Hi Jim - when I bought my Haflinger 10 years ago it had the 86mm mod done to it - the engine certainly ran well. I am not sure whether my 86mm experience will relate to you 83mm.
However the engine failed a couple of years into my ownership with the skirts on number one cylinder breaking off and the entire piston cracking.
Cause was not obvious and engine was rebuilt with new VW pistons and barrels (Mahle) using the old parts as the pattern. Things I noted - hole in the crankcase where the barrels fit in was enlarged and the shirts on the barrels reduced in length to clear conrods and the diameter on the skirts reduced slightly - so slightly thinner skirts and the hole in the crankcase slightly enlarged - a bit of mod to both to save taking too much metal off either one.
The issue is the pistons, as the standard VW pistons are too tall and the original builder used a step design with valve slots to fit the cylinder head with max reasonable compression.
So the engine was rebuilt and ran good but was a bit glackity. Anyway - the engine failed again about 6 months later with the piston metal between the rings cracking. This time we looked at everything more closely and noticed some "erosion" marks around the outside of the piston tops - came to the conclusion that the piston was hitting the cylinder head at the top of each stroke. Discovered the design flaw of this mod.
The barrel liner sits in a small ring in the head so the head and cylinder seal when heated up (no head gasket). The original designers had machined the pistons to match the top of the liner not realising it sits into into a little shallow slot in the head and what was happening was the piston was hitting the inner lip of this slot and over time causing damage to the piston and metal fatigue.
Now the new pistons were machined so the edges were a couple of thou lower than the originals. This has worked a treat and while a little less powerful due to slightly less compression, for the last 8 years it has been a totally reliable engine.
When tuned and with high speed gears and 14" wheels it will get close to 90kph on a good day but does burn a bit more fuel.
Some pics of the piston I have in now.
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