Time Required: 2 hours
Skills Required: Use of hand tools (screw driver, fixed wrench, socket driver, feeler gauge)
Degree of Difficulty: Easy to Moderate
Parts required: Slight chance of uncovering a damaged rocker cover O-ring seal
Actual complete itinerary of tools used:
**Valve lash can only be set on a cold engine, so let the scooter sit overnight
The first step is to remove the valve cover. First, loosen the clamp and remove the hose attached to it from above, through the seat bucket opening:
Next, remove the four 8mm bolts from the valve cover, which is easily accessed by removing the engine door panel:
A wobble or universal joint socket can help here. Also, disconnecting the rear shock can give you the ability to rotate the engine in respect to the frame to allow a clear shot to all the bolts:
Once you remove all four bolts, the valve cover can be removed through the engine door opening. Note that on LX's and S's, you may need to remove the small cable clip to the left of the opening in order to completely remove the valve cover.
The next steps involve rotating the crankshaft until the engine is at top dead center, compression. Note that it is much easier to rotate the engine if there is no compression, so if you're servicing your spark plug too, take it out before the valve job, and keep it out until afterwards.
Looking at the cam gear from the left side of the bike, you may be able to see one or both of the timing marks. For a two-valve engine, you're concerned with the 2V mark. You will need to align the 2V arrow on the gear with the mark on the cam holder just behind the gear as shown in this pic:
If you have a kickstart lever, rejoice! It will save you a lot of time aligning the cam. Slowly push down on the lever while watching the cam gear. Try to align the 2V mark. If you get close, you may be able to line it up the rest of the way with an 8mm box-end wrench on the cam gear bolt, but only turn very lightly. If a fair amount of torque is required, continue to use the kickstart lever until you can get it aligned.
If your bike is more recent, and the kickstart lever was omitted, or if you decided to remove your kickstart lever at the recommendation of MV'ers, then you need to align your cam by turning one of the ends of the crankshaft. If you have done a belt and roller service on your bike before, then you may feel comfortable turning the crank with the variator nut. If not, it is a bit less invasive to take off the cooling shroud fan and turn the crank from the right side of the bike. Here are the photos that illustrate this process (Note, you should not have to remove the exhaust as depicted in the photos):
Remove the fan shroud
Remove the cooling fan
With the cooling fan removed, you can turn the nut beneath until the 2V cam gear mark is aligned.
Now you can actually adjust the valves. The correct clearances are:
Intake (upper valve): 0.004in (0.10mm)
Exhaust (lower valve): 0.006in (0.15mm)
Valve Lash Tutorial:
With a screwdriver in the adjustment screw slot, loosen the lock nut. Slide an appropriate sized (.004 or .006in) feeler gauge under the adjustment screw, and turn the screw until you get a slight drag on the feeler gauge. While still holding the screwdriver in the slot, tighten the nut and double check the lash with the feeler gauge to make sure it didn't shift when tightening. If it is difficult to insert and remove the feeler, the valve is too tight.
**Note that the inset of this next photo has an incorrect label. The point at which the feeler should be inserted is BELOW the point indicated, just above the valve spring cap. Attached to the bottom adjustment screw is a wobbly cap. Although the photo indicates measuring the gap above this cap, there is no gap here. The gap is BELOW this cap.**
Inspect the valve cover o-ring for defects, and replace if warranted
Wipe down the o-ring and its mating surface on the head to assure there will not be a leak. Refit the valve cover and torque the 4 bolts to 8.1-9.6 ft-lbs (11 - 13 Nm)
Refit all remaining parts in reverse order of removal
all photos Copyright 2006 Gary (DBA Addicted) All Rights Reserved
Instructions severely edited by Drew Teague