Question for you machinists

[canuck750]

I took my 1978 Moto Morini out for its first spin around the block and there is an ugly wobble in the rear end, I checked front and back air pressure, down a bit but not enough to be the cause, back on the hoist and up on the centre stand. The swing arm bushes feel loose, I tightened up the swing arm but, not loose and tightening it made no difference.  Shock mounts good, tire is new, rim was professionally balanced.

Ok to the point, I dropped the rear wheel and pulled the swing arm off, the swing arm axle is true and it was not corroded nor did appear to be worn when I assembled it.... but, and I should have taken note of this at the time, but the bushings are worn, badly.   

I have a second used swing arm and axle and its just as bad or worse. The bushings are steel, I am measuring the inside at over 18mmm at least 0.33 mm of clearance / slop.

I have a couple lengths of bronze rod, will need to turn down to the correct diameter and trim the length, my issue is getting the ID correct. Axle measure 17.67mm, I have a 16.8mm and a 18mm reamer and an adjustable hand reamer.

Should I try the adjustable hand reamer to get as close to 17.67mm and what would you recommend I bore the ID to?

Would an inside small boring bar be an acceptable way to get the ID or is the hand reamer the better option? I know I have to get this very accurate just not sure what the clearance should be?

[RinkRat II]

  I would think using the boring bar to get you close and then hand ream to .0015 to.002 thou for clearance if that is Oilite bronze. If not  .002+ with really good waterproof grease  or  modify for a zerk fitting  and grease passage. My $.02

           Paul B

[pehayes]

Before you disassembled, did you rotate and examine the tire itself?  Perhaps the wheel is running true but the tire is not bead seated equally???

Also, think back on the wobble feel.  Was it cyclic and repetitive?  Or was it something random and varying?

Trying to lock in if it is a wheel issue or a swingarm issue.

Patrick Hayes
Fremont CA

[hauto]

Maybe I'm not seeing this correctly,but where is the rotation clearance.Bushing ID or OD. Right now when you tighten your axle everything is locked up. Bushings tight to frame members and the swing arm would rotate on the bushing OD. Usually the swing arm would have  pressed in needle bearings and then a hardened bushing would be locked solid when the axle is tightened.

[canuck750]

Before you disassembled, did you rotate and examine the tire itself?  Perhaps the wheel is running true but the tire is not bead seated equally???

Also, think back on the wobble feel.  Was it cyclic and repetitive?  Or was it something random and varying?

Trying to lock in if it is a wheel issue or a swingarm issue.

Patrick Hayes
Fremont CA

Hi Patrick

The wobble was erratic, seemed to be a side to side, not alwayys present but at low speed, turning it was quite pronounced. I spun the wheel but did not see anything off.

[Groover]

Warped rotor?

[canuck750]

Maybe I'm not seeing this correctly,but where is the rotation clearance.Bushing ID or OD. Right now when you tighten your axle everything is locked up. Bushings tight to frame members and the swing arm would rotate on the bushing OD. Usually the swing arm would have  pressed in needle bearings and then a hardened bushing would be locked solid when the axle is tightened.

It is the inside diamter of the pressed in steel bushings that is too large, difference between bushiung I.D. and the swing arm axle O.D. is about 0.33 mm

I would have thought taht the way the swing arm is supported in the Moto Morini frame, the swing arm axle being torqued up real tight that there would be very litle ability for the swing arm to move about the swing arm pivot but when I had the bike up on th elift and the wheel off, shocks off I could get some wiggle side to side out of the swin arm / frame.

I am assuming the bushing to swing arm axle clearance is way too large. I would have thought something in the ranfe of 0.03 ~ 0.10 max is in order?

[canuck750]

Warped rotor?

Rotors are brand new, new wheel bearings, cast alloy rims are straight

How much play in the swing arm side to side is to much?

[Mike Tashjian]

I use the plain bearing handbook for sizing bushing which usually says make your bushing a couple of thousandths larger for pressing in.  I would probably leave the bore at size to hand ream to fit.  Pressing usually reduces bore size if you follow the book.  That should give you the ability to get a free moving arm with very little play.   Mike

[canuck750]

I use the plain bearing handbook for sizing bushing which usually says make your bushing a couple of thousandths larger for pressing in.  I would probably leave the bore at size to hand ream to fit.  Pressing usually reduces bore size if you follow the book.  That should give you the ability to get a free moving arm with very little play.   Mike

Thank you Mike!

[Roy gardner]

Clearly the issue is worn swing arm bushes. .33mm = about .012" and multiply that by the length of the swing arm and the axle movement will be quite large enough to induce that unnerving twitch as you turn into a bend.

The bronze bar looks like what we know as LG2, not Oilite sintered bronze. LG2 will be fine, the pin should be hard, pass a file aver it to confirm?

I would turn the bush inside first with your boring bar,leaving it about .02MM undersize, then outside to about a .02 tight in the arm. Chamfer the ends for lead in when fitting. It will collapse the bore a little as its pressed in. In a perfect world you would hone both bushes to size, after fitting, on a Sunnen hone with a long mandrel but you clearly dont have that luxury. The next best thing is to use your adjustable hand reamer with a long pilot in the other bush. Line ream. This ensures that both bushes are perfectly in line with each other.
Make them .01 clearance on the pin max, the pin should be a tight hand push to light tap fit. Give the pin a polish in the lathe with fine emery tape or abrasive paper to remove any rust, pick up, or scuffing marks before attempting to fit it.
Final assembly with grease, obviously.
The suggestion of fitting grease nipples, zerk fittings is good. I would put them underneath as long as they wont get wiped off by the chain.   

[Antietam Classic Cycle]

The "spindle" is drilled and has grease fittings at each end already.

[Don G]

Just another reason why I like Moto Guzzi , Timken swing arm bearings!  DonG

[canuck750]

Well after a long day playing machinist (which I never will be) I got a pair of bushes made and installed, a pro would have done it in 1/4 the time and much cleaner. The swing arm pivots were actually out of alignment a bit as well which may explain why the original steel bushes were so worn?? I made a stainless dowel to thread through the swing arm pivot steel tubes, a  couple of straight edges, oxy/act heat and slowly brought the two tubes into alignment. A hand reamer passed through the two bronze bushes and I have a very tight fit, night and day.





Touched up the swing arm with Por 15 black epoxy paint and its back in business.

[Chuck in Indiana]

Nice work.. 

[Roy gardner]

The "spindle" is drilled and has grease fittings at each end already.

Brilliant, well done Morini. And well done Canuck. Nice work.

[Mike Tashjian]

Spending the day making it better than new is very satisfying, no matter how you look at it.  Nice work.     Mike

[Hymes Inc.]

Don't fret about how long it took you vs a pro. All that matters is that it's correct in the end. Well done.