ok, a little history. I ( with lots of help ) replaced the rings, but did not do the pistons. Sled ran fine for about 200 miles and then overheated. The coolant was very foamy. SO here is what we did: checked the oil pump, primed it, checked the water pump, bled the coolant, synched the carbs and tuned the air flow ( found some one with the tool ). It ran for about an hr and did not overheat. I am not sure the problrem is fixed any thoughts? I have one person who said I should have replaced the pistons? any thoughts/suggestions?