Author Topic: fork shims and oil weight? (Read 3884 times)

drumgod · « **on:** August 24, 2009, 08:08:05 PM »

Okay, have the forks ready to go back together on my '76 CB550K and I have a couple of questions:

This first one may fall into the "stupid" category... based on this from the "Thoughts of HondaMan":

Quote

The springs on the stock 500/550 were very soft, too soft for spirited riding, and they sagged quickly. Get 100 lb springs for the rear when you replace the shocks, and shim the front springs inside the fork tubes with at least 3 washers of the diameter that fits the tubes inside. Then add air valves to the caps to make air forks out of them: run 10 PSI without a fairing, 15 or so with a fairing.

I'm not a small guy. I weigh around 280 Lbs. I'm not thinking of doing the air fork conversion right now, but I'm thinking the shims would be a good idea... We'll say four to start... Uh, where do they go? At the bottom of the spring, at the top of the spring, or someplace else? Dropping the washers into the fork tubes and putting the springs on top seems like the easiest way to reassemble but is that the correct way?

Second question: What weight fork oil should I put in it? I have 10 weight here. Will that do or should I track down some 15 weight?

Last: How much oil? The 550 service manual hosted here states 5.3-5.6 oz. of "Honda ATF". However, the innards of my fork do not look anything like the illustration given. Do they still require the same amount?

GammaFlat · « **Reply #1 on:** August 24, 2009, 08:43:07 PM »

I'm not in any way a 550 guy... but I think you want the spacers in the top of the fork (based on my conversations with "the man"). In terms of weight... do a search, you'll get a lot of opinions... probably straight weight.

I am going to do the air forks. I'll probably do spacers as well - probably just enough of a spacer to compress the springs a bit. I will be using a piece of conduit

.

I did seals and new fork oil (Spectrum SAE 15).. and new steering head tapered bearings - dang, what an upgrade. The bike felt marvelous (K6 CB750). I also went with an Avon (AM26 I think). It is a different bike.

Good luck,

John

Industrial Rat400f Killer · « **Reply #2 on:** August 24, 2009, 08:55:28 PM »

I'm sorry I can't provide any info as to how much and what weight oil to use but I do think the spacers should go right under the threaded cap on top of the springs. If you can find a set of these that work with your size fork it will make finding the right stiffness a lot easier than changing shims.
http://www.400fourstore.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=4&Product_Code=1957&Category_Code=C

drumgod · « **Reply #3 on:** August 24, 2009, 09:30:26 PM »

Thanks guys, that brings up another shim question. Washers vary greatly in thickness. Perhaps instead of "number of washers" we should be talking about "actual shim height/length". It should be pretty simple to throw some aluminum (or whatever metal) stock into a lathe and take it down to the "correct" dia and length. I could even make them with a nipple that inserts slightly into the fork caps so they are easer to re-assemble. Heck, If I 'm going to go that far maybe I should just do the air fork mod as well... So, how long should the shims be and should I commit to the air mod?

Man, it seems like every step forward brings up twice as many more questions! Thanks again guys.

MoTo-BunnY · « **Reply #4 on:** August 24, 2009, 11:59:31 PM »

I used a silicon bronze "tractor bushing" (what the hardware store called them) of the right diameter, about an inch long, for like $3-4 each or something? It preloaded the front real good - almost a tad too stiff, if anything. I should have gotten the dimensions of the bushing before I installed them, but I will next time I change the fluid.

Kinda like the one on the left, in this picture:

I just figured they would be better than washers or pvc - the bronze is real strong and 'slippery'.

Industrial Rat400f Killer · « **Reply #5 on:** August 25, 2009, 08:51:50 AM »

Quote from: drumgod on August 24, 2009, 09:30:26 PM

So, how long should the shims be?

That's why I suggested the preload adjusters. The length varies from rider to rider and bike to bike. I cranked my preload adjusters down about 3/8" and that seemed to be perfect for awhile. I've had them in for about a month, last night I was on a pretty bumpy road and thought they were a little to stiff so in about 30 seconds I had them readjusted.
I'm not saying the spacer is the wrong way to go because it certainly works but if you can get preload adjuster they'll just make life a little easier.
If you have a metal lathe try making your own preload adjusters, if you're successful you can start selling them to all us SOHC owners.

drumgod · « **Reply #6 on:** August 25, 2009, 01:15:17 PM »

I took a look at the preload adjusters and appreciate the coolness factor of being able to change them practically on the fly. There are a few things that make me think I will pass on them though. I think they would interfere with my bars and if they where installed they would keep me from converting to an air fork. Also, I would think that once you got them dialed in, you would almost never change the settings.

