, this will air lock them...they will shove the oil out during compression, but won't pull it back in during rebound.   Two of mine had oil in the outer tube but the working cylinder was almost empty.  

The piston is a loose fit with no seals and it relies on the presence of fluid to provide not only drag and resistance for damping, but also surface tension to achieve a seal for creating suction to pull oil back from the outer tube into the working cylinder during the "rebound" or extension cycle.   According to several sources, it is for this very reason that twin tube, vented shocks should always be mounted vertically and should not be operated more than 35 degrees from vertical (more on this later).   But the old twin tube style is one of the strongest of all shocks.....the heavy piston rod gives them excellent lateral stability, something very useful to a sidecar driver, especially one with a LL front end.  I compared them to several cruiser shock components and basically there was no comparison.....the Russian shocks' springs, pistons and rods, while rougher in finish, were still of much heavier construction than those for a ~700 pound Japanese bike.

Disassembly and Service

Ural shocks require a spring compressor for disassembly.....this is a potential safety hazard and you should exercise caution while attempting this procedure.   I've heard of several close calls and at least one serious injury while attempting to disassemble a Ural shock with homemade compressors. 

Take care of yourself first!   You could put an eye out with those things! 
(your Mom was right!)

Here are some pictures of the spring compressor I modified for use with Ural shocks and some measurements for those who would like to try their own.  Even the stock compressor assembly (I paid $30 for this one) should be easy to fabricate....two pieces of steel and a few bolts.  The adaptor was made for $15.00 by a local machine shop.

The Adaptor

The Compressor

For ease of use, I bolted the compressor to a 4x4 door jamb in my shop.  I ran a 6" bolt through the tool then through the 4x4, very near the floor, as you can see.  There were two reasons for this....

  • I can work sitting down!
  • I can use a floor jack to do all the work if I'm feeling lazy!

The top adaptor is removed when not in use.  The 1.5" square steel tubing would be a bit easier to remove the uncompressed shock if it was 13 inches long instead of 12, but I just pulled the bottom clevis bolt for removal.


        My hairy assistant below is GreyBoy.

 

 

 

    

   

Always set the spring preload to the minimum setting before attempting to remove or disassemble the shocks.  (D'oh!) 

Removing the shocks was easier than I expected....well, once I unloaded the preload!   I already knew the LL front shocks would be a piece of cake but I heard the hack shock could be difficult.  Maybe it was just well worn in after 85000km but with the rear jacked up, it came out with little effort.  The right rear required the most effort just because of its location.

As you can see above, the compressor made disassembly effortless.   The first one took about 2-3 hours to finish (ok, I was playing with it!)   The last one took about 15-20 minutes.  With the right tool (and practice!) I'll bet you can do all 5 shocks on a Rugged model in about 2 hours....complete from roll up to roll away. After the retaining clips, dust cap, spring and cams are removed, the shock cylinder cap is unscrewed using the shock tool in your Ural toolkit.  Don't lose it!  Nothing else will work.

Note the 4 large holes in the top cap....this is your first important clue that this isn't a sealed shock!  Those are the holes the oil comes out when they leak. Once the cap is removed you can pull the inner cylinder and piston assembly and you should see this (or something similar.) 

Note the large hard washer "baffle" under the cap and the cut away relief on the top of the seal carrier block below it.   My theory is that hard fiber baffle is designed to keep things out, not to keep oil in....it is NOT a seal.

For normal service, this is as far as you need go. 

You simply drain the old fluid, clean all the components thoroughly, especially the outer and inner cylinders, then refill the working cylinder and reassemble.
Don't use volatile cleaners, like gasoline or carb cleaner if you leave the rod assembly intact while cleaning.....there are two rubber seals that won't like it!  If you need to do heavy cleaning, disassemble the piston and put the seals in a safe place.   Everything else inside the working cylinder is metal.

The manual specifies 105ml of oil, but I found that filling the working cylinder exactly to the top was even simpler.....I never measured how much that was, but with the piston fully inserted, the displaced oil came almost halfway up the outside of the working cylinder.  As for oil type, take your pick or brew your own!  The oil I emptied out looked like transmission fluid....a reddish tint. 

