Author Topic: 1973 CB750K3: Doing a front fork rebuild- what parts should I order? (Read 12842 times)

GreenHorn · « **on:** May 09, 2010, 08:53:43 PM »

I'm planning on doing a rebuild on my front forks this weekend on my CB750K3. I'm working quite a distance aways from the shop during the week, so the only time I have to work on the bike is when I'm home on the weekends. That said, I'm planning on ordering parts by Tuesday and would like to know what typically needs to be replaced. Assume the forks haven't been opened up since the intial assembly, no major damage- just a leaking seal, and I'm not using the gators and healdlight ears.

Here are the parts I'm planning on ordering:
51437 329 010 Ring, Piston
51622 292 010 Rub, Fr. Fork Cover
90543 273 000 Gasket, FR.
91255 KBH 003 Oil Seal (35x48x11)
94608 50000 O Ring (23x2.

Hopefully I don't open up a can of rust...

grumpy · « **Reply #1 on:** May 09, 2010, 10:06:01 PM »

Beer?

754 · « **Reply #2 on:** May 09, 2010, 10:14:32 PM »

Fork oil & seals will usually do it.

The copper washers on damper rods can be annealed.. if you cant get them

Johnie · « **Reply #3 on:** May 10, 2010, 05:36:15 AM »

Make sure you have some carb cleaner and I use a long shotgun cleaning rod to get all the crap out of the bottom of the lower tube. No sense in putting clean fork oil in there unless you clean the old gunk out of there. I have only replaced the seals and never had to replace any O rings, pistons, etc.

ekpent · « **Reply #4 on:** May 10, 2010, 05:39:05 AM »

Don't forget some decent snap ring pliers.I pry the old ones out with a large flat tire iron and a little block of wood to not damage the aluminum.Also the bolt at the bottom of the forks is a hex head,forgot the size,and have a broom handle to get the bolt out after you loosen it.

754 · « **Reply #5 on:** May 10, 2010, 08:28:19 AM »

I poke a couples small holes in metal part of seal, 180 degrees apart..using a drill or sharp awl..

Then screw in a couple screws and use claw hammer, and wood block to pull seals..never leaves marks..

GreenHorn · « **Reply #6 on:** May 10, 2010, 04:30:45 PM »

(I forgot to mention the beer) Thanks everyone- I'm sure it's going to get ugly.

Old Scrambler · « **Reply #7 on:** May 10, 2010, 05:03:34 PM »

Good so far but you will need a large ring of some kind to help drive the new seals home. Your forks will take 150 to 155cc of fresh ATF. Then you will enjoy the beer.

ksmith0034 · « **Reply #8 on:** May 10, 2010, 05:21:58 PM »

+1 on the broom handle. Tap it down in there to hold the innards from spinning, then loosen the hex on the bottom. You may have one or both just spin even with using a broom handle - in which case you will need to us an impact to break the hex free. If you are pulling the forks off completely you might as well replace the springs with progressive. Putting the top cap back on by yourself can be a bugger. Here's how I did mine: vice, cargo strap, and turned the upper tube to screw it onto the cap.

nancy · « **Reply #9 on:** May 10, 2010, 06:10:25 PM »

Hey - KSSMITH,..hope nobody lives above your garage...would've been real messy iof that top cap had've gone off..must remember your technique - I have to address new springs soon.

754 · « **Reply #10 on:** May 10, 2010, 07:37:09 PM »

Its way easier to get the nut on by clamping it in a triple tree, or padded vise.....use a socket, press down and turn..

Pounding the seal, you can use your old seal...do it with tube out, its a 73..

ekpent · « **Reply #11 on:** May 10, 2010, 09:07:02 PM »

Just a note: After I pull a drained fork on an older bike I usaully have to put the leg in a soft jaw vise to break that Allen bolt loose on the bottom. They can be tough at first,try to not to snap it, or round it out or "GIT" OUT THE DRILL"before the broom handle comes in.Get the right tools.

Johnie · « **Reply #12 on:** May 11, 2010, 04:48:14 AM »

Quote from: ekpent on May 10, 2010, 09:07:02 PM

Just a note: After I pull a drained fork on an older bike I usaully have to put the leg in a soft jaw vise to break that Allen bolt loose on the bottom. They can be tough at first,try to not to snap it, or round it out or "GIT" OUT THE DRILL"before the broom handle comes in.Get the right tools.

Agreed...I have yet to use the broom handle trick. I always put the fork in the vise with a pad before you take the top bolt off that holds the large spring. The has been enough tension for me to get that lower allen bolt out without spinning the guts.

Gears · « **Reply #13 on:** June 04, 2010, 07:00:43 PM »

I'm taking apart a pair of forks myself. I couldn't get the first one apart, and then felt like an idiot when found out there was a bolt on the bottom. XDD

When I did realize this mine came apart easily enough. I guess I got lucky. Now comes the fun part of cleaning everything. Whats a good way of cleaning up rust off the tubes?

