Splitting the Engine Case
Splitting the Engine Case
Virtually every Vespa motor uses a split case system with a separate cover for the clutch housing. In order to repair the engine’s internal components, you must split the cases by removing parts in order. Prior to splitting the case you should always drop the engine out of the frame, so you are comfortable and have access to all sides of the engine. The cases house mostly gearbox components, bearings and seals as well as the crankshaft and kickstart. If you are having problems with these components it is recommended that you buy all of the components in the list below along with the parts you suspect are worn. The cruciform is the most common problem on a Vespa and can be remedied with ease once the cases are apart. Work slowly and in a clean environment for best results. Do not work outside if at all possible, for this will often cause rushed repairs. Wear work clothes that you are not interested in keeping as the engine is usually oily and dirty from road grime. if at all possible, remove loose road dirt from the cases before opening to avoid contamination of the engine.
Tools & Parts Needed
Flywheel Puller (Available at scooter shops)
A Small Punch
Assembly Grease (Thick, high-temperature grease)
Socket Set (7-22mm)
Spanner set (7-22mm)
Long Handled Screwdriver Set
Spark Plug Wrench
Disposeable Shop Towels
A can of Carb Cleaner
A can of WD-40
Split Pin for Rear hub
Metal Hammer
Visegrips
Needlenose pliers
A length of pipe larger than the diameter the handle of your socket driver
A Large Chisel (see below)
A large bag and electrical tape
A Clutch Cable inner
A Rear Brake Cable Inner
Buy the following parts at your discretion
Set of Woodruff Keys (Flywheel and Clutch side)
Rear brake Shoes
Gaskets: Case gasket, Air Box to Case gasket, Selector Box Gasket, Clutch Cover O-Ring, Cylinder to Base Gasket, Oil Drain Plug Gasket.
Seals: Flywheel Side Seal, Clutch Side Seal, Rear hub Seal
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Step 1
Remove the nuts by loosening them slowly in this order. Do a quarter turn, go to the next, quarter turn, next, quarter turn, next, etc. until the nuts are removed. This will take a while, but you risk bending the aluminum head if you don’t do them in small steps and in order. The same is true for tightening. Carefully collect the hardware and remove the cylinder head. |
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Step 2
Remove the Cylinder Head; then remove the Cylinder Barrel, exposing the piston. Note imperfections on the piston. For example, the large black band directly below the piston rings suggests worn piston rings. See below for tips on repair. Prise the alloy cylinder seal off the edge of the engine case. |
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Step 3
Place a small metal punch lengthwise through wrist pin ensuring both sides touch the edges of the case. Rotate the flywheel until it is held tight by the punch. Using a socket, remove the flywheel nut. You may need more leverage so use a pipe length on the end of a socket. It is not adviseable to use a hammer. |
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Step 4
Remove the punch from the piston. Lightly oil the flywheel puller threads and thread the tool into the center of the flywheel. Get about 5 or 6 threads of the tool into the flywheel. Using a spanner and a socket, tighten with the socket and anchor with the spanner (pictured). |
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Step 5
The flywheel will pull away from the crank taper revealing the stator, taper and woodruff key. These are the key timing components of the engine. |
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Step 6
Pull the half-moon shaped woodruff key and inspect it for shearing (deep line in the metal), if there is no scoring then you may reuse it. Look for cold solder joints on the stator (disconnected or cracked solder joints) and repair them as neccessary. The picture depicts an example of a good solder joint. |
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Step 7
Though most P-series Vespas come with timing marks cast into the engine, it is a good idea to make a thinner line with a screwdriver, so you can get it dead on. A screwdriver and a hammer tap on the edge of the stator plate and case will quickly mark and accurate stock point. |
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Step 8
Here is the result. When realigning the stator, use this new mark as a base timing point. |
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Step 9
Remove the arrowed screws to get behind the stator plate. These screws strip easily, so push down on the screwdriver and use the proper sized driver. If you strip a screw, a pair of Visegrips will loosen it. Always replace stripped screws. |
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Step 10
Carefully dangle the stator from the case. NEVER ROLL THE CASE ONTO THE STATOR. There are a number of case screws to loosen (arrowed). Loosen them and store them somewhere safe. Many screws have a complimenting stud that will fall out as they are removed. |
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Step 11
There are a number of case screws to loosen (arrowed). Loosen them and store them somewhere safe. Many screws have a complimenting stud that will fall out as they are removed. The stud and nut under the flywheel is called the long case stud. It tends to rust and seize. If yours is siezed, order a new one from a scooter shop. |
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Step 12
With all the nuts removed you are ready to split the cases. Tap the point next to the oil plug (pictured) with a rubber mallet and a piece of wood and the cases will nudge apart. DO NOT move the kickstart lever. You should be able to simply pull away the case to reveal the gears. The picture shown depicts a metal hammer being used. After great debate, I have decided to amend this section. ***Ignore the metal hammer an use a rubber one instead. You risk damaging the cases with a metal hammer.*** |
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Step 13
