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My spare S2 engine had suffered a spun #3 bearing and the cylinder looked liked this.
I could catch ridges in the cylinder with my fingernail and the piston was scuffed While thinking thru all the overbore options a light went on in my brain. Maybe I was catching my fingernail on the softer piston material deposited on the harder cylinder wall. I purchased a can of Sunnen AN30 from a fellow Rennlister and armed with a soft rag I placed a small dab of AN90 on the rag and gently with my finger rubbed the affected in an overlapping circular motion. Here's how it turned out
No fingernail catching ridges in there now
Last edited by jhowell371; 05-05-2016 at 05:25 PM.
Reason: spelling
I have done a lot of research on resurfacing the bores on these cars. I would suggest everyone read this post on pelican http://forums.pelicanparts.com/911-e...g-alusils.html There is a lot of black magic and people that try to make assumptions on what is the best way to resurface the bores and although for the most part any attempt to resurface is probably better than nothing there is a correct way to do it and it not that hard. Sunnen is an American company and they pioneered the Alusil process in the "60s if you call them they will gladly help explain how to do it correctly (as explained in the Porsche factory manual). I had to buy a Sunnen hone and two different sets of stones as well as the lapping pads and the paste and cutting oil. the only way to resurface the bores is to lightly cut away the broken silica and embedded carbon and metal particles that are in the aluminum. This was shown in the Pelican article under an electron microscope. The an 90 is NEVER to be "cut" with mineral oil it kills its ability to remove the aluminum and expose the silica correctly. Call Sunnen tech support, read the Pelican article.
I didn't use mineral oil, I cut mine with snake oil Seriously, I have read about this process till I'm nearly nauseous. I figured nothing ventured nothing gained and couldn't hurt it with a small dab of AN90 so I tried it on that area. Knowing the microscopic area below the exposed crystals holds oil for the critical breaking in process when new it seem to me it would be advantageous to perhaps hand wipe the cylinders with AN90 lightly. This would remove the combustion byproducts that filled in these critical areas that aid in ring seating.
Last edited by jhowell371; 05-05-2016 at 02:37 PM.
Reason: double word
The proper honing method-
Put the paste away, send block out for iron sleeving and use new modern Pistons and modern rings. Done.
By the way, this is expensive as hell. LOL. But saving for this anyway.
Just thought I would stir the pot a little
But seriously jhowell, nice pics! And good save on the S2 block! You saved yourself a lot of $$$
05-05-2016, 12:07 AM
Bore cleaned with Sunnen AN30
While thinking thru all the overbore options a light went on in my brain. Maybe I was catching my fingernail on the softer piston material deposited on the harder cylinder wall. I purchased a can of Sunnen AN30 from a fellow Rennlister and armed with a soft rag I placed a small dab of AN90 on the rag and gently with my finger rubbed the affected in an overlapping circular motion. Here's how it turned out 
