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Machining Pistons
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Miken



Joined: 24 Dec 2012
Posts: 577

PostPosted: Wed Sep 10, 2025 4:15 pm    Post subject: Machining Pistons Reply with quote

I thought this might be of interest.
It has nothing to do with old cars. But it easily could have (and it is a Bentley engine!).
I needed to machine some pistons all over on my lathe, but how do you hold them?
All the pistons that Ive seen, cars or motorbikes have a turned register in the base of the skirt which is for locating it during the manufacturing process.
First you need to make an eye bolt.
Then you turn a mandrell to locate the piston on:






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Ray White



Joined: 02 Dec 2014
Posts: 7075
Location: Derby

PostPosted: Wed Sep 10, 2025 5:59 pm    Post subject: Reply with quote

I agree that is probably the best way.

How about some thin swarf. ? This was my final pass on a hollow distance peice for the bolt mounted Altette horn. Very Happy



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Penman



Joined: 23 Nov 2007
Posts: 4850
Location: Swindon, Wilts.

PostPosted: Wed Sep 10, 2025 8:23 pm    Post subject: Reply with quote

Strikes me that the set-up shown in the first 2 pics must have some tight "non-clearances" otherwise you would get a lot of chatter on the lathe.
_________________
Bristols should always come in pairs.

Any 2 from:-
Straight 6
V8 V10
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Miken



Joined: 24 Dec 2012
Posts: 577

PostPosted: Wed Sep 10, 2025 10:23 pm    Post subject: Reply with quote

Penman wrote:
Strikes me that the set-up shown in the first 2 pics must have some tight "non-clearances" otherwise you would get a lot of chatter on the lathe.


The spigot of the fixture held in the lathe chuck is made a snug fit so each piston runs true.
Each piston and eye-bolt is simply tightened by hand.
Pistons are made from cast iron. It's for a 9 cylinder engine.
Also;
slightly interesting design; W O Bentley designed this engine with hollow con-rods. Oil travels up the centre to lubricate the small ends.
I haven't seen this on an IC engine before.
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Ray White



Joined: 02 Dec 2014
Posts: 7075
Location: Derby

PostPosted: Thu Sep 11, 2025 12:00 pm    Post subject: Reply with quote

I think hollow con rods were often found in aero engines but not all used them to lubricate the small ends. I understand the system is still found in high performance engines but not necessary in everyday use.
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