Gregory Bender

Transmission leaks - four speed pre-selector shaft

Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models

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Please see the follow-up information at the bottom of this section.

Of the very few drawbacks unique to four speed transmissions, perhaps the most annoying is the oil that leaks from the pre-selector shaft. Five speed transmissions have an O-ring to prevent such leaks. But the mighty four speed was not so blessed. Having heard of other owner's who had an O-ring recess machined in the small triangle cover, I decided to do the same. I chose to use the standard 5-speed pre-selector shaft O-ring (MG# 90706140). Here are photos of the outcome.

The pre-selector shaft and casting.
The pre-selector shaft and casting.

Photo courtesy of Gregory Bender.

O-ring fit into machined groove.
O-ring fit into machined groove.

Photo courtesy of Gregory Bender.

The pre-selector shaft assembled into the casting.
The pre-selector shaft assembled into the casting.

Photo courtesy of Gregory Bender.

While easiest when the transmission is removed from the motorcycle, the small triangle cover may be extracted with the transmission in place. You will need a bit of patience, but it can be accomplished using a 10 mm combination wrench and 14 inch drive sockets, etc. Start with the transmission in neutral and do not rotate the shaft during disassembly, removal, or reassembly. This is also a great opportunity to replace the shift return spring.

Machining the groove

Patrick Hayes is a great Moto Guzzi enthusiast and has the machining capabilities to properly cut the needed groove for the O-ring. His work is top notch and his pricing is very affordable. I highly recommend that you use his services.

Here is Patrick Hayes' setup for cutting an O-ring groove in the 4-speed shift lever casting:

The LATHEJIG: This sets in my lathe so that the device is spinning concentric on the bore of the shifting shaft. I'll reach inside with a grooving tool and cut the necessary groove. The peripheral notch allows the user to leave the return spring eccentric bolt in place and unmolested for return to their transmission.

Lathe jig.
Lathe jig.

Photo courtesy of Patrick Hayes.

Casting mounted within the lathe jig.
Casting mounted within the lathe jig.

Photo courtesy of Patrick Hayes.

The TESTJIG: I made up the test apparatus so that I could use vacuum to determine how well the O-ring works to seal the shaft. I realize the shaft is installed backwards. The O-ring doesn't care which way the shaft is. Installing the shaft this way was the easiest way to fabricate a testing tool.

Test jig.
Test jig.

Photo courtesy of Patrick Hayes.

Test jig holding a vacuum.
Test jig holding a vacuum.

Photo courtesy of Patrick Hayes.

BTW, the casting in position on the testing jig is yours which has already been cut for an O-ring. I had some debate about the dimensions of the groove. As you can see, it is holding a 20 inch vacuum test and has been sitting that way without degradation for over an hour. I'd say that proves the quality of the O-ring retrofit.

Follow-up

I've had the O-ring installed for many thousands of miles now and it has done a very good job of preventing oil from escaping through the pre-selector shaft. I consider it a very worthwhile modification.