As we all know new barrels for the RD are close to impossible to find. If you do find them they cost a ton. And even if installed at best you have a stock bike performance wise. The metal and porting tech used is early 70's this is a serious limiting factor.
Porting is an option but very few of us can get to cut up a new set of barrels. When we know a slip of the hand or even 1mm here or there could well ruin the engine. Nobody wants to risk the only original set of barrels they own.
Sleeves have been tried and failed miserably in the past in India. There are many reason why they never took off the number one reason being the lack of proper equipment, skills and proper way of doing it. If your out by even a few microns the job is a waste. Another reason for their failure in the country has been the poor quality of liner material being used. And the process by which they are designed and cut. And installed.
Details of what's going wrong in India with our sleeves.
a. Material:
People believe sleeves should be made from Cast Iron. Most cast Iron in the south comes from Coimbotore. This is very crude steel. And is way too soft. Blocks are purchased and cut into sleeves. Actual material should be much much harder. The cast Iron being used in most cases is too soft. 10-12 HRC You need to start with a high carbon, silicate steel combo that has a hardness of at least 35 HRC.
b. Method.
They are starting with a block which has its OD and ID turned down on a lathe. They also use the Lathe to bore out the old liner. This is the wrong method. The right was is to use a Cylindrical grinder. Next the locking mechanism they use is at the bottom. It should really be on top. The only reason I can see for using the lock at the bottom is that the finished product looks more like the original. Looks don't matter here what does is making sure the sleeve doesn't move. Next for drilling the holes and tracing the ports there is a total lack off accuracy. You will often find ports opening at different times. And port sizes are never the same. Ring support between the liners are also never the same size.
Then to cut the ports they put the sleeve on a drill press and using drill bits start drilling a series of holes to cut out the ports. This pressure wraps the liner. Its always best to use a grinder with very little pressure on the liner to cut the ports.
c. Installation.
In most cases the liners are press fitted. In most cases the ports never line up properly so they push it in then they push it out. And halfway in they start rotating the liner with a bar while they are pressing it in. In most cases the fit starts to get too loose so they leave it a little out in the end.
IN some cases they dont bore out the complete old liner. A thin layer off the old liner is left. The new liner is then pressed in. This is called a half sleeve.
The problems with this is that 1. Now theres an extra layers for the heat to pass thru. First the new liner then the old liner and then the barrel. They have to leave a portion off the old liner in the new liner can only be 2-3mm thick. This isnt the thickness of a liner.
So how did we go about it.
a. Find a set of wasted barrels. Something that has been bored out or has an existing sleeve. Next we need to bore out the existing sleeve. This is the most critical part in getting the new sleeve to sit. Tolerance levels here are in microns. The old barrels are put on a computer controlled machine that centers and lines up the barrel to be cut. The old sleeve is then removed. What you will get looks something like this
You will notice that the ports are all much more accessible now. And you can clean them up or port them as you like. I normally do a clean up and if the exhaust or transfers need to be dropped this is done at this stage. You also need to have calculated your sleeve OD and ID so that you the bore you drill is 10-120 microns smaller than the sleeve's OD.
Next you need the Sleeves. The sleeves are sold as blanks depending on the size of piston. The ones pictured below are for the RD350.
The next step is to chose what type of porting setup you want. RD Stock / TZ / TD3 / Custom etc. Its important to get the collar right as this is the point from where all your ports are measured.
You either print out your port map or transfer it onto the barrel with a piece of carbon paper. I prefer inserting the sleeve into a dummy barrel I have then pour a mild acidic solution in. when the liner is removed the transfers and ports are traced on the liner. Another method is to do your port map on a computer print it out and stick it over the sleeve and trace out the ports.
Once you have your port shapes drawn on the sleeve you cut them out. Using what ever tool you like. I use a combination of various Dremel bits. With the Dremel Flexi shaft. Drilling is avoided because of the risk of wrapping the barrel..
Once you have your sleeve with the ports cut out. You have the inside dia and outside dia ground down. There is a special machine for this don't try doing it on a lathe you wont get the desired results. The outside dia of the sleeve has to be kept 10-20 microns more than the dia of the barrel.
