Bore size

[stusco]

So ive stripped my gpz1100 a1 1983 odo says 14000 its a us import ,to me and people that have seen it would say its never been apart all the screws are undamaged and the olive drab is undamaged ,the bike looks unrestored.
So off with the top end and first thing I notice is the pistons look new and there are fresh looking scratches around the gudgeon pin is from a screwdriver fitting the circlips, so out with my mic 50-75 and it’s 74.92mm the service manual says 72.5mm is standard the pistons have a C on the crown ,what do think ?

[Hard Road]

sounds like a big bore kit !!!!!

[stusco]

It does sound big must try some maths

[stusco]

1170cc

[Skid Mark]

I have a wiseco big bore on an A2. It’s approx 75mm. There should be numbers on the piston crown which will tell you what compressoion ratio you are running it could be 9.5/1if nos are 4380M07500 or if it’s 10.25/1 they are4255M07500. I’m sure there are other variations also. Also check stud diameters. This may affect oil delivery if they are larger and block was not reeked out to suit and also torque will increase if you have larger studs and higher compression. Hope this helps.

[stusco]

Ill post some pictures later today once i get the pistons off and the carbon scraped off

[stusco]

My studs are 8mm

[Skid Mark]

My studs are 8mm

Standard so, same as mine.

[stusco]

Here is some pics of the pistons can anyone identify them?

[Robw]

Look like Wiseco pistons to me.
Rob

[stusco]

High compression piston how could i tell?
It had low compression (115-130psi) and smoked a bit before I stripped it

[Robw]

Low compression, i have high comp in mine and the dome is much more pronounced

[Robw]

As you can see these 1170 wiseco pistons have a high dome. I had 1136 on my b1 and they had a dome similar to yours and they were low comp. J

[Skid Mark]

I agree with Robw. Mine look very similar to yours and are 9.5/1. Mine have two sets of no.s across the crown ( can’t upload from my phone) these appear to be laser etched so perhaps just new then yours.

[Skid Mark]

I agree with Robw. Mine look very similar to yours ( but without the small flat on the crown)and are 9.5/1. Mine have two sets of no.s across the crown ( can’t upload from my phone) these appear to be laser etched so perhaps just new then yours.