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Thread: Piston top markings

  1. 7th November 2010, 10:03 AM #1
    drifter Guest

    Piston top markings

    Hi all,

    The head came off the 2.25 petrol engine yesterday. I was surprised at how good it all looked, actually.

    My question relates to the markings on the top of the pistons. Specifically, I am trying to ascertain whether or not I have original or oversized ones in there.

    Each piston is numbered 1 through 4 (and that corresponds with their location)

    Each one has a circle in the centre with a P (or what looks like a P) inside the circle.

    Each one has an arrow pointing towards the front of the engine.

    No 1 and No 4 have an A stamped on them. 2 & 3 have a B

    Are these original?

    Thanks in advance for any info (pics would be good as a part of your explanation if you have them).
    John
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  2. 7th November 2010, 10:44 AM #2
    isuzutoo-eh's Avatar
    isuzutoo-eh
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    Mine have 0.040" stamped on them. Sorry I didn't take photos after I'd scraped the top surface clean. I assume this means they are 40 thou oversize. Thats not to say all oversize pistons are stamped with their relative size, but it is likely so.
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  3. 7th November 2010, 10:51 AM #3
    drifter Guest
    Thanks Mark

    Under closer examination what looked like an arrow is actually an X

    I am starting to assume that oversize markings would be as visible as the other markings.
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  4. 7th November 2010, 04:02 PM #4
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    Johnno1969
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    Yes, I would expect that they should be visible. Mine have "040" stamped on them very clearly.
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  5. 7th November 2010, 04:16 PM #5
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    Blknight.aus
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    that engines been apart before and had the orginal guts put back in.

    1-4 for the pot number x for which side to the front.

    a+B Im not sure.

    OEM oversize pistons have the oversize in thou marked on them.
    Dave

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  6. 7th November 2010, 04:18 PM #6
    drifter Guest
    Thanks guys

    Dave, what tells you it's been apart before? Just wondering - or, rather, trying to see what I have missed.

    One thing I didn't mention is that it is all carboned up in there - but under the carbon it looks great.
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  7. 7th November 2010, 04:18 PM #7
    d@rk51d3 Guest
    Piston sizing:

    "Z" Nominal to minus .0002in
    "A" Nominal to plus .0002in
    "B" .0002in to .0004in above normal
    "C" .0004in to .0006in above normal
    "D" .0006in to .0008in above normal
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  8. 7th November 2010, 04:24 PM #8
    drifter Guest
    ah - thanks - so 2 & 3 are 2 to 4 thou oversize.
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  9. 7th November 2010, 04:28 PM #9
    d@rk51d3 Guest
    Quote Originally Posted by drifter View Post
    ah - thanks - so 2 & 3 are 2 to 4 thou oversize.
    Not necessarily "oversize", as such. (according to the manual.)

    Still original pistons, just some slightly slightly bigger to take up discrepancies in the block when new, or when re-built in a near to new / low km condition.
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  10. 7th November 2010, 04:32 PM #10
    slug_burner
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    Quote Originally Posted by drifter View Post
    Thanks guys

    Dave, what tells you it's been apart before? Just wondering - or, rather, trying to see what I have missed.

    One thing I didn't mention is that it is all carboned up in there - but under the carbon it looks great.
    Piston do not normally come with their corresponding cylinder number marked on them, when new they can go in any cylinder of the appropriate size. Therefore if yours are marked 1 to 4 it is becasue someone was going to take the engine apart and wanted to ensure that the pistons went back into their corresponding bore.
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