Follow by Email

Tuesday, 12 April 2011

Replacing the Fork Oil Seals (Part 3)

Now that everything's apart, it's time for some cleaning. I bought one of these BBQ containers they sell at the supermarket for $2. It's big and relatively firm, and is not so light that it flies away easily.

I also got a paintbrush for cleaning for 80 cents. I tried to pick one with firm bristles.

I used paint thinner for solvent. It works very well for getting rid of dirt, oil and grease, but it really stinks. However, paint thinner doesn't leave any residue once it evaporates. If our local thinner is made from acetone, then it should also be a safe chemical to use, because acetone isn't harmful to health unlike things like gasoline (i.e. petrol). If it isn't, then there goes whatever's left of my brain cells.

You can also try kerosene or diesel, but please wear gloves. Some, if not most of these chemicals are carcinogenic (i.e. it causes cancer on prolonged contact).

I bought these nitrile gloves because I read that they work really well as a physical barrier against chemicals. These were a nice pair. I think they cost me around $5 a pair.

Cleaning the spring seat, spacer and bushing.

Cleaning the damper rod.
Being the tightwad that I am, I didn't want to waste a lot of thinner. So I saturated the brush with solvent, then dripped it into the interior of the damper rod to try to clean out the old oil.
The forks had some rust spots on them. So with the forks apart, I attempted to polish them up. My first attempt at using power tools for polishing.

I clamped the fork to the table and put some metal polish on it.

Then I attacked it with a teeny buffing "wheel" on the end of a drill.

Here's a close up shot.

Honestly it didn't work very well. I realize that I need to get proper polishing wheels and compounds, and this just isn't going to cut it. Another project for another day I guess.
I didn't take enough pictures for this project, so I don't have all the pictures for re-assembly. I'll take better pictures next time, promise.

But here's some other stuff I did before the forks went back on the bike. Here're all the parts cleaned up and laid out on the table. I lube the damper rod spring with fresh fork oil before re-assembly.
Then I lube the damper rod. I'm wary of that hole because of how much blood it's caused me.
I torque the screw according to the specifications in the manual.
I saw this torque adapter on sale on Amazon, and I thought it'd make a really neat tool. The reviews said that it was really accurate, so I actually bought it as a replacement for my torque wrench. Here's a closer view of it.
You can set the torque in various units, Kilogramme-meters, Newton-meters, Foot-pounds, or Inch-pounds. The torque readings only start to come on at 29 ft/lbs, so it isn't going to be able to measure anything below that. For working on a motorcycle, this just isn't going to cut it.

Moral of the story? Get a proper torque wrench.

After spending some time messing with it, I realized that it isn't very practical for several reasons. First, physical feedback is important in a torque wrench. This one beeps, and the LED changes colour when the torque setting is neared. That means you have to pull really slowly to hear that beep before exceeding the torque setting, and you need to be able to see the readout at all times. Besides, if you're working in a noisy area, things will go wrong.

Secondly, it's tricky to set the torque settings. The increments either move too slowly, or too quickly if you hold down the button.

Third, it's bulky and it doesn't ratchet. I cannot recommend getting this if you're thinking of using it as a replacement for a torque wrench. It might work as a calibration device, but not a tool for regular use. You'll also need a vice to use it as a calibration device for your torque wrenches.

To prevent damaging the inside lip of the new oil seals, I wrap a plastic bag over the top of the fork, and coat it liberally with fork oil. This is to enable the seals to slide over the top of the tubes without damaging the lip.
Next, you need to hammer in the fork oil seals. You're supposed to use a special tool for this, a fork seal driver. This is what the special tool looks like.

Before you do that, I highly recommend that you lube the inside of the fork lowers before you bang those seals in there. The fork oil is going to help the seals go in much easier. And they don't go in easy. On my first attempt, I spent close to 20 minutes hammering on the seal and didn't even get it to clear the retaining ring groove.

The picture below shows you where to apply the fork oil.

I didn't want to spend so much on a tool that I'm only going to be using very infrequently, so I made do with some PVC pipe. I got some 40mm PVC pipe and split it down the centre. Here's my improvised fork seal driving tool.
 Here I used my improvised seal driver to hammer in the fork oil seals.
 
Here's another shot of me driving my neighbours downstairs crazy.
Frankly, this plan didn't go very well. Problem was, the short PVC pipe was too light, and it just didn't give me enough leverage to drive the seals in properly. So I had another idea.

