Redoing front forks, what weight oil (big guy)

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Redoing front forks, what weight oil (big guy)

This is a discussion on Redoing front forks, what weight oil (big guy) within the General ZR-7 forums, part of the Kawasaki ZR-7 category; Ok, I was going to wait till winter to do this however, I've got everything else going good / smooth on the bike and have ...

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Thread: Redoing front forks, what weight oil (big guy)

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    Up-And Comer 99GrandTouring's Avatar
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    Redoing front forks, what weight oil (big guy)

    Ok, I was going to wait till winter to do this however, I've got everything else going good / smooth on the bike and have a set of wheel bearings for the front wheel so I've decided to do the front forks before this weekend as well.

    Now with it being said, I'm a big guy, 280lbs, If I'm under heavy braking from 70mph the front forks collapse... ALOT lol
    Can't afford new springs so what size spacer / weight oil would you guys reccomend?
    Thanks!

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    Up-And Comer 99GrandTouring's Avatar
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    Also is it ok to remove the fork cap with impact gun once fork is removed instead of loosening while it's in the mounts

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    Manual calls for SAE 10W or 10W-20 for a 150 lb rider. As I understand it, SAE 10W motor oil has about the same viscosity as 2.5 wt or 5 wt fork oil. Here's a chart showing SAE motor oil viscosities:

    SAE viscosity grades ? viscosity table and viscosity chart

    From that it looks like SAE 10W has a viscosity of 4.1 at 100 degrees C, and 20W would be 5.6.

    Here's a chart showing fork oil viscosities:

    Fork oil weights

    As you can see there is quite a bit of variation in fork oil viscosity even among oils that are supposed to be the same weight. Looks to me like 2.5 - 5 wt fork oils have viscosities of 4.1 - 5.6 @ 100 degrees C so I suppose that's what they recommend for 150 lb riders.

    Incidentally, I changed mine over the winter before I looked all this up. I read that the manual specified SAE 10W and didn't realize that fork oils seem to be different. I used 7.5 wt Silkolene ProRSF which is like most 10 wt fork oil. I weigh 170 lbs and after the change I thought the front end was a bit too stiff. Now I understand why! I am waiting for warmer weather which should thin the fork oil a bit and I hope make the bike ride more smoothly before I decide whether to change it or not. We'll see.

    Also, I suppose you could loosen the fork caps with an impact gun once forks are removed but why? It's very easy to break them loose on the bike. Just remember to loosen the top fork clamp bolt first. DAMHIK!
    TWOQUIDKEV likes this.

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    Site Elder lpscruggs's Avatar
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    Go with a dedicated fork oil. Multi viscosity is not the way to go. IMHO.
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    I agree with Lpscruggs, use a dedicated fork oil, single viscosity.

    The stock oil is 10w. To make the forks stiffer you can up the oil weight (15 or 20), however any increase in oil weight and preload (with the adjustable caps or the pvc spacer mod) will effect how it handles the daily bumps as much as it does the braking dive. Making it so it doesn't dive would mean it handles daily bumps like a frozen pig.

    I'd not recommend cap removal with an impact gun. You can easily strip the aluminum caps that way. Just clean any dirt from them and make sure you loosen the top triple clamp pinch bolts BEFORE you try and remove the caps. Keep the bottom triple tree bolts in. If you don't loosen / remove the upper clamp bolt you'll never get the cap off. After the caps are loose, loosen/remove the bottom triple tree bolts and slide the fork down and out.

    I did my forks last year (replaced the fluid and added in 3/4" spacers (as I recall)) and it made a big difference. If you go with the adjustable preload caps (either ones listed in the forum or ones from an older 1000 Concours) you won't need to put in the plastic preload spacer.

    Increasing the pressure in the forks through spacer and oil alone could result in the seals leaking if you don't do the spring as well. It's the spring that handles the "bump" and the fluid that handles the rebound.
    2004 Kawasaki ZR-7S
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    Obo
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    You do have a copy of the service manual correct?
    2004 Kawasaki ZR-7S
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    Up-And Comer 99GrandTouring's Avatar
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    Yes I do have a copy of the service manual,
    Forks are off all was going well until i bottomed out a shock and now it seems locked / can't get it to expand...
    Any ideas?

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    Up-And Comer 99GrandTouring's Avatar
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    I was using a small amount of kerosene sloshing in shock to clean it out as I had read in other forums / post, could it have cleaned / hydrolocked it?

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    FWIW... I ran the PVC mod with 10w Torco fork oil at 250lb plus gear and got good results for three years. My spacer was a hair over one inch. I tried 1.25 inch but couldn't get the caps on, so I trimmed it down slightly.

    Guess what? You just have to pull really hard; one of the bushings got locked up. It happened to me too and it just took a little time. Don't do anything you'll regret... walk away from it a little while, come back, pull on it, and it will break free.
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    Up-And Comer 99GrandTouring's Avatar
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    Cool thanks!
    I was figuring something as such but wanted to check, I'll wait till i get oil back in it to help free it up.
    So your suggesting I go 1inch spacer?

