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Thread: Pistons

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    Pistons

    Quick question- Are the pistons for the 818.302 & 818.303 engines the same (or at least interchangeable)? I assume yes, however I may be missing something. I'd like to confirm.

    Thanks in advance.

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    Re: Pistons

    Quote Originally Posted by OnSafari View Post
    Quick question- Are the pistons for the 818.302 & 818.303 engines the same (or at least interchangeable)? I assume yes, however I may be missing something. I'd like to confirm.

    Thanks in advance.
    Same bore, but the 302 piston is 9.0:1 compression while the 303 is 9.5:1.
    Ed Levin
    Fulvia 1,6 HF

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    Re: Pistons

    OnSafari

    I dont know if this is to any help.
    Before I dismantled my 818.342 HF engine i measured the head volume With a burette.
    This head volume gave me 9,5:1 CR, it should have been 10,5:1 in my HF engine.
    The head gasket was 1,2 mm. used crushed thicknes and the cylinder base gasket was 0,5 mm.

    I figured out that it could be two reasons for this:
    - Wrong pistons (303 type), my engine was at Maximum overbore 77,6 mm.
    - Valve seats cut too far in the head after several times With the valve seat cutter tool.

    Or maybe a combination of the reasons above.

    Since I have my old pistons on the bench, I have measured the dome heigth. Measurements done With piston in the bore, With top ring land flush With cyllinder Block.

    My old pistons have 3,3 mm. dome heigth, wich I think is a 303 type piston.

    Can anyone verify the differences in dome heigth between the 302, 303 and 340 (HF)?

    I think the head design gives same volume, except the bigger valves in the latter.


    Tor

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    Re: Pistons

    Onsafari,

    303 pistons have larger valve cutouts, possibly due to higher compression but also due to 303 valves being 1mm larger and 303 camshafts having greater overlap. (cam timing set with no.1 tappets at 2,2mm clearance on 303 vs 1mm on 302). Based on standard components, I think I am correct in saying you could use 303 pistons with 302 head and camshafts, but 302 pistons with 303 head will hit the valves.

    Will.

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    Legendary Lancista Marnix's Avatar
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    Re: Pistons

    The dome of the 303 piston is also more curved than that of the 302 engine, which is slightly flatter. The incresed curvature is probably what gives most of the higher CR. And also means the valve cutout is larger, as part of the dome comes higher at the valve locations. I am not convinced a 302 piston would not fit a 303 engine without hitting the valves, but it sounds like a bad idea to do so anyway.
    Lancia Fulvia 2C 1964
    Lancia Fulvia Coupe Rallye 1,3 1968
    Porsche 924 1979
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