After some tests with the working cylinder assembled and the foot valve sitting in a coffee can with some oil in the bottom, so I could actually extend and retract the cylinder with oil in it,  I decided on 10W-30 for the rear and hack and 20W-50 for the front to improve brake dive reaction.  I used Castrol SynTec since it's what I had.

While playing with the cylinder with its base in the coffee can,  I discovered that if I deliberately let a slug of air get sucked in the cylinder by tipping it over at a 45 degree angle, I could air lock the cylinder.   If the air bubble inside got to be as big as the piston's range of travel, it would stop pulling oil back into the cylinder during rebound and all damping was gone....even with lots of oil still around the foot valve.  The only way to remedy this was to open the working cylinder, letting the air out and refilling it with oil.

Another oddity.....the two shocks on the inside (right side of the bike) were in very good condition...they worked as expected.  The outside (two left side shocks) and the hack were almost dry....two had oil in the reservoir (outer tube) but the inner cylinder was almost empty.  I don't know if the position is relevant, but I'll mention it, anyway.

Before you reassemble, check the damping action.   You should be able to push the piston down with some resistance but it should require considerable effort to retract it.

Although I had new rod seals for the shocks and actually installed a couple of them, I discovered all of the original seals were still intact and pliable and did not need replacing.  I'll compare the ones I replaced with the ones I didn't to see if one is more prone to leakage.   If you intend to replace the seals any way, remove the nut from the piston rod and then all components.   I would recommend laying them out as removed with a careful reference of which side was up......unless you have a photographic memory ( and remember, even pictures can lie!).  The rod seals have a top and bottom...they're not symmetrical.   The pointed end goes down (towards the support washer) and the flat side goes up (towards the seal carrier block).  Deburr the piston rod near the threads before installing the new rod seal....this area was a bit ragged on a couple.  You don't want to cut slices or chunks out of the center hole of your rod seal.

 Here are the components in order of removal and a picture of some light damage caused by running the shocks without fluid....this is exactly the sort of "shock" you want to absorb!

      

A Modified Exploded Drawing

Here's a scan of the manual's drawing of a shock......I've added color to enhance some features I saw that are not apparent in the drawing. 

The seals are in red......the rod seal (#33) is the part we replace.  

The second seal (#30 - square o-ring) seals the seal carrier housing to the working cylinder cap.....it does not seal the outer tube.   There is a weep hole to allow oil that bleeds through the top cap to drain back into the reservoir.  For a while I thought THIS is the seal we should be replacing, but I came to see it wasn't intended to seal the tube, but only the seal carrier block to the working cylinder cap.   I confirmed this by actually buying and disassembling one brand new Ural shock.....there was detectable, often visible, clearance around this seal and the outer tube on all of mine as well as the brand new one.

The picture below shows how the O-ring seal works.

This is to allow air to flow in and out of the reservoir past this seal as oil is pushed in and out of the working cylinder.   It is inherent in the design.  Under the top cap is a thin hard fiber disk that prevents water, dust and small animals from entering the shock.  It is a baffle, not a seal....compress and extend the piston without the spring installed and you can feel and hear air moving through the holes in the cap. 

If you restrict the flow of air through the cap, you change the dynamics of the system....it won't work as efficiently.  As an experiment, I cut a piece of inner tube and installed it over the fiber baffle.  It more than doubled the effort to compress the piston by hand and I could not retract it at all...vacuum locked.  I had to disassemble it.  Sealed gas shocks work on a completely different principle.  You will likely get very slow (as in RIGID?) bump and rebound damping if you do manage to seal the top. 

Just understand the limitations of the shock, service it regularly and it will work forever.....it's almost indestructible.

 

A few observations on the design and why they leak....

         If the shocks have had a vigorous workout (say riding crossties down the railroad tracks for a few miles?).... the fluid will entrain air, becoming foamy and occupying greater volume in the reservoir. 
A good hard bump now will probably expel some oil.

