Topic: sohc 750 forks interchangability question

[galaxian]

Ok I did a search but did not come up with anything concrete.
Are all cb750 forks compatible or not? Are they all 35mm tubes? If they arent interchangable which years are?

[Geeto67]

depends on what part of the fork and what years you are talking about.  I do know that 1977-1978 cb750 f fork lowers are different and will not work with other year's brake systems. I think the cb750f forks are a little stiffer from the factory than K bikes and might be a little taller too (by a very small amount). AS far as I know all fork uppers interchange.

[galaxian]

Are all upper tubes 35mm?

Can You swap a "K" fork onto any other "k" bike?

[ride_a_honda]

Galaxian,

I too have a 750K2 and the "upper" tube diameter is 37mm. This being said, newer 750's (F models) I believe had 35mm.
I had severe corrosion on the top part of the tubes (between triple clamps) and had been searching for the past couple of years for replacement. I was about to purchase from "Frank's Forks" out of Chicago (I think...I can confirm if you like) when I came across a really good looking set on eBay. I won the item and when it arrived, I found out they were not from a 750 as advertised, but from a Gold Wing (unknown vintage). The good part to all this is that they are 37mm and fit like a glove. They can be used with your original lower forks, although you need some "minor" machining to allow the use of the "bushings and sliders". I can provide photos if you would like.

Cheers,
Lou

[galaxian]

Lou,

Thanks for the info but mine measure 35mm not 37mm as you stated. So once again I am a bit confused as to the tube diameters for different years.

Galaxian

[ride_a_honda]

Galaxian,

when your forks are mounted in the triple clamps, is there gap at the pinch bolt? There should be a small spacer in the gap (resembles a washer, but is a specific item) when the bolt is torqued.  If that gap is completely closed, due to a smaller diameter fork tube, you might compromise the triple clamp as they are known to break at that location.

I have the parts breakdown and can scan it for you if you wish.

Lou.

[galaxian]

IF you could that would be great! Since I dont think I have the piece you describe.

[frostypuck]

Easy way to check is to find a place that sells the fork seals, and any bikes that take the seals same as yours will fit. JC Whitney I think has a chart. You may find Kawasaki fork tubes will interchange.
Later,
Chris in Boston

[ride_a_honda]

Hello again Galaxian,

I must apologize, the correct size for the fork tubes IS 35mm. I was at work when I responded to your post and figured I had better ensure what I was saying was correct. WELL... ...it wasn't. I borrowed a digital Vernier Caliper and set it to Metric, measured and the result is 35mm. Sorry for the confusion. To ensure I had not purchased the wrong tubes, I measure all 3 other sets I have. Yes, all are 35mm. (I suspect that the 37mm thing came about when I tried to "eyeball" the measurement using a ruler")

Let me take a photo of my fork tubes, and I'll scan that page for you and post it later on today.

OK....I'm back....with photos. You'll find below some photos of my fork set up. First up will be the "parts" page from the Honda Micro-fiche that shows the "spacer" washer item number 14. It is required to maintain a good gap in the "top" triple clamp only and to prevent it from breaking. (bottom doesn't have them) Next up will be photos of my re-built fork tubes using what I thought were Gold Wing tubes. (am now starting to think they are from a 750F) I had to have a machinist cut a couple of grooves at the bottom for the retaining clips. (note the one and only hole) This will allow me to use the original fork lowers as they have a much larger diameter bore. (750F / Gold Wing fork lowers were the same size as the upper tube)  As I understand, the damping is much better in the newer forks anyways. The next photo shows my old tubes and the holes. There were many more holes than on the newer tubes. Makes for stiffer damping.

If you need new tubes, there is a place in Illinois that makes them. They claim that they are exact reproductions and have a much harder chrome.
They are Frank's Maintenance and Engineering Inc, 945 Pitner, Evanston, Illinois, 60202 Ph (847) 869-6792 (known as Frank's Forks) The price in 2004 for a "set" of Honda tubes (stock to 6" over) was $199 U.S. + freight  ($22) and if you want over +6" then it is an additional $5 per 2". They have been doing this type of work since 1966.

Enjoy the photos and e-mail me if you have any questions.

Sorry for making this post so  long, it is actually 2 in 1 as I returned to edit it.

Cheers,
Lou.

[galaxian]

Thanks for the pics and info. I didnt want to spend $200 on tubes but may give it a go.

[Clyde]

Firstly all 750 forks are 35mm, but there are differences internally and also with the caliper and caliper hanger
The forks for the K0, K1 and early K2 are interchangeable. They use an internal bush which is replaceable as per the picture above and they have a detachable piston.  In these early forks it is difficult to pull out the tube as you have to pull out the seal at the same time.
The caliper hanger used on the early forks is commonally called the 'C' version.
The later K3-K6 forks do not have the bush or piston and the tube runs in the aluminium lower leg. When you remove the tube it comes out easy once the allen bolt at the bottom is undone-without damaging the seal. At the same time they changed the caliper hanger (now known as the 'T' Version), but not the caliper. The caliper hangers are not interchangeable, and only can be used with the matching fork leg. As you can appreciate the tube can only be used with the later forks
For the F, F1 they lengthened the lower leg and changed the caliper and hanger. However the K3-K6 hanger and caliper will work OK, but you must use both together.
I am not 100% sure about the K7/K8 except they use the F/F1 caliper and hanger. The tubes are the same, but they may be a bit longer.
Terry is the expert on F2 but I believe the fork leg lower are quite different, but the tubes are interchangeable with the post 1972 forks.
I have used F1 fork legs with K6 tubes with no problem, and have used K6 lowers with F1 tubes- no problem providing you use the correct hanger/caliper combination ie F1 hanger with F1 caliper
Having re read this it sounds confusing- hope it helps

[dusterdude]

speaking of forks,can someone guide me on how to remove the tube from the leg on the bike to replace seals on a k1,or do i need to remove the front end from the bike and then do it.

[Richard]

Replacing seals on K1 forks should be able to done with stanchions still mounted in triple clamps. I removed the stanchion as lower leg as one unit when replacing mine however due to a fractured upper triple calmp requiring welding. As it is only 5 min extra work to remove the whole unit I would recomend this as it allows you to give the parts a good clean up on the bench top.
Removing the seals invloves first emptying the fork oil  - out of lower drain screw on leg base - or more easily by pouring out of top of stanchion when removed from triple clamps). At this time the fork spring can be pulled out of the top of the tube. You then need to remove the large internal circlip under the gaitor on top of the lower leg. This will allow you to then use the fork tube as a type of puller to hammer out the seal. The entire stanchion can then be removed. Use an old seal to drive new seal into place or a suitable sized piece of tube. Remember stanchion has to be back in fork leg before replacing seal.
Long answer to your post  - I presume all of the above could be done with stanchion still mounted in triple clamp. Good Luck.