To overbore, or not to overbore? that is the question

[biglebowski]

I pulled apart the blaster a couple weeks ago and saw that it has had a couple overbores. Right now the piston size is 67.25 and there is definitely blow-by on the exhaust side. My concern is that the piston skirt is too thin towards the bottom as is, let alone to rebore to 68. any thoughts?

 

[YFS101]

Measure it...
Blow by is the rings, no the piston

measure the piston to cyclinder clearance.
If the piston is worn but the ncylinder is ok replace it and the rings. If the cylinder is worn out of specs, have it bored .010" and fitted with the next size piston.

 

[biglebowski]

what is the biggest clearance i can have?

 

[YFS101]

depends on the piston type.

004"

also the ring end gap. if the piston and bore are ok, but the ring gap is too large you need new rings (and fresh hone)

I dont have the oe specs in front of me for the ring end gap or the wiseco/oe piston clearances. ill try to get that tommorow

 

[biglebowski]

i measure the distance and its around .007" the number on top of the piston is 573mo6725. the last 4 numbers are the bore size right? Someone who had this thing apart for me hogged out the piston sleeve by the transfers so there is no way this can get another bore. what a facking gomer X(

 

[YFS101]

These are all service limits so if you are at or above these you need to bore.

Piston-Cylinder limit: 0.1mm (0.004 in.)
Taper limit: 0.08mm (0.003 in.)
Out of round limit: 0.05mm (0.002 in.)
Ring end gap is .20mm- .40mm (.008"-.016")