Fork Seals

[GaryZ]

I'm no expert either. I do not think air is compressed in a fork so much as the oil has someplace to go after being forced through the damping restriction. Too much oil and the travel is limited (This is probably my problem at this time). The oil viscosity affects how fast the oil can be forced through the restriction and that is why 10wt oil offers more damping action versus 7.5wt oil. (BTW: I have read an article that suggests that the wt number on fork oil is a wild ass guess)

 

It is also said that reducing the amount of oil versus the recommended amount will reduce damping. More damping equals stiffer.

[BlueSky]

I am not saying the other member is wrong. However, I slightly under filled my '92 forks and used more than 360mL (12oz) per fork. If the other member is a heavy rider, and you are a lightweight, you might be needing more oil to accomplish the correct damping. BTW: I am a heavyweight

 

According to my calculation, 360ml is a hair under 12.7 ounces.

[BlueSky]

Deleted The site was running very slowly and posted twice when it finally did.

[BlueSky]

I'm no expert either. I do not think air is compressed in a fork so much as the oil has someplace to go after being forced through the damping restriction. Too much oil and the travel is limited (This is probably my problem at this time). The oil viscosity affects how fast the oil can be forced through the restriction and that is why 10wt oil offers more damping action versus 7.5wt oil. (BTW: I have read an article that suggests that the wt number on fork oil is a wild ass guess)

 

It is also said that reducing the amount of oil versus the recommended amount will reduce damping. More damping equals stiffer.

 

If the volume the air occupies is reduced by 1/2, the fork air pressure is doubled. This will have some effect. The bike does rise when air pressure is added. But air does not dampen the action very much. It acts as a cushion.

[GaryZ]

According to my calculation, 360ml is a hair under 12.7 ounces.

 

If each fork has 12.7 oz for a total of 25.4 oz, what is left of the 33.8 would be about what I have left in my bottle.

Darn, I hate it when you are right . . .

[camos]

I purchased a 1 liter bottle of fork oil and used about 66% of the bottle for both forks.

Ahh yes, 360 ml each. Thanks.

Measuring height might be a better choice than measuring volume unless there is certainty both forks were absolutely empty before re-filling.

 

The manual specified SAE 20W. The second set of seals are holding up much better. I just ordered All Ball Racing seals for my Venture. I may use the SAE 5W30 or maybe 5W20 when I replace the seals in my Venture. I suspect fork oil is just overpriced motor oil. Then again, I'm just learning.

Have you used motor oil as a substitute or talked to anyone who has? Viscosity will change with temperature so starting with 7.5 or 10 could lead to who knows what viscosity after pounding through a few twisties.

[BlueSky]

Ahh yes, 360 ml each. Thanks.

 

Have you used motor oil as a substitute or talked to anyone who has? Viscosity will change with temperature so starting with 7.5 or 10 could lead to who knows what viscosity after pounding through a few twisties.

 

As I stated, I used Walmart SAE 5W30 engine oil for fork oil in my 85 Kawasaki ZN700. It has been a few years of mostly running around town and commuting to work since then and it has worked just fine. The fork springs are stock and the dampening is fine for that bike. I can add air to those forks but I haven't. The viscosity will change less with the multi-weight engine oil than with fork oil but then the temp doesn't change as much as it does in an engine. I'll most likely use engine oil in my Venture when I install the new seals and progressive springs. Maybe 10W30 would be best for use with the stiffer progressives.

[camos]

As I stated, I used Walmart SAE 5W30 engine oil for fork oil in my 85 Kawasaki ZN700. ...

I'll most likely use engine oil in my Venture when I install the new seals and progressive springs. Maybe 10W30 would be best for use with the stiffer progressives.

I'm planning on repacking the head bearings then flushing and changing the fork oil on my next days off. My inclination is to go with 5W-20, not for any logical reason other than splitting the difference relative to 10-12.5 Wt fork oil.

[BlueSky]

I'm planning on repacking the head bearings then flushing and changing the fork oil on my next days off. My inclination is to go with 5W-20, not for any logical reason other than splitting the difference relative to 10-12.5 Wt fork oil.