Next the sleeve is submerged in a liquid nitrogen bath to super cool it.
At the same time the barrels are heated. Wearing gloves you can now drop the sleeve into the barrel and rotate it to get the ports to line up.
Porting:
With the sleeve in the barrel. Depending on the porting design you will find that the barrel and sleeves don't line up in certain places. You have to use a grinder or porting tool and remove material from the barrel to line it up to the sleeves. How much and where depends on how much you did before putting the sleeve in. I normally only leave the exhaust port and the transfer widths for this stage. If your using a really radical TZ design with bridged exhausts and Intakes you will need to have filled in the old ports. And now remove material leaving support for the bridges so the heat can be transferred.
Preparing for Boring:
Many people talk about chamfering the ports after they get it back from a re-bore this isn't something I recommend. You dont want to be touching your barrels once they are bored. The hone finish is done in microns. And can be ruined by even dust. Much less and emery paper or power tool. So prepare and dress your ports before you send them into be re-bored. Chamfer the ports with a nice big chamfer so the edges are well radiuses. My friend T-Rex tells me this helps flow.
The single most important step in your complete engine rebuild is the quality of the re-bore. Go to somebody who has the necessary equipment. Take both pistons with you and mark them left and right. Engine life and performance depend more on the quality of your re-bore than they do on your porting or any other factor. So make sure that the person who will be honing your cylinders or sleeves is offering you an accuracy of 1-2 microns. And has the special honing attachment for ported 2 strokes. Which is different from the honing setup used on 4 strokes.
A clearance of 2 thousandth of an inch is recommended but I used 30 microns on this set.
This is how the hone finish looks like.
At this point the barrels should be wiped clean with a lint free cloth and packed in a polythene bad. The person who does you rebore will do this for you. Be careful not to let any dust or dirt enter the barrels they will result in small micro scratches that will prevent your rings from sealing latter.
This is the finished product.
A rubber abrasive wheel will be used to smoothen out the transfers, and radius the port edges. And the barrels washed in petrol. I regret not having finished the final touch up stages on this barrel before getting it re-bored. Because this could result in dirt getting onto the sleeves. Next time I hope to finish everything before the re-bore. There was a huge waiting period to use the new boring and honing tool so when we got a chance to have it done the same day we rushed with the barrels. The black marks you see on the sides of the boost port show where the ring gap will be. As you can see the boost port can be widened quite a bit still.
Tip for big bore kits. As you have total control over the design of the sleeve you can either opt for a big bore setup or a setup that will allow you more re-bores. i.e. if you keep the liner thick enough you can keep re-boring the sleeve well past 2mm oversize. The tip for the big bore kit is to bore out the old sleeve off center towards the exhaust port this allows you to use a big bore sleeve without seriously effecting your the area of your transfer ports.
I'm no expert at this. So if you feel there are any mistakes or areas for improvement we would love to hear from you. The complete exercise was conducted while my PC was down hence the lack of Photos for the complete process. We have experimented a lot with different porting setups. The setup you see pictured above basically has the Aux transfers enlarged quite a bit i.e. Aux Transfer width is now at 18mm. The Boost port width has been widened marginally and cut back. The size of the main transfer has been reduced with the wall close to the exhausts cut at angle. This allows the exhaust port to be widened quite a bit while still providing good ring support.
The previous set which is already running in the bike has much larger and radical porting. And has produced amazing results. I will try and dig up pictures I took of the sleeve.
At present we are offering Re-sleeving of old barrels to stock or any porting spec you want for 75$ a barrel or 150$ for both. This includes the cost of the sleeve and porting and boring. But not the cost of the pistons. You have to send in your old barrels. We haven't worked out a cost as of yet for the Bridged Intake and Exhaust setup as yet. But expect it to be around 150$ for each barrel. We honestly feel that this setup will perform better than the stock barrels and are targeting the local market with this idea.
What next you ask. Well we are tying to build a block with a water jacket.
Cheers and ride hard.
Update: