Author Topic: CB750 K1 rear fork (or rear swing arm) (Read 3784 times)

_mark · « **on:** November 06, 2015, 11:00:18 PM »

Hi guys. I have a CB750 K1.
Visually seems everything ok except for one thing that I denoted later: the rear fork seems to be to own to another motorcycle such as cb 750 k7-k8 or a CB 500; it is approximately 30-40 mm longer but its weldings, shapes, sections are the same. In few words is coming from another Honda model...

See the position of rear wheel and its proximity to mudguard and the inclination of dampers...

Can anyone that has a K1 tell me this measures

and tell me, if knows, that the rear fork is the same for series from k1 to k6 ? This is important for find another and correct fork...
Thanks a lot in advance

Airborne 82nd · « **Reply #1 on:** November 06, 2015, 11:15:33 PM »

That is your swing arm. The forks are up from.

Kevin D · « **Reply #2 on:** November 06, 2015, 11:34:22 PM »

Maybe you have a 102 link chain instead of 100. Your chain adjusters look to be way back. When I have a new chain (100 links) the axle is at the front of the slot and the tire is right up to the swing arm. Do you have a 48t rear sprocket?

_mark · « **Reply #3 on:** November 07, 2015, 12:18:07 AM »

Hi Kevin thanks for the reply . Chain adjusters is roughly in the middle but whether wheel is shifted forward or backward dampers are in my opinion too inclined.

Sprocket is 48 teeth.
When motorbike is on central kickstand, rear wheel is lifted roughly 30 mm from carpet and that is correct so may be something is wrong in the geometry of the bike...
I guess a later swing arm (from k6 to k7 the wheelbase has increased of 40mm may be increasing the lenght of swing arm) or may be a cb 500 swing arm.. only suppositions...
I don't understand...

754 · « **Reply #4 on:** November 07, 2015, 08:08:02 AM »

Your fender appears to be hanging down a bit at the back.
Your swingarm is 71-76, can tell by the bolt at tge back that holds the block in thecend of swingarm. Those years are all same length.
I believe the manual does refer to it as afork.

Tews19 · « **Reply #5 on:** November 07, 2015, 08:34:29 AM »

Lol, maybe it's just me but when I clicked on OP pictures on the bottom it has asian girl pictures below?

Kevin D · « **Reply #6 on:** November 07, 2015, 09:33:10 AM »

Quote

Your fender appears to be hanging down a bit at the back

and thats not a K1 tailight either, turnsigs been moved back too.
Sorry, won't get a chance to measure today.

Does the shock angle look much different than this?

_mark · « **Reply #7 on:** November 07, 2015, 10:32:27 AM »

Hi all and thanks for cooperation.
I called it "fork" because I did't know correct word is "swingarm" and in the parts manual is called "fork"

The set of rear lights should be ok because is, I think, is a version for Holland and German markets, also in the official part list is present ; see here another bike similar to mine:

@Kevin: I can't appreciate the difference ... not easy, we are talking about 30-40 mm ... but I'm afraid that the swing arm is to be too long..

754 · « **Reply #8 on:** November 07, 2015, 12:45:33 PM »

From center of swigarm pivot to end of actual swingarm , is approx 19 1/4 inches..
That is on a K4 and is the correct length for 69-76. K models.

_mark · « **Reply #9 on:** November 07, 2015, 03:00:25 PM »

Quote from: 754 on November 07, 2015, 12:45:33 PM

From center of swigarm pivot to end of actual swingarm , is approx 19 1/4 inches..
That is on a K4 and is the correct length for 69-76. K models.

I can' t measure now it's nigthtime here. But what about the distance between center of swingarm pivot and the center of dampers pivot ?(see A quote in the drawing I attached in the first message). thank you.

_mark · « **Reply #10 on:** November 08, 2015, 04:08:11 AM »

Quote from: 754 on November 07, 2015, 12:45:33 PM

From center of swigarm pivot to end of actual swingarm , is approx 19 1/4 inches..
That is on a K4 and is the correct length for 69-76. K models.

"end of actual swingarm" is this ?

if yes the length is correct...

754 · « **Reply #11 on:** November 08, 2015, 08:55:02 AM »

Yes, that is where i measured to.
Look back at your first pic.. The lower part of fender where it extends past the end of frame..
The straight part appears to be going downhill , but should be level, and that brings, he whole fender too close to the wheel.. I dont know if the inner is slid back or the rear is bent.

Kevin D · « **Reply #12 on:** November 08, 2015, 02:02:11 PM »

Okay mark, dimension A 15 5/8" 397mm
Sorry I didn't recognize the european market lighting.
My few years old, 100L chain, adjusters on the first mark.
Also measured shock inclination 3 3/8" 84mm from vertical

_mark · « **Reply #13 on:** November 08, 2015, 11:31:51 PM »

Quote from: Kevin D on November 08, 2015, 02:02:11 PM

Okay mark, dimension A 15 5/8" 397mm
Sorry I didn't recognize the european market lighting.
My few years old, 100L chain, adjusters on the first mark.
Also measured shock inclination 3 3/8" 84mm from vertical

Perfect thanks. I'll check today schock inclination.