 

The 20 means it has the same viscosity as a straight 20 weight at 210 degrees F. And it has the viscosity of a 5 weight at some specified cold temp. So, it is a guess as to what temp it will equal a 10 weight oil in normal bike riding??

[yamagrl]

A friend of mine runs 10 wt non detergent. He got it at O'Riley's. I think they ordered it from their warehouse. He did his forks in our shop last month. The empty Qt bottle may still be out there. If not and anyone wants to know I'll contact him.

[camos]

The 20 means it has the same viscosity as a straight 20 weight at 210 degrees F. And it has the viscosity of a 5 weight at some specified cold temp. So, it is a guess as to what temp it will equal a 10 weight oil in normal bike riding??

Just to complicate matters, what happens to 10wt fork oil at temperature extremes? I used 20wt fork oil in my Virago and it worked OK in both summer and winter. The ride was a little too firm but did a good job of reducing diving. The local dealer has fork oil from 5wt up to 20wt for $20/litre. I haven't specifically looked for 10wt hydraulic oil but I think it is/was readily available. In any case, this is what I will try this time MotoMaster Formula 1 High-Mileage Motor Oil 5W20

[BlueSky]

I would be afraid to use hydraulic oil. Brake fluid is hydraulic oil and I wouldn't use it. My ZN700 manual says use SAE 20. So, I assume engine oil of the proper viscosity is acceptable.

[camos]

I would be afraid to use hydraulic oil. Brake fluid is hydraulic oil and I wouldn't use it. My ZN700 manual says use SAE 20. So, I assume engine oil of the proper viscosity is acceptable.

In my opinion, fork oil is a lightweight version of hydraulic oil both non detergent and anti-foaming. Hydraulic oil does not have an issue with absorbing moisture which tells me brake fluid is quite different although I can't remember how it differs beyond that. Automatic transmission fluid is also hydraulic oil and was used in forks for many years in the 80's. Even recommended by OEM's such as Honda.

 

From what I have read, there is no standard determination of weight for either fork oil or ATF. The viscosity reading apparently varies from one manufacturer to another. 32W hydraulic oil is the most commonly used and apparently also is rated differently so 32W hydraulic oil does not relate to 20W fork oil.

All very up in the air.

 

I'm having second thoughts about using engine oil and might decide to use an ATF like Dextron. Yesterday I dismantled to the point of removing the top fork plug but could not find my 17 mm Allen socket.

Put it back together and will have to wait for a couple of weeks until I have time to try again.

[GaryZ]

 

Yesterday I dismantled to the point of removing the top fork plug but could not find my 17 mm Allen socket.

 

My 17mm hex socket is a 17mm bolt with the nut welded on . . . Works great!

[camos]

My 17mm hex socket is a 17mm bolt with the nut welded on . . . Works great!

Yeah thanks....If I remember correctly, I used a 9/16 bolt with two nuts jammed on when I re-did my 90. That is actually what I could not find but it seemed easier to say 17mm Allen socket just because everyone would know what I meant.

[yamagrl]

My 17mm hex socket is a 17mm bolt with the nut welded on . . . Works great!

 

 

I used a coupler for all-thread. I got it at the hardware store. No welding. I just wrapped it with electrical tape so it doesn't slip out of the socket.

 

(I think I'll add this to Poor Man's Tips and Tricks)

 

 

I

[bongobobny]

Hmmm, clever trick Heather!! I used a friend's welded nut tool myself, along with his complete fork rebuilding tools that included a long handled tool for loosening the bottoms, a neat slider type tool for pounding in the seals, etc. It's been about 5 or 6 years since I did my last rebuild so there's a lot of stuff I forgot...

[Patmac6075]

Also check out Harbor Frieght....they sell a metric hex key set for like $12-$15....with the largest key being the 17mm (I actually got my set for about $8 because a couple of the smaller keys were missing).

Also a real good "poor man's tool" to hold the bottom screw in the fork is an inverted 13/16 spark plug socket....just need a long 3/8 extension (again cheapie HF tool) and you're in business!

I'm not a big advocate for HF because I think most of their stuff is junk....but for these "one time" use tools...IMO you can get by with the cheapie stuff.

[GaryZ]

I used a coupler for all-thread. I got it at the hardware store. No welding. I just wrapped it with electrical tape so it doesn't slip out of the socket.

