fork oil?



26 replies to this topic
  • yz400fmaniac

Posted April 12, 2016 - 02:18 PM

#1

i noticed today my forks are leaking on my 98 yz400f i am going to buy the kit with the bushings seals clips and the hole deal i am a heavier rider so I think i should get heavier weight oil but i dont know what wt so thats one of my questions. The other is that i dont know what brand, i am leaning tword maxima and i also need to know how much i will need thanks.



  • yz400fmaniac

Posted April 12, 2016 - 02:20 PM

#2

also idk if this matters i dont race i mostly ride trails, fast and jump whenever i get a chance to!!!!!



  • Rooster72

Posted April 12, 2016 - 03:08 PM

#3

I'd go with a 5w

  • little_wing

Posted April 12, 2016 - 04:34 PM

#4

when I did my forks I needed 1.5 bottles... so 2 bottles. the best thing to do would be to download the service manual for your bike. there is a ton of great info on there .. it will tell you exactly how many CC to put in each fork.



  • Krannie McKranface

Posted April 12, 2016 - 04:58 PM

#5

Don't go with heavier fork oil.

Dont' meausure the oil by volume, measure it by height.

The Yamaha OEM service manual can be downloaded from Yamaha's website.



  • Rooster72

Posted April 12, 2016 - 07:20 PM

#6

Don't go with heavier fork oil.
Dont' meausure the oil by volume, measure it by height.
The Yamaha OEM service manual can be downloaded from Yamaha's website.

Curious, why not heavier oil?

  • Krannie McKranface

Posted April 12, 2016 - 08:15 PM

#7

Curious, why not heavier oil?

 

The fork is designed for a specific oil weight.

Older 'damper rod' forks were tuned with varying oil weights.

Now days a shim stack and vavle system does that.

Yes, if you know what you are doing you can still fine tune with oil weight, but by itself, it not going to help.

The very best thing you can do is get the correct springs front and rear, and put in an upgrade kit from Smart Performance, or similar.



  • grayracer513

Posted April 13, 2016 - 06:14 AM

#8

Heavier oil is the wrong solution for a rider who is heavier than what the bike was designed for.  The correct way to address that is with heavier springs suitable for your weight.  Only the springs support weight, the oil and the damping system controls the fork action, and all that you will accomplish with heavier than normal oil is to make the fork harsher than it is. 

 

To take an exaggerated example, if I put 3000 pounds in the back of a Tacoma, do you think stiffer shocks would help it carry that?



  • MotoTribology

Posted April 13, 2016 - 07:49 AM

#9

Heavier oil is the wrong solution for a rider who is heavier than what the bike was designed for.  The correct way to address that is with heavier springs suitable for your weight.  Only the springs support weight, the oil and the damping system controls the fork action, and all that you will accomplish with heavier than normal oil is to make the fork harsher than it is. 

 

To take an exaggerated example, if I put 3000 pounds in the back of a Tacoma, do you think stiffer shocks would help it carry that?

 

+1 for heavier oil not being the solution and springs being the right way to go.

 

It is a give and take with the forks. Too light and the rebound will be too harsh. Too heavy and the compression will be too rigid.

 

You never really mentioned why you were thinking of changing the set-up other than you are a heavier rider. Were you bottoming out or were the forks bouncing before the leak?



  • toten

Posted April 13, 2016 - 09:32 AM

#10

I didn't realize you could download the full service manual. I see it for $75 but that seems excessive, I picked one up for $8 shipped off ebay, not pristine but intact. I don't see any for your YZ400F that cheap right now, but there's one for $14. It's worth having for $75, I'm just cheap and would rather spend less if there's no downside.

 

I agree that springs are important to get right. With heavier springs you'll want a little more damping. The right way to do that is playing with the shim stack. Mildly heavier oil might be better than nothing, but I can't say for sure (meaning 5 to 7.5... don't go to 10 or 20). Heavier oil with stock springs isn't going to work well. 



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  • grayracer513

Posted April 13, 2016 - 10:44 AM

#11

You can get the owner service manual for nothing, direct from Yamaha.

 

http://api.viglink.c...uals/index.aspx

 

http://api.viglink.c...ook.com.au/?r=0



  • toten

Posted April 13, 2016 - 11:44 AM

#12

Thanks, I hadn't thought to look at the overseas sites, only US.



  • yz400fmaniac

Posted April 13, 2016 - 01:30 PM

#13

Ok the shocks are plenty stiff now for my liking all I want to know is what weight oil I should go with and what brand I already have an owners manual downloaded and It dident say the exact amount to put in it it just says where to fill it up to and it does not specify what weight oil I should use in it. So ALL I NEED TO KNOW is what weight oil and what brand, short and and to the point thanks!

  • grayracer513

Posted April 13, 2016 - 01:42 PM

#14

Any brand you want labeled as fork oil and between 3-7wt.  Maxima and Amsoil Shock Therapy are my favorite conventional suspension oils. 

 

Within limits, the oil viscosity is not important, since the internal valving is in fact much like a pressure regulator, and self-adapts to viscosity changes because of how they work.  There is normally about a 4X or greater change in viscosity between a cold and warmed up 5wt than there is between a 5wt and a 10wt at any given temp.

 

The old open bath 46mm fork like yours generally requires about 36 ounces total for both sides.  Always drain all the old oil before adding new.  I have found that filling them to right at 110-115mm works best. 



  • lumpy790

Posted April 13, 2016 - 03:36 PM

#15

Golden Spectro 125/150 suspension fluid for KYB forks.

Heavier weight oils would cause more heat and the oils would break down quicker plus have more stiction.

  • yz400fmaniac

Posted April 13, 2016 - 04:06 PM

#16

Ok thank you @grayracer513 so just to clarify a little I should fill them 110 to 115 millimeters Down from the top of the shock when I check it or 110-115mm from bottom of shock to where oil is. thanks

  • yz400fmaniac

Posted April 13, 2016 - 04:20 PM

#17

also do i need a seal driver is there something else i can use to do it like a socket if i can find the right size or something i really dont want to spent 30 bucks on a peace of metal and is that all i would need extra to do the job 



  • grayracer513

Posted April 14, 2016 - 06:39 AM

#18

Oil level measurement is made with the springs removed, and the damper rods and main tubes fully compressed.  Measure from the top of the inner main tube to the top of the oil. 

 

You need a seal driver, but seal drivers for forks like these have to be a split sleeve because the inner tube of the fork is smaller than the lug on the bottom, and the tube must be in place for the seal to be driven in.  The real seal driver works much better than anything you can cob up, but it is possible to do the job by splitting a short length of PVC pipe, clamping it over the tube, and using the axle lug to bash the seal into place. 

 

The manual outlines the process for a complete fork tear down, but you do NOT have to remove the dampers from the lower fork tube in order to replace the seals, which means you won't need to have a cartridge holding tool. 



  • yz400fmaniac

Posted April 14, 2016 - 08:15 AM

#19

Ok thanks

  • Goforaride

Posted April 14, 2016 - 03:12 PM

#20

Don't go with heavier fork oil.
Dont' meausure the oil by volume, measure it by height.
The Yamaha OEM service manual can be downloaded from Yamaha's website.

the manual only references oil volume for the outer. Or am i missing something? It gives the height for the inner but that's mostly irrelevant.





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