As for requesting a length, I understand that there are many variables that contribute to the setting that works best for each bike and rider... I was just hoping someone could provide me with an educated guess that would be a good starting point for me and my bike. ('76 CB550K, 280 Lbs.)

Unless someone suggests a better plan I think I am going to stop by Farm and Fleet and see if I can find a ~1 inch "tractor bushing" as mentioned by moto-bunny. I will use the 10 weight oil I have and add a touch more if I feel it needs to be stiffer... As for how much to add, I'm still not sure. Maybe I'll start with 5oz. and go up from there.

I'm still open to suggestions. Thanks guys.

MoTo-BunnY · « **Reply #7 on:** August 25, 2009, 03:08:09 PM »

Quote from: drumgod on August 25, 2009, 01:15:17 PM

I took a look at the preload adjusters and appreciate the coolness factor of being able to change them practically on the fly. There are a few things that make me think I will pass on them though. I think they would interfere with my bars and if they where installed they would keep me from converting to an air fork. Also, I would think that once you got them dialed in, you would almost never change the settings.

As for requesting a length, I understand that there are many variables that contribute to the setting that works best for each bike and rider... I was just hoping someone could provide me with an educated guess that would be a good starting point for me and my bike. ('76 CB550K, 280 Lbs.)

Unless someone suggests a better plan I think I am going to stop by Farm and Fleet and see if I can find a ~1 inch "tractor bushing" as mentioned by moto-bunny. I will use the 10 weight oil I have and add a touch more if I feel it needs to be stiffer... As for how much to add, I'm still not sure. Maybe I'll start with 5oz. and go up from there.

I'm still open to suggestions. Thanks guys.

I wish I could give you the exact dimensions, but like I said I forgot to measure it. They will have quite an assortment of different sizes so you will have to know ahead of time, for sure. I assume you have the forks opened up or dimensions estimated?

I remember the posts that mention the PVC 'adapters' and if I recall, and just based the dimensions on that. (I think I actually measured the PVC pipe at the store, standing there with my calipers looking all mech geek. . . lol)

Steve_K · « **Reply #8 on:** August 25, 2009, 06:40:50 PM »

On my Duck and GIXXER I used PVC pipe and cut it to length. 550's have smaller tubes and they may not be the right diameter. I put the spacers under the forkcap. Racers used to used quarters and used the money amount to track preload. Race tech's website has a formula for finding spacer length. Starting point then ride and adjust.
Steve_K

drumgod · « **Reply #9 on:** August 28, 2009, 06:38:19 AM »

Okay, I spent yesterday's lunch at our machine shop and made these shims. They are currently 1". If they seem too stiff I'll knock them back bit by bit until I like the feel. The "nipple" seats in the cap and should make them little easier to jam in on top of the springs. I left space and center drilled them so I can still do the air fork mod later.

I'm still not super familiar with the functionality of the front forks. Anyone see any reason that these won't work?

Johnny5 · « **Reply #10 on:** August 28, 2009, 07:51:07 AM »

With the spacers, do you have to have gorilla strength to get the oil filler cap back on? It's hard enough without a spacer....
Maybe there's a trick I dont know?

Industrial Rat400f Killer · « **Reply #11 on:** August 28, 2009, 08:16:23 AM »

Quote from: Johnny5 on August 28, 2009, 07:51:07 AM

With the spacers, do you have to have gorilla strength to get the oil filler cap back on? It's hard enough without a spacer....
Maybe there's a trick I dont know?

I'm sure there is some tricks to it, you definitely want to get the front tire off the ground. If you had a steering wheel puller you could clamp it under the top triple and crank it down maybe, if you were real creative.
Considering how much I cranked down my preload adjusters I would think that 1" is to long but it's a differnt bike with different forks so maybe they'll be perfect.

drumgod · « **Reply #12 on:** August 28, 2009, 08:22:23 AM »

I am reasonably gorilla like I guess. $:-\$ Guess which one is me.

I did not have much of a problem re-assembling the fork without the shim. I guess we will see what happens when I finish cleaning the lowers and try it again with them. I think that 1" might be too long as well, but it's easier to remove material than to put it back...

