2618 forged pistons w/0.001" clearance at skirt?
2618 forged pistons w/0.001" clearance at skirt?
(OP)
I am putting together a 4.6L Ford V8 modular (alloy block). The bores have been bored to 3.572". The gauge point on the CP branded pistons is 0.5" from the bottom of the skirt and at this point they measure 3.5685". However, these pistons flare towards the bottom of the skirt where the clearance is only 0.001"!! They are so tight they nearly scuff when sliding them down the bores. CP Pistons Inc. says to disregard everything but the gauge point measurement. I feel squeamish installing a 2618 forged piston with only 0.001" clearance... measured at any point along the piston. Is this feeling justified? Thanks for reading.
Walter Carter
Walter Carter





RE: 2618 forged pistons w/0.001" clearance at skirt?
Mike Halloran
Pembroke Pines, FL, USA
RE: 2618 forged pistons w/0.001" clearance at skirt?
Walter Carter
RE: 2618 forged pistons w/0.001" clearance at skirt?
Mike Halloran
Pembroke Pines, FL, USA
RE: 2618 forged pistons w/0.001" clearance at skirt?
It will depend on the aluminium alloy to some extent with high silicon alloys requiring a tighter fit.
The skirts have some flex and this varies with length, design and alloy. That is why piston manufacturers specify the very robust part of the skirt near the pin boss as the reference point as it is stable and does not flex so much.
Take their advice. They know what they are doing.
One word of caution, use the weight of oil specified. The tight clearance might be somewhat to do with light weight oil being used.
Regards
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RE: 2618 forged pistons w/0.001" clearance at skirt?
I may have pin size or dome request to a piston manufacturer but as far as the bore fit I leave it to the pros
Cheers
I don't know anything but the people that do.
RE: 2618 forged pistons w/0.001" clearance at skirt?
That's 0.0035 inch clearance.
Squeeze the skirt tab/tails with one hand and measure.
They might be quite flexible.
Do they have slots, or hole for oil return in the oil ring groove?
The fancy ones in this picture call for 0.006 inch. htt
RE: 2618 forged pistons w/0.001" clearance at skirt?
Pistons do not expand evenly down, across or in any other geometrically definable manner. Alloy 2618 ("Mahle metal") is a superior alloy for forging pistons. However, not all piston forgers know how to take advantage of CONTROLLED piston thermal growth. So, to cover their A** they recommend huge clearances, i.e., .006".
CP knows how to design, and manufacture pistons. Follow their guidance and you can rest assured.
Regards,
Will
RE: 2618 forged pistons w/0.001" clearance at skirt?
I have heard of Ford modular engines having Nicasil liners custom made for them, is this the case?
RE: 2618 forged pistons w/0.001" clearance at skirt?