Engine work
So far, I’ve not had to dismantle the engine further than taking the heads, cam-belt covers and left-side casing off. It hasn’t been tuned for increased performance, though some improvement to the gas-flowing was made when the cylinder heads were overhauled and converted to unleaded petrol. Bits replaced included valves and guides, one rocker and a camshaft, all the worn alloy belt pulleys and of course the cam-belts, and the heads were bead-blasted. This work was carried out by DTS, a one- man-band Ducati engine shop of high reputation and 30 years of experience, in N. England. Very expensive, but I bit the bullet...As mentioned above, the engine has the shorter stroke of the 600, but does have 650 barrels and pistons, giving an actual capacity of 606cc as opposed to the 583cc of the nominal 600 motor. Quite possibly, the compression ratio is lower than it should be. This pick-and-mix Ducati engine did not surprise Paul at DTS!
The air intake system has been retained as standard, so as to limit the induction roar and guarantee clean air. Some people (though not DTS) claim that the Pantah air filter/box is very restrictive, but my experiments with opening it up led to an unacceptable increase in noise with no obvious performance benefit. I use low to medium revs mostly, but the engine still pulls very well at 7Krevs and above, so I am happy to stick with the maker’s intake system.
Pantah silencers, without shields, raised to the max on de-emphasised alloy hangers, giving clearance for wheel spindle. Longer Hagon shrouded shocks suit black frame and increase ride height. Oversize (130/80) rear tyre. Polished grab handles and extra trim, and painted indicators all add emphasis to rear, as does fat seat. Damn that frame tube across the cam-belt casing!!
My bike also still had the standard twin exhausts, but I replaced the rusted silencers with new Silentium Pantah units from The Italian Vintage Co., which carry the same Ducati part number as the originals. Though otherwise identical, these came without the attachments for the shroud and heat-shield that were fitted to the Alazzurra, and that bothered me initially. I now feel that these items were a styling mistake as they clutter the line of the elegant slim exhaust system without serving any practical purpose, so I am pleased to be rid of them. I tried the aural effects of reducing the silencer tail-pipe stubs but have returned to the standard dimensions, as the sound is quite loud enough as it is. This may, in part, be due to the unlined stainless cross-pipe that Gazelle Exhausts made for me, to avoid the old corroded section rusting into the new silencer stubs.
The pipes could do with being rechromed, but a concours restoration was never my aim so that comes low on the list of priorities. By the way, I’m a great fan of the finned exhaust port clamps, and feel that the later adoption of plain steel plates and/or flanges by Ducati is indicative of their abandonment of aesthetic design in their engines. Modern Duke power plants look purely functional, and are better kept covered!
Other work related to the engine included replacing the cam-belt tensioner bearings and the oil pressure sender, replacing degenerate insulation on the ignition pickup wires, fitting what are hopefully rain- proof NGK spark-plug caps and Denso Iridium plugs, and servicing the starter motor.
The outer plain bearing in the starter motor had run dry and had partially seized on the shaft, making starting a noisy business. Removing the complete starter motor was not easy, but actual wear was minimal, so I was able to polish the shaft and bond the bush back into the housing. The lubrication reservoir of this bearing is very small, so I drilled and plugged a hole in the end of the casing to permit occasional oiling and prevent a reoccurrence of this problem. The brushes are close behind this bearing, so lubrication must be sparing.
The Dellorto pumper carbs were stripped and fitted with complete service kits, and an odd selection of oversize jets and needles was replaced with items to the original Ducati/Cagiva 600/650 specification.
I had to improvise new isolators for the carb manifold mounting bolts as the originals had long gone, and without them the gas-flowed manifolds and ports did not line up. Tubular spacers made from oil-resistant rubber piping with flat- and spring-washers and locknuts work well.
A worthwhile modification was to revamp the throttle cables. The original one-into-two system has far too many junctions where slack and/or poor cable alignment make establishment and maintenance of correct length, and thus carb synchrony, almost impossible. The simple solution was to convert to twin cables, as the OEM twist-grip is actually made for two, with the exit for one blanked-off. I made my own cables from nylon-lined outers and stainless pedal-cycle inners, each being cut to exact length such that it only requires the single cable adjuster that is integral with the carb top. That interface was also stabilised by a thin brass sleeve to ensure the cable entered on line, and I paid particular attention to the run of the cables from twistgrip to carbs. The end result is the sweetest action ever, and the stability of the system makes adjustment of the carbs (using a Morgan Carbtune and Colortune glass plugs) a rewarding exercise.
...continue in next post.
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