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74 GTV 76 Alfetta GT
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Discussion Starter #1 (Edited)
I have a set of used pistons that I'm measuring compression ring side clearance on.
I'm able to get a .0025" feeler gauge in there with noticable drag and a .002" feeler gauge with slight drag.
I'm measuring with a new piston ring.
Is this side clearance a bit high or ok?
I believe the upper limit is .0026" as per Alfa Romeo.
PXL_20201218_201156758.jpg
 

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12,242 Posts
Used rings? Used bores? Different rings will have different clearances depending on ring end gaps as well as type of ring. If its apart, as photographed, bores can be measured for taper with an inside mic.
If liner bores are good, and cross hatch correct to seat new rings, those with end gaps cut to mfg spec eliminates the need for your measurements. With forged pistons, skirt to wall clearance is a more important measurement to avoid low speed piston slap noise. Cast usually have expansion control inserts and won't rattle unless bores and pistons have some wear. Generally, older design forged slipper skirt seem to rattle more than current design.
 

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74 GTV 76 Alfetta GT
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Discussion Starter #3 (Edited)
This is what I'm measuring.
Trying to figure out how much life these pistons have left in them.
FG-24-4.jpg
 

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Ok, I see. Those are set to mfg spec. Some rings are available in different thicknesses, and the piston ring lands can be cut wider for special or race applications. Generally, the book clearance here is set to a factory clearance for factory spec rings and pistons. If clearance is excessive, it's a clue that it's time for new pistons.
 

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If clearance is excessive, it's a clue that it's time for new pistons.
Exactly. Because if you don't go on with new pistons, you'll add a multifunction to your old piston set : They will start to work as an oil pump, too.
 
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