discoleration piston skirt

[ief]

tried on 2 other forums but no joy so i'll try here as well

the thing is, i have a set of 'race' pipes but somehow they make this of my pistons: (about 100 km)



it's about upper side of the piston witch lookes like they are polished, i know for sure it's the pipes, i guess the temperature gets to high, oil gets burnt of or something like that ?

Top of the piston lookes great, I now did the mk modification (oil lube holes in the piston) but am wondering if that will do the trick or am i risking an engine if i keep using the pipes as they are or will the pistons be allright now?

Another side question is, the pipes are build up on 31k headers and the powerband is from 8000 rpm till say 11500 rpm, i can use 4l headers, they are 4 cm's longer so the powerband will come down a bit. What that also does is increasing the volume of the pipes, might that be a good thing given the circumstances or isn't there any way to tell but to try it?

[schrauberlehrling2]

This Piston got a bit to hot, the color is same to the one I burned away after just 600KM. By looking at the Picture it seems like the camfered Edge in the Exhaust area already started to melt.

I guess it is the left Hand Piston? If so i would use a Main Jet at least 10% bigger. Using a tad bigger main on the other cylinder might also be a good idea, just to be on the safe side.

If this was the right hand Cylinders Piston, check the timing. If the middle Part of the Crank is twisted the Timing of right Hand Cylinder will be out. The Pistons should be exactly 180° apart at TDC.
Witch Plugs do u use? Try NGK=B10, Bosch W1cc, or similar ones and go down one step if they foul.


The scratches might also be caused by the overheating. In other cases this caused by dirt getting in during installation.

About the Headers/Pipes, try. For comparison look into the FAQ-Section, there is an Article about Pipes.

The lube holes on the exhaust side have to be on sides where they do not interfere with the Exhaust neither the Transfer Ports.

conclusion: The Mixture is to lean OR Too mutch Ignition-Advance OR Both.

Hope i could help a bit
Groet Florian


p.s. if you find the time it might be interesting to get the lenghts and diameters of your pipes for the Forum. Also Feedback about the Powerband with the new Headers would be appreciated.

[ief]

hi florian,

tnx for ur answers.

It's both pistons, plugs used are iridium 9's from ngk. The lube holes i made were done as per mk manual so not on the point's you're saying
Ignition is original so i hope upping the mains will do the trick then.

Here is my pipe, the 43 must be 41 btw: