face_off Posted December 5, 2005 Report Share Posted December 5, 2005 hi all i open my engine last week and notes this problem and its after a fresh top end rebulid and after 4 weeks of rideing ? and is this caused of lean main jet or to much timing ? Quote Link to comment Share on other sites More sharing options...
banshee tuner Posted December 5, 2005 Report Share Posted December 5, 2005 I would say timing, how much advance and what octane fuel are you running. Quote Link to comment Share on other sites More sharing options...
ad_stroker Posted December 5, 2005 Report Share Posted December 5, 2005 i guess u have a broken piston..same happened to me a year ago Quote Link to comment Share on other sites More sharing options...
wayfst Posted December 5, 2005 Report Share Posted December 5, 2005 hows the bearings in your crank, broken ring, broken piston could be alot of thing not related to jetting or timing. Quote Link to comment Share on other sites More sharing options...
Ducman Posted December 5, 2005 Report Share Posted December 5, 2005 Its hard to tell from the picture if there is detontaion because it leaves really small pits, but its obvious you have dammage from a broken piston. The question is what broke the piston. Look at the piston for small pits which will make the surface look real ruff and eroded especially around the edges. If one side is detonation the other probably will show signs of detonation too. If you dont see any evidence of detonation then it could have been several things, snagged ring on a port, crank/rod bearings getting sloppy, bore was too far out of spec, ect. Quote Link to comment Share on other sites More sharing options...
face_off Posted December 5, 2005 Author Report Share Posted December 5, 2005 this problem is only on the right side and the timing is set to +4 and 96 octaine with mild head 148 lb on both side . the last blow up piston on the same side with the same small pits on the head dome and the piston was cracked and stick on the cylinder wall on the exaust side Quote Link to comment Share on other sites More sharing options...
ScrewMachine Posted December 5, 2005 Report Share Posted December 5, 2005 If the piston is in pieces, this question may be irrelavent, but what does the top of the blown piston look like? Does it have a large black spot on top? (The larger the black spot, the leaner your air/fuel mixture was) Does the black spot reach to the edge of the piston? If so, heat caused by the lean condition was reaching the rings/cylinder wall (cause of seizing). Does the right side carb have an air leak?? I need to go back and look at the picture, but I noticed a black streak on the head leading down from the spark plug hole. Could it be heat from a lean condition; sucking air down into the cylinder from a loose spark plug??? Never seen that before, maybe someone else has and can chime in? Good luck. Quote Link to comment Share on other sites More sharing options...
2twin350s Posted December 5, 2005 Report Share Posted December 5, 2005 you have dropped a crank bearing. that is all there is to it. it is not lean or whatever. you are chewing up rod and or crank bearingand they are bouncing off the piston. time to split the cases and put a crank in it. or you can just keep boring it and puttin in pistons until you run out of bores Quote Link to comment Share on other sites More sharing options...
face_off Posted December 6, 2005 Author Report Share Posted December 6, 2005 ScrewMachine i have single C.V. carb 35mm 2twin350s you think this caused off crank bearing and is it normal only one side of the engine have this marks on the piston and dome head ? Quote Link to comment Share on other sites More sharing options...
Shee-Male Posted December 6, 2005 Report Share Posted December 6, 2005 looks like a broken piston ring to me....I just went through this with my own engine yesterday, looks like it met the same fate Usually with a rod bearing gone the piston will hit the head and make a hell of a racket! maybee when it was honed the edges of the port were'nt chamfered? Quote Link to comment Share on other sites More sharing options...
2twin350s Posted December 6, 2005 Report Share Posted December 6, 2005 yes i think the crank has issues.pull off the jugs and clucth and stator covers. you should have no up or down play in the crank.grab the ends of the crank and lift it up and down. it should be tight. also there should be no up or down play in the rods.regardless, after all the damage from the 2 piston fialures, i am sure there is debris in the crank bearings. and yes a crank can be bad on one side and not the other,hence damaging only that 1 affected cylinder.then make sure when you redo the top end ,whoever does the boring,make sure the relieve or chamfer the portsn in the cylinders.other wise you will clip your rings on the sharp edges. Quote Link to comment Share on other sites More sharing options...
ScrewMachine Posted December 6, 2005 Report Share Posted December 6, 2005 ScrewMachinei have single C.V. carb 35mm 445519[/snapback] Aight...guess I missed that. What about the top of the piston, what does it look like? Quote Link to comment Share on other sites More sharing options...
face_off Posted December 7, 2005 Author Report Share Posted December 7, 2005 its the same as the pic of the dome only on the right side and the left piston has some carbon in the middle only. Quote Link to comment Share on other sites More sharing options...
ScrewMachine Posted December 7, 2005 Report Share Posted December 7, 2005 its the same as the pic of the dome only on the right side and the left piston has some carbon in the middle only. 445879[/snapback] If that carbon patch reached the edge of the piston, that cylinder was running lean. No doubt about it ...IMHO... Ya got an airleak on the right side somewhere. Could be intakes, could be in the case seals. Quote Link to comment Share on other sites More sharing options...
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