0.08mm is ~0.003": measured at the skirt, that is a bit loose, for a street engine, but is not too tight.
Frank, you must check for the type and make of piston and exact place of measurement. Short skirt solid piston forged/cast may be different from semi-split and/or wire-wound originals. Place of measurement (skirt side or front/back) etc.
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My Mahle pistons are specced at .004. which I thought was quite loose…but…that’s the makers spec…hard to argue. As a comparison, racing pistons…forged…are often given as much as 7 thou.
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I presume it’s all about thermal growth. Some pistons are made of materials designed to grow at the same rate as the cylinder so they can fit pretty tightly. Other pistons are made of the strongest stuff available and have to be looser to avoid seizing when they get hot.
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Racing pistons with that much clearance are certainly forged…high growth rate.
Hi Lee, thank you for this information, yes DIY the boring with a hone machine, so was not sure. But I made it ok with 0,08mm or 0.003".
The new/old engine is 0.003 extra wide, can I use standard pistons or do I have to buy oversized? Then it is a lot of work to be done.
Please advice.
Frank.
Kilbert, hi, Thermal growth, yes, that’s the question here, how much they can grow which in the cylinder, so that they won’t seized.
Is there a table for it. Is it 0.01 or 0.02, really don’t know.
Advice needed.
Photo ; this engine has STD pistons, but the weiring is 0.003, can I use new STD?
frank.
If new pistons measure (properly) at 0.003", and the cylinders are unscored, with not much taper, yes.
I agree, fwiw…you won’t notice any noise or performance issues at .003…just treat the engine like the days of old…meaning proper warm up.
Oh, and here’s a stat that’ll blow your mind…the 120 manual shows one of the pistons used on those older models as tight as .0007!!!
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Hi Paul, yes I have a little taper to the lower side of the cylinder it’s 0.05mm. If I bought just new STD pistons and hone s little, it would be 0.007 inch.
Otherwise the first oversized piston with 010" or 0.25mm.
Frank.
I hope you are all keeping track of your units gentlemen - otherwise I suspect there may be some nonsense being written here. Potentially expensive nonsense. Measure twice, cut once kinda thing… I will tell you where, if you prefer, but the lesson will stick better if you do your own mental arithmetic (no calculators required).
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Dead tight! Tappets are what the name implies! To get silent tappets can be very expensive to achieve on a 60 year old engine!
If it’s functioning, live with it! It’s part of the cars charm surely.
