ST1100 - Determine If Front Forks/Triple Tree Bent

[DannoXYZ]

You could that without the dial indicators or anything. Remove the fork assembled, clamp the lower end down with C clamps or wood clamps to a solid work table along the table top not off the edge and rotate the tube in the lower. Watch for up and down on the little end as you rotate. If it is bent any it will move up off the table farther. if it is straight the tube will not go up or down.

This is assuming fork bushings aren’t worn. Straight fork tubes with worn bushings will show wobble.

String/straight-edge test won’t show that both fork tubes are bent straight backwards by 100mm on both sides in frontal impact because sides of tyres will still be parallel. Wheelbase will just have been shortened by 100mm.

Ultimately measuring individual pieces of fork assembly is sure way to determine how bent they are. V-block for tubes and dial indicator to measure actual run-out amount. Can bend back minor damage with C-clamp.


For larger amounts of damage on impossible-to-replace tubes, use sturdier arrangement.



Due to high strength of these tubes, large amounts of bending needed to reverse damage.



Once confirmed that both tubes are straight, they can be used as guides to gauge alignment of upper & lower triple-T clamps (without sliders). Better than that MotionPro tool is large piece of plate glass. About 30cm tall and wide enough to cover both fork tubes. Place it over tubes near bottom tips and verify that contact is even on both tubes. If triple clamps aren’t aligned, glass will wobble and only touch in 2 spots.

 

[John OoSTerhuis]

Minor point: what is a fork ’blade’? Thanks.

John

 

[DannoXYZ]

Minor point: what is a fork ’blade’? Thanks.

John

Sorry, "tube". I was thinking of swords and scabbards.

 

[motornut]

Try to loosen the fork clamps without removing the wheel assembly and slide the forks up and down to see if they bind in the triple tree, keep an I on the tire to see if it stays in the middle when sliding up and down it will move a bit. Pull the wheel and slide the forks up and down and rotate see if they bind in the tree. Check the axle bolt to see if it slides easily through to bore at different levels.
Then Drain the tube and see if they bind during the stroke, the lathe method works best as stated above. I have used this method when rebuilding hydraulic rams and it is accurate. Don't be surprised by a small amount of bend, measure at ends and middle to check mounting on the lathe. Most machine shops will let you use your lathe if you grovel or beg or suck up to them. It is amazing what you can get by complimenting people.
It is a good time to put fork seal any way. Plus if it is on the lathe you can polish them too.
With the larger forks today you have to be really hard on them to bend them, and your probably fine. If you laid it down the forks are probably the last thing to worry about. The old forks when I started riding used to wind up and the swingarm would twist, and that was with normal.
If I duplicate anybody's info, i am sorry, it is because great minds think alike.
IGOFAR has a excellent way to align the forks which are probably better than my long winded BS. I am sure it is out there somewhere.

 

[Ron]

A quick check for the lower part of the fork. Take of wheel and front fender. Use a 2' or so level or carpenters square to check straightness. Mark the fork with a sharpie in 5-6 places around the fork and check at the marks. Worry about straightening it then.

While you're there maybe check for play in the fork bushing.

I'll be surprised if it is bent. The cowl stay is probably scrap. A new one supposedly available from mother Honda for a tad over $200. That's if Uncle Phil's supply house doesn't have a non-ABS one in stock.

 

[Uncle Phil]

Well, I'm simple feller and after noodling it around for a while I came up with a simple solution.
I did not relish removing the forks if I didn't need to as I have done that several times.
I had good straight strip of .100 aluminum that I thought would work as 'template' straight edge.
I laid it edgewise on a glass countertop and it was straight (no gaps).
Then I laid it along a 4 foot carpenter's level and it was straight (no gaps).
So I had confidence the 'template' was straight (at least to my satisfaction).
So I cut out a couple of notches in the edge that would allow the piece to fit over the places where the triple tree held the forks.
If they were bent, it would probably be at the triple tree and/or at the lowers.
That way I could move the strip all the way around the forks to see if there was any deflection in the front, back, sides, etc.
The fork tubes and the edge of the 'template' line up perfectly below and above the triple tree clamps.
Running it up from the bottoms of the fork, there is no deflection there.
They move up and down fine into the lowers.
So I am satisfied at this point that the forks are straight as they ever were and the headstock appears to be straight also.
Once I was able to remove a bunch of stuff, it appears the fairing stay/bodywork absorbed the brunt of the crash.
So now I am confident that I can get RedBird back on the road at some point.
Thanks for all of your input on this and I hope none of you have to go through this exercise!

 

[DannoXYZ]

Woohoo!!!

 

[motornut]

Works for me! loosening one fork at a time and rotating it in each triple clamp will work okay to, it will bind when trying to pass over opposing fork alignment. ( Thought of this when I went to sleep last night)

 

[SMSW]

Phil, string is easy to use to check the side to side alignment of of the front and back wheels. Of course you can use a straight edge though a single one will require less fussing around than several short ones. One fly in the ointment is the center stand - it is usually in the way. String can be threaded under the stand and between the legs. If you can hold the bike upright without the center stand, any straightedge will work. Maybe try a laser pointer and white card?