 

(I think I'll add this to Poor Man's Tips and Tricks)

 

 

I[ATTACH=CONFIG]105851[/ATTACH]

 

 

NICE!

[camos]

Yeah thanks....If I remember correctly, I used a 9/16 bolt with two nuts jammed on when I re-did my 90. That is actually what I could not find but it seemed easier to say 17mm Allen socket just because everyone would know what I meant.

Well, no surprise here, I only half remembered.

 

For clarification, a 5/16" bolt head is 17 mm. The 5/16" nut is 9/16".

 

Speaking from experience, it is my recommendation to use a 6" long bolt rather than a 1 1/2" bolt for this purpose. While using it, the short bolt can easily fall out of the socket whereas a longer bolt can be held and can also substitute for a ratchet extension. Of course a bit of tape would also have prevented the small bolt from falling out.

[garyS-NJ]

35mm film? like photographic film or mylar?

 

Does anyone have a recommended parts list for re-building the forks?

I have a set of '86 forks I plan on installing on my 83 along with the R6 brakes, I hope to install the progressive springs as well.

My thoughts on proper fluid in the forks; I solicit feedback on my thoughts here as I haven't done this.

When draining the existing oil measure how much is in there as you pour it out. Just FYI record that number. Check out how much came out against the book amount FYI.

Service the fork with the book's recommended amount of oil and (using some tape) mark the level on the outside of the fork tube and install new spring; (hopefully it won't overflow) note how far up the tube the oil moved with the increased displacement of the larger spring. If it looks like it will overflow the fork tube you could remove the spring, reclaim the oil, reinstall the spring and refill the tube until the original oil lever is reached. Note how much you used and record. If it doesn't overflow you can use a straw (or any other tool that can draw oil from the fork tube) remove the (now) excessive amount of oil to the original level you put in there to start with. Note how much you remove, subtract that number form the book amount and record that in your notes for the next time you change the oil or for a subsequent owner.

Measuring how much comes out also tells you if you have a seal leak. I just installed progressives in my '84 & forgot to measure what came out and now see one seal slightly leaking.. (Bought bike last year and didn't see a fork oil leak). Btw, for filling, I didn't do any level measuring.. I just added the 405cc per manual spec.

 

Sent from my VS987 using Tapatalk

[garyS-NJ]

Hmmmm, Interesting.

I just went from 10W to 12.5 W and felt the "pogoing" at low speed got worse, I am thinking of trying 15W next.

I just put progressives in my '84 with manual specified amount 405cc of 15w fork oil and have no pogo.. And it doesn't feel hard at all up front. (I don't know what kind of oil or springs were in there but it does feel a little softer over bumps but not squishy at all (firm at speeds through dips and turns.

 

Sent from my VS987 using Tapatalk

[garyS-NJ]

I'm no expert. But, I think as long as oil covers the cylinders that restrict oil flow when the fork tubes move it doesn't matter how much higher the oil is from that standpoint. However, the higher the oil level is, the less air above the oil that compresses. When the forks compress, this smaller amount of air is compressed to a higher pressure quicker making the fork action stiffer. The danger as I see it is putting in too much oil to the point that it locks up the forks when they are compressed. That is why if you measure from the top, you have to compress the forks to get the reading. If you have stock springs, Yamaha tells you exactly how much oil to put in. If you have progressive springs, they occupy much more space and less oil is needed.

I'm assuming I pulled stock springs out of my '84 but they didn't look much different than my progressives (progressives have a tighter wind on one end) So I put stock amount of fork oil in and neglected to measure oil height .. Ride doesn't feel overly harsh in general but in trying to "feel" how much better the front might be eating the road, is swear I might have felt some sticksion in the tubes. And at a stop when I work the forks up and down I can now hear the springs rattling like ching ching... I didn't hear that with old springs

 

Sent from my VS987 using Tapatalk

[garyS-NJ]

If the volume the air occupies is reduced by 1/2, the fork air pressure is doubled. This will have some effect. The bike does rise when air pressure is added. But air does not dampen the action very much. It acts as a cushion.

Yes, air sets height, oil viscosity sets dampening. Increasing oil volume will make a progressivly stiffer shock as it compresses

 

Sent from my VS987 using Tapatalk