drain & remove gearbox

1 remove expansion chamber 4 nuts and carefully prise out rubber/brass pipe feed from cyl

2 remove gearbox

drain oil - remove the big nut under the propflange, alternately lift the whole unit into a sump tray after undoing bottom bolts, so when parted the oil is contained

use a lump hammer/ pair of big srewdrivers, some stone chisels etc to prize the gearbox backwards, use rag underneath joint to collect drips



 

3 remove cylinder, and piston

next, loosen the front two cylinder nust using a tight fitting and open ended spanner (12mm) to avoid rounding them off. the rear nut is a bit bigger (15mm?)

loosen all 3 nuts a couple of turns, and break the seal using a lump hammer to loosen the cylinder.

carefully detach the gasket from one complete side using feeler blades to preserve it as it is often good enough to reuse.

slip off the clinder

remove the piston for safe keeping - first scratching an arrow foreward, then drifting back/foreward the piston pin with a 1/4" drive extension, which you will find fits neatly inside the hollow end of the pin - so drift it out toward the closed end, by holding the piston in your palm, and gently tapping the extension with a light hammer - this way you cant possibly damage the con-rod, or the piston. Note my hand would be cupping the piston but has to take a photo

4 remove pulley, cover, magneto

using impact driver/large screwdriver, tap long end with hammer to loosen, and remove. you may wish to paint/mark the alignement of the boss/pulley to TDC (remove spark pug and use rod onto piston crown to find TDC)

using 24mm ring spanner/adjustable/socket, tap loose and unscrew flywheel nut. if you find it too tight, you can lock the crank up by jamming a wooden hammer shaft imbetween the flat of the crank, and the crankcase - thru the cylinder orifice. whatever you do, dont touch the small end

prise out crank's woodruff key and keep it safe.

use Vire flywheel/flange removal tool if you have one (with the boss allen bolts) or alternately a three leg puller with a lot of care and ocassional whacks with a lump hammer onto the end.

Magneto removal

remove the 3 slotted bolts with a screwdriver, marking the alignement/ timinng with paint/scratch first.

using thin pliers, detatch the LT wire from the points, reattach the nut for safe keeping

unwind the HT cap from the HT lead, and pull the magneto with HT intact away from the crankcase - allowing the HT to slip through the rubber grommet

5 split crankcase & remove front section

there are 6 bolts on the magneto side (6mm allen) remove them with a spanner on the short leg.

part the front casing away from the crank carefully by loosening with lump hammer, then evenly wedging screwdrivers etc between the gaps in the engine mountings, after some gentl prising and wiggling it will pull the crank out of its front bearing dont be tempted to bash the crank end, as this will ruin the threads neccesary to be able to change points during onboard-servicing later.

6 drift out crank

now you can drift out the crank from the rear housing/bearing with great care as follows..

reassemble the front casing onto the crank and using a workmate, wood or whatever - support the casing so the crank-front can move  downward, but the casing cant.

Using a piece of hardwood as protection - beat down the crank till it touches the front casing (the hardwood washer protects the dog-end from burring over)

(having already removed the front casing/bearing, use that as a support with additional 70mm wooden blocks on top, then refit the rear houning with embedded crank to rest on the blocks. This will allow you to drift down the crank 70mm, thus releasing it from the bearing.)

then remove the front casings bearing and oil seal together by drifting it out with a socke(30mm) that fits onto the inner race and a lump hammer.

Do the same for the rear housing oil seal and bearing.

now remove the front casing and driver the remaining crank out (should now be loose)

if you are unlucky and the bearing came out of the housing instead of the crank, it is stuck/rusted on the crank, here is how to remove it:

remove the rear main bearing by symetrically prising it off with a pair of bolsters/ large screwdrivers etc, gradually inserting spanner heads under the wedges until the bearing is off. alternately use a puller - but it might be difficult to find one that will grab under the bearings skirt initially anyway!

If its completely rusted, i suggest grind off the outer race, ball race, and grind a ledge into the outside of the inner race (thus not damaging the crank in any way). with a heavy hammer/chisel you should be able to drift into the ledge to make the race spin on the crank, then add penetrating fluid, and the rest is easy.

Note:

You cannot strip the big end as it is pressed together in the Finnish factory with 20-40 tonnes