set of new pistons + 0.5

[BRECH65]

Hello there,

I am looking to buy a set of new pistons for my Essex 3 liters (SE5 a) and found a set on ebay which is oversized by 0.5 so my question is : what is the point in this oversize ? is it better to rebuild an engine as I would like to do with mine ? I mean does this oversized pistons allow to widen the sleeves ? and thus to have a brand new upper engine ?

thank you for your explanation

cheers

Eric

[philhoward]

Did my email explanation not answer your question, Eric?

If the cylinder bores are excessively worn, then the normal procedure is to rebore them to the next oversize; these are usually in steps of .020" (inch) - which is almost exactly 0.5mm so you would find +0.5mm, +1.0mm and probably +1.5mm (0.020", 0.040" and 0.060"). Until your engine block has been checked, then it is best not to order pistons in advance for two reasons:

1) Your engine may have been rebuilt before, using oversize pistons already (+0.5mm or maybe even +1.0mm or 1.5mm), or
2) Your engine requires greater amounts machined from the bores to make them usable - maybe to +1.0mm (0.040")

Your mechanic should be able to advise when the engine is in pieces - you may not need new pistons at all, just a new set of piston rings - but it won't be known until then. The largest available are +1.5mm (+0.060") which makes the engine 3.1 litres (a common upgrade path 30 years ago to mimic the engine in the Capri RS3100) - after this, the engine is scrap, or needs cylinder liners installed.

[efi_sprintgte]

I mean does this oversized pistons allow to widen the sleeves ? and thus to have a brand new upper engine ?

In a word yes,

As Phil has said a machine shop over bores the block so it’s bores are new, round and not scored. Then you fit a oversize piston to fit the oversize hole.

[BRECH65]

thank you very much to both of you

regards

eric