Hello
I searching for information of pistons size and clearance. Dismantle engine and measured. Pistons are 64,5mm and clearance is 0,016mm. My question is how much is clearance need to be and what size is std pistons.
Looking for info to order parts.
Engine number AF 30940
Pistons Austin 10/4
Re: Pistons Austin 10/4
Nominal standard bore is 63,5 mm /2.50 inch so your block appears to be rebored to +1mm/+0.040 inches oversize already.
I believe the Austin official maximum allowable oversize was 1/16inch/0.0625 inch/1,5mm.
The A10 guys on here will have their own suggestions based on real-world experience, but my 10 cents:
Are you sure you don't mean 0,16mm clearance? Because if your measured clearance value really is 0,016mm (< 0.001 inch) it is actually pretty good especially if you are measuring a split-skirt piston on the skirt area (as below)
If its 0,16/0.006 inches then it is getting to maximum allowable in generic terms (1,5 - 2 times the nominal new clearance)
My information gives the nominal piston clearances as 0,228mm/0.009 inch at the top ring land and 0,0812mm - 0,0965mm /0.0032 - 0.0038 inch at the skirt, both measured at right angles to the gudgeon pin.
I believe the Austin official maximum allowable oversize was 1/16inch/0.0625 inch/1,5mm.
The A10 guys on here will have their own suggestions based on real-world experience, but my 10 cents:
Are you sure you don't mean 0,16mm clearance? Because if your measured clearance value really is 0,016mm (< 0.001 inch) it is actually pretty good especially if you are measuring a split-skirt piston on the skirt area (as below)
If its 0,16/0.006 inches then it is getting to maximum allowable in generic terms (1,5 - 2 times the nominal new clearance)
My information gives the nominal piston clearances as 0,228mm/0.009 inch at the top ring land and 0,0812mm - 0,0965mm /0.0032 - 0.0038 inch at the skirt, both measured at right angles to the gudgeon pin.
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nikolapendo
- Posts: 2
- Joined: Thu Jun 29, 2023 4:08 pm
Re: Pistons Austin 10/4
Thanks Rod
You are right is 0,16mm. I will look for ,60” new pistons.
You are right is 0,16mm. I will look for ,60” new pistons.
Re: Pistons Austin 10/4
You're welcome!
If you use your favourite Search Engine, there are a number of on-line sites advertising pistons, either new or NOS. You can also have new ones made to sample if you have to go that way.
I would suggest talking to the people that are going to rebore your block before choosing an oversize. Very frequently the amount of taper and ovality in the existing bores means to ensure an acceptable service life, they may have to skip an oversize to get a cylindrical bore accurately centered and perpendicular to the crankshaft.
Especially if the engine has been bored in frame (as was customary practice in the 1940s and 1950s) using a portable boring bar. You may end up having to find another block, or sleeve your existing one back to standard.
If you use your favourite Search Engine, there are a number of on-line sites advertising pistons, either new or NOS. You can also have new ones made to sample if you have to go that way.
I would suggest talking to the people that are going to rebore your block before choosing an oversize. Very frequently the amount of taper and ovality in the existing bores means to ensure an acceptable service life, they may have to skip an oversize to get a cylindrical bore accurately centered and perpendicular to the crankshaft.
Especially if the engine has been bored in frame (as was customary practice in the 1940s and 1950s) using a portable boring bar. You may end up having to find another block, or sleeve your existing one back to standard.