Also, anybody know how you get that cartridge out of the bottom of the fork tube? Mine is the later style forks(like the disassembled one Johnie posted)

Johnie · « **Reply #14 on:** June 04, 2010, 07:31:43 PM »

That lower cartridge will come out once the lower bolt under the lower leg is out. But yours is probably stuck in there. Mine was stuck to but came out with some help. There is a lot of dirt and crap sticking it to the bottom of that leg.

Doctor_D · « **Reply #15 on:** June 04, 2010, 07:39:40 PM »

Didn't see it in your post, but while you've got the front end apart - get yourself some tapered steering stem bearings.

Gears · « **Reply #16 on:** June 05, 2010, 08:16:37 AM »

Quote from: Johnie on June 04, 2010, 07:31:43 PM

That lower cartridge will come out once the lower bolt under the lower leg is out. But yours is probably stuck in there. Mine was stuck to but came out with some help. There is a lot of dirt and crap sticking it to the bottom of that leg.

Johnie, how did you get your's out? By the way, are you talking about the fork tube or the lower case?

climbingaz · « **Reply #17 on:** June 05, 2010, 08:23:11 AM »

I gotta do this soon. Good info!

Tex · « **Reply #18 on:** June 05, 2010, 08:28:05 AM »

here is video off of youtube that is perfect has all the tools you need
it helped me out a bunch

Hinomaru · « **Reply #19 on:** June 05, 2010, 09:43:42 AM »

Progressive springs were mentioned earlier in the thread. I put a pair (part no: 11-1104) in my stock 750K4 to replace the original springs during my fork rebuild. They give a factory-like ride while reducing front end dive under hard braking.

Dennis Kirk and other aftermarket suppliers carry them.

http://www.denniskirk.com/jsp/product_catalog/Product.jsp;jsessionid=QWIYVEBUB0N4PLA0WTKSM4VMDK0NCIV0?store=&skuId=58321&mmy=

Progressive Part No. 11-1104 fits the following machines:

1975 Honda CB750F Super Sport
1976 Honda CB750F Super Sport
1977 Honda CB750F Super Sport
1978 Honda CB750F Super Sport
1979 Honda CB750F Super Sport
1980 Honda CB750F Super Sport
1969 Honda CB750K
1970 Honda CB750K
1971 Honda CB750K
1972 Honda CB750K
1973 Honda CB750K
1974 Honda CB750K
1975 Honda CB750K
1976 Honda CB750K
1977 Honda CB750K
1978 Honda CB750K
1979 Honda CB750K
1980 Honda CB750K
1981 Honda CB750K
1982 Honda CB750K

Gears · « **Reply #20 on:** June 05, 2010, 06:51:37 PM »

Has anyone tried using Race-Tech's cartridge inserts when rebuilding their forks?

jaguar · « **Reply #21 on:** June 05, 2010, 06:59:45 PM »

there are a few threads on them and the Mikes XS ones that are about $75
i have those.

some say you can run progressive springs and the cartridges some say that you cant
i plan to run both in my cb750F front end but its not on the road so i cant tell you if it worked well or not

Johnie · « **Reply #22 on:** June 05, 2010, 07:00:16 PM »

Quote from: Gears on June 05, 2010, 08:16:37 AM

Quote from: Johnie on June 04, 2010, 07:31:43 PM
That lower cartridge will come out once the lower bolt under the lower leg is out. But yours is probably stuck in there. Mine was stuck to but came out with some help. There is a lot of dirt and crap sticking it to the bottom of that leg.

Johnie, how did you get your's out? By the way, are you talking about the fork tube or the lower case?

I am talking about the lower fork tube or case as you call it. That allen bolt will thread into the cartridge you are trying to get out. You could squirt some PB Blaster in there to try to free it up. Or try screwing the bolt back in a bit and give it a few light taps. Maybe that will free it up.

Gears · « **Reply #23 on:** June 05, 2010, 07:20:14 PM »

Thanks Johnie. I looked and saw the cartridge at the bottom of the lower. I'll give it a shot with the PB Blaster and see if that gets it out.

But that creates another question. I can feel something inside the bottom of the fork tube. Seems like a seal or something. Does anyone have any idea what that is?

Johnie · « **Reply #24 on:** June 06, 2010, 07:02:34 AM »

Quote from: Gears on June 05, 2010, 07:20:14 PM

Thanks Johnie. I looked and saw the cartridge at the bottom of the lower. I'll give it a shot with the PB Blaster and see if that gets it out.

But that creates another question. I can feel something inside the bottom of the fork tube. Seems like a seal or something. Does anyone have any idea what that is?

Hmmmm...feel something in the bottom of the lower tube? No seals down there except the oil lock and pipe which is what the parts book calls them.
You can see them with a light from the top.

Gears · « **Reply #25 on:** June 06, 2010, 07:19:45 AM »

That could be it. It's a kind of ring in a groove. My honda service manual doesn't show them. I guess I need to get my hands on the parts book.

Luckily, I'm not going to replace the fork tubes this season, but I do plan to next winter, so good to know what I'll need for the new ones.

