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Guzzi conversion - progress report


Alan Walker

Alan Walker is upgrading his Pembleton to Guzzi power. Like me he has chosen the small block engine option. This engine weighs 30kg which is much lighter than the big block engines (see Peter Johnson's report for the big block engine weight) and the later diaphram clutch 2CV flywheel weighs 50kg. Perhaps some might know the weight of the 2CV engine for a comparison and let me know.

I have appended a drawing of my flywheel carrier and dimensions for machining the plate to join the engine to gearbox. The editor

Mike Meakin has already raised the subject with you so you will know that I am also planning a Guzzi conversion. I have just bought a 750 bike on Ebay and assume it will be the short block smaller engine, pick it up next Friday. I have had my Brooklands on the road for a year now and am thoroughly enjoying it, but am having withdrawal symptoms now the build is all over, hence the new project to upgrade the engine. I know you are well on the way with a similar task and would appreciate a drawing of the adaptor plate and the material used as I would like to have a go at making my own.
Mike and I picked up my Guzzi 750 on Friday as planned and it has turned out to be an excellent buy. I still haven't positively identified the model but the 1991 750 SP seems likely. The speedo reads just over 10,000 miles and I'm inclined to think this is correct as the engine runs very sweetly with the minimum of mechanical noise. The bike has been off the road since 2002 but has not been stored very well which has lead to corrosion getting under a lot of the lacquered aluminium castings, I also think battery acid has been leaking. It is still worthwhile restoring so having removed the engine for the Pembleton I shall probably lookout for another to replace it sometime in the future.
I have discovered that the ignition set - up on the Strada engine is not suitable for our conversions. The electronic trigger is incorporated in the flywheel with the pick - up sensor in the bell housing, and neither of these components are used. The solution has been to buy a complete Lucas ignition system off Ebay, I am hoping this will fit straight onto the trigger drive next to the alternator. Luckily Moto Guzzi left this intact when they made the change to the flywheel arrangement.
No information available No information available
The Rita uses two coils which appear, from the diagram, to fire together so a lost spark system. All the technical information is with Michael Moore , website --, email -- very helpful guy. Also I have a local expert on the Rita , apparently the amplifier can be repaired if required, another thing in its favour. Would you know from your workshop manuals if all the small block engines have the same timing characteristics, will the Strada be the same as the Targa?

The answer is 'yes'. All the small block engines except the V35 and some V50 models use the same timing and advance curve. The advance curve is the same as the classic big British twins (Norton/BSA/Triumph) and a Boyer Bandson electronic ignition system is suitable. I bought an un-asembled system, made a PCB for the two pick-up coils but still need to make a magnet carrier. With hindsight I might have chosen an optical Phazor system if the advance curve is suitable as its easier to adapt. The editor

I though you were due a progress report --- the engine is now out of the bike and sitting on my bench. The only damage on the removal was a sheared exhaust stud, at the nut end so I should be able to remove the rest without too much trouble. I think I mentioned that the main problem with the bike aluminium components was corrosion, which looked pretty awful. Upon investigation I have found that all the aluminium has been powder coated and moisture has got underneath causing the problem. The answer has turned out to be a simple one --- paint stripper removes the coating and leaves an attractive metal finish. The bike is in such good order that Mike and I are looking for another engine to put it back on the road, 350, 500, 650, and 750 all will fit. Mike has got a spare 2CV g/box so I will be able to take the engine plus g/box together with your drawings and dimensions to the machining guy which should make things really easy for him.

Moto Guzzi small block engine and 2CV gearbox measurements

All these dimensions were measured using a 3 axis measuring machine - there are slight rotational inaccuracies which are not worth worry about. All the PCDs were calcuated from the X-Y coordinates.

Moto Guzzi crankshaft

Centre boss 22.00mm diameter holding flywheel with 6 equi-spaced M8 bolts at 39.00mm PCD and the flywheel mounting face is 6.00mm recessed below the plane of the clutch housing face.

2CV Gearbox

Clutch housing/adaptor plate; four M10 bolts

Positions relative to crankshaft centre and facing gearbox

Hole X coord Y coord PCR Comments
Bottom left -95.126mm -117.761mm 151.38mm tap M10
Top left -74.898mm 131.761mm 151.56mm Bore 14.00mm diameter 4.00mm deep and tap M10
Top right 74.957mm 131.536mm 151.39mm tap M10
Bottom right 94.837mm -118.068mm 151.44mm Bore 14.00mm diameter 4.00mm deep and tap M10

Moto Guzzi Block

Engine/adaptor plate; six M8 Allen head bolts fully countersunk

Positions relative to crankshaft centre and facing engine going clockwise from the bottom

Location X coord Y coord PCR Comments
Bottom0.000mm 126.983mm 126.983mm Ream 12.00mm for hollow dowel
Lower left 67.102mm 128.859 145.284mm Oil return; 30mm
Lower left 99.430mm 78.674mm 126.791mm M8 clearance
Upper left 99.355mm -79.213mm 127.067mm M8 clearance
Top -0.143mm -127.055mm 127.055mm Ream 12.00mm for hollow dowel
Upper right -99.624mm -78.988mm 127.138mm M8 clearance
Lower right -121.944mm 36.022mm 127.154mm M8 clearance

Click to enlarge The adaptor is milled from 15mm aluminium plate. Remember to mill a pocket for the starter motor pinion bearing housing. There are pictures and further information here. The flywheel carrier is in two parts both made from EN1A(?) steel. It has to mate the flywheel to the engine crankshaft. Most dimensions are not critical but the key one is the overall thickness of the assembled adaptor. The 2CV crankshaft face is 3.5mm proud of the clutch housing joint so the engine side of the 2CV flywheel sits 6+15+3.5=24.5mm forward of the Moto Guzzi crankshaft/flywheel face.

The rationale of my design for the flywheel carrier was

Note I have no objections to one-off use of the design but not commercial production without prior agreement. David Tocher