As a minimum you are going to need:- 

Parts  

Piston kit – you will only know what size when you have stripped the top end down unless you have a record & are performing a routine rebuild. From my experiences I recommend Wossner – check phoenixmotos.com for part numbers  

Little end bearing – check phoenixmotos.com for part numbers 

Top end gasket set – check phoenixmotos.com for part numbers 

2 stroke oil 

Petroleum jelly (Vaseline) – others advocate grease 

Spark plug – check phoenixmotos.com for part numbers 

Coolant – for water cooled bikes 

Carb & choke OR brake cleaner 

Supply of clean rags 

You then may need some extra parts as mentioned above in the previous section. 

Sometimes there are curve balls thrown in for example I have just started doing a top end where I discovered that some of the cylinder base studs were incorrect and therefore needed replacing.  

As I discover something that needs replacing I like to add it to my list for this particular job and then try to order everything all together once all the inspections have been carried out. 

Prepping the parts 

Any items that need external work should be sent off for that to be done and all parts required should be ordered 

While you are waiting you may as well do things like scraping the gasket off the crank case and cleaning the carb.  If we didn’t need to send the cylinder away for work then we can deglaze it too if this is needed 

Gasket scraping 

OK so this is mundane. When my kids want to come and help me building engines I invariably give them a bit if gasket scraping to do.  They hate it but it’s such an important part of the job it’s important to learn how to do it and to have the patience to do this properly. The gaskets we are talking about are cylinder related gaskets:- 

• Base gasket 
• Power valve gaskets 
• Inlet manifold 

The Gasket scraper should be used with some pressure but not too much and at a shallow angle. We want to avoid using the corners of the scraper and we DO NOT WANT to damage the metal surface.  The gasket is there to create a seal between the 2 sealing surfaces, a damaged surface will prevent a seal being created. 

First of all we want to make sure the rag is still stuffed in the crankcase preventing anything getting in there (bits of gasket). Starting with the crankcase use the gasket scraper to scrape the gasket from the sealing surface – it either comes off easily OR it doesn’t! Now do the same for each of the other sealing surfaces including the bottom of the cylinder if you have it to hand. 

Airbox clean and fresh air filter 

If you’ve not got a clean oiled air filter in the bike, remove the old one. Now clean the inside of the air box and air boot.  Be very careful not to get debris OR water (if using water) in the crankcase (try putting a plastic bag over the conrod and taping it to the crankcase). I prefer to use Carb cleaner and a rag for cleaning. 

Install your freshly cleaned OR new freshly oiled air filter into the airbox. I like to smear a ring of grease onto the airfilter sealing surface that mates up to the airbox as this creates an extra seal preventing dirt getting through to our beautifully built top end! 

Carb cleaning 

Turn the carb upside down (you may need to rest it on something) and remove the float bowl.  

If the bowl is stuck, lightly heating with the hot air gun / hair dryer and tapping lightly all around with a non-damaging object (ideally plastic) – patience here as it’s better to take the time using something light and do this slowly rather than damage something.  Keep lightly heating and lightly tapping and it will eventually come free 

Remove the floats and float needle, The pin will either slide out easily or can often be stuck. Again patience is needed.  

If it won’t easily slide out:-  

• soak it overnight in WD40 / penetrating oil 
• Rest the underside post on something like a socket 
• Use a fine punch and a very light screwdriver to carefully tap the pin out 

Remove  

• Air screw 

• Choke 
• Main jet 
• Pilot jet – be very careful to select a suitable screwdriver so as not to damage the jet 

you can check the standard jet sizes and specs at phoenixmotos.com 

Use carb and choke cleaner, an old screwdriver and nylon brush.  Soak the jets and clean anything you can get to.  use an air line blower to blow through all holes if you are using compressed air.   

Use the carb cleaning wires to ensure the pilot and main jets are clear  

if using an ultrasonic cleaner – this can be used at any stage. You ideally want some carburetor ultrasonic cleaning solution as this helps.  I like to get the worst of the dirt off before using the ultrasonic cleaner so that it doesn’t wreck the fluid.  If it is still quite heavily soiled you can run through a few cleaning cycles with water & washing up liquid before using your carb cleaning solution to get the carb assembly and jets really clean. 

The cleaner can help clear the holes in the jets and also in the removal of the float pin so it is worth making use of it where you can. 

Once everything is cleaned, reassemble the carb.  

Now is a good point to check your float height, ideally get the manufacturer spec BUT if you cannot find that a good rule of thumb is that the float should sit parallel to the carb body when help upside down.  If not, you need to bend the tab which sits on the float needle until you are at the correct height. 

Once you have the float bowl reinstalled I like to check to see if the carb is overflowing as it’s easier to correct with the carb off the bike – hook it up to fuel whilst holding it level and wait.  If it is overflowing check float height and or change the float needle. 

Cylinder prep 

You can deglaze your cylinder at home or you can take it to an engineer who can hone it to spec.  The professional hone is the best solution to get the bore to spec but if the bore is in good order just a bit shiny a deglaze is the what I would do.  I do plenty of deglazing of cylinders at top end rebuild stage.   

The Glaze buster is simply going to re cut the cross hatch marks into the bore which will mean that the piston rings will seal against the bore – the cross hatching won’t be as uniformly perfect as a professionally honed cylinder but in most cases it is all that is needed.  

