Okay guys, One of my buddies have a 1998 Yamaha Blaster 200. Well We are going to trade for a 50 cal Muzzleloader. The only problem is...... Its blew up. He said it just needs a piston and rings. Well Here is what im confused on. I can replace the piston and rings for 150$ but he said its bored out to a 250. so .50 over i think. Not sure. If he blew it up will i have to have it rebored or anything like that? Or just get a new piston for the size of the Cylinder?
Call me a Newbie!!
- Thread starter 1998BlasterYama
- Start date
You need to take the cylinder to a shop and they will tell you what size you need. 50 over doesn't make it 250cc.
A huge bore! CWR has a 250 kit. A half mm is only .020 so from a 195 it's around 198-200~ 2mm overbore only makes a 209 I think
Blaner
Your Friendly South African Ambassador
you need a big bore kit and a +4 inch crank to get it to a 247cc. 0.5 over bore means instead of the bore being 66mm in diamter it is now 66.5mm. Do the maths with some volume of a cylinder calculations and you will see what we mean. stroke is 57mm.
so π x r 2 x h = Volume of cylinder
therefore: π x 33.25 2 x 57 = 197.93cc
so π x r 2 x h = Volume of cylinder
therefore: π x 33.25 2 x 57 = 197.93cc
The correct way is to measure the bore or have it measured, Most machine shops will do this for you and bore/chamfer the ports, to the next size piston. Cheap piston are $65, good weisco piston is $90ish bore is about $50ish. That is the correct way to do it!
This is the next size weisco available- 66.75mm 0.75mm Cylinders: 1
Displacement: 199cc
Stroke: 57.00mm
Again , boring a cylinder over stock does not increase the cc by the same amount!
Wow guys thanks for the input!! I really Appreciate it, Do you think thats a good deal though? Trading for a 150$ gun if i have to replace the piston?
Sounds like a decent trade as long as the problem is isolated to the top end. MOST of the time, a "blown up" 2 stroke engine only needs a bore job and a new piston. This work can be performed by *most* local machine shops (I've heard horror stories about particular shops in some people's area) as long as the specification is provided.
2 strokes (and blasters in particular) are quite simple beasts in that they do not have a valve train that needs adjusting or any valve timing that has to be looked over. The downside is that they have some specialized maintenance that needs to be attended to (less than a 4 stroke of similar power output, just different). This includes leakdown tests performed after any maintenance and compression tests on the regular to assess the piston/cylinder/ring life.
The very first thing I recommend you do is go to the general support section and download the downloadable manual. If it helps, you can print out the PDF version and make a hard copy service manual. You can read through some of the procedures for caring, disassembly, and reassembly of your new ride.
The second thing is to read, read, read, read. There are tons and tons of posts on here giving good solid information (and dispelling myths that exist about 2 strokes, AND BLASTERS!) in the engine, general support, and ask a pro sections.
Third thing is, if you still don't understand, ASK! We're pretty forgiving around here about noob questions I:I
Boring a cylinder involves removing a small amount of the iron liner (the black part the piston rides in) in order to clear up damage. This process involves removing a specified amount of material (in the case of a blaster, stock being 66mm and largest available 68.25mm bore sizes in .25 or .010" increments) to go to the next "upsize" piston.
Boring a cylinder .050" (50 thousandths of an inch) or 1.25mm (to 67.25mm) does NOT increase power output or displacement significantly. It's only there to clean up damage to the cylinder from previous running.
In order to hit 250cc's you need a 240cc big bore kit on it's last life (73mm versus the stock cylinder's 68.25mm) and at least a +3mm stroker crank. while this could be a "wild" ride, it's also generally short lived and thus nor recommended to someone who doesn't know the pitfalls associated (and the risks involved). When you get the engine back together and running properly, the first thing you're probably going to want to do is upgrade. You didn't mention if this is a completely stock blaster or not but I'm assuming so for a moment.
A decent pipe kit, carburetor rejet, airbox lid removal, replacement rear tires (to ditch the balloonies), and consider upgrading the front brake setup. Doing all of that will run you a little cheddar, but you'd be AMAZED at how well it wakes up the stock "lazy" blaster.
Once you've done all of the "bolt ons" then you can get into things like stroker cranks, heavy porting, head rechambers, bigger carbs, higher end pipes, stretched a-arms, and stretched swingarms.
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