Swing arm


Refer to rear drive overview discussion. The swing arm contains a large carrier bearing for the U-joint coupler and two smaller taper bearings for the pivot pins that rotate the arm (and hence its “swing” name).

Taper bearings

Taper bearing and race

After unscrewing the pins, the two taper bearings can be easily pulled off of their races along with the circular oil seals. A taper bearing has a larger outside diameter and its corresponding race has a matching slope unlike the flat races of more typical cylindrical ball or roller bearings.

While the taper bearings practically fall out of their position, the situation is quite different for the taper races. These are nearly impossible to remove given the design of the California 1100 swing arm. Usually, the race can be tapped out from the back by hitting it on the inside edge with a suitable rod or punch. But the swing arm location precludes hitting the race from the back; it is a “blind” installation. A cylindrical race can be extracted using a blind bearing puller, but not a tapered race.

TIG welder extraction method

The extraction method is ugly and requires a TIG welder (a MIG welder will splatter material all over). Every 90 degrees, four segments on the race are carefully heated and softened. This essentially shrinks the metal, and hopefully the reduced diameter of the race makes it possible to pull it out by hand. If not, a small hook can be welded on the race to help pull it out. There is really no other way that doesn’t risk substantial damage to the swing arm itself.

So the key question is whether the condition of the races is good enough to simply leave them in place; in other words, can just the taper bearing and oil seal be replaced, not the bearing race?

Inspection of swing arm taper bearing races shows expected wear marks but no damage

Visual inspection reveals no cracks, pitting, corrosion, excessive heat marks, or other obvious damage. Both races have slight wear “rings” that appear reasonably even and are not a concern. So the races will stay in!

New taper bearing and oil seal

The swing arm taper bearings handle a light load since they only rotate a few degrees and the weight is low. The original pivot pins will be replaced with the older specification (T3 type, part number 14547000) to fit the cyclecar chassis, but the oil seals and spacer specifications remain the same.

New taper bearings were packed with Mobil 1 synthetic grease and are held in place with the oil seals (part number 90403040).

The pivot pin spacer can be reused and fits inside the oil seal.

U-joint coupler

OEM 30328031 U-joint from MGCycle.com

The Moto Guzzi U-joint coupler is one of those critical parts that is difficult to access, difficult to evaluate its condition, and difficult to remove or install. Furthermore, the dimensions are non-standard, making the part hard to find and very expensive. Prior to the launch of the California 1100 models in 1994, Moto Guzzi improved the U-joint — the new part number is 30328031 — to eliminate unwanted movement in the fit with the carrier bearing. If the U-joint is loose in its bearing, this can cause an irritating vibration.

In 2002, Moto Guzzi redesigned the U-joint again — part number 03328050 — to allow for added tire clearance. This part is not interchangeable with 30328031.

Any looseness is probably due to inaccurate machining of the U-joint. One outside surface end of the U-joint is turned down to fit the bearing (and the spline part isn’t used), while the other end is left “as is” from the manufacturer (and the spline part is used). A careful measurement of either end caps should reveal a slight difference in diameter.

Due to the interference fit, the bearing and one end of U-joint will probably have insertion marks. It makes sense to at least replace the bearing if the bike has over 30,000 miles (as ours does). To remove the bearing, the U-joint must first be taken out. A circlip holds the bearing in place, and this can’t be reached with the U-joint installed.


Removal of the U-joint coupler from its carrier bearing interference fit requires a special punch tool. Bruce fabricated one as illustrated in the drawing below (note this is not to scale).

The tip of the punch rests inside the U-joint spline (this end of the coupler spline is not used) to position the punch exactly on the spline face, just missing the bearing face in the swing arm tube. Several hard taps with a heavy hammer dislodges the coupler.

Getting the large circlip, or snap ring, out is also difficult. When this is removed, the bearing itself can be pressed out from the back of the swing arm tube.

The coupler is an expensive part — around $250 — and critical to safe operation. Visual inspection showed no damage, but rotating the joint through all its degrees of motion revealed two “bumps” on either end. This may be due to corrosion caused by the joint resting in the same position for a long time (like several years), or it may be evidence of stress wear. After all, the part is twenty-five years old.

In any case, Moto Guzzi recommends replacing the U-joint and carrier bearing assembly every 43,500 miles. Since our donor cycle has 42,500 miles, we’ll install all new parts.


Assembly is the opposite of removal, as is often neatly said in service manuals, but inserting a new U-joint coupler without damaging it requires another special tool (less than $10 in part cost); simply hammering the end of the U-joint may distort its needle bearings. An insertion tool fixes the coupler in position so that it can be pressed into place without wobbling around.

U-joint insertion tool made from PVC parts

To fabricate the PVC tool, place two 2-inch couplers together in the swing arm to align them exactly. “Spot weld” them in a few places on in inside to fix their position, then withdraw the couplers and finish plastic welding all around the outside circumference. Sand smooth to avoid catching the tool on the swing arm interior.

PVC extraction tool

Shape the adapter so that the cutouts (see 3D CAD drawing above) rest on the “shoulders” of the U-joint. Wedge the adapter into the inside of one end of the welded couplers, and “spot weld” the tips of the octagon fitting to the inside wall.

Drill a hole through the threaded end of the tool; if the tool gets stuck inside the swing arm, a rod through this hole will help pull it out.

Blue 242 Loctite applied to U-joint end

NOTE: Guzzi makes a special tool for inserting the U-joint, but according to parts supplier MGCycle, this tool no longer fits the slightly modified dimensions of the replacement OEM U-joint … go figure!

When inserted with the U-joint, the tool edge should rest against the inside rim that holds the carrier bearing. For added holding power, we applied Blue 242 Loctite, a fastener assembly liquid with anti-vibration characteristics that is still removable with hand tools.

When the U-joint is nested into the carrier bearing, press it in for a secure interference fit.

Exterior finish

After cleaning and sanding, we applied POR 15, an excellent protective paint that prevents rust and corrosion. POR 15 is sensitive to UV light, but the swing arm will be hidden under sheet metal so that isn’t an issue.

Painted and restored swing arm