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Piston and ring size markings

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Laverda Dave:
Thank you Bryan. Yep you are right, that thought entered my head at about midnight last night when I couldn't sleep! Of course the rings are designed to wear and I measured worn rings in a glaze busted bore...oops :-[.
Anyway, the good news is I finally had the opportunity to use a brand new Helios bore gauge I bought about 20 years ago at an engineering tool sale to measure the bores this evening.
I took six measurements of each bore front to back, side to side, top, middle and bottom of each cylinder.  The maximum bore measurements from 1- 4 were:
1 = 51.63
2 = 51.64
3 = 51.64
4 = 51.64
The measurements were the same throughout the bore but I would expect that as they were all glaze busted only last Friday so should be the same!  The engineer didn't have the pistons when he used the glaze buster but did advise me the piston to bore clearance would be about 2.5 thousand if it was a standard piston (it is) following the glaze bust.  The Haynes manual states a maximum piston to bore clearance of 0.050mm. He was also unable to remove the wear marks at the top of each bore (about 7mm of the bore is untouched by the glaze bust at the tops).  This is because the engineer didn't want to remove too much material.

I compared the measurements with the Haynes manual specs that states ' The difference between the lower bore measurement and the top bore measurement should not be greater than 0.12mm, if it is the cylinder requires a rebore'.  Not much use to me as the measurements are the same at the top and bottom due to the glaze bust!
The Clymer manual advises the cylinder wear limit is 51.1mm.
Going on the Clymer wear limit I'm not sure if I need a rebore or not, by my calculation I am up to 0.36mm below the maximum wear limit or I could be wrong and actually be 0.54mm above the wear limit and require a 0.75mm rebore although I will have to go 1mm oversize as 0.75 pistons are unavailable  :-\
My head hurts after all this  ???
Dave

Bryanj:
If standard bore is exactly 51mm and your measurements are accurate you are 0.14mm(5.6 Thou) worn on a 0.5mm oversize bore

Laverda Dave:
Thanks Bryan.
So, if I'm already worn 5.6 thou on a 0.50 oversize bore I'm going to need a rebore of 0.75 thou oversize then. The problem here is I am unable to find anyone WHO has any 0.75 oversize pistons despite going through the usual suspects including DS and Cruzinimage. This means going the full 1mm oversize then. There is only one set of pistons I can find as 1mm oversize made by IMD on e-bay. Has anyone had an experience with these pistons or better still, does anyone have a spare set of 0.75 pistons they want to sell?
I did think about going the 460 big bore route but that would entail a whole host of other work so that's a no go.

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