[mictang]

Hi Everyone,

I am replacing my N52B30 block due to an oil leak (yes, it's actually the block itself, bit of a long story) and would like some advice on piston and cylinder wear tolerances.

The original engine worked fine without issues, all parts came out looking good and clean.

Pistons measured around 84.95mm with a ~0.005mm variation (piston is marked 84.99, so wear should be ~0.4mm).

The replacement used block measured a fairly consistent +0.05mm (0.005mm to 0.01mm variation) from 85mm, with just one spot near the top of cylinder 5 having a slight out-of-round at +0.07mm.

The Alusil coating looks good and intact, with no noticeable lip at the end of stroke travel as well.

The piston rings are right at the upper limit of 0.3mm for gap, so I am replacing them just to be safe; side clearance were good.

So according to ISTA, Piston clearance is 0 to 0.03mm for new, and 0.02mm to 0.08mm for used pistons, I should be good there.

As for the cylinders, ISTA only states a reworking tolerance of +0.02mm (from 85mm) and 0.01mm for conicality and out-of-round, but it does state a permissible total wear tolerance of 0.15mm (piston and cylinder combined).


From my understanding, I am within the total wear tolerance requirements and should be good to go with simply new rings and putting everything else back together right? I am not too worried about cylinder 5 since it's a small deviation at a small spot.