So I tore down my engine today...

[wwholden]

Ok so I found a shop that will bore out my cylinder for $35. Over the phone they told me that I need to bring the new piston to them also. So the can get the clearances right Im assuming. I measured my bore and It looks to be a .40 over or 67mm. My question is what size piston should I go with? Based on my pics from the first page will a 67.25mm be enough to take out the scores or should I go 67.5mm?

 

[Triple_B]

A bored .040 cylinder is 67.00 mm. Therefore, you will need a .040 piston.
I must warn you, ONLY buy a Wiseco piston, there are no other better pistons out there. ProX, Namura, and all those other brands are all CRAP! Cast pistons are garbage, so Wiseco is the way to go since their pistons are forged aluminum. You can get a .040 Wiseco Piston off of ebay for $87 shipped, or you can get one off of Woodward Specialties for the $83 shipped. Either way, only buy Wiseco.

eBay link: Yamaha Blaster .040 Wiseco Prolite Piston Kit 573M06700 | eBay

Woodward Specialties's website isn't working for me, but you can just search for Wiseco and it'll come up

 

[sicivicdude]

A bored .040 cylinder is 67.00 mm. Therefore, you will need a .040 piston.
I must warn you, ONLY buy a Wiseco piston, there are no other better pistons out there. ProX, Namura, and all those other brands are all CRAP! Cast pistons are garbage, so Wiseco is the way to go since their pistons are forged aluminum. You can get a .040 Wiseco Piston off of ebay for $87 shipped, or you can get one off of Woodward Specialties for the $83 shipped. Either way, only buy Wiseco.

eBay link: Yamaha Blaster .040 Wiseco Prolite Piston Kit 573M06700 | eBay

Woodward Specialties's website isn't working for me, but you can just search for Wiseco and it'll come up

Or Paul can be contacted by looking up the member "woodward specialties" on here and sending him a PM. He cuts the same deal for members here, $83 shipped for a new wiseco piston kit and you'll save him Ebay fees...help him sell it to the next guy for a dollar cheaper!


I'm with trips, I run wiseco pistons in completely stock engines and in HOT applications. Good luck out of both.

 

[wwholden]

Yeah but my current bore it 67mm. I need to increase the bore to take out the scores in the cylinder wall. I want to know how much I should go out based on my scores? Would 67.25mm be enough or should i go 67.5mm?

 

[Triple_B]

Yeah but my current bore it 67mm. I need to increase the bore to take out the scores in the cylinder wall. I want to know how much I should go out based on my scores? Would 67.25mm be enough or should i go 67.5mm?

Depends how deep the scores are. You will need a machine shop to determine that correctly.

 

[sicivicdude]

Yeah but my current bore it 67mm. I need to increase the bore to take out the scores in the cylinder wall. I want to know how much I should go out based on my scores? Would 67.25mm be enough or should i go 67.5mm?

I have to say, I'm not a fan of killing any more cylinder bores than necessary...

It's hard to judge the depth of that gouge by looking at a picture, it could be .005" or it could be .008" or it could be .011" without having it my hand, I'd hate to guess except to say I do think you'd be "safer" going with a 67.5mm piston because the gouge "looks" deep enough to need more than .010" taken out (.020" bore means only .010" on each side so if the gouge is .008" deep, a .010" overbore will leave .003" of the gouge because .010" is only .005" per side).

 

[wwholden]

So go with a .60 over or 67.5mm piston then?

 

[wwholden]

Which of these top end kits should I get on eBay. Do I need to buy the one with a top end gasket kit? My current gaskets are not torn or dryed out. Will they still be good enough for a leak down test or should I buy all new gaskets? Looks like I could save almost $30 if I don't need the gaskets. Also see that the kit that comes with the gaskets also includes a wrist bearing. Which of the kits should I buy?
Yamaha Blaster Wiseco .060 (67.50)mm Piston Kit YFS200 | eBay

Yamaha Blaster Wiseco .060 Piston Gaskets Bearing Kit | eBay

 

[Triple_B]

Well first of all, your going to want to make 100% sure that your cylinder will need to be bored .060 over. You should do that before ANYTHING! Just to be safe. Your not going to want to buy a piston kit and find out you wont need that big or you will need bigger.
Now, I have been told by many members on here that it is best to just buy a piston kit, no gaskets or wrist pin bearing. Wiseco gaskets are ok, but deffinately not the best. You would be much better off buying Cometic gaskets, they sell complete top end gasket kits for around $30. They are a little bit more $$$ than Wiseco gaskets, but they are the better choice. And for a wrist pin bearing, just go with Wiseco.