So I have to understand where the fender is coming from. Onestly I like it more than the original one but I have to see if I don't risk to rasp the wheel on bumps or/with passenger aboard.

I highlighted the radius of fender and wheel on my bike and a normal one.

Kevin D · « **Reply #14 on:** November 09, 2015, 03:36:06 AM »

Another measurement, bike on centerstand
floor to upper shock mount 28 7/8" 733mm
floor to lowest tip of fender 23 1/8" 587mm
difference 5 3/4" 146mm

Also, fender mounting partsfiche shows two flat washers item 12, item 17, per mounting bolt item 13.
The larger flatwasher goes underneath the frame mount, at least, that's where it is on mine.
http://www.cmsnl.com/honda-cb750k1-four-netherlands_model14359/partslist/F22.html#results
A missing or misplaced flatwasher would affect the fender angle.

_mark · « **Reply #15 on:** November 09, 2015, 05:41:46 AM »

Thanks all I'll check the washer too.

See also the inclination of black body

_mark · « **Reply #16 on:** November 12, 2015, 08:00:48 AM »

Hi guys back on issue.

bike on centerstand
floor to upper shock mount 28 7/8" 733mm OK
floor to lowest tip of fender 23 1/8" 587mm 555mm
shock inclination 3 3/8" 84mm from vertical OK

I have some doubts over the transverse final beam someone can tell me if is reasonable this inclination compared to set square ?

the position of rubber wedge compared to hole. (rubber wedge is not matching the transverse beam and is located more in the front).

Under the beam there is only one metallic washer but the beam itself has one circoular black gaper (see the photo) or is plastic one.. I have to check deeper. Is the same for your bikes?

further, is the black plastic fender OVER the metallic one?

Set square alligned with end and planar with central transverse beam distance to center of bolts 203 mm circa

MCRider · « **Reply #17 on:** November 12, 2015, 08:12:08 AM »

"I called it "fork" because I did't know correct word is "swingarm" and in the parts manual is called "fork"".

Either are correct. Stateside, you'll get fewer raised eyebrows with "swingarm".

Kevin D · « **Reply #18 on:** November 15, 2015, 12:12:32 PM »

Yes, that rear frame looks more inclined than what I have, pic to follow later today.
(Picture 1)

7.75" 197mm from fender bolts centerline to edge of frame.
(Picture 6)

Seat pan rubber is 1" 25mm in front of hole.
Seat rubber hits rear frame hoop dead on center.
(Picture 2)

Fender mount washers look ok.
Plastic fender on top.
(Pictures 3 and 4)

Picture 5 That last frame tab looks like it is turned down a bit. Has your CB had a frame repair?

Have you tried loosening the fender bolts, lifting the rear edge, and retightening?

Nice day here, sunny and 63f, time to ride!

Kevin D · « **Reply #19 on:** November 15, 2015, 02:54:54 PM »

Pic as requested.

_mark · « **Reply #20 on:** November 16, 2015, 02:45:22 AM »

Hi Kevin thank You again for your precious informations and your commitment.

from today I'm away from motorbike for one month circa because I'm in a business trip (and previous days was too cold to work outside...)

By the way the difference between 203mm and 197 mm is roughly the space is missing to the rubber wedge to hit the frame of the fender in correct position.

Quote

Have you tried loosening the fender bolts, lifting the rear edge, and retightening?

Next steps I will try to do it or to charge the motorbike with two heavy weight fellows to understand if there is the potential contact of wheel on fender (I never switched on and run the motorbike yet but this another story...)
Another option is to use a couple of not planar washers to gain some of the lost inclination.

Quote

Picture 5 That last frame tab looks like it is turned down a bit. Has your CB had a frame repair?

Onestly I don't know ! I bought nowadays the bike and this in the past has jumped in the hands of many owners... What I can say is that the frame has been painted and each welding seems ok to the original except for the transverse beam where the welding aspect is much more irregular and "fat".
I analized many photos of other cb 750 k and the welding in that area is very thin and precise except for my bike and ... yours ! Did your bike has been modified too ?

Thanks for your help

Kevin D · « **Reply #21 on:** November 19, 2015, 07:43:39 PM »

The Honda frame welders get no points for style, irregular with spatters is typical, InMyHumbleOpinion.
There have been no modifications or repairs to my frame, I should know, I'm the original owner.

I'll get one more dimension, from floor to center of fender mount bolt, tomorrow, when the car is out of the garage.

29 1/4". 743mm

_mark · « **Reply #22 on:** January 08, 2016, 04:13:19 PM »

Hi guys. Works are going on...

Can anyone tell me what is the exact interax of the dampers ? are drawings somewhere ? thanks

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Author Topic: CB750 K1 rear fork (or rear swing arm) (Read 3784 times)