XJ650 fork tubes

Hi I am restoring a 1980 XJ650 Seca. I have started on the forks now and i
have found them to be no longer servicable. The end caps are hopelessly
rusted in and they have deep rust scores where the seals have to ride up and
down. I am having trouble getting new XJ650 fork tubes. Was wondering if
any other XJ forks complete will fit in the XJ650. I want to keep using the front wheel that the bike now has.
From Bob
A week or so later. I have pulled the rusted fork plugs out. I had to end up by drilling a hole right through the 2 plugs and tapping a thread into the
holes to take a 3/8NF bolt. I then put a big thick washer on top of the fork
tube. I then put the bolt through the washer and started screwing it into the
stuck plug. As the bolt screwed into the plug it started to pull up on it. When
I could not screw it up any tighter I hit the top of the bolt that I had been screwing with a hammer and hey presto the whole lot came flying out under the pressure
of the fork spring. I was very surprised and very happy. If you do this wear safety gear. Gloves and glasses. Only use this method of plug removal if you are doing a complete fork rebuild because steel drillings go down inside the fork tubes and have to be cleaned out.

 

Time to see THE MAN.
http://xjbikes.com/Forums/viewtopic/t=14561.html
If you don't see what you need here, or shipping to OZ is impractical, shoot Chacal a pm. He can at least tell you what to look for, and probably where to find it.

 

I have bought 2 XJ750 forks complete and I am hoping to fit them up when they arrive. It seems that most everything will fit up from the XJ650 forks,
wheel axel brake disks and speedo drive.
According to my info search I will have to buy a left and right brake caliper
as the XJ650 ones bolt up in a diffrerent position on the forks.

 

They not only bolt in a different position, they're a completely different style of caliper.

You may have a rotor-offset spacing issue; I'm not sure. But you very well may need 750 discs too.

 

Hi bigfitz52. I have rang the wrecker that I bought the XJ750 forks from and they said to return them if they do not fit. I have found a place over here in
Australia that fully refurbishes pitted fork tubes back to there origional specs.
Rad Hardchrome Brisbane Australia. 150 dollars for each tube. The conversion from 650 to 750 forks has its problems. Not knowing what will fit up. The air system, the anti dive, differences in the brakes etc. Thanks to all
the help that I have received from this XJ website. I have spent many hours
looking things up about this motorcycle and I would have been sunk without
this site. This is the last restoration area for this bike and once the forks are done I will be riding a fully restored 1980 XJ650 Seca Yamaha.

 

Well, the 1980 650 (4K0 model) is like the North American 650 Seca, and uses the same forking system.

The North American ("NA") XJ750 Maxim and 1981-83 XJ750 Seca models do not share the same forking systems. Also, be aware that what is described as a NA 1981-83 XJ750 Seca is the same as the rest-of-the-world "XJ750" model (there was no Maxim or Seca designation for overseas models, as there was only one "version", and that version was basically the same as the NA XJ750 Seca model from 1981-83). There is a 1984 XJ750 Seca model (750RL) that is really an XJ900 model frame, body, suspension (etc.), and it shares the same basic front suspension as the XJ900 models, which is completely different from all of the others mentioned above (for instance, it uses 37mm tubes).

And the 650 Seca and all the 750 Maxim and Seca models (except 1984 750RL models) all use the same size fork tubes (36mm OD), so they will fit up inside the tree brackets.

And the 650 Seca and all 750 Maxim and Seca models use the same front wheel (1.85 x 19"), so you're good to go there.

Those front wheels will accept either the 650 Seca or the 750 Maxim or 750 Seca style front disc brake rotors.

The 650 Seca models used a 10.5" (267mm) OD brake rotor, same as the 750 Maxim models. The 750 Seca models used the larger 11-.75" (298mm) rotors.

Of course, the brake calipers are different between all three models, and as best as I can tell, will not interchange with each other, due to mounting bolt spacing and placement on the fork tubes (which interacts with the size of the brake rotor, too.)

Since the wheel is the same size between all models, and all the rotors fit that wheel, then the prudent choice would be to secure the brake system (rotors, calipers) that corresponds with the FORK TUBES that you plan to use.

However, be aware that the 650 fork tubes secure the front axle directly underneath the lower tubes, whereas the 750 models (both Maxim and Seca) use a "leading axle" design, where the front axle is located forward of the fork tubes.

This change in axle placement can/will change the rake profile of the bike, and thus the steering/braking/handling characteristics of the bike, sometimes in a not-so-good way. The "tilt angle" of the steering headpipe on the frame, along with the length of the fork tubes, are designed to work with each other to provide a desired performance level from the front suspension system.

Just be aware of that.


And the first thing that I would do is to try and identify which actual model bike the forking system that you have purchased came off of (the VIN of the bike will tell that story, rather than the vague description from the wrecker of "it's a Yamaha 750".........). The knowledge of which forking system it actually is will provide you with a wealth of valuable information, both for now and in the future.


P.S. used fork tubes should also be checked for straightness (precise straightedge, run-out dial gauge, or roll them across a piece of glass), as well as for pitting.

 

Hi chacal. Thanks for all the info that you have given to me. It is exactly what I have been looking for. You and fitz have answered all of my questions
and I now have a clear direction as to where I will go with my fork problems.
I am going to refurbish the fork tubes that I now have for my XJ650 Seca.
I will get Rad Hardchrome Of Brisbane to do the job for me with
all the imperfections lathed out then hard chrome and relathed back to
origional specs. I have ordered 2 more plugs that go at the top of the fork
tubes with all there o rings circlips etc. I have ordered 2 new oil seals and
2 dust covers. Every thing else is ok. With all this new gear I should not
have any more trouble from the forks. I will send the XJ750 forks back for
a refund. Thank you for all your help this site is a god send. I only wish I
had have known about it when I started restoring the XJ650 eighteen months ago.