FAC damper rebuild information
Moto Guzzi V7 Sport, 750 S, 750 S3, 850 T, 850 T3, 850 T3 California, V1000 I-Convert, V1000 G5, 1000 SP, Le Mans, Le Mans II, Le Mans CX 100, Le Mans 1000, 1000 SP III, 1000 S, California II, California III, California 1100, California Jackal, California EV, California EV Touring, California Aluminium, California Titanium, California Special, California Special Sport, California Stone-Metal, California Stone-Touring, California Classic, California Touring, and California Vintage models
Thanks to Mike Jones for sending me this information via email:
I recently had to rebuild the FAC fork dampers on my Convert. They had 50,000 miles on them. One had leaked all of its oil and the other had leaked half of it. They were doing very little damping by that time, of course! I had a hard time finding rebuild kits, though I did find one European supplier, but eventually I opted to just buy new seals and O-rings, basically assembling my own rebuild kit. The hard part was finding the seals. On your web site you list a Canadian company that has the seals in stock, but I opted to buy SEA seals from McMaster-Carr instead (cheaper and faster than ordering from the Canadian company). I bought part number 9505K14, which is a 5⁄16 inch × 9⁄16 inch × 1⁄8 inch O-ring supported cup seal. I removed the O-rings (they pop out easily) so that they are just cup seals like the originals. They seem to fit well and seal well. There's some stiction when I work the damper by hand, but I don't notice it now that they're installed on the bike. I have no way of knowing how long they will last, but at USD $2.94 each, they certainly are affordable.
SA Guzzi, Greg Field,
Goose for posting this information on the Wild Guzzi and GuzziTech forums. In their own words:
Checked my front shocks on my 83 LM3 this evening and found one of the dampers not working at all.
So started a strip down. Once i was able to get the bottom fitting undone, she came apart quite easily. There was no oil in the damper at all, must have leaked out from the lower seal. Been searching the web for a seal kit but no go so far.
Have also found the reason the seals leaked. Inside the lower part of the damper, there are two aluminium parts separated by an O-ring. Inside the threaded half, are the two shaft seals. These are the ones i have been trying to get. The upper half is a round aluminium bush with a small hole in. This is the part that is worn oval causing excessive sideways movement of the shaft. When this happens, the oil inside the damper runs out through the two seals.
Off to the engineering shop in the morning to have a new bush made up.
Here are some pics so far.
George Dockray has the seal number. If he doesn't pipe in here, I'll get it fir you.
I was told by a Guzzi owner who also owns a machine shop that all seals are standard dimensions, fork seals also.
He said just take the seals into a good bearing or seal supplier and they can match it up and sell you seals at a fraction of the dealer cost. I don't know if this is true but it makes perfect sense, I'm sure Guzzi aren't in the business of manufacturing seals.
Thanks for the info guys.
The seals i am looking for are the two small ones inside the lower damper fitting, there are two back to back with a washer between them.
A friend of mine with a machine shop made me two new aluminium bushes yesterday, they fit perfectly, no more sideways play. He incidentally also has Guzzi's, a 750S3, a LM III and two LM IV's. He also made me a proper tool to remove the lower fitting on the damper. Will post pics soon.
Anybody know what weight oil i should refill the damper with. I can get Castrol 10W fork oil. Motul has a range 5W, 10W and 20W, they call it light, medium and heavy fork oil. I measured about 65 ml in the damper that was still working.
Thanks again guys,
ATF is what comes in them.
FACs have almost zero compression damping. You can improve that by filling in one or more of the damper holes with epoxy.
Link with seal #'s is here:
Extract from GuzziTech forum:
I see that this has been a topic before, but with no answer. Maybe now somebody has the low-down:
Have some FAC's installed on an 850 Le Mans that are being refreshed. Like to install new seals, but before emailing the usual suspects, has anyone gotten them from a particular source? The cap are easy, but the 2 per side cup seals are a little unusual. I'll be tryingFluid Sealin Vancouver tomorrow for a match-up, but they look a bit special so I doubt a generic match-up.
I stopped in at the seal place and here are the part numbers for the shaft seals:
Cup seal: 840400312/4180
The installation takes 2 seals per side and 1 spacer in between. The spacer is needed because the cup seals are slightly shorter than the originals so they take u that clearance.
The numbers are supposed to be generic so any large fluid seal dealer can match them.
Thanks for the info Greg and George,
Will Motul fork oil work in the damper and give better damping than the ATF?
I have used fork oil everytime I've gone inside FACs. The Motul should work fine.
What weight and what volume?
Motul or Castrol 10W, i used Motul and about 70 ml in each damper.