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Judging by the condition of the rings pictured, it is likely that the ferrous skirt coatings of the pistons are no longer serviceable either.
More detail photos of the pistons please. Is your 924 engine also tolerance group 1?
I would have the condition of the pistons assessed, first hand, by someone very familiar with these specific engines. You will also need to carefully measure them, and the cylinders in your block to make sure the clearances are good. And of course you should install new rings. Why would you not?
if group 1 tolerance, Has anyone changed the rings without doing alusil treatment?
People have successfully run new rings without prepping the bores, but it seems like a gamble not worth taking. Just do it right so you have one less thing to worry about. Regardless of your pistons being the same tolerance group as what may have been removed, you still want to carefully measure everything. Good to see you have new piston rings-make sure you check the end gaps!
Alusil isn't something you buy. The block itself is an 'Alusil' block. What's needed is an acidic paste that dissolves a very small amount of the aluminum so as to expose some silicone carbide. This silicone carbide acts to trap a layer of oil for the pistons & rings to wear against. The acidic paste is sold by Sunnen. Originally the process is done in a proper honing machine, but some here claim success using a drill motor with the paste applied using paper towels wrapped around the stones on a cylinder hone attachment.
08-08-2022, 06:28 PM
engine 924s - 944 pistons
