VeloSolex 3300 Engine Rebuild

This article shows the steps needed to tear down and rebuild the VeloSoleX 3300 engine assembly.

The 3300 engine was only produced for a few years (between 1962 and 1965), because it was a transition model between the 2200 and the 3800.

For this reason the bottom of the engine is the same as the older 2200 model and the cylinder and fuel system the same as the later 3800 machine.

Extracting the crank from the Solex engine

Special tools

There are a number of special tools available to make a rebuild easier but this document tries to avoid most of these, instead using some improvised tooling and homemade parts.

Three specific tools that were made for this task were a flywheel puller, a stator extractor and a crank locking tool.

The flywheel puller was made on the lathe and a drawing for this design can be found here, however there are simpler designs made from a washer and a few bolts. One of these designs is shown here.

The bolts must be M6 x 1mm to match the flywheel threads.

Flywheel Puller
The stator extractor tool was made from a single block of metal drilled and tapped to take some M10 threaded rod and two bent finger plates to grip the stator.

One of the finger plates was "nibbled" with a grinder to clear the condenser.
Alternatively the condenser can be removed.

Basic dimensions are given here.

Stator Puller
The crank locking tool is simply an M6 bolt of the correct length which screws into a plugged hole at the front of the engine. Ideally the end of this bolt should have the threads removed so they can't get damaged making it difficult to remove the bolt, but with care a normal bolt should suffice.
Crank Locking Tool.


As a minimum a gasket set will be needed to reassemble the engine; furthermore there are two bearings in the lower half of the engine. In particular the crank bearing must be sealed well to allow the vacuum in the engine sump to operate the fuel pump and also transfer fuel to the cylinder.

Replacement bearings are
Crank bearing
6203 2RS* 40mm OD x 17mm ID x 12mm Thick. 

Stator Bearing
6202 2RS* 35mm OD x 15mm ID x 11mm Thick

2RS = 2 rubber seals

Go for a branded, double rubber sealed bearings for best results.

Bearings and gasket set for engine rebuild
For top end work then a new spark plug, new decompresser valve are a good idea
Replacing the fuel and air filters is also good practice.

Engine strip down
Working on the removed engine assembly is easier with the motor held securely. This can be done using a special holding bracket or some old Solex forks.

However if neither are available a piece of hard wood cut to fit between the mounting plates makes suitable alternative. Here the motor is shown mounted on a piece of wood held in the vice. The motor was held to the wood with 4 short self-tapping screws.

Care should be used not to over stress the wood when torquing or undoing screws.

Before mounting the engine and starting the work it is wise to tip the fuel out of the tank into a container.

Holding the engine in the vice
The crank was locked in place by inserting a longer M6 screw into the plugged hole at the front of the engine.
Remove this bolt and replace with the crank locking bolt.
With the flywheel cover removed, the centre 21mm nut was undone.
This can be done with a plug spanner if nothing else is available.

Removing the flywheel centre nut.
With the nut removed the flywheel puller was used to pull the flywheel off the crankshaft.
Extracting the flywheel
With the flywheel removed the stator plate is visible.
To remove the plate first the three securing bolts are removed with a 9mm spanner.
It is important not to pull the stator plate by the outer edge as it is easily bent.
Instead it should be pulled by the ends of the coils.
Force to remove the plate is not high but it should be applied evenly and this can be done with a simple puller as shown here.

Stator puller
Behind the stator plate is the clutch. The nut on the clutch can be very tight and a box spanner (or the plug spanner) can be used.
Undoing the clutch nut
With the nut a spring washer removed the clutch mechanism can be extracted by pulling it apart as shown and withdrawing it from the clutch housing.

(ignore the clutch nut in the photo which should be removed at this point).

Expand the inner clutch arms to release clutch grip
Be sure to retain the spacer washer behind the clutch mechanism

At this point there is a special tool to extract the drive roller assembly and clutch housing along with the surrounding mounting plate.
However these parts can also be drifted out from the other end.

Clutch removed
To remove the crank case cover first the cylinder must be removed.

Start by removing the spark plug and then undo the 4 cylinder head bolts (9mm), but leave them in place.

Undoing cylinder head
Lift the cylinder head off complete with decompresser valve, bolts, spacers, washers and the engine lever.
Removing cylinder head
Disconnect and remove the emptied fuel tank.

The tank is secured to the engine by 3 screws (9mm).

There is an overflow connection at the top and a fuel outlet at the bottom (9mm).

Disconnect overflow

Unscrew fuel outlet pipe
To remove the carburettor and inlet manifold unscrew the fuel line union at the bottom of the carb.

Then undo the 2 bolts holding the manifold onto the cylinder.

