Hyperpro fork springs on Gen II - HOW MUCH OIL?

[tiz]

I'm installing hyperpro front fork springs, after having drained the forks and sent them to the dealer for new seals and bushings.

I followed the EPM instructions meticulously, but came up short of enough oil to finish the second fork. They specify an air gap of 230mm. I'm sure the first fork was fully compressed and measured to exactly 230mm air gap. any extra oil went back in the container.

Second fork fills to only 260mm air gap.

Has anyone else with a GEN 2 bike had experience with the hyperpro springs and the EPM installation steps? Klaus at EPM feels sure 1 liter of fork oil should have been enough. I feel sure I followed directions exactly.

I ordered more oil but I'd rather feel confident that this is normal.

--Kevin

 

[Fred W]

Really? They recommended 230mm with the inner tube fully compressed in the lower leg? That seems rather large.

The stock fork fill level is considerably higher @ 92 mm. and this results in a 696cc expected fill volume, so it normally takes much more than 1 liter to do the job on both sides.

The difference between 92mm fill level and their recommendation of 230mm is 138mm. The inner diameter of the upper fork leg is probably around 40mm (48mm outside diameter, 4mm thick tubing?) which gives a volume difference of about 170cc. So you should have used ~526cc on the first fork leg.

Maybe the tube walls are thicker, and inner diameter is smaller than 40? If so that would mean you would have used more than 526cc.

 

[ahchiu]

Did you purge all the air out before you measured.

 

[Fred W]

Did you purge all the air out before you measured.

That would have made him use less in the first leg, making it easier to fill the second leg.

 

[radiummadman]

why don't you put in the amount the book says to put in, so many ml per leg & go from there.

 

[ionbeam]

why don't you put in the amount the book says to put in, so many ml per leg & go from there.

Aftermarket springs don't necessarily displace the same volume of fluid as OEM. Many aftermarket suppliers specify a different oil weight to go with the springs and use the air dome as an air spring which is compressible, unlike the fluid which is forced through orifices to control compression and damping.

 

[radiummadman]

so follow the fuggin directions

 

[Fred W]

The "friggen directions" say to set the fluid level at X millimeters air space from the top of the inner tube with the springs removed. Even the factory service manual has you do that.

The OP tried to follow the friggen directions from HyperPro, but needed more than 1000cc of fluid, which is understandable since it usually requires significantly more than 1 liter.

 

[tiz]

Thanks guys. I was kind of hoping for someone that had done this on their own bike.

I did ask about the large difference from stock oil level to the hyperpro recommendation. I was told in no uncertain terms to set it up as instructed if I wanted the hyperpro spring/oil combination to work. Different springs and oil, different set up. With these, the springs are longer and a different weight, so you don't use the 150mm spacer from the stock fork. The fork oil is sae15 so much heavier than stock (was sae10?).

I can accept that it's different but can't resolve why I came out with different results than the install steps indicate and that EPM thinks I should have.

--Kevin

 

[ionbeam]

...I can accept that it's different but can't resolve why I came out with different results than the install steps indicate and that EPM thinks I should have...

Mistakes, oversights and errors happen. Even the FSM and owners manual are wrong in places and they are written by the designer that has familiarity with the exact motorcycle model being documented.

Spend a quarter and give 'em a call or kill a few electrons and send an email and see what they say.

 

[Fred W]

Couple of thoughts:

1 - Did they realize you werer working on a 2nd gen? Not sure if the inside dimensions are identical on 1st and 2nd gen fork internals.

2 - Did you push the inner tube down into the outer leg pretty forcefully? On my 1st gen I noticed there was a point where you first hit some "soft resistance" but you could continue to push the inner tube in a bit further. Then there was a hard, solid stop when the tube really bottomed out. It did that both before and after fully disassembling and replacing seals, bushings and damping valves inside the cartridges with GP suspension parts. If you quit pushing on first resistance you may have put too much oil in the first leg.

 

[tiz]

Yes - I've been in touch with EPM/Hyperpro on this issue. As mentioned, he think I set the forks up wrong, I'm sure that I followed all the steps exactly.

Yes - 2nd gen was specified a few times. Outer tube was pressed until "metal-to-metal" was felt as the tube bottomed out. Same with damper rod.

I'm not so far along that I couldn't open the first fork and check the level again. But I'd have to figure out a way to reclaim the oil that now would coat the spring. And I'm sure that the fork was compressed, spring out, 230mm air gap, as the install instructions are clear on that.

--Kevin

 

[Fred W]

Any chance you could provide an inside diameter of those upper fork tubes?

My calculations should be close, based on the OEM fill spec and volume, but I don't know what the ID of those are. I also did not account for the damper shaft taking up space inside that volume.

 

[tiz]

I'll try to get that for you Fred.

--Kevin

 

[tiz]

Fred - The ID is 44mm.

I finally completed the fork setup and reinstalled everything. The difference is completely amazing and the EPM recommended settings are so close to spot on it's spooky. Bike now corners like it's on rails, with almost no upset over bumps in corners. Rides over highway bumps/cracks like they aren't there.

--Kevin

 

[Fred W]

Fred - The ID is 44mm.

Hmmm... that makes it a bit confusing then. The stock level fill volume is just under 700 cc's. By dropping the level 138mm from stock you left a cylinder of air with a volume of ~210cc's meaning you should have used only 490. Which should have left 510cc of oil in the bottle, assuming that it actually was a liter.

It wasn't a quart bottle by some chance, was it? That might explain the shortfall.

Congrats on the new suspension. Enjoy!

 

[tiz]

I just ASSumed it was a liter. I'll check tonight.

--Kevin

 

[redneckj]

In our last NW tech day, JohnnyB installed some Hyperpro springs in his 2010 FJR. He had oil left over. Any yes the Hyperpro springs displace much much more oil than ANY other spring you can install into a stock FJR fork. Johnny says the springs ride very nice and make the bike handle very nice.

 

[Fred W]

Any yes the Hyperpro springs displace much much more oil than ANY other spring you can install into a stock FJR fork.

Might be interesting to measure the final air space with both springs installed and compare. I really can't see how the spring would displace that much more. (210cc each)

My assumption was that Hyperpro calls for such a low oil level because they want to reduce the contribution of the progressive air spring from that head space, relying more on a stiffer single spring rate of the coil springs. Theoretically that would provide somewhat more bump (compression) compliance for a give spring rate.

Edit - The plot thickens... I just went to the Hyperpro web site and can see that their springs are not fixed rate springs. They are progressively wound springs. This explains why they want to get rid of the air spring effect. They have built in a proigressive rate into the coil spring and do not want the air springs contribution messing up their pre-defined rates.

The added coils on the soft end may produce some added displacement too, but still not an additional 210 cc's.. Do they have you install them soft end up or down?