Decided to clean up and adjust the front fork lower links. The uppers had been done last year and the I'm not ready to rebush and install the other girder I have, so...
Pulled the pin(s) Is that still a thing?
Decided to record some dimensions while at it:
upper pivot pin diameter = 11 mm
upper pivot pin bushing ID = 11 mm
OD = 14 mm
upper bronze thrust washers (#8050 ter x4) ID = 11.2 mm (left side may be 13.2 mm to clear shoulder on pin)
- specs from Super Alce parts book OD = 23 mm
thickness = 1 mm
lower pivot pin diameter = 13 mm
lower pivot pin bushing ID = 13 mm
OD = 16 mm
lower bronze thrust washers (#8054 bis x4) ID = 13.2 mm (left side may be 15.2 mm to clear shoulder on pin)
- dimensions based on #8050 ter OD = 25 mm
thickness = 1 mm
maximum play in pivots due to wear = 0.10 mm (0.004”) From Alce and Sport 15 shop manuals.
steel side plates for damper = 2 mm thick
phenolic friction material for damper = 4 mm thick
Width of girder and steering head at upper and lower pivots is 167 mm.
The bushings were egg shaped and the pivot pins quite worn. New pins were too large for the bushings so gave the opportunity to restore the bushings by reaming to fit.
Only weirdness was that the shoulders (yellow arrows top fotos) on the new pins were 6mm wide. Original is 3mm with so the shoulders either required thicker spacers or had to be cut down on the lathe. I cut them to 3mm.
If the girder and links are true, the trick to setting up a parallelogram fork is to reduce the end play on the pivot pins to zero without locking it up. Install pins from the left and install the 4 bronze thrust washers. Thread the pins into the right link until there is little end play. (a ratchet strap can compress the mainspring if needed) Install and tighten the left link and check that at least 1 bronze washer on each pin can be turned (i.e., pin is not locked up). Then tighten the nuts on the right link. Again, check that one of the bronze washers can still be rotated. If not, loosen the nuts at both ends and unscrew the pin a little from the right link. Repeat until the play is taken up and nuts on both ends of each pin can be tightened without locking up both bronze washers. Guzzi manuals state that 0.1mm (0.004") is the maximum permissible slop in bushings or endplay.
Once endplay is adjusted the left side nuts can be loosened and the damper plate and friction material placed over the ends of the pins. Thread the wingnut all the way onto its nut. Hold the 8 little springs with dabs of grease and thread the nut onto the pin. Tighten both left side pivot pin nuts, then tighten the wingnut against the damper plate. Repeat for the right side. Once both sides are complete confirm that at least one thrust washer on each pivot pin can still rotate.
Adjust damper wingnuts to road conditions and speed.
My experience is that girder fork bikes handle well. https://youtu.be/Ag6jspgSwos