Removing Casting Flash
What is casting flash?? Casting flash is material left by casting molds when parts are cast. Everything cast has "flash". Usually it poses no problem. But on an air-cooled engine, it can spell disaster or at the least higher engine temps.
There's two areas where you should look for, and remove casting flash.
1. The piston cylinder fins. Below are 2 photos (before & after) of a 90.5mm cylinder that went in my 1776cc motor. Note how the flash is literally filling-in the cooling fins. It was like this on just about all the cylinders in my set. There's NO way for air to get through!! I had to carefully use a hack saw to remove the flash between every fin. It takes a while, but your hard work will pay HUGE dividends by giving you a cooler running motor. The second photo is the "after" removal shot. Note the difference!!
2. The heads. You should look over your heads and inspect the fins on these as well. At a minimum, run a hack saw blade down each fin to help clean the flash. For the areas below the spark plugs, use a thin screwdriver and a light hammer to gently remove the small bits of flash. Don't get too crazy and go breaking a fin, just remove the flash.
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