Bore Size

[Miker]

I have measured the bores on my barrel with a micrometer and they seem to read average 2.771" or 70.3834. Allowing for piston clearance would that be standard or +020" . Trying to figure out what next size up  pistons to buy. 

[ironhead]

What is the reading for the Most  worn part ? ( 1/2" or so from the top, front to rear)  The size you have would seem to be a worn 0.010 O/S
Or a really flogged out STD.   70.5mm  would be +0.020"

[muskrat]

G'day Miker.
70.500mm is +20 thou. Double check your measurements and the accuracy of your measuring sticks.
1mm = 0.0393701"
Cheers
ironhead beat me.

[Miker]

Now that you mention it the cases did have +010" pistons in them but I have a few barrels that came with all the parts and wasn't sure if this barrel was from that engine. If that is right would I be able to go +020" assuming my measurements are right(I will take it to an engine place to get it double checked) There is a slight lip at the top and minor surface rust. What is the clearance for 7:25:1 pistons?

[muskrat]

G'day Miker.
The piston manufacturer normally quotes the clearance required. Modern material pistons require a little less than the originals. 2 to 3 thou with solid skirt pistons should be OK, 1&1/2 thou for split skirts.
Cheers

[RDfella]

dunno what happened to my post - I'll try again....
.060" is roughly 1.5mm. Your bore @ 88mm is 3mm oversize, or 1/8" (.125 ins)

[Triton Thrasher]

dunno what happened to my post - I'll try again....
.060" is roughly 1.5mm. Your bore @ 88mm is 3mm oversize, or 1/8" (.125 ins)

Who’s got an 88 mm bore?

[groily]

https://en.wikipedia.org/wiki/8.8_cm_Flak_18/36/37/41

An anti-aircraft gun like this one maybe?

[RDfella]

TT / groily - dunno what's going on here. Originally I was replying to a post about 'what barrel do I have' or similar, where someone said std was 85mm but their barrel was 88mm. Then my reply disappeared and I ended up on this post. Summat strange going on ..........