Measuring Triple Clamps for Twist

[pinholenz]

Reassembling forks, I have found that the Lower triple  clamps  do not line up with the upper pinch openings. One tube is nearly 1/4 inch out of alignment

I have used some fork tubes from a donor bike and found that one was slightly bent. This has been straightened by an engineering shop. Because the Lower Triple clamp was in better condition, I also used that from the donor bike. Can triple clamps be damaged?

I have pulled it all down again and now I want to compare both sets of Triple clamps to see if there is a twist in them. My plan is to  clamp the fork tubes in place on the lower triple, extending them to the height of the steering stem. Next I will carefully measure to see if I have equidistant triangles between the tubes and the steering stem at the top and bottom of the tubes.

Are there any other ways to work out if the steering head is aligned or not? Thanks.

[The Prophet of Doom]

Yikes !


Don't know the best way to do this, but best of luck.  With any luck it's the replaceable steering stem alignment rather than the head.

[dingleberry]

I would be inclined to put a straight edge on all parts to check for anything slightly bent and an engineer's square on the stem/bottom clamp. Install bottom clamp with bearings then see if that's square to the steering tube. 

[Ken Williams]

For your consideration:

To check fork tubes for straightness you can roll them on a flat surface.  To check an assembled fork leg for a bent upper tube, spin the upper tube with the lower tube stationary.  In either test, check for runout. 

To check the lower triple clamps, insert straight fork tubes or legs, tighten the pinch bolts and view from the side.  If the 2 sides are not parallel, the lowers are bent.  Next, assemble the upper tubes into the upper triple clamps.  With the lower pinch bolts sufficiently tight to keep the tubes from falling, grab both tubes and wiggle them around to eliminate any twist between the upper and lower triple clamps.  Then, tighten the lower and then upper pinch bolts.  Once again, view from the side and check for parallel tubes. 

[pinholenz]

Thanks for the advice;

Tubes appear straight with little runout. (The tube that I had straightened is to within 0.002" tolerance)
I have put the tubes in the lowers up to the height of the steering stem and clamped them. Next I measured the distance between each tube and the steering stem at the top and the bottom with a vernier caliper. These measurements were within 0.5mm of each other which I thought was acceptable.

First time around I assembled the steering column on its own and nipped it up tight. I discovered the misalignment when inserting the tubes.

Next time around I will have the top and bottom clamps gently in place while I tighten the steering head nuts to position the taper bearing on the steering shaft.  After that I will slacken the clamps, lower the tubes, give them a good wiggle, and see if they line up with the uppers.

I am wondering if my bearing outers were not seated properly? I hope its a simple mechanical fix and that the tests suggested are positive.

[fret not]

This stuff is difficult to see if it's only a little bit bent, much easier to detect if severely bent.  I used to write estimates for the wreck jobs at a dealership and learned from the insurance adjuster some quick and critical things to look for, one being the front end.  In this case you run your finger over the pinch gap on the lower tree, it should be level across the machined surface, and you can feel if it is out enough to make a difference in operation.  If you are unsure, take a straight edge and place it on that surface and see it it rocks.  Another obvious sign is any checked and flaking paint, but that is usually the result of a more severe deformation.

[The Prophet of Doom]

For your consideration:

To check fork tubes for straightness you can roll them on a flat surface.  To check an assembled fork leg for a bent upper tube, spin the upper tube with the lower tube stationary.  In either test, check for runout. 

To check the lower triple clamps, insert straight fork tubes or legs, tighten the pinch bolts and view from the side.  If the 2 sides are not parallel, the lowers are bent.  Next, assemble the upper tubes into the upper triple clamps.  With the lower pinch bolts sufficiently tight to keep the tubes from falling, grab both tubes and wiggle them around to eliminate any twist between the upper and lower triple clamps.  Then, tighten the lower and then upper pinch bolts.  Once again, view from the side and check for parallel tubes. 

If you don't have a certified flat surface laying the tubes against each other and run a feeler gauge between. Turn one 1/4 turn and repeat till you have measure each 1/4 against each 1/4.

I find it hard to judge straightness of forks by eye, but I dropped some 20mm plate across them and checked for wobble.  A piece of glass or perhaps even a decent quality ceramic tile would probably be close enough.

[pinholenz]

Problem solved. In the end it was clear that the triple clamp I was using was bent or twisted. There was no getting around the fact that the tubes just didn't want to line up without putting strain on them.

I went to the junk pile and dug out the other triple clamp, cleaned it up and everything came together smoothly and snugly. Phew. Thanks for the advice and measuring tips.