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Old 07-26-2006, 01:32 AM   #1
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Default dirt in engine...now double pops

Hi

The air filter came off my nice new Max power mod, less than a gallon in....anyway...i took it apart cleaned it and when i put it back it double pops at TDC if that makes any sense...

I looked at it, the rod is scratched on the bottom half, where it goes down into the groove in the main housing.

other than that, the bearings were smooth, not pits or grittiness.....

any suggestions what could be wrong? Still has good pinch.
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Old 07-26-2006, 04:33 AM   #2
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Can you take a pic, could be machining marks but not sure. Not sure what you mean by double pops, could be the oil making a noise when the exhaust port closes and seals and then when you uncover it, is it audible or do you feel double notches when you rotate near TDC?
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Old 07-27-2006, 01:38 AM   #3
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Quote:
Originally Posted by BritRacer
it double pops at TDC if that makes any sense...
If I understand you correctly, I think it is normal.
Because your engine being as good as new, it still has pinch at TDC, but because of the small amount of play between your conrod and crankshaft, you might feel something you describe as "double pops"
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Old 07-27-2006, 01:52 AM   #4
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Quote:
Originally Posted by BritRacer
Hi

The air filter came off my nice new Max power mod, less than a gallon in....anyway...i took it apart cleaned it and when i put it back it double pops at TDC if that makes any sense...

I looked at it, the rod is scratched on the bottom half, where it goes down into the groove in the main housing.

other than that, the bearings were smooth, not pits or grittiness.....

any suggestions what could be wrong? Still has good pinch.

i would take the whole engine out, bearings and all, and flush the whole engine out. get a tooth brush and clean the whole crank case. make sure all dirt is remove from the rod bushing. and crank pin.

re-install. put some oil between the rod and crankpin, turn the engine over and see if there is air bubble forms.

oh and please cable tie air filter.
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Old 07-27-2006, 07:46 AM   #5
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Quote:
Originally Posted by BritRacer
Hi

The air filter came off my nice new Max power mod, less than a gallon in....anyway...i took it apart cleaned it and when i put it back it double pops at TDC if that makes any sense...

I looked at it, the rod is scratched on the bottom half, where it goes down into the groove in the main housing.

other than that, the bearings were smooth, not pits or grittiness.....

any suggestions what could be wrong? Still has good pinch.
The 'double pop' you are feeling is the piston going up in compression and then after tdc going down in suction until the ex port opens. This happens when engines loose perfect piston seal (probably from your mishap with the air cleaner). Inspect the piston and sleeve VERY closely for vertical scratches, as this is sure to be the culprit.

The best method I have found for checking for piston wear (or general compression condition) is to put a drop of light oil (WD40, bearing oil or equivelant) on top the piston, reinstall the plug tight, and rotate the engine over in your hand and listen to the ex. port closely for compression leakage (slight hissing). If there is a noticeable hiss then you need a new piston/sleeve set (also good idea to replace the con-rod at the same time).

BK
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