Tearing down my M103 for a rebuild. Purchased the car after it had been sitting for 4 years, and my guess is that the blemish is due to it sitting. Broadly the cylinders look like they;re in great shape except for a small pit in cylinder 5.

Worth fixing? Can I overbore slightly? Ignore? I’d like the engine to run for a while, plan on upgrading to EFI and coil on plug, then some light boost, targeting HP in the high 300s.

First pic shows the pit - then a wider picture of the cylinder. There’s a slight discoloration of the finish around the area where the pitting is:

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1986 Porsche 3.2 Carrera - 1987 W124 300E - 1999 Land Cruiser 100 - 2015 MKVII GTI - SLK32 AMG (sold) - 1998 3rd Gen 4Runner Limited (sold)

That low in the bore, I wouldn't be losing any sleep.

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90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff

I agree duxthe1. Dont mess with the cylinders. But I would pull the pistons and check the rings are clean and not frozen in the grooves.

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John Roncallo

Does this engine look like it was apart before? I wonder of this engine saw water then a piston was pulled, bore honed to clean it up and engine run for a while. This pitting is old and almost looks like a casting flaw.

Regardless, pull all pistons and replace the rings. Boost requires larger ring gaps so the pistons need to come out anyway.