Johnie · « **Reply #26 on:** June 06, 2010, 09:01:13 AM »

If you look at the pic below part #17 is at the very bottom of the lower fork tube. That is the part the allen bolt screws into or through (I can not recall which). Part #19 inserts into the top of part #17. Those may be what you are seeing or hearing down there. Don't loose the copper washer at the bottom of the allen bolt. Click the pic to enlarge it...

Bob750 · « **Reply #27 on:** June 06, 2010, 05:25:53 PM »

Yeah, That's the oil lock. It's not threaded, just sits like a washer down there between the "Pipe, Lower" and the "Case." The Allen bolt goes through it and holds it tightly onto the Lower Pipe. It's very lightweight aluminum--low mass. I inverted my cases and vertically pounded them on 1" thick carpet in garage. A few blows, and "tink" there it was, ready for cleaning. Alternately you might poke at it through the bolt hole in the bottom...

Forgot to mention... look up Leak Proof Pro-Moly fork seals...

Gears · « **Reply #28 on:** June 09, 2010, 10:22:42 AM »

Okay guys, I have pictures for you.

So everything is disassembled. I did find the oil locks at the bottom of the lower tubes

This was the part I was talking about. These shots are of the bottom of the fork tube and its about 2" in. I can't seem to find it in any schematic for my K5. Anybody know what it is?

Bob750 · « **Reply #29 on:** June 09, 2010, 10:43:04 AM »

Quote from: Gears on June 09, 2010, 10:22:42 AM

This was the part I was talking about. These shots are of the bottom of the fork tube and its about 2" in. I can't seem to find it in any schematic for my K5. Anybody know what it is?

Here's a shot I took of the same internal structure. I think it's a secret or something... Dunno where to find info on it. No schematic I've seen shows it. I've found that the sleeve will turn a tiny bit, but not like it's threaded, I think it's pressed in during manufacture. I just ordered a new set of US made repro upper fork tubes here that I'm waiting to be delivered, well because my tubes were crap. (See second photo.)

Gears · « **Reply #30 on:** June 09, 2010, 10:48:32 AM »

Yeah, that's what I'm curious about. As you can see, my forks are rusty as hell up around the triple trees(damn headlight ears), and I want to replace them, but I'm not sure if I'd have to order that piece or not.

I'm going to wait until next season to replace my forks, but let me know how those new ones turn out for you Bob750.

squeakywheelz · « **Reply #31 on:** July 06, 2010, 03:53:00 PM »

A month late, but for what it's worth - just received a replacement set of fork tubes from cycle-x and that little internal lip you point out has already been pressed in. As I don't see a good way to remove it from the old tube, I can only assume that it is pressed in and not readily serviceable. Trying to recall what sits under it - holds the smaller rebound spring in place?

Bob750 · « **Reply #32 on:** July 06, 2010, 04:17:42 PM »

Here are some pics of the fork tubes I received from TAS Classic Motorsports. They come from Frank's.

Bob750 · « **Reply #33 on:** July 06, 2010, 04:24:58 PM »

More pics. Notice that in one of the images I had installed the forks without the boots and boot rings. When I went to pull them so that I could slide the boots on, I noticed that I also had them mixed up left to right. It's all fixed now of course. the fender and brake hardware would have been difficult to reinstall don't you think? Heh.

rbirkhan · « **Reply #34 on:** July 06, 2010, 05:13:55 PM »

Really great info im about to install cycleX tubes. I know this is off topic but its related where is everyone getting new fork gators? Also dont forget the fork tripple tree d shaped spacer washers. I didnt see it in the fork rebuild video and can ruin your day fast.

Gears · « **Reply #35 on:** July 06, 2010, 06:08:38 PM »

Quote from: squeakywheelz on July 06, 2010, 03:53:00 PM

A month late, but for what it's worth - just received a replacement set of fork tubes from cycle-x and that little internal lip you point out has already been pressed in. As I don't see a good way to remove it from the old tube, I can only assume that it is pressed in and not readily serviceable. Trying to recall what sits under it - holds the smaller rebound spring in place?

Great. That's one mystery solved.

Bob750 · « **Reply #36 on:** July 06, 2010, 07:15:45 PM »

Quote from: rbirkhan on July 06, 2010, 05:13:55 PM

Really great info im about to install cycleX tubes. I know this is off topic but its related where is everyone getting new fork gators? Also dont forget the fork tripple tree d shaped spacer washers. I didnt see it in the fork rebuild video and can ruin your day fast.

Gators aka Front Fork Boot, schematic part #17: http://www.bikebandit.com/houseofmotorcycles/1974-honda-motorcycle-cb750k4-front-fork/o/m9235sch398553
Spacer, schematic part #9: (not available, but you could cut or grind a washer): http://www.bikebandit.com/houseofmotorcycles/1974-honda-motorcycle-cb750k4-handlebar-fork-top-bridge/o/m9235sch397875

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Author Topic: 1973 CB750K3: Doing a front fork rebuild- what parts should I order? (Read 12842 times)

Hinomaru