Just got my Holbay engine block and head from the machine shop. The machine shop guy supplied a set of pistons. The pistons are flattop Hepolite 17747 +20thou oversize. However the pistons supplied are different from the originals in that they have a longer skirt and also an extra scraper ring approx 1.25 inches below the upper ring. IE. the piston has four rings. I have not actually come across this pattern before and I have rebuilt a number of engines. My question is are these pistons compatible to the 1725 Holbay Engine and if fitted will they have an adverse effect on the engine operation and performance. Can these pistons be machined to the same length dimensions as the original without adverse effect, the lower ring looks very close to the gudgeon pin support web.
Many thanks for your help.
Tom.
Ireland.

I rebuilt my Holbay engine not so long ago and it had four sets of rings. As far as I know, four rings are standard on a Holbay. I've just sold a set of +020 rings which I bought in error, should have been +030

An additional oil ring is something from the past. With new pistons you leave the lower oil control ring out. It's supposed to go in when the engine is old and start using oil.
Original pistons for Holbay are Powermax but as they can't be found so you have to use the flat top pistons from the 5-bearing 1500 engine.
Powermax and these are 3-ring pistons.

Thanks to all for your help.
Regards,
Tom.
Ireland.