Topic: CLUNK from front end cb750k5

[alacrity]

I put this together from parts that came in several bins and from other parts I sourced here and via Facebook groups.  Everything in the forks looked right, but my fear is that I have a bad mix of old style and newer style fork internals. The upper tubes and springs  are new (from race tech) and the measurements of those are all good as per stock.

I cannot imagine that I omitted the top out springs. I mean I guess it’s possible but these are prob the 20th set I have done and I had it all laid out and measured before assembly.  Maybe one of the damper tubes is a mismatch for that spring? Maybe something else? Forks work great on compression stroke and the bike rides nicely. It’s just that when it unloads, it makes an awful clunk. In the garage you can see the wheel jump when making this happen.

The clunk isn’t coming from the brake caliper (I disconnected/removed it and there was no change).

I don’t think it’s coming from the assembled and properly torqued front wheel.  I did however notice some scoring and minor galling inside the axle collar (spacer) but given that (functionally)it’s really just along for the ride, and that its length along the axle shaft is as new, a little extra play there shouldn’t matter since it can’t move once it is squeezed against the inner bearing race to the tune of 46 lb.ft torque. Right?

I tried adding a bit more fluid to see if that would slow/calm the rebound circuit.  I am using 15 weight fork oil as I always prefer how that feels.  It didn’t help, and now I don’t have enough air gap per specs, so I might pull that back out.

Open to suggestions.   Thanks in advance and I’ll send a gift to whomever helps me solve this so I can sell the bike.

[SuperDave]

Have you checked your steering stem bearing nut? This will cause a clunk if the bearings are loose.

[david 750f]

Check that the front axle nut is torqued properly.

[alacrity]

I wonder what helpful suggestion you would have if you read my post first.

Check that the front axle nut is torqued properly.

[newday777]

As Dave said, loose steering bearings can cause a clunk. Do you have the round ball bearings in there (stock)? New bearings and races or replacement tapered bearings? Properly torqued with a torque wrench and castle nut socket? Torquing without a torque wrench doesn't always work well.
Old round ball bearings and races most often have dents in the races that give a loose point in the straight ahead position from hitting hard bumps(normal riding position as we lean in to the corners without moving the steering much). The dents leave a loose torque point and you can feel the 'notch' slowly moving the bars back and forth with the front wheel off the ground.

Did you put in new piston rings, #10, when you assembled the forks?

The other possible point would be egg shaped lower fork legs. Did you inspect the leg bores carefully for different sheen in the bores or measure them for out of spec with an internal bore micrometer? I've seen egg shaped legs on goldwings I've worked on where I learned from a suspension specialist.

[alacrity]

Is my original post not visible to all?

[Alan F.]

It's visible.

If it were me I'd tear them down again and figure it out rather than speculate.

[alacrity]

<<Did you put in new piston rings, #10, when you assembled the forks?>>

I did not.  They seemed to be ok/good fit. Not sure what the tolerance limit for this would be. I guess I can try to find a set of new ones and rebuild the forks again.

<<The other possible point would be egg shaped lower fork legs. Did you inspect the leg bores carefully for different sheen in the bores or measure them for out of spec with an internal bore micrometer? I've seen egg shaped legs on goldwings I've worked on where I learned from a suspension specialist.>>

I don’t have a small enough bore micrometer with a long enough extension to reach down into fork legs.  The only one I have is for engine cylinders etc.  It’s a very specialized tool… 😕 also these lower legs came off a bike with 19,000 miles on it.  Seems (at best) unlikely there could have been catastrophic egging-out with such limited use.  I’ve rebuilt fork sets from donor bikes with 4x that mileage and they were totally fine

[alacrity]

It's visible.

If it were me I'd tear them down again and figure it out rather than speculate.

Yeah…that’s prob what I am gonna have to do.  Thanks. I was posting this in the hope that I could have an “ah HA” moment and know exactly which parts to order so I can disassemble, R&R, reassemble in one pass.

[newday777]

And..... What about the steering bearings???

[Alan F.]

And..... What about the steering bearings???

That would be the simplest cause of a clunking sound in the front end, have you checked to see if they're loose? Raise front wheel.....