What caused this?

[ArmandTanzarian]

hello all,

Having put a new top end on my Jet I did about fifty miles and then realised that the crank bearings were knackered. I have just stripped it all down and found that the piston looks like this



There was no more smoke than normal, the plug was a brown colour but the amount of crud on the piston is mental. It's like treacle. The only thing I can maybe think of is that I just sealed the tank with that bright red goo that stains the petrol for the first couple of tankfulls. I'm using fully synthetic Heine Gerricke two stroke oils at 3%.

[johnny diamond]

ive seen simalar when copious amounts of oil were used,to assemble an engine, IE;- a few squirts from the old oil can to
lubricate initial start up,or crankcase oil ingestion,but wouldnt have thought it anything to do with tank sealer unless you
used a cheapo brand, i use POR tank sealer when required to garauntee quality ive never come across discoleration of
fuel...are you sure it was mixed correctly ??

[ArmandTanzarian]

Iused the same sealer that lots of other people recommended on here and elsewhere. I suppose it could be assembly oil and grease but there seems masses of it. Odd that there was no smoke either.

[J1MS]

If youve been running it in and taking it easy, then the piston wouldnt get hot enough to burn off the deposits of oil that have stuck to it.... so probably nothing wrong, just running on the cold side... Maybe ???

[Knowledge]

Interesting. The black smudge matches the combustion chamber perfectly, except for a lighter patch in the centre where the plug is located.

What was it like under the piston crown? Is it black on the underside of the piston crown?

[ArmandTanzarian]

What was it like under the piston crown? Is it black on the underside of the piston crown?

The underneath of the piston is also discoloured but it isn't really burned on it was still faintly soft.

[cezeta]

ive always assumed blacking top and bottom of a piston is drive seal failure but dont hold me to that...i assume all kinds

[ArmandTanzarian]

ive always assumed blacking top and bottom of a piston is drive seal failure but dont hold me to that...i assume all kinds

The seals on the crank were damaged (on the flywheel side at least), I discovered the piston muck when I was swapping the crank. However, the gearbox oil was all present and correct and the scoot wasn't smoking. My best guess is the tank sealer but no-one else seems to have had this problem with it. The fuel is certainly coloured by it. This is what came out when I drained the system and it is the second load I've put in since sealing the tank. Its very red, despite the fact that the 2-stroke I'm using is green.

[cezeta]

eeew glue isnt a good lubricant is it

bit late to mention this but you can use rust eater to clean you tank, clean with liquid not spray brake cleaner first then use a liquid rust eater. you can re use the rust eater usualy and do a few tanks.

i did use pet seal once and it kept gluing the filler cap on to the point that the tools had to come out every time it was filled.

hows the carb looking?

[soulsurfer]

If it's the Tank Care Products sealer, the description says...

"Our New Tank Sealant is made from modern Aerospace Quality formula, and forms a flexible yet petrol resistant coating which will not vibrate loose or brake up with age. Available in Standard 250ml or Value 500ml containers. Contains a red dye which will initially turn your petrol red, there is no need to be concerned about this as it will not damage your engine, it is added to the sealant to act as a guide for even coverage when applying."

So doesn't seem to be something to worry about