You need to select the right deglazing tool for the job:- 

• For a 2 stroke cylinder you want a 3 jaw deglazing tool 
• iron bore =  Silicone Carbide deglazing stones OR Nikasil = Aluminium Oxide 

Set the diameter of the deglazing tool to just greater than the bore itself.  hold the cylinder still on your bench (I often drill 2 holes and bolt it – it sounds destructive but it’s a good solution). Set your drill to a low speed and run up and down the cylinder a few times until you have a cross hatched pattern 

If you sent your cylinder for replating you should have already followed the chamfering advice here as your ports needed to be chamfered before sending your cylinder away.  If you have just had a rebore or a new liner it will come back needing chamfering. 

We need to address every port in the cylinder. We are most concerned with the horizontal port edges as they will cause the most damage to the piston rings. I use a dremel with a cylindrical sanding drum to make a chamfer on the port therefore removing the sharp edges and slight burrs. Be careful on the corners. and although it is more critical to do the horizontal port edges I do chamfer or at least clean up all of the edges as any sharp edge has a potential to cause slight damage to the ring. 

Now you have smooth chamfered edges to your ports we can move on to the rest of the prep and the easy bit – the actual build! 

Cylinder cleaning 

We have more than likely done work to the cylinder and that work will have caused debris. We want to get this debris out of the cylinder as it will cause wear to the parts we are installing which we don’t want. 

First wash the cylinder thoroughly in warm soapy water then rinse in clean water 

Dry the cylinder thoroughly – ideally with an airline blower if you have one 

Use brake or carb and choke cleaner to give the cylinder an extra clean with solvent and blow off or wipe clean with a clean white cloth to ensure it is thoroughly clean. 

Re-install your reeds and inlet manifold with fresh gaskets and a light smear of gasket sealant – this area is prone to leaks which can be catastrophic. Any time you need to remove it always use new gaskets and gasket sealant. 

Power valve cleaning 

The power valve assembly and associated parts need to be cleaned as thoroughly as you possibly can to ensure a smooth operation when reinstalling into the cylinder. 

Spend time making it as clean as it can be and lubricate moving parts to ensure everything will operate flawlessly. I choose 2 stroke oil to lubricate these parts as they are involved in the combustion cycle 

Power valve re installation 

Install the power valve – Have a look in the Resources section at phoenixmotos.com for guidance on installing your specific power valve.  If you can’t find your specific model email me at [email protected]  

Piston and rings 

If your cylinder has an exhaust port with a bridge, you need to drill exhaust port lubrication holes in the piston.  I see this as a critical stage if you have an exhaust bridge. It vastly improves longevity and significantly reduces the chances of a seize in this area. In order to do this you need to temporarily install your piston. 

Coat the little end bearing in 2 stroke oil and install in the conrod 

Coat the wrist pin in 2 stroke oil and insert it into 1 side of the piston 

Align your piston and wrist pin with the little end bearing (ensure the arrow on the top of the piston is facing to the exhaust end of the crankcase) and push the wrist pin through so that there is no pin exposed on either side of the piston 

Remove the rag from the crankcase 

Slide the cylinder over the piston and down into place on the cylinder studs 

Rotate the engine so that the piston is at the top of it’s stroke, double check that the cylinder is in place 

Using a scribe score the piston on either side of the exhaust bridge 

Remove the cylinder 

Remove the wristpin and piston – put the wrist pin somewhere clean (I often use a sandwich bag) 

Using the same scribe and a straight edge (metal ruler), draw a straight line in the middle of the 2 lines you drew on the piston 

Protecting the piston with a rag, install the piston into a vise or a drill press vise if you have one 

Use a centre punch or other punch to mark your 2x drilling locations – they do not have to be exact but approx 10mm from the top of the drawn lines and approx 10mm up from the bottom of the drawn lines 

Now use your drill or drill press to drill a 2mm hole in each of the marked locations – drill slowly and cautiously so as not to slip 

Ideally use a counter sink drill bit to clean up the edges of the holes you drilled (similar to chamfering ports this should remove all sharp edges) 

Use a fine file or dremel on the inside of the piston to clean up the insides of the lubrication holes 

Now you need to thoroughly clean the piston to ensure no little bits of piston swarf are left – especially as there has been 2 stroke oil used to lubricate the wrist pin. 

Replace the rag into the crankcase 

Piston ring gap – this is a highly important BUT for the Wossner piston kits I recommend the rings are pre measured and set with the correct gap for the desired bore size and do not need measuring or setting. Over the years since using Wossner I have measure many ring gaps and never found them to be out of spec. 

Copper Gasket 

If you use a copper head gasket – it will need to be annealed. Annealing the copper makes It softer and that will make it seal between the cylinder and the head once torqued down 

Annealing is a hotly debated topic but it is required.  

The gasket needs to be heated to a cherry red colour – I personally think Oxy acetylene is needed, I haven’t been able to get them hot enough with propane or MAPP gas. I know people swear by ovens and electric hobs but I have not tried this.  I believe you need to get the gasket to 400c so I know my oven won’t do that. 

I place the gasket flat on my vise and heat up to the cherry red state and then leave to cool down naturally. 

Once cooled use steel wool to clean the oxidisation from the surface of the gasket – clean with a little solvent (brake or carb and choke cleaner). The Gasket is now ready to use.