Thread: Piston Damage
07-26-2007, 05:58 PM #1
Any ideas what could have caused this?
This is the mag piston of a 750
Good Compression (before)
New Bores and hone (.5 over)
Might have been a little lean but we were adjusting that
happened while at 3/4 throttle
07-26-2007, 06:00 PM #2
07-26-2007, 06:03 PM #3
It looks very lean!!! and or over heat. And when the pieces start melting at 5000 rpm is not good.. How does the cylinder look?
07-26-2007, 06:16 PM #4
yes to triple hi flow pump
cylinder looks ok, matching surface scuff,
Do youthink its possible that my engine shop didnt give me the correct bore?
Definate scaring around the exhaust ports
like it clipped the edges
07-26-2007, 06:25 PM #5
How can I richen that cylinder up any more, My high screw has a tap on it that only allows for an adjustment of about 1/4 turn
07-26-2007, 06:31 PM #6
- Join Date
- Aug 2006
cut the tab off the cap! Z
07-26-2007, 06:33 PM #7
of course, why didnt I think of that
07-26-2007, 06:37 PM #8
Those tabs are a fitting that goes over the brass adjuster. A pair of needle nose should be able to pull it off with no prob. Then reinstall when done.
07-26-2007, 07:23 PM #9
cut the part of the tab that sticks out toward the needle, then close the needle and install the cap with the remainder of the tab straigt up or down, whatever. That way you can tund them 360* and have the tab for reference on you adjustments so that you don't have to keep closing them
were the carbs rebuilte when the rebuild was done? lines and filters checked? oil pump and lines checked?
07-26-2007, 08:22 PM #10
looks to me like a lean sieze.
did you champfer your ports after the bore?
what was the piston to cylinder clearance?
did you break it in properly?
impropper/bad fuel would prob caused deto before it went and i dont see any signs of deto. looks like lean on fuel or lean on oil.
front cylinder runs hotter since its next to the stator section, if your carbs have a little plastic cap with a notch on them, just pull it off with a pair of plyers and richen it up past what you had.
remember after rebuilds, compression usually goes up compared to stock compression readings since you now have a little more cc's of air that is being compressed. hence, thats why the major rebuild companies redo the squish and widen the bore on the head a little to compensate.
whats crappy about three cylinders is that it cost more to rebuild, and now you have to do all three again and go even bigger due to the damage.
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