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Author Topic: Fulvia pistons  (Read 1397 times)
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« on: 01 June, 2010, 10:12:46 PM »

Can anyone explain the difference in pistons marked A and B ?

Rebel Poster
Posts: 980

« Reply #1 on: 01 June, 2010, 10:31:03 PM »

It's a manufacturing tolerance. The blocks are bored on multihead machines and it is not possible (or certainly not then) to have a controlled tolerance on the bore tight enough to enable a single piston diameter on the build line. So they used two "as new" piston sizes (on a Fulvia: absolute, A and +0.05, B). This kept the manufacturing line ticking along nicely.

On a Fulvia the tops of pistons are stamped, and the block is stamped next to the cylinder on the top face with the appropriate class type that was fitted at build in that position. My engine has two A and two B pistons. It's quite common on engines (I would imagine Gammas have something similar?). I seem to remember from my Integrale days that the piston class (A or B) was stamped on the outside of the block on that engine.

1969 Fanalone, Mazda RX-8, Fiat Multipla
« Reply #2 on: 02 June, 2010, 09:17:11 AM »

Thank you.

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