A spring and the kickstart pinion will usually fall out of the case. collect them and inspect the pinion for wear. If any teeth are missing, renew the gear. The one pictured is not worn. |
Reassembly
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Step 1
Pull the old case gasket and rub remenants away with a wire brush. Rub a ring of assembly grease around the case edge and replace the gasket with a new one. If the old gasket is not torn, it may be reused in a pinch. Always renew the case gasket while the engine is open. |
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Step 15
Replace the kickstart pinion onto the layshaft with the teeth facing down. (pictured) |
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Step 16
Kickstart pinion Spring should be retained with a large glob of assembly grease, now flip the case and place it onto the other case half. Watch that the spring does not fall. press the cases together, moving the kickstart lever to mesh the gears. Tap the cases on any flat spot to push them together. Now follow the disassembly instructions to finish the job. |
So now you’re finished cracking the cases (use the reassembly instructions above after you have repaired the problem). You can return to the engine repair section and select a topic related to the inside of the cases. Above, I talked about blowback marks on the piston. These marks show that combusting gas is escaping past the piston. This is generally not a huge problem, but it should be remedied. To fix this situation you should take the cylinder to a machine shop to be honed and the piston rings should be renewed. The rings will just continue to deteriorate and a loss of power will result. The piston showed no signs of heat seizing, but it is generally identifiable by oval shaped scratches up and down the piston head. If you note such marks, this represents the engine overheating or the cylinder out of tolerance. Replace the seals, have a shop hone the inside barrel and renew the rings to prevent further siezes. You should also inspect your carb and timing if these marks are observed. Consult a scooter shop for further assistance.
Cruciform Renewal
Cruciform Renewal
Ever riding up a hill and your bike surges or slips out of gear? This is often the fault of a component in the engine called the Cruciform (or spider). The cruciform is a small cross-shaped alloy part used to select gears. It works by fitting into square cut outs in the gears themselves. This is a high wear part. Since there is almost no buffering between the gears, this part receives damage with almost every shift. Sloppy shifting will expediate its demise. Luckily, this piece will not hurt the steel gears when it slips. Unfortunately, it is buried deep within the engine. To get at it, start by dropping the engine, then split the cases and follow the procedure below. Before you attempt this repair, check that your gear selector box does not have any side to side play. Sometimes this play will make the bike jump out of gear. Replace the gear selector box components and try to make the bike jump. If it doesn’t jump, you have solved the problem. Otherwise change the cruciform and inspect the gear shims.
Tools & Parts Needed
Cruciform
Circlip Removal Tool
Red Grease Pencil
2 Feeler Guage Tools
Multi Screwdriver
Spark Plug Wrench
Disposeable Shop Towels
A can of Carb Cleaner
A Tube of Anti-Sieze Lubricant
13mm and 11mm Deep Socket
Torque Wrench (Absolutely neccessary, DO NOT perform without this item)
Plastic Bondo (Body Filler) Scraper
Plastic “Wire” Brush
Tub of All-Purpose / Bearing Grease (“Green Goop”)
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Step 1
First check the play in the gears. The gears should remain tight when jostled. To see a bad shim washer click here. More information about shim washers can be found below Using the circlip tool, remove the circlip around the rear axle. This will allow for the shim washer and the gears to be removed. |
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Step 2
Remove the shim washers and the gears. Marking the gears with a grease pencil will identify which side faces up when reassembling. |
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Step 3
You can now remove the selector rod, the rod washer and the cruciform. This shaft uses a left hand thread, meaning everything is backwards. To loosen turn clockwise, to tighten turn counter-clockwise. |
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Step 4
Sinch the lighting was pretty bad, we took the rear axle out of the engine to give you a better view of this part. You don’t have to do this. For all this work, you can now treat yourself to a pickle. We certainly did |
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Step 5
Here’s the selector rod. It’s a chunk of metal with a small washer on the end. The threaded piece threads into the cruciform. |
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Step 6
Turn the cruciform by hand until it is parallel with the rear axle slot. You can now just push the cruciform out through the side of the slot. place the new cruciform into the slot. The Cruciform will be fitted with the bend in the legs facing the rear wheel. |
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Step 7
This picture illustrates the damage caused to the cruciform by shifting between the gears. Always use Piaggio cruciforms when replacing the old one. The cheaper parts tend to wear faster and do not have as pronounced of a bend making them hard to fit correctly. |
The shim washer is incredibly important to the operation of the gears. You should make sure that this item is sound before closing the engine. To test the space use two feeler guage tools and place them under the shim washer. The allowable slack limit is 0.50mm (0.020 in). Oversizes are: Stock – 2.05mm (0.081in), 1st oversize – 2.20mm (0.087in), 2nd oversize – 2.35mm (0.093in), 3rd oversize – 2.50mm (0.098in), 4th oversize 2.65mm (0.104in). Once everything is in good condition, replace all the gears, the washer and the circlip. Then continue to reassemble the engine cases or continue to fix problems in the engine.
