piston black spot

N

narx

gefufn tjuner
Does this brown/black area mean that engine was overheating? As I know it`s carbon deposit from oil and that means piston crown was too hot.
I saw this on lot of used pistons from different engines and it`s a bit strange that all of them were running at to high temperatures, but sure it`s possible.


ResizeofDSC04060.jpg
 
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narx said:
Does this brown/black area mean that engine was overheating? As I know it`s carbon deposit from oil and that means piston crown was too hot.
I saw this on lot of used pistons from different engines and it`s a bit strange that all of them were running at to high temperatures, but sure it`s possible.


http://i57.photobucket.com/albums/g206/narx_1982/ResizeofDSC04060.jpg
Click to expand...


This isn't normal!! This black spot shows overheating!!! Normal piston -even if it's in a race engine doesn't have any spot, brown spot is the first sign of the heating, the second is the black and after that you maybe have a dameged piston (or if you are very lucky you never have problem with it)!! But this is not 100% engine!!

If you have a piston with this black spot, don't need to replace it, cause it's still usable, but try to find the reasons!!

P.S: if you see 100 pieces of pistons like this, it doesn't mean all of them are good! That mean you never saw a right one!
 
Last edited:
melf #50 said:
this is normal ...
Click to expand...

??????????????????????????

Please do not say this is normal!!! I think you are an experienced 2T tuner, so maybe you are just kidding!!
 
Last edited:
Browni said:
Hey man!! Relax! Don't ask if you don't care the -right- answers!! Your style is not very funny!
Click to expand...

Please read again tiba's post, I understood this as a joke, and I have good reasons for it, caps text and "oh my god" style. I answered that way, where is the problem dude?

Tiba, I appologize if your answer wasn't ment to be a joke.
 
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it was a joke dude. :D

as for the stuff i'm on it's smoke coming from the C21 pipe, it's VP C14 mixed with Motul Kart Racing oil, start the engine & inhale the smoke from the pipe, ahhhhhhhhh......... look at those pretty colors!!! :D
 
narx said:
Please read again tiba's post, I understood this as a joke, and I have good reasons for it, caps text and "oh my god" style. I answered that way, where is the problem dude?

Tiba, I appologize if your answer wasn't ment to be a joke.
Click to expand...


Sorry narx!
 
I don't know what to say. I've always read that it is a sign of overheating. But all my pistons AC and LC have shown brown spots. Even the stock 50cc. I don't race. I always keep an eye on my temp guage. I'm very conservative with my tuning. I run on the rich side with a number 6 spark plug to keep her clean. I value reliability above performance. That's why I use strokers. I get my power by vertue of engine size. Not because it is tuned to squize the last hp out of it. And yet. The brown spot is always there ! So... go figure !
 
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tiba_karotsu said:
that is the nature of things, even 4stroke engines have that.
Click to expand...


I have lot off race pistons from my race cylinder, and none of them have black spot or even brown spots, sorry one has a brown spot, and yes it was little bit overheated! I saw dozen of race pistons for racing kart engines, the experience is the same! I also saw various pistons from other engines too, like 50 cc engines, 125, 180 cc Gilera, Yamaha Dt, other motorcycles 4-stroke engines, and they were totally clear at the inner side, cause they worked in a good condition!


However as I said, maybe you never have problem with this type of black spots, but they aren't "healthy". That's why you quys saying it is natural!

I think this is a quite pointless talking, everybody say their own truth ! :)
 
Aloha, I also thought that the black spot was OK, but doing a google I find the evidence from: Eric Gorr
BLACK SPOT HOT
The underside of this piston has a black spot. The black spot is a carbon deposit that resulted from pre-mix oil burning on to the piston because the piston's crown was too hot. The main reasons for this problem are overheating due to too lean carb jetting or coolant system failure.

http://www.smellofdeath.com/lloydy/piston_diag_guide.htm
 
adas said:
Aloha, I also thought that the black spot was OK, but doing a google I find the evidence from: Eric Gorr
BLACK SPOT HOT
The underside of this piston has a black spot. The black spot is a carbon deposit that resulted from pre-mix oil burning on to the piston because the piston's crown was too hot. The main reasons for this problem are overheating due to too lean carb jetting or coolant system failure.

http://www.smellofdeath.com/lloydy/piston_diag_guide.htm
Click to expand...


Guys.... this is only one INDICATOR!!!! What is the burn like on the piston crown? What is the plug reading like? What do the deposits in the exhaust port and pipe look like? What does the head look like?

One thing I keep seeing on this and many other forums or NG's is that people keep trying to tune based on one indicator or another only. If one indicator leads you to believe the engine is running hot CHECK OTHER INDICATORS!!! They will either back your initial ASSUMPTIONS up or prove you need to keep looking.

If it looks like a duck and quacks like a duck it most likely is a duck. But if it looks like a duck but barks like a dog don't assume it was a duck beacause of your first impression nor assume it is a dog because it barked.
 

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