Fork Oil

[Carguz]

OK - I'm going to start on the fork seal change out.

What fork oil do you recommend for an '85 K 100?

I've heard some say Marvel Mystery is good.

Would like something easy from the local parts store if possible. Also what is the exact quantity.



Thanks.

Carlos

[PHMarvin]

Hi, Carlos,
I've never heard that Marvel Mystery Oil was good for fork oil or anything else, for that matter, except driving off mosquitos. I have heard that ATF was good. However, what I use in my K75's is BMW 7.5 weight fork oil. The last that I bought was about $5.00 for a quart. It is purple. Some advocate a heavier oil or a lighter oil to alleviate certain real or perceived problems. Me, I change the oil once a year and ride the bikes - except now, when one had a fork seal leak and the other is weeping oil from the pump weep hole. I'm sorry, but I'm not home now, so I can't check and tell you the quantity per side. I'm sure someone will do that shortly.

[58058D]

Same here, I used BMW 7.5 weight on my K100RS. I seem to remember using a different brand and maybe going to 10 weight later on my K1100RS, but still, the jug said Fork Oil......quantity is listed in the manual - you aren't doing new-to-you mechanic work without a manual, are you?

[Carguz]

Thanks for the info -
I have a Haynes manual. The entry says 360cc +/- 10cc (12.17 +/- .34 oz)
(pg 160)

Since this is my first DIY, I wanted to hear the voice of experience.

I would assume the quantity is fairly critical.

The manual actually recommends SAE 5 wt.

The replies however suggest 7.5 as a better weight.

[PGlaves]

I read stuff on this Forum and just sit here shaking my head.

Marvel Mystery Oil? ATF?

How about the 330 cc of 5 wt fork oil that BMW specified in 1985.

Oh, I know, back in the old days when BMW specified 3 wt fork oil for the /5 bikes some folks decided ATF was close enough and a lot cheaper. I have never seen a viscosity rating on Marvel Mystery Oil but suspect it is about 1 wt. Like kerosene. ATF is about 2 wt. Light even for the /5 bikes, but a fellow could save at least $1 using it.

The 85 K100 (unless since modified) has the long (7.28") travel forks which many folks - including me - think dive too much under braking. They are both undersprung and underdamped. To reduce dive and increase damping I used 360 cc of 7.5 wt fork oil.

The increased volume (by 30cc) reduces the volume of the air column above the oil by the same amount - which compresses more quickly, increasing the effective spring rate and reducing dive. The increased viscosity from 5 to 7.5 wt improves the rebound damping. If your normal riding is in the hot south or southwest, 10 wt is OK.

[Carguz]

Yeah - South FL is already hot and I may go for the 10 wt. 360 cc sounds like the magic number.

Thank you all for your help.

[JALAIMO146577]

Yeah - South FL is already hot and I may go for the 10 wt. 360 cc sounds like the magic number.

Thank you all for your help.

Hey neighbor. I live in Boynton Beach. My manual says:
- 11 ounces per leg
- Bel-Ray Fork Oil with "Seal Swell" SAE 5
- Spectro SAE 10
- Shell Aero Fluid 4
- Castro Fork Oil AWH 15
- Mobil Aero HFA, DTE 11
The list goes on. I'm doing a seal and fork tube change out and I'm going to go with the Bel-Ray SAE 10 w/seal swell

[Carguz]

Thanks neighbor. Where do you get the stuff?

What shop do you go? - Do you go to the 441 dealer in Plantation?

Although, no immediate work required, any insight on local mechanics would be much appreciated.

Thanks and take care.

Carlos

[JALAIMO146577]

Any bike shop will have the chemiclals and lubes. Mail order Dennis Kirk, http://www.denniskirk.com/jsp/common/Frontpage.jsp Bike Bandit http://www.bikebandit.com/

There is a shop in Delray that the previous owner used that did some great work on my bike. I'll get the name for us both. Although I do most of my own work as a hobby.

[MichiganMike]

Just a warning, if you haven't done this before twist those drain plugs back in very carefully or you will strip them out. No heavy hands or maybe just a little tighter so they don't leak philosphy. That applies to most fasteners on the bikes.

Don't be afraid but just go slowly.