Johnny5 · « **Reply #13 on:** August 28, 2009, 08:45:10 AM »

Whenever I've had to work on forks, they've always been off the bike.

MoTo-BunnY · « **Reply #14 on:** August 28, 2009, 01:18:55 PM »

Quote from: Johnny5 on August 28, 2009, 07:51:07 AM

With the spacers, do you have to have gorilla strength to get the oil filler cap back on? It's hard enough without a spacer....
Maybe there's a trick I dont know?

I don't recall having any problems with my 1" spacers and skinny little arms. . .lol, so no gorilla strength should be needed.

I think I used a socket and ratchet and just pushed down and turned until they threaded - I don't remember it being hard at all?

jimbir · « **Reply #15 on:** August 28, 2009, 03:22:52 PM »

On my 550F I found that if you jacked the bike up from under the front of engine, The weight of the front wheel will cause the forks to extend and draw the fork caps down on to the threads in the fork. Do this until they just touch and you don't have to push on them very hard to engage the threads.

Johnny5 · « **Reply #16 on:** August 28, 2009, 04:23:13 PM »

Quote from: MoTo-BunnY on August 28, 2009, 01:18:55 PM

Quote from: Johnny5 on August 28, 2009, 07:51:07 AM
With the spacers, do you have to have gorilla strength to get the oil filler cap back on? It's hard enough without a spacer....
Maybe there's a trick I dont know?

I don't recall having any problems with my 1" spacers and skinny little arms. . .lol, so no gorilla strength should be needed.

I think I used a socket and ratchet and just pushed down and turned until they threaded - I don't remember it being hard at all?

I wonder if the spacing is different between the 750's and 550's?

MoTo-BunnY · « **Reply #17 on:** August 28, 2009, 05:01:13 PM »

Quote from: jimbir on August 28, 2009, 03:22:52 PM

On my 550F I found that if you jacked the bike up from under the front of engine, The weight of the front wheel will cause the forks to extend and draw the fork caps down on to the threads in the fork. Do this until they just touch and you don't have to push on them very hard to engage the threads.

Oh, I definitely had the cycle frame jacked up - I guess I assumed that was a given?

GammaFlat · « **Reply #18 on:** August 28, 2009, 05:08:45 PM »

Quote from: Johnny5 on August 28, 2009, 04:23:13 PM

I wonder if the spacing is different between the 750's and 550's?

It is a function of how worn your springs are. If your springs are compressed and tired, you'll need more spacing. If you have brand new springs, you'll not need spacers unless you want to stiffen things up a bit.

jimbir · « **Reply #19 on:** August 29, 2009, 06:31:22 AM »

Quote

Oh, I definitely had the cycle frame jacked up - I guess I assumed that was a given?

I'm surprised that the front wheel didn't drop when you jacked the frame. Did you have both caps off at the same time? It won't drop unless you do. It could be the seals in your forks are a lot tighter than mine were.

MoTo-BunnY · « **Reply #20 on:** August 29, 2009, 01:28:24 PM »

Quote from: jimbir on August 29, 2009, 06:31:22 AM

Quote
Oh, I definitely had the cycle frame jacked up - I guess I assumed that was a given?

I'm surprised that the front wheel didn't drop when you jacked the frame. Did you have both caps off at the same time? It won't drop unless you do. It could be the seals in your forks are a lot tighter than mine were.

No, I just had it so the weight was mostly off the front end but the wheel wasn't up in the air or anything.

Tretnine · « **Reply #21 on:** August 30, 2009, 02:57:18 PM »

I did some of the work in this post today, and my 550 is a different bike entirely. The performance of the front end is entirely different, all the way around much better, and it's such a significant performance increase for such a small amount of work, easy work, and the cost is next to nothing.

I shimmed my forks with some thing from tractor supply company. I don't remember what the actual name was, but it looked like a fat washer with a small interior diameter and a small hole drilled through the side wall. They were $2.29 each. The 1/2" size slid in relatively easily. I also measured the amount of fork oil going into the forks from the top with the springs out and forks compressed so that it was between 5 1/2 - 6" away from the top. Even my wife who was riding on the back said she noticed a difference.

I'm blown away, it really feels like a different bike. Next step is to try to get the old head bearings replaced with modern ones. Exciting!

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Author Topic: fork shims and oil weight? (Read 3884 times)