Piston Identification

[NickZ]

ive pulled down my new grey motor its a b series so its out oft FB.
Thee doesn't seem to be much lip on the bore, Im trying to work out if its original bore, the pistons are marked with "RB2075 F40" and "Top .001" i know what the top means. 2 of the pistons dont have the F before the 40.
From what i know "RB2075" is the part number does the "F40" mean .40 over sized?
but measuring with the calipers i get 3.065 on the pistions and 3.90 on the top of the bore.

any clues. i think its standard.

[Stewy]

Hi Nick, in the workshop manual for the FC it lists the Bore at 3 inches.
In the EK workshop manual it lists the bore as 3.062 inches.
So I would think that you are right for a B block that it is standard.
In the parts book it only lists holden part numbers.
Standard        FB,EK     7406476
(.003"  o/s)    FB,EK     7406470
(.010"  o/s)    FB,EK     7406471
(.020"  o/s)    FB,EK     7406472
(.030"  o/s)    FB,EK     7406473
(.040"  o/s)    FB,EK     7406474
(SEMI-FINISHED)         7406475
Then there are Opt. service 4 ring type with part #  M32518

Probably no use to you !

Cheers Stewy    

[ardiesse]

Nick,

Your engine has been fitted with Repco pistons.  Just to confirm, the piston crown should not have a countersink in the centre, unlike the GMH pistons, which do.

Repco stamped their pistons with a code for (over)size, with STD being standard size, and then you'd have 020, 040, 060 etc for oversize.  So I figure that you have a set of three-and-a-sixteenth-plus-40 thou pistons, which would equal 3.0625 + 0.040 = 3.1025 inches.

If you are measuring the bores at the top of the block, you need to take care.  Remove all carbon build-up with fine wet-and-dry, and stay away from the ring ridge.

Note also that the piston crown above the first compression ring is machined to less than the nominal bore size.  The correct place to measure the pistons is across the skirts, about half an inch up from the "hem", at right angles to the piston pin.

A much better place to measure the bore diameter is right down at the bottom of the bore, parallel with the axis of the crankshaft.  This part of the cylinder bore does not wear.

And one more thing: Repco pistons use different rings from GMH pistons.  The good news is that replacement rings for Repco pistons are cheaper and easier to get than for GMH pistons.

Hope this helps.

Rob

[NickZ]

Thank you all for you answers.
In my post I made a mistake with the bore size.
Should have been 3.095 ish so now it all makes sense.