Low compression what should i do.

ATrain666

New Member
Apr 26, 2009
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Tioga, PA
I took a compression check on my 2003 blaster today and i came out with a reading of around 70 psi. Should i just replace the rings since the motor isn't blown or should i just go ahead and to a top end rebuild on it and do all the break in stuff for it. If i do end up going with a top end rebuild then what should i mix my gas at for the break in peroid. Normally i run 32-1 ratio in it, premixed.
 
thats pretty much what i was thinking of doing but i dunno if i should spend the 130 bucks on the top end rebuild kit or just buy the piston kit for like 100 bucks. Or just replacing the rings for 35 bucks.
 
piston and rings def and incase u didnt know since i just figured out u have to kick it over with the throttle wide open idk if u know which u probly already knew but yeh ... piston and rings
 
i don't have to kick it over with the throttle wide open though it will start up without even touching the throttle. its already has a wiseco pro lite piston in it from somebody else put in it. im also thinking about just boring it out since its still the stock bore and going with the 40 over kit.
 
oh i didn't kno you already were running a wiseco piston.. in that case i would pull the top end off and inspect the piston make sure it looks good, and i would just replace the rings. i wouldn't bore it out until you need too. i would just spend the extra money on some other mods for ur blasty..
 
thats the thing i dunno how long the piston has been in the bore for. i was thinking about just boring it out but i dunno if i want to go 20 over or 40 over that way its already done with a fresh piston and rings and bearing and i dont have to do it again a short while later.
 
i just bought a wiseco pro light piston kit on ebay for 95 bucks, 105 shipped. New piston, rings, pin, clips, bearing and all gaskets. IM no expert but couldnt you just buy one of those like i did for the stock bore. Couple hours later and out 105 bucks and you have a new blaster, lol.
 
If it was me I would spend the 10 minutes it takes to remove the head. I would inspect the cylinder wall and see what else I can see. At that point I would make a decision...

A. Cylinder wall looks ok... I'm gonna get some rings.
B. Cylinder wall is in bad shape, or possible bad shape... at that point I would spend 20 minutes to remove the jug and get a real good look.

I'd then hone the jug with my el cheapo $30 hone, then take it to a place that can check the cylinder to see if I can get away with the hone or I need a new piston and bore.

Then I'd buy the piston, give the piston and jug to the bore guy, a day later my craps done and I spend an hour to put it back together.
 
Kick at least 8 times for best reading.

Also dont bore it unlesss it needs it,boring add's NO power,just takes away from your jugs life. So check it out and tell us.
 
Maybe I'm thinking way out of line but why would you bore a stock cylinder to a point that is not needed? If it needs bored, bore it to the the smallest overbore you can get away with. That way if or when you have top end problems you have a bigger chance of saving the cylinder.
 
I've finally decided that im just going to hone my cylinder and put new rings in it if my bore isnt to bad. I checked it about a week ago just to see what my piston looked like and check the bore size. it looked pretty good to me. thanks for your guys help with this.
 
Just bought a top end kit of ebay for 105 bucks shipped in the standard bore so im gonan hone and hopefully it works out for me. Thanks for all your help guys.
 
Alright got an update for you guys. I sent my cylinder out to be honed only to find out that the place i took it doesn't have the right tools to do it. I talked with a local Yamaha dealer around here and gave him my situation and he told me that i need to get it bored to the next size up. I talked to another dealer around here and he told me to bring it in and he will look at it. I am unsure of what to do with it. I already got a stock 66 mm replacement kit for the top end and everything but the gaskets and jug are installed. what do you guys think i need done?
 
either take pics and post them up or let the dealer look at it, if it needs bored then theres no way around it you have to order a bigger piston, but if its ok just have it honed and put it together