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piston tops

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Now that the head is off, I scraped the small amount of carbon off the piston tops with a plastic scraper leaving a discolored but smooth surface that I lightly oiled. Question - should I clean off the remaining film with either fine emery cloth or something else that does not leave scratches - or just let well enough alone and let it be? I've seen some pistons that look like new after a valve job.
 
Scrape, then scotch brite, and...if you are really anal, you can sand with 600 grit and buff to a high gloss. Don't know that the engine cares, but it sure looks purdy.
 
Unless you have the pistons out and the rings off, I would be hesitant to use any kind of abrasive. Too easy to leave particles behind.
 
Here's what is said in the Bentley publication of the Workshop Manual
"Using a wooden spatula remove carbon from the piston crowns leaving a band of carbon round the periphery of the piston crown"
 
Only 3 pistons had any caked carbon - and then not much. And I don't remember any carbon around the rim - most of it was in the center. I think I'll leave well enough alone.
 
The only thing to really be concerned with: Carbon buildup concentrated in a non-uniform pattern will act as a heat-riser which will increase the risk of pre-ignition. This is why some high performance engine builders (not necessarily building triumph engines) will actually sandblast the piston domes with glass-bead to promote even, consistent carbon buildup. I had it done for me by an engine builder on an engine I had built on 250hp 2L engine a previous project and had saw it's results 5000 miles later - very impressive.
 
Here (if I can upload it) is a picture of the piston tops. I'll try to upload that picture and my cluttered garage - what a garage should look like. hole in firewall1.jpgII made a mistake & got the hole in the firewall!
 
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