Unscrewing fuel feed

Removing inlet manifold
The two fuel lines can be unscrewed from the pump using a 9mm spanner.
Removing fuel lines.
The 4x 9mm nuts at the base of the cylinder can be removed and the cylinder lifted clear with the base gasket.
Lifting the cylinder off 
If it is planned to service just the bottom half of the engine the piston can be left in the cylinder barrel to avoid the need to compress the piston rings.
To do this the cylinder should be lifted until the gudgeon pin of the piston is exposed.

The circlip on one end can then be removed and the gudgeon pin slid out to release the piston in the cylinder.

Removing a circlip to release gudgeon pin
If the piston is to be removed then is should be withdrawn through the bottom of the cylinder.
The crank end cover plate can be removed by undoing the eight 9mm  bolts.

Note the top screws are longer.

Removing crank cover bolts

Crank cover screws.
The connecting rod can be removed by undoing the big-end nut with a 14mm spanner.
Removing big-end nut
The crank can then be removed by tapping out gently from the flywheel end. The flywheel nut can be used to protect the thread on the crank and a soft mallet should be used.
Drifting out crank
The crank can be extracted taking care to note the position of any bearing shims.
Extracting crank

Bearing shim
The drive roller can be removed with the mounting plate and clutch housing.
There are a number of spacers and sleeves in and around this assembly which should be kept in the correct order.

On the 3300 engine this is a press fit assembly and further disassembly maybe possible but not easy.

Removing drive roller assembly
The crank bearing can be drifted out from the flywheel end using a suitable shouldered rod or threaded rod with a nut and washer.

There should be another shim on the other side of it.

Drifting out the crank bearing

Engine rebuild.

Rebuild is the reverse of disassembly with the following notes.

The new crank bearing should be replaced with the original shims.

Gentle tapping with a soft mallet is all that should be needed to seat the bearing fully home.

New bearing and shim
Ensure all spacers and collars are reassembled including the washer behind the clutch mechanism.
Drive roller sleeve

Clutch washer
The crank cover gasket should be lightly oiled to stick it in place on the engine housing.
The crank cover should be located but not tightened until the cylinder has been replaced. This is necessary to ensure the cylinder has a flat surface to bolt to.

Crank cover located

Trimming end cover gasket.
Any gasket protruding above the cylinder mounting surface should be trimmed off.
After the cylinder is torqued down the end cover plate bolts can be tightened.
If the piston was removed the ring gap can be checked during reassembly and should be between 0.15mm to 0.3mm. Each ring should be placed in the bore and squared up using the piston skirt as a guide.
Then the gap can be checked with some feeler gauges.

To reinsert the piston in the cylinder it should be inserted from the bottom with each piston ring compressed in turn with the fingers. The cylinder bore has a taper on the bottom to aid insertion.

The ring gap from one of the piston rings
Checking the ring gap
Pushing piston back into cylinder.
If the piston and cylinder are measured the nominal dimensions should be as follows.
Piston diameter : 39.35mm
Cylinder Bore : 39.50mm

If oversized parts have been fitted then the difference between the piston diameter and the cylider bore should be a maximum of 0.15mm
To decoke the decompresser channel a 5mm drill can be wound into the vertical channel in the cylinder.

Likewise, a 3.5mm drill can be used to clear the angled channel in the cylinder head.

The decompresser valve is best replaced but if it has not been disturbed then it should be OK.
If the valve has been removed and a new valve is not available then the old one should be "bedded in" by turning it in its seat with some light oil applied.

Clearing the cylinder channel 5mm drill

Clearing the cylinder head channel 3.5mm drill

Crud from the decompresser channel
To test the decompressor seal, the head can be held inverted and the combustion chamber filled with fuel to look for leaks.

This is not a pressure test so will only show major problems with the valve.

Look for any petroil leaking out the angled port in the head (arrowed).

Petroil mix in the cylinder head.
To reassemble the decompresser valve screw the housing all the way in and then back it off 1.5 turns.

The cylinder head should be assembled with a new gasket and tightened to 105 pound inches of torque. A spanner and spring balance can be used to set this if a torque wrench is not available. This torque should be re-done when the engine is warm.

Torquing cylinder head bolts
The stator bearing should be pushed into the stator plate before pushing the whole assembly onto the crankshaft.
Stator with new bearing.
The clutch should be installed with the little + signs facing outward, otherwise the clutch will work in reverse.

The clutch nut should be done up properly tight. Ideally 284 inch pounds of torque

Tightening clutch nut

Correct clutch orientation
It is important that the stator plate be pushed into position by pulling against the crank. Just pressing the stator plate on may may move the crank out of its own bearing.

Two lengths of 15mm tube (from an old towel rail) were used to allow the clutch nut to be used to perform this pressing operation.

Press tube parts
The stator was correctly positioned rotationally, and the fixing bolts were used finger tight to hold this orientation.

The shorter tube was used with the clutch nut to push the bearing part way on, then the larger tube was used to push it fully home.

Finally the three stator fixing bolts were tightened.

Pressing the stator plate home using the clutch nut