Installing the HyperPro fork upgrade on a 1989 R100GS

Hi

You may have seen my post on installing a HyperPro 3D shock on my 1989 R100GS. I also bought a HyperPro front fork upgrade kit at the same time and I thought I would share my experience of installing it.

Here is the box with the kit ready to start work.



The contents of the kit are a pair of fork springs; a bottle of SAE 7.5 fork oil; some grease and a manual.



The manual is generic and covers all their spring kits. The only information specific to my bike was on the label on the front. This specified that the kit was for BMW R100GS paralever 88-96, the spring was a 2020X; the oil was SAE 7.5 and the oil level was 160mm. I followed the steps in the manual interpreting as I went with frequent reference to the BMW manual. The procedure I used for removing the forks does not follow that in the BMW manual as I did not want to disturb the steering head bearing.

The first step in the HyperPro manual is to “measure the distance from the top of the tubes to the top fork clamp”. To do this I first put tape on the handlebar to record its position. The idea was sound but instead of pencil I should have used blue marker pen.



I then put an old towel on the tank to protect it and removed the 4 bolts to drop the handlebar. Removing the protective caps I used the BMW hook wrench to undo the slotted nuts and remove the indicators. You can see that on my bike the caps are level with the top fork clamp. The BMW manual does not specify this but states that “The stanchions must both project evenly 176mm over the bottom fork bridge”.



Looks like my bike is OK!

The next step in the HyperPro manual is to loosen but not remove the fork screw caps. HyperPro state that the caps must be loosened on the bike as holding a stanchion in a vice will damage it. After searching my garage for a hex driver and trying to remember what I had used the last time I had disassembled the forks I ended up using a tube spanner from the BMW tool kit. It is not a good fit and I would recommend buying a hex driver before doing this upgrade.



On this first stanchion I removed the oil filler bolt before loosening the cap, but I did not bother on the second one.

Next I removed the 4 cap nuts holding the front mudguard, unfastened the front caliper from the right-hand sliding tube and removed the front wheel and axle.



I upgraded each side separately. To remove the left fork assembly I undid the two bolts holding the sliding tube to the fork brace, loosened the remaining fork clamp bolts and slid the tube assembly downwards out of the fork clamps.



The next step is to remove the gaiter, then the fork screw cap and empty out the old fork oil. As the cap is under the pressure of the fork pre-load it needs to be removed carefully and I did this in the garage next to a bucket. Once the cap is off, the spacer tube and old spring are removed and the fork assembly is inverted over the bucket and fully compressed and extended to completely work out the old oil. HyperPro specify 10 to 20 times.



Before filling the fork assembly with the new oil I considered removing the fork seal and greasing the stanchion with the grease HyperPro provided and in retrospect this may have been the way to go, but I decided to stick with the order in the HyperPro manual. At this stage you should also oil the thread on the fork screw cap and screw it fully in and out a couple of times to make it easier to refit the screw cap later. It is safe to hold the sliding tube in a vice by the axle holes using rubber jaws and this makes the filling process easier.



HyperPro state that the fork should be filled till 200mm from the top with the assembly fully compressed and then extended and compressed fully 10 to 20 times to remove all the air from the internals. I measured the oil level using a standard steel 12in ruler. Once the air is all out the oil is topped up to the distance specified on the front label, in this case 160mm. Again using the ruler I added oil in small amounts until it reached 160mm. It is surprisingly easy to get to within a mm of the right figure.

Now I lowered the spring into the stanchion tube full of oil. The spacer tube is not used as the HyperPro spring is much longer than the BMW spring. Next the fork screw cap needs to be replaced. This is not easy because you need to apply quite a lot of pressure to the cap at the same time as screwing on the stanchion tube whilst holding the whole thing vertical so you don’t spill any oil. It is very easy to cross thread the cap. A second pair of hands at this stage will make things easier. I found the best approach to be resting the end of the sliding tube on the ground, pushing the screw cap down with the left hand using a bit of wood whilst raising and turning the stanchion with the right hand.

Once the cap was on a couple of turns I replaced the gaiter and slid the whole assembly back onto the bike.



I tightened a couple of clamp bolts to hold the tube assembly and then tightened the fork cap with the tube spanner.

I repeated the process a second time for the right hand tube assembly and it was much quicker this time. Once both tube assemblies were assembled and on the bike I loosened the fork clamping bolts and set the tops of the stanchions level with the top fork brace.

Next the front axle is inserted and then the fork brace, brake caliper, fork brace and front mudguard reattached. Then I replaced the front wheel. Next I replaced the indicators using the hook wrench, put on the protective caps and replaced the handle bars. With all the relevant bolts lightly torqued I bounced the front fork a few times before torquing everything to the correct torque with a torque wrench.

HyperPro state that the rubber seal on the sliding tube should now be pulled out and their grease put onto the sliding tube. It seems the BMW seals can’t be removed at this stage so I carefully opened the seals with a plastic trim tool and inserted the HyperPro grease with a small screwdriver. Bounce the front fork to spread the grease over the correct area, then do the whole process over again. I used string to keep the gaiters out of the way.



