Engine Rebuild 3: Re-assembly - Bottom End.

With the crank removed, thouroughly clean the inside of the cases. Pack any openenings with clean cloth to prevent loose sealer from working its way into the transmission or oil galleries, and clean any residual sealer from the crankcase mating surfaces. Double check the oil feed holes to the crank once again.

Always use new crank seals when replacing the crank. This may sound obvious, but a new Honda crank is not supplied as a matter-of-course with fresh seals, so don't be tempted to use the old ones if you neglected to order them, just to save time! Unlike some 2-stroke engines, the crank seals CAN NOT  be replaced without splitting the cases.

The next job is to pre-lubricate the main bearings with 2-stroke engine oil.

Pre-lube the Main Bearings...

Pre-fit the crank to align the seals and bearings. You will notice the seal on the flywheel side has lugs to help locate it in the cases, and the clutch side has a lip around its' entire edge, and neither actually sit flush to the bearings. The bearings have locating pins to help prevent them spinning in the cases and align correctly. Pre-fitting the crank will ensure that it can be fitted with minimum time and fuss once the new sealer has been applied to the cases.

Once the seals and bearings are aligned, lift the crank back out and carefully set to one side. Apply a light smear of high temperature grease to the seal and bearing seats. This will help prevent the bearings and seals moving as the cases are reassembled, and also act as a liquid gasket.

Instant gasket applied to the lower crankcase...

Use Honda/HRC recommended Triple Bond 1207B wherever possible, or a high quality liquid gasket such as Triple Bond 1104 or Solvol Blue Hylomar (listed in order of preference, however Blue Hylomar will not generally last as long as the Triple Bond sealants, but will still perform to a high standard), and apply a light even coating to both crankcase halves. Lower the crank into position, checking the alignment of the seals and bearings as in the picture below.

Lower the new crank into position...

Once the crank is lowered into position, re-check the alignment of the bearings and seals. The seal on the clutch side is a little awkward to seat correctly as it is a tight fit, so make sure its' lip seats correctly in the groove. If necessary, gently tap the crank webs with a rubber mallet to seat the seals. Only use just enough force to seat the seals.

After tightening the cases, clean up excess sealer...

Lower the top crankcase into position, the case will need to be tapped down to seat it correctly. Before finally tapping the case home, check the alignment of the primary drive seal. Insert the 5 bolts into the top case and fasten them "finger tight". Stand the engine upright (it will sit quite stably on the upper and lower rear engine mounts) and insert the 5 M8 bolts into the underside of the casing, again tightening "finger tight". Once all 10 bolts are inserted, it's time to tighten them to the specified torque.

NOTE: Torque wrenches are precision instuments, and should be handled andused only as stated in the manufacturers operating instructions. Only a correctly calibrated torque wrench should be used as incorrect readings on the gauge can lead to premature failure of components or shearing of the smaller bolts if overtightened.

Always return a torque wrench to the neutral setting after use.

Starting with the bolts on the top, tighten them in 2 stages in the order specified in the diagram below. The M6 bolts should be tightened to 0.8kg-m first, and then 1.4kg-m, the M8 bolt tightened to 1.5kg-m and then 2.5kg-m.

Tighten the bolts to the specified torque in the order shown...

On the underside, tighten the bolts up in the specified order, again in 2 stages. As each bolt is tightened, turn the crank through approximately 45 degrees, torque them first to 1.5kg-m, and then hit them with a plastic mallet as this helps to settle the cases. Finally, torque the bolts down to 2.1 - 2.5kg-m.

With the crankcase bolts tightened, reassebly of the various components is simply the reverse procedure to the strip-down. Each component being reused should be checked for excessive signs of wear. Close inspection of the components will also usually act as a guide to their orientation upon reassembly. Starting with the clutch, refit the inner collar (part# 15 - wet clutch, part# 17 - dry clutch, see below) if removed, and then the 2 needle-roller bearings to the input shaft.

  Allply a little grease to O-rings to hold them in place...

Apply a little grease to the seats of the drive gear o-rings to hold them in place, and fit the locating dowel-pins, then refit the drive gear. Use a little thread-lock to the 3 Allen screws securing the drive gear and tighten them to a torque of 8Nm. Tap the primary drive gear into its' position on the end of the crank, noting the white balance alignment marks, and tighten the securing bolt to 9.0 - 10kg-m. Insert the pushrod into the input shaft.

Collar, needle-roller bearings,  pushrod, drive gear and primary drive pinion refitted... 

Note the alignment mark on the secondry gear on the clutch basket. Turn the crank until the white dots will line up with the basket (or gear in the case of the dry clutch models), once it is slotted into position. Remember the thrust washer behind the hub, and then slot the hub into position.  Refit the outer thrust washer and centre-nut. Lock the crank as shown in the previous section with the clutch holding tool, and tighten the centre-nut to 5.5 - 6.5kg-m.

The clutch plates can now be installed. Refer to your notes from disassembling the clutch to check the order the various plates (and other components) should be fitted.

Wet Clutch models: Fit the flat judder spring first, and the shaped spring with its OUTER edge raised away from the engine, so it appears 'concave' as you look at the assembly.
Dry Clutch models: We advise the fitment of new damper rubbers to the inner-most friction plate because as these wear the clutch can become rather noisy and harsh.

NOTE: Dry clutch models can benefit from a simple upgrade by replacing the 2.0mm steel plate closest to the engine with a 2.9mm plate as utilised thoughout the rest of the assembly. This adds a little extra pre-load to the clutch springs, and is an effective way to increase the clutch's resistance to slipping.

With the plates installed, replace the ball-bearing and pressure plate spacer and then fit the pressure plate. Torque the 5 plate retaining screws to 5Nm.

NOTE: Take extra care not to over-tighten the 5 pressure plate screws asthe hub can be easily damaged.

Apply a thin smear of instant gasket to the engine case in preparation for refitting of the gasket and clutch cover. Do not overlook the waterpump drive shim/washer, which can be temporarily held in place on the engine casing with a small dab of grease. Now fit the new gasket. Dowels help align it, and the instant gasket will hold it in place around bolt-holes.

Click to enlarge

Apply grease to the kickstart shaft seal to ease fitting, and carefully refit the clutch cover.

Torque the cover retaining screws to 1.0 - 1.4kg-m.

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