Cleaning The Top-End (Decoking)
Cleaning The Top-End (Decoking)
This tutorial will demonstrate the process of decoking the top end, or removing the carbon deposits from the engine. This is a standard maintenance and should be performed every 6000km (4000 miles), or every year for machines that are never heating up (quick hops about town). It will be virtually impossible to get all the crud off of the engine parts, so don’t be overly compulsive about it. Though the process seems daunting, like putting a wheel together, it is one of those chores that you will be able to fly through after your first go. I would give it a few hours for the first time. I hear some asking, “why should I do this; my engine runs fine?” This procedure is important because of the heat and power restrictions a two stroke engine has to contend with. By letting junk build up on the piston, cylinder and head, you are effectively decreasing the fuel capacity of your motor (ie 200 cc to something slightly less). Since waste carbon, commonly called coke, is left from burning two stroke oil, the engine will suffer from an overly “rich” condition and generally run badly or start hard. A few signs that your top-end may need to be cleaned are oily, constantly fouling spark plugs; hard starting (more than 4 kicks) and lots of exhaust smoke. I would reccomend you preced this operation with a carb rebuild when attempting for the first time. Synthetic lubricants will increase the period of this procedure, but it is still worthwhile to consider attempting every year. This procedure is best done in a covered, well lit area (like a garage) so no crap gets into your top end.
Tools & Parts Needed
Multi Screwdriver
Spark Plug Wrench
Disposeable Shop Towels
A can of Carb Cleaner
A Tube of Anti-Sieze Lubricant
13mm and 11mm Deep Socket
Torque Wrench (Absolutely neccessary, DO NOT perform without this item)
Plastic Bondo (Body Filler) Scraper
Plastic “Wire” Brush
Tub of All-Purpose / Bearing Grease (“Green Goop”)
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Step 1
Undo the arrowed screws and the flywheel shroud will fall right off. Put the shroud and all the little screws in a safe place (or sand it down and paint it if you have a day or two). |
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Step 2
Gently prise off the spark plug connector and put it one side. Undo the Shroud bolt right next to the spark plug. Unhook the air bellows from the frame and push it to one side. Slide the cylinder shroud off of the engine by pulling towards the front of the bike. You should now be able to see the cylinder. Remove the sparkplug with the sparkplug wrench. |
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Step 3
Remove the nuts by loosening them slowly in this order. Do a quarter turn, go to the next, quarter turn, next, quarter turn, next, etc. until the nuts are removed. This will take a while, but you risk bending the aluminum head if you don’t do them in small steps and in order. The same is true for tightening. Carefully collect the hardware and remove the cylinder head. |
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Step 4
Since the flywheel is connected to the crank, you can raise and lower the piston simply by turning the flywheel by hand. To start, position the piston to the top of the bore. You are now ready to start cleaning. |
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Step 5
With the piston at the top of the bore, rub a ring of all purpose grease around the circumference of the piston head. This will catch any little chunks of carbon. If your piston is totally coated in carbon (like mine) use a plastic scraper to get most of the crud off. When you are done scraping, remove the remainder with a plastic “wire” brush. Metal is NOT reccomended. |
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Step 6
Wipe off all of the grease from the scraping. To clean the sides of the piston and bore, apply another ring of grease and turn the flywheel slowly. The piston will recede into the bore. Go halfway down, rub away some of the grease with a disposeable towel then go to the bottom and repeat. Keep re-applying grease until the metal on the bore is clean. |
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Step 7
To clean the cylinder head, use copious amounts of carb cleaner and shop towel, the carbon doesn’t tend to stick quite as badly to the head and there’s more room to work on it. This part, if any, should be sparkly aluminum grey by the end. Once you finish cleaning the head, spread some anti sieze lubricant (stops threads from stripping) on the thread on the cylinder studs. |
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Step 8
Put the head back on. Hand tighten the screws in order until each becomes snug. Then, using the quarter turn method, tighten the screws with a torque wrench, in order, using a torque of 1.7-2.2 kgf m (12.30-15.91 lbf ft). Re assemble the bodywork in the reverse order. Install the Spark Plug last and reconnect the bellows be stretching the rubber around the lip on the frame. |
Once all the panels are back on the bike, kick start the engine as usual. The engine should roar to life after a few kicks. If the kickstart lever doesn’t feel firm or if the the engine will only run when the choke is turned on, you have an air leak. This will probably be caused by the sparkplug not being tight enough (*The plug is touchy, don’t tighten it too strongly or you will rip the threads out of the aluminum*). If you did rip the threads, there will be a leak around the damage — take the piece to a machine shop and have them install a “helicoil insert”, and remind them of the fact it is a cylinder head so they can use a high heat transfer coil. This will replace the old threads and make a much stronger thread. If the plug IS seated properly, the cylinder head may be warped from improper tightening. IF YOU FOLLOW THE RULES, THIS WILL NOT HAPPEN. However, if it is warped, you will need some 400 grit wet/dry sandpaper and a piece of glass. Tape the paper to the glass and wet it. Hold the cylinder head in your palm and rotate the bottom on the paper until it is flat. Once you are done remount it and try again. This maintenance should be done yearly for year round riders, every 6000km (4000 miles) for the “rally only” types.
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