25 psi of compression!!! Now what

U

Uptown_Blaster

New Member
Mar 15, 2010
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Philadelphia
I was riding last thursday and my blaster decided it did not want to start. It always took my 10 to 15 kicks to start but this time it just started backfiring. I took it to the shop and they said it had 25 psi of compression and Im lookin at $1000 worth of work.
So I smiled and brought it home. From searching on here Im pretty sure I need a top end rebuild but im still extremely new to this. So my question . . .what the hell am I looking at. The guy at the shop made it seem like I should my back but I just got it a month ago. The plug is new, reeds are good, carb is clean. I have no idea how to pick a new piston. I see wiseco is the way to go but im looking for a little guidance. Im tryna understand exactly whats it means to "bore over 20" etc. Im gonna take it apart tonight and hopefully somebody will reply by then. (sorry for writing so much).
thanks
 
basically "bore over" means that you take it to a machine shop and they actually enlarge the bore to fix any imperfections in the bore. the machine shop will be able to tell you how big you need to go. its not that hard of a job to do and it'll only be about 200-250 bucks for a full top end rebuild

60-70 for bore/hone
90-100 for the wiseco piston kit w/ rings
like 30-35 for a cometic gasket

some parts stores have machine shops like some napa's and such
 
Well, first pull your cylinder off, if it has scars or deep scratches, it will need to be bored over...But in order for a machine shop to bore it out the correct way, you will need to order a Wiseco piston kit...There is different kits....if the scars arent very deep, a Wiseco Piston Kit PK1090 will be the best choice...Take your piston kit, cylinder, and head all down to the machine shop to get a bore and hone....If you need anymore help just send me a PM (Private Message)
 
Blaster200boy said:
Well, first pull your cylinder off, if it has scars or deep scratches, it will need to be bored over...But in order for a machine shop to bore it out the correct way, you will need to order a Wiseco piston kit...There is different kits....if the scars arent very deep, a Wiseco Piston Kit PK1090 will be the best choice...Take your piston kit, cylinder, and head all down to the machine shop to get a bore and hone....If you need anymore help just send me a PM (Private Message)
Click to expand...

u gotta take the cylinder to the machine shop first to see what size piston to get
 
yes!!!! make sure the machine shop tells you what piston to get otherwise you'll either get one too small or one that's too big and you'll waste bores and make the machine work more expensive
 
i would get a oem book make sure u have all of the tooles like a torq wrench. since its ganna be your first time doing a top end read the book first make sure u understand it use zip lock bags and a sharpe to label where you pull bolts from. ask questions when needed and take your time. 20 over 30 over is the size of over bore needed to clean up any flaws or scratch or wear to the pistion wall of the cylinder. its not hard one u do it once ot twice. good luck
 
Thanks for all the help. This all def helps. What would be a good place to go?? I dont wanna go back to the bike shop because they are obviously trying to get over on me. I am def sure I can do this myself I just dont wanna make a mistake and its a great way for me to learn.

O and since my psi was so very low, is there a possibility that something else could be wrong or is it normally a straight forward process when there is low compression?
 
the low compression is either bad rings or an extremely severe air leak, but being that bad i'd say rings.
 
Ok, I'm probably going to put some pics up as soon as I tear it down and get the cylinder off. I'm assuming once I get the cylinder bored and honed, and i find out and order the correct size piston, the actual installation of the new piston is a fairly simple process or is there something special. Do the rings go on the piston a certain way or do they just slide right on.
 
Why dont you get a compresion tester and test it yourself first......

As for the piston install it is straight foward. The piston has an arrow on the top that points to the front of the motor( Towards the exhaust) and there are spots on the piston where the rings go. When you have the cylinder bored/hones the shop should gap your rings for you also.
 
OEM style rings have an up and down side, not positive about wiseco, but the guy at your machine shop (hopefully a bike shop) should put them on the piston for free. They can break if installed incorrectly.

The hardest part of the disassembly (and reassembly) is getting the circlip out of the piston so that you can remove the piston pin and get the piston off the rod. A very small screwdriver works ok for this. Def read the manual and look at lots of pics.

If you can't find another shop to deal with, don't be too afraid to go back to the $1000 guys. They just saw lots of dollar signs cuz their shop rate is prob about $100/hr and there is a bit of time involved in a rebuild (plus parts markup). But you are cutting out most of that by doing it yourself, right?
 
This is all very helpful.

Just some pics to go with my situation. I pulled the cylinder and the piston. There appears to be a couple of deep scratches in the cylinder wall. I hope the pictures are clear to everyone. Im not sure what the numbers on top of the piston say. it looks like the second one ends in 6600, does that mean its 66.00. Like I said i'm still new to this so I'm tryna figure out what size piston I'm going to have to order. I know I'm going to have to go to the machine shop but a little insight never hurt anybody.

Thanks

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looks like the top ring is seized up in the piston. the 66mm is a good thing though that means its a stock bore, and that bore doesn't look that horrible
 
That doesnt look to bad bro. As for the 6600 on the top of the piston you are correct in that is 66.00mm which is stock bore. The way it looks you will be fine ordering a .10 over 66.25mm Wiseco Pro-Lite piston kit. But just to be on the safe side you should take it to a machine shop and have the cylinder checked out meaning measured and checked for roundness.
 
ya i agree u you should have it bore first then get the pistion then u will know what to get this will save u time and money. that would be like buy 38" tires when u dont know if u are getting a car or a truck.
 
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