43mm USD Marzocchi fork oil amount/height???

[elgallo73]

I'm getting ready to re-assemble the forks on my 2011 696 following a spring change but am unsure as to how much fork oil to dump in and/or the proper level.  I have the workshop manual for the 2009 696 which was equipped with Showa's and 538cc +/- 2.5cc is the listed amount (no oil level listed).  This roughly correlates to what came out but would love some input from someone here who is more "in the know"...

[Curmudgeon]

The manual on my 2011 796 calls for 500cc of 7,5W per leg. If you have the new Marzocchis, then that applies.

How different are the springs you added and are they going to occupy more volume? THAT is the question.

[elgallo73]

Having the workshop in my case proved a detractor, I did not even think to check the owner's manual...

I'm glad you noted potential differences on the springs, however.  The stock springs are progressive and while comparing them I noted that the new ones have less material in the same area where the oil resides, likely displacing a greater amount it.

I'll compare them in a container to check amount displaced and adjust accordingly, thanks a million!!!

[Speeddog]

Amount you need to add depends on how effectively you can empty the cartridge(s)......
Some are easy, some are quite insistent to not give up all of the oil.

I'd set the oil level 120mm down with the fork fully compressed and no springs.

[elgallo73]

Thanks for the help guys!  I checked both old and new springs in cylinder with factory recommended amount of oil (I know, the springs sit somewhat higher in the forks) and the difference was negligible, even when considering the somewhat larger cylinder diameter and spring position.  I'll try the 500cc amount and measure the height, fine tuning as necessary...

[elgallo73]

Update:  500cc's proved to a bit much, affecting travel and stiffness.  After emptying both forks I added a little over 400cc's and the ride is much better with a static sag of 17.5mm, rider sag of 38.1mm, spring rate is perfect for my burgeoning waistline.  I may add an additional 25cc's of oil depending on how things work on the road.  Overall, the Racetech springs really improve the stock suspension on the 696, likely the 796 as well.

Learned a great deal as well while performing this mod.  In hindsight, I probably would have just sent the forks off to Racetech for the installation but my curiosity got the better of me...

[Curmudgeon]

It isn't as simple as that, given all the variables. What weight oil did you use? Did you increase the spring rate with the new springs? The manual calls for 7.5W which is a little hard to find. Fork oil viscosity also varies between brands and 50/50 mix of 5W/10W does not yield 7.5W precisely.

Speeddog's suggestion was a good one since you may not really know how much you've got in there. 120mm from the top is a good starting point with the springs out and the tubes fully compressed. A larger air gap yields a larger air spring which "may" be softer than the spring you installed. Naturally if you fill the tube, you'll get hydraulic lock and blown seals.

So..., how much DO you weigh? (Let's not even DISCUSS waistlines!!!  )

Further to the discussion of different brands of fork oil, BMW used to specify 10W on many of the blkes with conventional forks. That was always too harsh for me but Spectro 10W was just right. Either it was more slippery or was really comparatively an 8W.

At 175# plus gear I'm fine with the stock Marzocchi on the 796. My dealer was going to play with mine before delivery but after fitting a cheap custom Ohlins out back and setting that up, he saw no need to mess with the forks. They worked very well together.

Not to say that mine can't be improved 10% but not within my budget.  I'm fussy too. If this fork had a drain, I'd probably experiment to get a more supple initial response. (It's on the firm side but never harsh.) Any premium oil has got to be better than Shell Advance! My dealer, an Ohlins tech, probably uses Red Line 5W which is a replacement for OEM 7W, so will ask what he thinks when I'm up there for service next. He's a perfectionist. Rare bird these days and amusing to watch. He's used Red Line oils exclusively since his racing days. http://www.redlineoil.com/Products.aspx?pcid=18

[elgallo73]

Thank you all for the feedback!  Curmudgeon, the stock progressive springs were replaced with Racetech linear versions with a .95kg/mm rate.  My weight is 205 without gear and I'm 5' 9".  I used a 15wt oil in the forks, I'm experimenting with different setups right now, the last time I worked on forks was in my dirt bike days, using ATF (sounds crazy, but that is what was called for in the manual) and air pressure to "stiffen things up".

Racetech recommended the spring rate and it seems they hit the nail on the head, I was initially looking at a .90kg/mm rate but their tech department suggested a little higher.

When I emptied the forks during disassembly, it did not appear that 500cc's came out, and I emptied the tubes thoroughly.  In hindsight, I probably should have tried measuring oil height but was trying to keep things as simple as I could.  500cc's was definitely TOO MUCH as the forks were basically locking up with minimal air space.  I have roughly 425cc's in both right now and it works very well, SIGNIFICANT improvement over stock!