I fastened the gaiters on, carefully checked that everything had been replaced and torqued correctly, that the brakes worked and the clearances on the carb cables were correct…..then I was ready for that scary first test ride……

Steve

Nice write up Steve.

I'm curious how this is going to work out on the road. The 7.5w oil is half that recommended for the paralevers (in warm weather). I tried lighter oil in mine with the standard springs but the whole plot just bounced all over the place. Interesting to see what this spring/oil combo work like.

I have this set up in my r100r and the bike rides very well big improvement
over the standard springs. It is fitted with a YSS rear shock total up grade
cost for both front and rear was about £470 which was money well spent.
I also have the progressive front springs in my r80 which is ok
but i think the hyperpros would be better.


cheers Davey

Steve, re putting grease in the seals, would it have been possible to use a syringe- open up enough room for syringe using your plastic bit and insert syringe and just keep moving the nozzle around while squeezing the grease through. I'm thinking that if a screwdriver will fit the space then a syringe nozzle would too.

Did you keep a record of how much oil you ended up putting in the forks? might save a bit of work next time if you did.

Hyperpro also sell GS springs to match the HPN inserts which I have on my GS. They are a little stiffer than stock and perfect match for the 450lb spring Ohlins recommend for a 80/90 kg rider on the GS.
HPN supply 15 wt oil with their inserts - and nominate the quantity, but the fork is dry by the time you get the inserts in place, so just the total amount is all you need, and it isnt as easy to measure the level with cartridge inserts-----.
With the 15 wt oil I need about 25% of the compression damping and about 75 % of the available rebound, 50 % being the base setting.
So with 7 1/2 in the compression side you should be about right, but , as Rob says, you are probably going to be a long way short on rebound - 20 wt sounds nearer it.

Oil level, like sag, is something which I consider to be a tuning item, that is, set to suit you, your bike and the riding you do, so dont be afraid to change it as part of the final fine tune process - the Race Tech site is one of the few places there is any mention of it.
I have ended up with 55 / 50 ish mm sag F/R , and that gives the Ohlins magic carpet ride both ends - for the type of riding I do slightly softish suits me best, but for fast road work a little stiffer might suit some folks better.
The exact height of the fork tubes in the clamps is also a fine tune item, and where you set it depends on if you like a quick or slow turn in,and what tires you fit. I have adjustable caps on the forks of my G/S and they are probably more useful for dialing in the ride height/turn in than setting preload /sag

Hi All

A syringe is a good idea.

No I am afraid I didn't record the amount I used. This was because after I put the first lot of oil in I managed to knock over the open bottle of fork oil. This resulted in a lot of swearing and I lost the plot for a bit.

Over the years I have experimented with different fork oils in both sides in an attempt to improve the standard front end. Once I am familiar with the forks with the HyperPro springs and oil I will write a post about this. All I will say now is that the current front end is nothing like the standard springs would be with SAE 7.5

Anybody know what tool you are actually supposed to use to screw the screw caps? Looking closely at the cap it is not hexagonal as the sides are curved.

Steve

Steve

I did this for a customer just two weeks ago on his R100R. no need to remove the forks at all.. did it all in situ.

Also fitted an Ohlins rear shock ££££££££

What did he think too the fork springs Steptoe ?
they could be on my shopping list in the near future

Did this on my 80 G/S a couple of months ago, didnt need to remove my forks either....:

solidstate100 said:

Did this on my 80 G/S a couple of months ago, didnt need to remove my forks either....:

Click to expand...

And what did you think?

Arkwright said:

And what did you think?

Click to expand...

On balance a worthwhile upgrade. To be fair the springs in mine were probably the 30 year old originals, completely knackered and of different lengths, and the oil was completely shot too, so it was likely that things would improve!

The ride is certainly firmer, but plusher, all surfaces seem smoother, and coupled with the Ohlins I am running on the rear, all is much more comfortable and serene up top...There is still some dive but much much less that the comedy levels previously, and the bike handles much better all round with turn in more controlled, corners more stable, and braking seemingly more effective. There is still a bit of tweaking to do if I can be bothered - the fork oil supplied (cant remember the weight off the top of my head) is about in the middle of where it needs to be as a compromise, but I feel a touch more compression and a touch less rebound damping would optimise things - I may fiddle with different weights in each leg to sort that, but its minor really, OK 95% of the time, just that some of the roads here are brutal bad and show it up a bit.

All good tho!

Thank you, I'm thinking about the front and rear set up, got Hyperpro's on my 12..............very good!

The problem with so called progressive springs is that the only way that they become progressive is if the closely spaced springs become coil bound, and as it seems that all gaps in the spring close by the same percentage and not much becomes coil bound most progressive springs have any meaningful change in spring rate, after they are installed.

I think Rob F measured the rate and found no change whatsoever in a so called progressive spring , but I thing he has given up trying to convince people that they do not exist- the myth is too well entrenched!

The other problem is that the close wound coils soon sag out and become solid - the Wirth springs the PO fitted to my G/S had 40 coils forming a 200mm long spacer and 44 coils 340 long doing the work!
A well set up fork will dive under braking - if it doesnt the spring is far too stiff. If you want to reduce the dive the simplest way is to raise the oil level - air is actually progressive so you will actually get a rising rate suspension - the Racetech site has the details.