Text and pictures by Ron Hogan
Remove the belt and large reduction pulley. If you look at the reduction plate, the one that has the big pulley inserted in it, you will notice a slot on the top of the plate. There is a HEX bolt that goes trough (horizontally). If you look at the back of the same plate, you will notice a # 13 mm bolt that is screwed into the eccentric shaft of the big pulley. By loosening the Hex/Allen head bolt and the normal# 13 mm bolt the eccentric shaft can be turned. This allows you to remove the belt once it is loosened.
You may have to take a large flat blade screwdriver to pry the reduction plate open a bit so the big pulley slides out.
Remove the spark plug. Bring the piston to TDC, and then lower it about one inch. Insert a rope that is about the size of the spark plug hole. Insert the rope in one inch to two inches. Move the piston up towards the spark plug hole by turning the shaft until the rope prevents it from moving. This will keep the drive shaft from moving as you remove the nut from it.
Note: JPX Italia does NOT recommend this method because as they state, it may stress the needle bearings.
However, the "rope" method is used by mechanics in the US.
Once the nut is removed, attach a puller (I got one on loan from my local auto parts store). The puller will contact the cooling disk at three points and the center screw of the puller will contact the middle of the drive shaft. Start to tension the puller by turning the puller bolt clockwise. BE CAREFUL NOT TO OVER TENSION ON THE REDUCTION PULLEY AND COOLING DISK AS YOU CAN BEND THE COOLING DISK!
The trick is that you do NOT need to apply to much force on the disc.
The rest will be done by....heat!
There are other pullers that can be used.
Below we can see a home made one:
Next we present a universal puller. Just remove the jaws and insert the two small bolts in the two threaded holes of the small pulley. Next, slightly tighten the central bolt.
Take a heat gun and apply heat directly to the pulley. It may take a while, but once the pulley gets hot enough it will pop off by itself!
Make sure to wear gloves to catch the pulley as it pops off. You may want to put something soft on the floor in case you don't catch the pulley.
This will keep it from getting marred if it hits the floor.
Once the pulley is removed, we can inspect the end of the shaft.
Get one of those green scouring pads and clean the shaft in a circular motion of any debris such as old Locktite. Install the new reduction drive, but add a bit of high temp blue Medium Strength Locktite to the shaft.
As you install it, turn it clockwise to get it to go on evenly, even though there are no threads involved. You want to seat it as far back on the shaft as possible. Take a rubber hammer and give it a knock.
Add Locktite to the nut. Add the washer, if you had one and tighten the nut to 4.5 Kgm. Remember to use our little rope trick to keep the shaft from moving or an impact wrench.
Reinstall the large pulley as you normally do, along with the belt. Apply a bit of red paint to all nuts, bolt heads and a bit on the shaft for future pre-flight reference.
Note: Alex Varv gave me all this info, but I thought it would be nice to have it written down for any pilots that have to perform this in the future.
These pictures will be a good reference for all other pilots who have belt driven propellers on other engines as well.