Bore size

[stusco]

Cheers lads

[Skid Mark]

I’m to buy a lotto ticket! I managed to upload a photo of my wiseco piston crown in last post. You can make a comparison.

[Mark W]

Very similar markings to my pistons

[stusco]

That’s them cheers lads ,cant do any fettling just now hurt my back and had surgery on my hand this morning and the anaesthetic has just worn off.
Is it too early for an alcoholic painkiller?
Forgot to ask what make are they?

[Mark W]

The good news is yours look identical to mine but a little bigger.Now the bad news ,my bike was imported from the states early 1990’s and these were some sort of aftermarket high compression piston.I damaged one of the oil rings and could not find a like for like replacement .In the end managed to find something similar from Dave at z power

[stusco]

Id better be careful with them

[zed1015]

The good news is yours look identical to mine but a little bigger.Now the bad news ,my bike was imported from the states early 1990’s and these were some sort of aftermarket high compression piston.I damaged one of the oil rings and could not find a like for like replacement .In the end managed to find something similar from Dave at z power

Those are Wiseco pistons.
The C stands for the ring type which is XC and currently commonly used on Wiseco and MTC pistons amongst others.
2756XC is the code for the 70mm rings .

[stusco]

Ok im doing a bit off measuring today, my pistons look new with no blow past .however it smoked a bit and the compression was 115-130 psi checked with two decent testers,the valve stem oil seal were soft and the valve to guide clearance is good (hardly any sideways movement) .Ive not gapped the rings yet. How do you check your piston bore clearance and what would you expect on a 75mm wiseco piston?

[zed1015]

For the Wiseco pistons it's 2 thou ( 0.051mm ) measured at the skirt.

[stusco]

Cheers are the ring gaps the same as the workshop manual

[Al]

Top ring 'N' uppermost
Or Top ring bevel uppermost
Second ring ~ no bevel

Top ring 0.014" inch and no less
Second ring 0.016" inch and no less

These are for 75mm / 2.953 inch bore.
Are those vertical scores in the bore like on the skirts of the pistons or an optical illusion?

AL

[stusco]

There are vertical lines but i cant feel them with my finger nails ill try to get better pictures.im trying to find a reason for poor compression and smoke but theres no real smoking gun yet ,

[stusco]

For the Wiseco pistons it's 2 thou ( 0.051mm ) measured at the skirt.

How far up the liner from the bottom

[zed1015]

For the Wiseco pistons it's 2 thou ( 0.051mm ) measured at the skirt.

How far up the liner from the bottom

Anywhere where on the liner where the lower portion of the skirt travels .
Intake or exhaust side of the pistons.
Not the sides.

[stusco]

Top ring 'N' uppermost
Or Top ring bevel uppermost
Second ring ~ no bevel

Top ring 0.013" inch and no less
Second ring 0.016" inch and no less

These are for 75mm / 2.8 inch bore.
Are those vertical scores in the bore like on the skirts of the pistons or an optical illusion?

AL

so wiseco is the opposite of standard