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    Quote Originally Posted by 99GrandTouring View Post
    I was using a small amount of kerosene sloshing in shock to clean it out as I had read in other forums / post, could it have cleaned / hydrolocked it?
    It's common for it to lock. Nothing to do with the fluids though. I just used a rubber mallet and gently tapped on the lower lip (where the seals are) while holding the upper tube in my hand and voila, it came free. It doesn't take much force to free it & it's fine to do it without oil in it.
    2004 Kawasaki ZR-7S
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    Site Elder lpscruggs's Avatar
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    I have used a 7/8" spacers and Red Line brand Light weight 5wt oil. Very good oil, synthetic and very stable in it's performance. I highly recommend getting Kevin Cameron's fantastic book "Sportbike Performance Handbook. He is of Cycle World magazines writing staff (Top Dead Center) and one of the most notable authorities on motorcycle performance. This book has one of the very best sections on motorcycle suspension setup.
    Last edited by lpscruggs; 04-20-17 at 10:19 AM.
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    Obo
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    I remembered to dig thru my old files and found copies of the "how to's" on the old zr7.com site.

    If anyone wants the word documents emailed to them just pm me with your email address.

    Write up #1:

    Contributed by Philip Darnall
    I disliked the soft springs in the front forks of my ZR-7. Nobody made a replacement spring for the ZR-7 that I could find. So I went ahead and perform surgery on the forks and made my own parts.

    I took a 2" long PVC Schedule 40 end-to-end connector and cut it into half. This gave me two 1" spacers for each fork. I removed the fork caps with a socket wrench. (Make sure that you have backed off the pinch bolts or the caps will never come off!) Once the caps were off, I pulled out the factory metal spacer. It is about 6" long and made of thin steel. I wanted to get a look at the spring and other goodies in the fork, so I needed to fish out more parts.

    I made a simple hook out of a handy coat hanger. Reaching down into the fork about 8" I pulled up the spring. The factory setup had a real nice metal washer/spacer that sat between the spring and the main spacer tube. I took the spacer/washer off and let the spring fall back down into the stanchion tube. The spring had a nice lip on the top edge where the metal washer/spacer sat. So I dropped the PVC spacer into the fork.

    I took my hook and made sure my custom spacer was fully seated on the spring. Next I dropped the factory washer/spacer on top of the PVC spacer. Then in went the original 6" metal spacer. I tried to put the caps back on.

    Their was no way that I could compress the spring enough to screw the cap back on. I pulled the PVC spacer out and cut it down by 1/4" and put everything back together. This time the cap went on with a minimum of cussing!

    I repeated the same steps for the other side.

    Oh what a difference a small spacer makes. My ZR-7 sits up much higher now with the extra preload. When I sat on the bike (post modification) the fork sagged down about 3/4" at the most. The old setup would drop down about 2"! I could slam on the brakes and the front wouldn't dive near as bad as the original setup.

    With the bike riding higher and diving less I could last longer on the ride home. My hands didn't go numb in the first ten minutes.

    Total cost for the modification was under one dollar.


    -----------------------------------------------------------------------------

    Write up #2 :

    PVC Fork Modification Kawasaki ZR-7S
    Contributed by Josh Leonard (aka Qheuie)
    The pictures here were taken when I was replacing the original inserts I had made (1 3/4") with shorter ones (1")
    (just pictures of the left fork leg)
    The diameter of PVC coupler to use is 3/4". The coupler is 2" long so you will have to cut it down.
    Make sure you debur the plastic after you cut it. You probably don't want plastic flakes floating around in your fork.

    1.jpg

    Here I took the bars off.. simple enough. Then I loosened the clamp pinch bolts by the caps, make sure you do this or turning the fork caps out will be a pain.
    I also took the bolts that hold the cable guides to the fork off so I could move the bars out of the way.
    (an old pair of jeans worked great to catch spills and protect the paint)

    2.jpg

    This is how much the spacers stuck out when I opened the fork (there is a 1 3/4" spacer in already,
    sorry for the dark image

    3.jpg

    This is what the stack of spacer(s) and washer looked like before I put it back in. Notice the order of insertion.
    I made sure to put the "factory" (non-cut) side of the PVC down to meet the spring, the washer meets the cut side then.
    (the washer is between the PVC and the metal.)

    4.jpg

    This is the stack sticking out just before I capped it with a 1" spacer (1 3/4" was too stiff for me)
    Notice the difference in material hanging out (about 3/4", ha)

    5.jpg

    This is where the fun began. When I put in a 1 3/4" spacer, I had to have my roommate help me push and turn the cap in.
    The 1" spacer was manageable by just myself.
    Tip: thread the cap on without the factory spacer in just to find where it "catches" the threads in the fork. That way you can make a good guess as to where to start turning the cap when compressing the stack. (Did that make sense??) Make sure you don't cross thread the cap/fork tube! You can feel when the cap starts to thread, if it turns easy you are ok. If not, try again until it turns in easy

    I repeated this procedure for the right fork leg and then put it all back together and torqued the bolts with my spanky new Craftsman torque wrench

    I thought this was a neat, cheap upgrade. For the money it seems to help reduce sag quite a bit. I didn't like the feel of the 1 3/4" spacer so I went to a 1" spacer. I think 1" is going to be too soft, so I may go to a 1 3/8" spacer next. Also, I used the tool kit that came with the bike (yucky). If you have a 22mm 6 point socket or wrench, I would recommend using it on the caps.
    2004 Kawasaki ZR-7S
    complete with extra "stuff"

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    Obo
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    Here's what my couplers looked like before I cut them:

    insert.jpg
    2004 Kawasaki ZR-7S
    complete with extra "stuff"

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    Obo
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    I also made a DIY fork oil tool to set the correct height.

    Based on the "real tool"

    fork oil tool 1.jpgfork oil tool.jpg
    IMG_8219.JPGIMG_8216.JPG

    Syringe, plastic fish airline tubing, spare bathroom sink supply line and a rubber bushing.
    2004 Kawasaki ZR-7S
    complete with extra "stuff"

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