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Archive: Ducati Darmah DD Engine Strip: part nine

REBUILDING the two separate heads of a V-twin Ducati is almost a case of reversing the stripdown procedure explained in part six. There are, however, some areas that need further explanation.

• If the cam bevel box was removed to gain access to the camshaft, the timing dot on the drive gear (pic one) must be realigned with the timing dot on the camshaft bevel gear (pic two).

• Rotate the camshaft so the Woodruff key groove is in the 12 o'clock position and push the cam bevel box just onto the end of the camshaft. Rotate the drive shaft so the timing dot on its bevel gear is facing the camshaft. Now replace the bevel gear shims on the end of the camshaft (pic three).
• Place the camshaft bevel gear on the end of the camshaft making sure that the two timing marks are aligned (pic four).
• Tap the cam bevel box together with the camshaft bevel gear further onto the camshaft using a soft mallet. Fit the Woodruff key in its groove (pic five) ensuring the two timing dots are still aligned.
• The valve clearance shims are replaced by reversing the stripdown procedure in part six. Note: Make sure the rocker positioning shims are put back in the correct positions. Push the rocker pin into the head so the shims on the opposite side from the cam box can be placed over the end of the pin (pic six). Place the rocker into position over the end of the pin and push the pin so that it just presses against the shims placed between the rocker and the head (pic seven). Move the shims into position and push the pin fully home.
• Remember to check the valve again to double check that they're right (pic eight). (This procedure was explained in parts five and six.)

 

Now we can turn our attention to the rebuilt bottom end. The method here follows the rebuild of the rear head, the procedure for the front cylinder is the same.

• Push clean rags into the rear crankcase barrel mouth and place the piston over the end of the conrod. By rotating the crankshaft the little end can be positioned so that the rags help hold the piston in place. Line the gudgeon pin up with the little end and gently tap the gudgeon pin through the little end (pic nine).
• Fit the gudgeon pin circlip into its groove in the piston. This is a fiddly operation best done with a pair of long nose pliers to get the circlip to stay in position before pushing home with a screwdriver (pic 10).
• Fit the bottom piston ring spring in the bottom groove (pic 11), followed by the oil scraper ring (pic 12).
• Fit the middle and top rings their grooves (pic 13). The middle ring has ‘top’ stamped on the top edge to ensure it’s not fitted upside down.
• Take the rags out from the barrel mouth and smear a little gasket glue around the crankcase mating surface. Fit the base gasket. Pic 14 shows: right the rear base gasket with two cutaways; and left — the front base gasket.
• Place the rags back in the barrel mouth as a precaution in case you break a ring fitting the barrel as the bits could fall inside the engine.

• Rotate the piston rings so their open ends are at 120 degrees from each other and then smear clean engine oil round the edge of the piston (pic 15) and inside the barrel (pic 16). Note: The rear barrel is easy to distinguish as it has horizontal fins. The front has vertical fins (pic 17). The cutaway for the head driveshaft should be positioned towards the right hand side of the engine.
• Smear a little gasket glue round the mating surface of the barrel (pic 18) and gently lower the barrel down over the four head studs so that it’s just touching the top piston ring.

• Squeeze the top piston ring ends together so the barrel can be lowered over it (pic 19). Repeat with the following two rings ensuring the bottom ring is correctly seated over its spring. This is where you need an extra pair of hands. It’s easier to fit the rear barrel with someone else lowering the barrel as you squeeze the rings. Yes, Rosie finally gave in and got her hands dirty!
• Lower the barrel fully down onto the crankcase (pic 20).
• Rotate the drive shaft for the rear head so that the timing dots on the head bevel gears are aligned (pic 21). Now rotate the crankshaft so the timing dots on the bottom gears of the drive shaft are also aligned. They're difficult to see but are usually marked by the factory with a blob of yellow paint.
• By lowering the head over its studs the driveshaft cutaway should match the cutaway in the bottom support plate (pic 22). If not, either the head timing dots, or the bottom timing dots are not aligned. Rotate either the crankshaft or drive shaft until the timings dots and the cutaways align.
• Place new oil seals over the oilway dowels on top of the barrel (pic 23). Always use new seals.
• Smear a little grease round the of the cylinder head (pic 24).

• Push the drive shaft sleeve onto the lower shaft cutaway (pic 25).
• Push the drive shaft tube over the drive shaft so it fits into the cylinder head (pic 26).
• Lower the cylinder over the studs. Replace the cylinder head nuts (pic 27) before lowering the head fully otherwise there is not enough clearance to get them in due to the position of the cam bevel box and camshaft support block.
• Tighten the nuts in a diagonal sequence.
• That completes the rear head (pic 28).

• The front barrel and head are replaced repeating the method for the rear. Unlike the rear barrel with its cutaway for the camshaft drive shaft, the front barrel has now obvious features for correct positioning, so remember the larger of the two oilways must be at the five o'clock position, the smaller oilway in the ten o'clock position (pic 29).
• There are only two oil seals to be fitted between the barrel and the cylinder, unlike the rear’s three. The larger oilway dowel is in the barrel, with the smaller oil seal fitted over the dowel in the cylinder head (pic 30).
• With the front barrel and cylinder fitted this just leaves the three Allen screws to be replaced in the crankcases just below the barrels (pic 31).

THIS completes the engine rebuild prior to refitting in the frame. I haven't replaced the engine side cases yet, because it’s easier to get the engine between the front down tubes with the cases off.

• As editor Bob has kindly consented to ‘just one more’ episode I'll deal with this next month and fire the bugger up!