         Twin tube shocks need to be near vertical while in operation.   When flying the chair, you tip them on their side at an extreme angle (possibly more than 45 degrees?).   At this steep angle, with the shock on it's side and all the rig's weight on two tires, compressing the springs even more, the surplus oil in the outer tube is now near the top cap.  
A good hard bump now will expel some oil....maybe a lot of it.

         If you ride in winter (or heavy rain?) and accumulate water on the top of the cap, and then hit a pothole (rapid extension), as the piston pulls oil back up into the working cylinder, air flows in from the top .....
and some water with it. 

         With any vented system, there will be some condensation.
  

         The point is.....some water is going to get in there and some oil is going to get out, given the above conditions.

This doesn't mean the shock is poorly designed, damaged or defective......
it only means you need to service them occasionally and put in some fresh oil.   If you ride rough roads frequently, fly the chair a lot, like to get airbourne on speed bumps,  do wheelies or stoppies, jump parked vehicles or love to ride the railroad tracks...... you need to service your shocks more frequently.

85,000km is probably too long to wait.  :)

 

Improving older shocks.

The piston, springs and valves determine the performance features of the shock.  With some work (and a few spare parts!), these shocks can be tuned, but that's another topic....our purpose here is to just make sure they're working as designed.  

Here's a picture of the heart of the shock:

This is the piston.  It's also the primary valve body.   The large slots in the outer circle are the "bump" or compression circuit and the smaller round holes are the "rebound" or extension circuit.   In operation, when you hit a bump, the bump valve opens and the shock compresses fast as oil flows freely through the outer holes from the bottom side of the cylinder to the top side, but the space above the piston is reduced by the volume of the piston rod, so some oil is forced through the restricted foot valve out into the outer reservoir.   During rebound, the outer holes are now blocked and oil flow is restricted from the top of the piston to the bottom through the smaller holes, but the foot valve now allows faster flow from the reservoir back into the working cylinder.

If the piston is corroded or grungy, to insure a good seal and proper operation, you may want to lightly stone the exposed top face of the piston above.    Any surface build up will affect how the valve disk seats to the face of the piston.  Lightly stoning the face will provide a better seat for the check valve and much better damping action. 

Don't grind it or file it!   Just lay the surface shown in the picture above flat on a good fine grain Arkansas stone and polish the face a bit.  A few strokes is all it should take....you don't want to remove metal, just rust or crud.  A good seal on this surface will give your LL bike the best anti-dive performance possible.    This is the compression seal...at low speed compression (hard braking) this seal restricts flow bottom to top, but if you hit a bump (fast compression), the valve compresses its' spring and opens, letting more oil flow through the outer ports.

One last surprise............  
I thought the only difference in the front and rear shocks was the steel insert in the top bushings, but Urals often have neat surprises.   Here's a picture showing two different orientations of the "bump circuit" valve washer from the front shocks.   The valve washers were different on the 2 front shocks.   If the valve disk is rotated a few degrees, four little tabs on it will cover half of the 8 center ports.   Only the two shocks on the front had this feature....on the other 3 shocks, the valve disk did not cover any of the holes when rotated.  In fact, the valve disks on them were even narrower, covering only the outer holes.

I have no idea whether this was intentional or just a fluke, BUT.......

Guess which orientation resulted in more resistance to travel?
 (Duh?) 

 

 

Some Conclusions

Servicing your shocks will make a major improvement in handling.  It will also save stress and perhaps damage to the frame hard points and suspension components.  You may even find you need to do a hack re-alignment when you're through, if its been a while. 

A few additional tips on shocks:

If your shocks are not damping properly (low on oil), set them to the highest preload until you can service them.  At least you're protecting the shock from bottoming out and preventing random oscillating movement from stiction.

This is especially true of the hack shock.....if it's low on oil and you're riding solo, it will extend and retract from minor corrections in steering.  Stiction (static friction) can cause it to randomly change height (and stay there!) while riding....this has the same result as changing your lean-out on the fly.   The effect is your rig wants to wander aimlessly from side to side down the highway.  Setting the hack's preload to high will reduce this. 

