Author Topic: Bore Size  (Read 158 times)

Online Miker

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Bore Size
« on: 11.09. 2020 08:32 »
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.  *conf*
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Online ironhead

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Re: Bore Size
« Reply #1 on: 11.09. 2020 08:55 »
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"
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SA

Online muskrat

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Re: Bore Size
« Reply #2 on: 11.09. 2020 09:04 »
G'day Miker.
70.500mm is +20 thou. Double check your measurements and the accuracy of your measuring sticks.
1mm = 0.0393701"
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ironhead beat me.
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'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
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Online Miker

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Re: Bore Size
« Reply #3 on: 11.09. 2020 09:36 »
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?
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Online muskrat

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Re: Bore Size
« Reply #4 on: 11.09. 2020 10:18 »
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.
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'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
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Online RDfella

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Re: Bore Size
« Reply #5 on: 11.09. 2020 16:09 »
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)
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Offline Triton Thrasher

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Re: Bore Size
« Reply #6 on: 11.09. 2020 16:27 »
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?
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Online groily

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Re: Bore Size
« Reply #7 on: 11.09. 2020 16:35 »
https://en.wikipedia.org/wiki/8.8_cm_Flak_18/36/37/41

An anti-aircraft gun like this one maybe?
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Bill

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Re: Bore Size
« Reply #8 on: 11.09. 2020 16:42 »
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 ..........
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