I've tried every thing but have found nothing that will take the baked on discolor on the piston liner. I have several old Fox's that I am trying to restore and get running for vintage A/C. I just thought maybe the stuff bikers use to restore chrome exhaust might work...……….

  Crock pot and anti-freeze, with some occasional scrubbing. But be advised, removing the varnish from a Fox 35 liner may not be to your advantage (read Randy's pinned fuel post about cleaning varnish off of old engine liners).

    Brett

p.s. do not use chemical cleaners (other than anti-freeze) like oven cleaner or dishwashing agent (Cascade). Don't *scrape it with a sharp object*. A copper brush (10 or 12-gauge shotgun cleaning brush) is probably safe enough, but really, use antifreeze in a crock-pot and there will be no marks on the underlying metal when you are done.

    I would also note - my Foxes ran perfectly well (for a Fox) with no attempts at cleaning at all. You don't want to take any chance on damaging anything when a bit of varnish here or there makes no difference to the performance.

When all the miracle cleaners fail, do the crockpot/antifreeze and old toothbrush. Cook on low with straight antifreeze. Pull out every couple hours and brush. On heavily blackened ones I use wood tooth picks between cooling fins to speed the process up. Piston skirts are the last hold out and I use half of a wood clothespin to scrub with. It may take overnight or a week but nothing will get it cleaner. No need to panic about flushing afterward either. I set engines on my bench after cooking without flushing and they don't rust or corrode after weeks of sitting. Might be different if you add water to the antifreeze. 

A / . !

' De Lacuuering ' engines . Usually THEY SAID  " DONT " do the last 1/16 up the wall / to the cown , of the piston . ( as thats where it seals ) .
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I usually use the green 3M scotch pads , from the supermarket . Best used on pots a few times first , to soften . For working surfaces ,
as they can scratch .

ACETONE while it wont disolve grunge , usually softens it . A BRASS bristled ' wire brush ' can be fairly usefull .

really want to blow out all the bolt / screw holes too . Grit etc inem isnt good .

Torn / cut strips of the 3M for wrist pin holes in piston & rod , like wringing a tea towel .Or with a wire to hold agaist the face your de gungeing .
A wire thru wrist pin , & 600 or 800 or 1200 paper , on glass , to clean & polish . Crank journals tooo .

Tooners'd polish the insides of the passages . But opion varies , and has for decades .