This effect will be exaggerated if you have recently serviced all your other shocks first,  but not the hack.   Yeah, that's how I did it!   (D'OH!!)  
Stiff bike shocks and a sloppy hack shock is a good formula for wild weaving.  For steering control, the hack shock may be the most important on the rig!  
Do it first. 

Too much oil is better than too little oil (well, within reason!). 
Like the final drive, the Ural will puke out what it doesn't need....it won't blow any seals or anything terrible, but if you fill the entire reservoir with oil, leaving no air space, you just converted your bike to a hardtail...fluids don't compress well.  Too little oil and you risk air locking it....having more oil in the reservoir than in the working cylinder.....no damping!

The preload cam adjuster ridges are 180 degrees out and may work better in one position than the other.  There are two cam ridges and on most of my shocks the adjuster fit much better at one point than at 180 degrees.  As confusing as that sounds, just check yours.....you may need to turn it 180 degrees to get the best fit.

Don't forget to check out the top mount bushings.  On mine these showed some wear but were serviceable.  It might be a good idea to have a couple on hand just in case.  The front shock bushing has a steel sleeve insert, the rear and hack do not....the insert is a hard point welded on the frame.

If you need a little extra preload for the springs, the rings that sit on top of the cams and under the springs, make great adjustment shims.   This is part #10 in the drawing (green).   Each one will add ~1/8 inch of preload....my guess is with the stiff Ural springs, that would equal about 25 pounds of preload.

Clean and lubricate the top cap threads and those in the outer tube body carefully.   This cap needs to be extremely tight to hold the internal parts in compression and prevent any movement.  Torque it until it squeaks!

When reassembling your shocks, don't forget to grease the preload cams ID and the actual cam surface....it will save you busted knuckles and much grunting.   I used synthetic grease.

How to stress test your shocks

To test my "new" shocks I took a short ride.....
from Bethany, North Carolina to just east of Billings, Montana.

Actually, they already had a few hundred km before we left.  We were riding out to visit an old friend we had not seen in several years.   He lives just west of Sturgis, SD... in Wyoming.    Originally I was to ride one of the Hondas.
After much discussion with my 2 co-riders, they agreed I could ride the Ural for this trip if we followed the: "I'll meet you at Hardees" rule of travel.   Simply stated, this rule says each day we ride out alone, setting our own pace and we meet up that evening at preset location.   This allows bikes and riders of different capabilities (or speeds?) to share a common ride without slowing each other down.  It also allows each of us to "do our own thing" ... pursue our own interests and separate sight-seeing trips on the road, while still providing backup and assistance to each other via cell phone, as well as companionship in camp each night. 

On the longest day, 600+ miles, they beat me by about 2 hours.  On one 330 mile day, I beat them by an hour...thanks to my handy eMap GPS with local detail maps and some neat Ural cross country shortcuts!

We rode 4520 miles in 17 days, according to the GPS. The Jap bike speedos said it was a bit more...one said 4650 miles.   This works out to way over 7000km but  Oksana's speedometer only indicated 6560km since it reads about 10% slow because of the Excelsior car tire's diameter.  I tried to stay around 60mph for most of the trip....with this many miles I didn't want to blow her up now.   There were some Interstate portions mixed with state roads....about 40/60.

Oksana earned her keep on the road.....she fetched a new tire the next morning after the Kaw had a blowout and the patched tire went flat over night.  And at one point, I loaned Van the aux radio battery from my ammo box until he got a new one. 

She did get two oil changes along the way and she turned over 90000km during the trip. 

And we added 6 new states to her BTDT list..... look out, Bill! 

Current odometer reading.... 92568km.  
Allowing for a 10% speedometer error from the 29" tall Excelsior tires, that means she is real close to 100,000km.... maybe over it already. 

The shocks worked great, BTW.  It's a joy to ride on firm shocks again.
And so far, they haven't leaked!  

I know they will eventually, but now I know it isn't serious if they do and how easy it is to fix.    :-)

 

Ed Paynter

 

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