Swing arm pivot tube install - help?

[TheMonkey]

New bronze bushings are installed. Was very tight, but threaded rod did the trick, pulled bushings in tight.

The original pivot tube felt way too tight, and there was galling, so I ordered a new tube.

The new tube into new bushings felt real tight, but it barely started by hand so I greased up, whacked with rubber mallet until it just wouldn’t go anymore. About 2 inches in. I upped to a 3# maul hammer with wood block. About 1/4 inch more and now it’s just stuck.

If I can get it out and hone the bronze bushings, how tight should the fit be? Isn’t the pivot tube supposed to rotate in bronze bushings? As it is now, there’s no chance. Zero.

Thanks in advance for any help.

 

[gggGary]

Did the shaft fit the bushings before you pressed them in?
A tight to interference fit is not unusual, varies by bushing brand and (sorry) how perfectly clean the bores in the swing arm are, as you press in the brass the ID shrinks.
A good machine shop should be able to ream the bushings to a proper fit on the tube, it needs to have enough room for grease but not allow any wiggle.
Couple opinions on a similar set up from a machinist's forum.
"you will need .001-.003" running clearance between the bushing and shaft, generally speaking."
"Should have .0005-.0015" running clearance."
Some general installation info from the oilite company;

 

[member28833]

Hello from Vancouver.

The new tube into new bushings felt real tight, but it barely started by hand so I greased up, whacked with rubber mallet until it just wouldn’t go anymore. About 2 inches in.

Assuming the new pivot tube did pass a "fit check" in the bronze bushings? Its seems that there is likely a misalignment of the bushing bores causing even more "tightness" now.

Was very tight, but threaded rod did the trick, pulled bushings in tight.

So it may be best to completely disassemble the pivot tube and bushings to confirm those components still fit each other. A heat gun on the swingarm ends may help get the bushings back out?
If you do get lucky by knocking the pivot tube back out and that does fit from the other end perhaps? Hope those bushing bores are still round so you can have a 2nd chance at it.
-R

 

[member28833]

"Should have .0005-.0015" running clearance."

That does seem very tight. Those tolerances would require very good alignment.

 

[gggGary]

No machinist am I, but an adjustable reamer in competent hands should get both a correct ID and proper alignment for both sides?

 

[Jim]

Since the pivot tube is stuck in one bushing only, it doesn't point to a misalignment problem. I found out when I hacked a swingarm for the speed twin that the tube Yamaha used (to make the swingarm) is actually a pretty beefy machined part. So unless it's damaged (bent), there shouldn't be any misalignment issues. Use a hardwood dowel to whack the pivot tube back out. It's plain mild steel and will mushroom pretty easy if you drive it out with a metal drift... don't ask how I know...
Like Gary sez, an adjustable ream will do the trick. There's also a backyard hackers way
Take a long 1/4" bolt, slot one end and cut the head off the other end. Slide a red scotchbrite piece into the slot and commence to honing. It'll be slow going, but that's good...lessons the chance of taking too much out of the bushing. Work it in and out for 'bout 30 sec and test fit. Rinse and repeat 'till you get a snug, sliding fit.

 

[member28833]

. About 2 inches in.

I see now stuck in one bushing. Well, thats better

 

[TheMonkey]

Thanks guys.
I’ll work on an extraction and massage the bushings. I’d imagine a brake cylinder hone would do the trick?

 

[Jim]

Thanks guys.
I’ll work on an extraction and massage the bushings. I’d imagine a brake cylinder hone would do the trick?

The bronze tends to clog the stones.... but yeah, it'll work. just use tons of light machine oil to help keep 'em clean.

 

[gggGary]

....................... the tube Yamaha used (to make the swingarm) is actually a pretty beefy machined part. So unless it's damaged (bent), there shouldn't be any misalignment issues................
View attachment 173349

Depends on if the machining was done before or after the welding eh?
You might be surprised at the answer.

 

[Jim]

Funny that.... been sittin' here ponderin' how they pulled it off. The machining was definitely done before welding.... yet I never heard of a case of 'em being misaligned. My guess is they reamed or line bored it to spec. after it was welded.

 

[gggGary]

Funny that.... been sittin' here ponderin' how they pulled it off. The machining was definitely done before welding.... yet I never heard of a case of 'em being misaligned. My guess is they reamed or line bored it to spec. after it was welded.

Or just used "self aligning" plastic bushings..............

 

[Jim]

Or just used "self aligning" plastic bushings..............

You sayin' you seen 'em misaligned?
Thinkin' as a production engineer... machined tube + welding on one side only = bent tube.... equals... problem.
Solution in production environment.... slap it in a jig, run a shaft through it with cutters on both ends... remove shaft... check with go/no go gauge... send it down the line. 1 person could easily keep up with 50-100 frame jigs. Sounds low cost to me. Maybe the cheap plastic was just icing on the profit cake.

 

[TheMonkey]

Extraction went fine,

The pivot tube was surprisingly straight and round. Consistently 21.91mm

I set a telescoping bore gauge to that same amount and plunged the bushings. They were definitely tight in some spots. I’ll give the bushings a kiss in the morning and report back, hopefully good news. Thx

 

[TheMonkey]

The brake hone worked a treat. It still felt pretty tight but it greased up fine and it took about 38 ft lb squeeze on the bolt before it slowly dropped on its own which I believe is in spec.

Note to anyone that may try the hone... be wary of too deep a plunge, the hone can go past bushing and expand and get stuck.

 

[gggGary]

Note to anyone that may try the hone... be wary of too deep a plunge, the hone can go past bushing and expand and get stuck.

Hmm, that just an educated guess?

did you use flood coolant for the honing?

 

[TheMonkey]

Hmm, that just an educated guess?

did you use flood coolant for the honing?

It was a close call lol. The stones start to go diagonal on an edge and can feel it begin to pull. Fortunately, I recognized the risk before it bit me. Had to smile, I’ve learned a lot the hard way.

I just used some thin cutting oil. It didn’t take many turns, stones never really had a chance to choke up.