Introducing the "Big Kahuna."
It's a half a metre long 40mm PVC pipe. I suggest getting a larger size, perhaps 42mm. This one didn't fit the OD of the seals perfectly, although it did the job very well.

In fact, with this pipe, I took less than 15 seconds to bang the seals in so that they sit below the retaining clip's groove. Contrast that to the 20 mins I spent with the previous tool.

Here's another view:
I probably should clean up the edges with a file.

After I re-assembled everything, now it's time to fill it up with fresh fork oil. If I remember correctly, it calls for 472ml in each fork. I didn't want to dirty the only measuring flask I had in the house, which my wife uses for baking (I don't really fancy the taste of fork oil in cookies, do you?), so here's what I did.

I took a regular drinking water bottle, and cleaned and dried it. Then I measured 472ml of water with the measuring flask, and poured that into the bottle. Then I marked off the level of the water with a marker, and poured out the water, and let the bottle dry.

When it came time to refill the oil, I just poured the oil to the mark I made, and there should be 472ml in there. See? I didn't sleep during physics class.
It's important to get equal amounts of oil in both forks. I've read that unequal amounts will cause handling problems. Initially, I thought I'd just eyeball the oil level using a tape measure. I think the manual calls for the oil to be filled up to 137mm from the top of the fork.
At this point, I actually put everything back and fixed the forks back on the bike. But I kept having the nagging feeling that the levels were not level on both forks.

So I made tihs tool instead to help me accurately measure the level of oil in there. First you need a big syringe.
Then I get some clear tubing and fix it to the syringe. I taped a wooden chopstick on the end to make the tubing straight, so that it measures the level accurately. Then I mark off the required measurement (137mm) from the tip of the tubing.

With more time, I'll probably scrounge up some parts to make a better tool.
To use this, I just insert the tubing into the fork tube till the mark aligns with the top of the fork. Any excess oil can then be sucked out with the syringe, so the final level of oil in the fork is 137mm.

After that's done, the spring, spring seat and the spacer gets put back in.

The easiest way I've found to get the fork cap back on, is to push the fork cap down, and turn the fork tube (not the fork cap) anticlockwise, until you feel the threads engage. I found this much easier then trying to push down and screw in the fork cap at the same time.

Tighten it up, and that's one side done, and ready to go back onto the bike.

Well, that concludes our series on fork seal replacement. If you haven't already, please follow this blog.

If you have ideas or methods to do this better, please comment on the blog!

Thanks for reading, use your tools, and happy wrenching!

10 comments:

  1. Very useful. Now I know what I'm in for when I also do this. How many miles are on your NH?

    ReplyDelete
  2. Hi P,
    If I remember correctly, it's about 40k miles. But my bike hasn't been well taken care of, as you can tell.

    Let me know how it goes when you do yours, and feel free to write if you encounter problems.

    ReplyDelete
  3. Hi Pepper Crab,

    Thanks for the offer. My NH is also at 40k. Have had it since 25k. I'm the third owner (or so I was told). A good and dependable ride with no surprises during my maintenance work (yet).

    I look forward to reading your adventures and discoveries.

    Peter

    ReplyDelete
  4. Pepper crab. Thank for this photo doc. I found it very helpful and it gave me the courage to go ahead and do the fork seals on my 91 NH. I really appreciated the pictures. The step that was holding me back was needing to purchase the special tool to drive home the seals, but for $6.00 I fashioned my own out of PVC. Thanks again and I look forward to your future posts. Brian

    ReplyDelete
  5. Brian,
    Good to hear that! Let me know how it goes. If you encounter difficulties, feel free to write.

    I'll try to find time to post up the job I did on a stainless brake line replacement, as well as the brake caliper rebuild.

    ReplyDelete
  6. Thanks. Great write-up. I decided to just change the oil first, while still mounted. Dumb things I did...
    1) try to undo the fork-cap with the top-clamp still tightened. Not going happen!
    2) underestimate the distance of the first gush of oil on draining and while 'pumping'.
    Smart things
    1) replace oil in situ: left drained with gunk, right clean. I may still do this once-over with seal kit, but the fresh (atf) oil will have cleaned the left leg.
    2) couldn't buy a 17mm hex bit nearby. Found a 17 mm bolt, force on a 11/16 nut. Welded nut to bolt-shaft. Now I have a 2-sized large hex-bit.
    3) used a 20", 1x1 piece of wood wedged under frame cross-member to keep bike up high before undoing and redoing topcap.
    4) used a short 1/2 vinyl tube, with a 3/8 vinyl tube wedged into it, to just slide over the 1/4" drain nipple to aim the oil down.
    5) measure new oil with springs removed and tubes pushed in.
    6) made a marked 'dip-stick' from plastic rod in small wood crossmember with hole...
    7) 472 ml? Sound precise, but it it simply 1/2 a quart.
    8) used 1/2" pipe as pipette, closed with thumb, to remove
    excess fill.
    9) did the flush/fill with cheap ATF first. Now I know I want heavier (ASE 10?) oil for the real job.

