Re: Dhadley, talk to me
I am not sure how this happened. Pistons were black on top. NO signs of detonation. Exhaust cavity was black. The piston scoring occured at apporox. 45deg from the top centerline. ie.. if you hold the piston with the exhaust side down, it occured at 2:00 and 8:00 O'clock. There is only light scoring on the intake side of both pistons. The majority is on the exhaust side of hte piston 8'O'clock. There is evidence of blow by. There was some very light skirt scratching on #2 and #4, but nothing to worry about(slight centerpoint scratching(very slight).<br /><br />One pecular thing I noticed about these(all of them) pistons on the intake side, on the land, are 5 marks, evenly spaced. These marks go all the way down to the aluminum. The aluminum is not scratched, but there is NO carbon in these spots. The width of these marks are .2085, the length is from the bottom radius of piston protrusion to the outside of the piston. The thickness of the carbon on the intake side is .0115 at the edges of these marks. It looks like something was hitting the pistons and moved the carbon outward. But I can assure you... nothing was hitting the pistons.<br /><br />Block was decked .005 and heads .005, but.. the heads were also relieved on the outside edge .0255 to accomadate any piston to head clearance issues.(this cut is next to the sealing edge of the head.)<br /><br />There is no ash on the pistons. All piston pins were dark in color, but came out with little force. All bearings were nicely coated with oil, including top bearing, lower and all bearings.<br /><br />Water PSI was 2 psi@ idle, 5-10 @ 1200-1500 and 20-22 psi @ 6100. 17psi @ 5000. <br /><br />Timing was set pr. your instructions, statically @ 26 deg(22 statically, conpensating 4 deg for computer advance).<br /><br />I will say this... I did not throughly clean the block like I should have after the bore. After reading here methods of cleaning, I have failed in that department. BUT, I could be over exaggerating due to the fact that #2 and #4 did not get this scoring.<br /><br />I used the 1 3/8th's carbs from the get go. The ones with only 2 jets. I later switched to the 1 3/8th's 78 carbs? Has idle air jets, intermediate and high jets. there is no choke plate and no orafices for a primer circuit. I had to make a primer circuit for these since I did not want to drill the port covers. when I changed carbs I lost about 300 rpm on top with this change.<br /><br />All along I was experiencing wet plugs from idle. On the high end the plugs were paper bag in color and dry(with the first carbs) second carbs I only ran twice, fishing. didn't check plugs with them.<br /><br />Motor was more noisy at 5800 to 6100 vs. 4000-5000. 4k was smooth as silk and 5k. But more than that it was noticably louder(could be prop imbalance, not sure). SO... what I did at that point was reduce the timing 2 full turns. Ran motor... noise was gone, but much less power(seat-o-pants meter)I see NO bearing damage whatsoever. There is NO evidence of detonation.<br /><br />Piston top is evenly coated with carbon and wet looking.<br /><br />Is the megaphone different for the higher HP motors?<br /><br />The powerband in this motor seemed to be in the 4k-5k range. I would like it to be 3000-6500.<br /><br />DH, is there more to the intake mod than just removing the divider and what will the characteristics be?<br /><br />I have pictures of everything, if you would like to look at them I can email them to you.
