Gregory Bender

Distributor clamp improvement

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



// //

I extracted this information from Patrick Hayes off of his own website after he made notice of it on the old Yahoo! Loopframe_Guzzi news group (which has now moved to In Patrick's own words:

The Problem:

The single point Magneti Marelli distributor used on the loop frame Moto Guzzi has a minor nuisance fault. When the spark timing is set, a pinch bolt is tightened to hold the distributor in fixed position. If secured with a little too much force, the pinch bolt head and its support washer can gradually become somewhat embedded into the machined surface of the adjustment arc on the distributor body and form a surface crater in the casting. The distributor body is cast from a very soft alloy. When you next try to set the ignition timing, the pinch bolt and this subsequent crater have a mated relationship. Unless the pinch bolt is loosened completely, the distributor body can not rotate easily for adjustment. When the pinch bolt is re-tightened, it has a tendency to ramp the distributor back into the old position rather than the required new position. This is a picture of a mildly cratered adjustment arc on the distributor body.

Photo courtesy of Patrick Hayes.

The Solution:

I have fabricated a clamping piece to improve the load distribution of the pinch bolt and help alleviate the tendency of the adjustment arc on the distributor body to become cratered. The clamp piece is fabricated from stainless steel, so no additional finish is required. The material is 2.4 mm thick so it is not likely to bend or distort at all under the clamping stress. The clamping piece will lift the pinch bolt head by this 2.4 mm thickness dimension, so you will need to fit a longer screw. I recommend a stainless steel Allen head cap screw, 6 mm diameter by 1 mm pitch by 25 mm length below the head. Using a screw of insufficient length presents an increased risk of stripping threads from the cast distributor base.

What YOU have to do:

Source a new screw. Don't use the original. It is already not long enough to utilize the full thread available in the lower body. Now the head will be lifted by 2.4 mm. A new screw at 25 mm below the head would be best. I suggest an Allen head screw. It will be easier to access using a ball-end T handle wrench for easier clamping.

You need to determine how badly your own distributor clamp area has been cratered and what to do about it. It is possible that you may be able to just install this clamp plate and be done. If the distributor arc is badly cratered, then consider removing it and carefully hand filing the upper surface so that it presents a single, smooth surface for the clamp to slide. If at all possible, I highly recommend that you find someone with a lathe and use that to cut the cratering from the upper surface. Using a lathe will ensure that the cut surface is now true and perpendicular to the axis of the distributor shaft. Search your neighborhood for a lathe. The most basic lathe setup should be able to do this cut in a minute. Below is the result of a lathe-cut surface. This is the same distributor body whose crater is shown above. Three-fourths of a millimeter had to be cut away to remove all trace of the clamping crater.

Photo courtesy of Patrick Hayes.

You are welcome to mail your distributor to me for this lathe service, but that isn't really practical. Hopefully you can find someone local and ask for their help.

Here is the final product installed. It helps to use a wavy washer under the screw head so that you have a little residual spring pressure on the clamp when you are adjusting the distributor. I'll include a wavy washer for you in the mail.

Photo courtesy of Patrick Hayes.

The Cost:

I'm not in the fabrication business. I do little tasks like this just out of curiosity and to help the Guzzi community. I do have to buy the metal stock material. I have invested in a lot of tools. There is a substantial time element to push these out. Charlie Mullendore of Antietam Classic Cycle generously donated the distributor body template, added some design opinions, and tested the first production units. I think these are certainly worth the equivalent of a favorite local brew. Its not practical to mail a can of beer and I can't wait until we meet at some rally. What I would like YOU to do is to pledge an equivalent donation value ($5 seems about right) to your favorite charitable cause. Buy some Girl Scout cookies. Put a FIN into the bell-ringer's kettle. Buy a bat for your local Little League team. You don't need to tell me what you do for a donation. There is no one, other than your own internal moral compass, to check up on you to assure you have followed through with the donation. Provide your postal address and I will post one of these off for your machine. I had the stock to produce about 50. I still have to cover the postage to you. I doubt I will make any more of these. Please don't ask for one unless you think it represents a functional improvement to your motorbike.

Patrick Hayes
Fremont CA
pehayes at comcast dot net

No local machinist?

If you do not have a local machinist, Charlie Mullendore of Antietam Classic Cycle can easily clean up your distributor clamping surface. This would also be a great opportunity to have him to refresh your distributor with a rebuild.

Distributor clamping surface cleaned up by Charlie Mullendore of Antietam Classic Cycle.
Distributor clamping surface cleaned up by Charlie Mullendore of Antietam Classic Cycle.

Photo courtesy of Charlie Mullendore of Antietam Classic Cycle.

Distributor clamping surface cleaned up by Charlie Mullendore of Antietam Classic Cycle.
Distributor clamping surface cleaned up by Charlie Mullendore of Antietam Classic Cycle.

Photo courtesy of Charlie Mullendore of Antietam Classic Cycle.