    ReplyDelete
  7. Pepper Crab, Thanks for the write ups you have done.

    I have a 92' Nighthawk, 16k when I bought it, now has just over 30k. Noticed oil on the right fork tube riding home a couple weeks ago. Ordered the required parts based on the Honda Service Manual I have. Your post really helped shed some light on the job. I fabed a stand from 1" 1/8 gage steel tubing used some old roller blade wheels for the pivot. The stand supports the front end holding the front wheel about 4 to 6" off the ground. This gave me a stable platform to remove the front wheel and not be concerned about working on the forks.

    A 15/16" socket also fits the axel nut if a 22mm socket is not available. I purchased a Hex set from Harbor Freight for $15 that has a 17mm hex for the fork caps.

    I loosened the damper bolt on the bottom while the forks were still on the bike, loosened the top yoke pinch bolts and removed the caps with the forks on the bike, this allowed me to drain the oil. After the oil drained I loosened the bottom yoke bolts and removed the fork tube. Everything came apart with no problems. Only one of the seals had a slight tear which left some corrosion were the seal seats in the tube. I used a steel brush on a drill to clean lightly clean the seats. After cleaning everything I also made a seal seating tool from 1 1/2" PVC coupling and then used a second 2" coupling and a 2" PVC 18" tube, taping with a rubber hammer with the fork resting on a piece of wood. Put a light coating on oil on the seal and it went right in. Used to 2" coupling to seat the dust cover after filling with 15.96 oz of HD Type E fork oil. Everything is back together and I can definitely tell the difference in the way it handles. It appeared the forks had not ever been serviced.

    I have also used the site http://www.nighthawk750.com/ done by David Doster. There are instructionso on stock exahust and carburator modifications which result in some suprising performance gains. I am planning on adding a jet kit soon and open up the stock exhaust some more. I love this bike and ride it often. Thanks again for your entries on this blog.

    Mark

    ReplyDelete
  8. Pepper Crab, Thanks for the write ups you have done. I have a 92' Nighthawk, 16k when I bought it, now has just over 30k. Noticed oil on the right fork tube riding home a couple weeks ago. Ordered the required parts based on the Honda Service Manual I have.

    Your post really helped shed some light on the job. I fabed a stand from 1" 1/8 gage steel tubing used some old roller blade wheels for the pivot. The stand supports the front end holding the front wheel about 4 to 6" off the ground. This gave me a stable platform to remove the front wheel and not be concerned about working on the forks.

    A 15/16" socket also fits the axel nut if a 22mm socket is not available. I purchased a Hex set from Harbor Freight for $15 that has a 17mm hex for the fork caps. I loosened the damper bolt on the bottom while the forks were still on the bike, loosened the top yoke pinch bolts and removed the caps with the forks on the bike, this allowed me to drain the oil. After the oil drained I loosened the bottom yoke bolts and removed the fork tube. Everything came apart with no problems. Only one of the seals had a slight tear which left some corrosion were the seal seats in the tube. I used a steel brush on a drill to clean lightly clean the seats. After cleaning everything I also made a seal seating tool from 1 1/2" PVC coupling and then used a second 2" coupling and a 2" PVC 18" tube, taping with a rubber hammer with the fork resting on a piece of wood. Put a light coating on oil on the seal and it went right in. Used to 2" coupling to seat the dust cover after filling with 15.96 oz of HD Type E fork oil. Everything is back together and I can definitely tell the difference in the way it handles. It appeared the forks had not ever been serviced.

    I have also used the site http://www.nighthawk750.com/ done by David Doster. There are instruction so on stock exhaust and carburetor modifications which result in some surprising performance gains. I am planning on adding a jet kit soon and open up the stock exhaust some more. I love this bike and ride it often. Thanks again for your entries on this blog.

    ReplyDelete
  9. Thanks for the tutorial. I just taught my friend, who bought my Nighthawk years ago, how to do this job. I knew how but it sure helped to have photos to show him along.

    ReplyDelete
  10. Glad you found it useful! Thanks for dropping by.

    ReplyDelete