What would cause this, Pics included

[Indread]

Hi everyone, so I decided to take my blaster out for a rip in the snow storm we had wednesday. I mixed up some fresh gas/oil 32:1, fired her up and left it to idle while I got geared up for the winter weather. I bet it idle'd for a good 5 mins before I took it up and down the back roads for a good 20 minute adventure. While headed home I saw a field and decided I was going to break trail through 5 inches of snow, or so I thought I was going to anyway.

I got about 1,000ft into the field roosting it out the whole way shes been laboring pretty good and only going about 15/20mphs in 6th gear. while im feathering the throttle between half/wide open trying not to over rev in the snow, All of a sudden it went from 8-9k rpm to 0, pretty much locked the tires right up and there I sat. I thought maybe it over heated and I seized it somehow, so I slowly kicked it over and it had decent compression still and didnt sound " bad " while slowly turning it over. I decided I wasnt going to try and start it again and that I was going to push it back to the road and load it up into the truck for further inspection. Well today I decided id rip into it and see what I had done to my beloved friend, Here is what I found.

Not sure what caused that dmg to the head, but oddly enough there is no damage to the piston surface.

Those weird marks on the piston line up with the edges of my transfer ports, sadly I forgot to get a picture of it with the piston at its lowest position. When I tried to feel them marks with my finger nail I cant feel them, they appear to be superficial only.

Heres a shot of the cylinder, its a crappy picture but theres no damage inside the cylinder that I could see. No dark spots in the metal, no scoring, no scratching, hell I can still see defined cross hatching when I move the cylinder around under some light.

Theres one more picture of the piston showing the skirt looks to be ok.

So thats where im at, any input anyone has as to what may have caused that damage would be appreciated. I dont want to put it back together until I figure out what my problem is. Has anyone ever seen those marks on a piston before, it looks almost like how a pipe gets that gold/blue hue in its finish.

 

[Triple_B]

Looks like maybe the ground electrode on the spark plug may have broke off? All I can think off....

 

[scotj77]

you need to inspect the big end rod bearing. is there a dent in the top of the piston to match that gouge in the head? can we get some pix of the crank

 

[Awk08]

sounds like you overheated it by lugging thru the snow with no airflow passing over the engine to cool it
i saw my whole head pipe turn cherry red once doing the same thing

 

[scotj77]

also is that a ding i see in the top of the exhaust port and in the transfer port on the oppisite side?

 

[Indread]

Tripple B: Ground electrode was still intact on the spark plug, I forgot to mention in the post that the plug did appear to be a touch on the lean side.

Scottj77: Rod bearing play seems very minimal, havent pulled the motor out of the frame yet just pulled the top half off so far. No dings in the cylinder, im guessing the 2 specs are lint from my shop towel I used to wipe out and re coat the cylinder with oil so it didnt rust. Also there is no damage in the top of the piston as you can see in the photos which i mentioned that I found odd in my original post.

Awk08: The RPM's where up there pretty high the entire time, just couldnt get enough traction to gain anymore speed then 15/20mph, even though the wheels were turning 50+. The bike did seem hot to be honest, I recall a piece of electrical tape was sizzling and bubbling on top of the head when I got off the wheeler to inspect.

 

[scotj77]

hmm sounds like this isn't a piston or crank issue. i would probably search elsewhere as long as the crank will spin freely with the tranny in neutral

 

[Indread]

Yea, crank spins easy and smooth, I spent probably 5 minutes going back and forth with the crank trying to feel for a hitch or any kind of badness. I've no idea what hit the head to do that kind of damage and yet leave the piston without a scratch. I checked my reed screws and they are all accounted for. I also have never seen those marks on a piston before, anyone else, what causes it?

 

[scotj77]

it looks like a casting flaw to me. impact would have left the spot shinny with a raised area around the divet. there would also be a huge dent in the pison. maybe that piece of alluminum came loose and shorted the spark out. then got spit out the exhaust.. seen weirder things happen

 

[Indread]

Ha, thats a theory. Better then anything i've managed to think of so far, just cant believe that it took HOURS of abuse to make that flaw in the head show up.

 

[Indread]

Opinions on this, is it possible that the fuel charge was igniting in the base and the ports were shooting out fire into the cylinder causing them marks on the piston. On the last picture it kind of looks like a candle flame with a bunch of black soot around it, maybe im crazy. I dont even know if this is possible, im just thinking out loud trying to figure them odd marks out on the piston.

 

[Larry's Shee]

You know for a fact that divot wasn't in head before? ie, you had it apart before?

As to the piston markings, known as "piston wash" : Let me google that for you

Also, have you rejetted for colder weather.

 

[scotj77]

Opinions on this, is it possible that the fuel charge was igniting in the base and the ports were shooting out fire into the cylinder causing them marks on the piston. On the last picture it kind of looks like a candle flame with a bunch of black soot around it, maybe im crazy. I dont even know if this is possible, im just thinking out loud trying to figure them odd marks out on the piston.

the marks on the top of the piston are from the ports. if you look closely the marks on the piston crown will line up with the various different ports. very normal to have marks like that on a two stroke.

If you overheated teh motor the piston would probably have scoring marks on it. I think that chip in the head is a casting flaw and there is a different issue to your blaster shutting down on you. might still want to look into replacing that head bc it will create a "hot spot" durring opperation. btw what fuel are you running?

 

[Indread]

Larry's Shee: Thanks for explaining the marks on the piston, im fairly new to the insides of a 2 stroke. Yes, I know the head was fine before hand as I had rebuilt the motor probably 20-25hrs ago. I went up 1 jet size but it had been 20+ degrees colder then the last time I checked it, and it did show lean on the spark plug.

Scottj77: I agree that the head needs to be rechamberd before running it, that mark was not in the head before I assembled it I know that much haha.

Thanks for all the help thus far from everyone thats chimed in really appreciate it.

 

[Indread]

Scottj77: Im running 91 octane pump gas, Highest octane in my area unless I travel to the airport for 100LL, or to the racetrack for 110. My engine is mostly stock, freshly rebuilt crank to piston, uni air filter, no air box lid, fmf fatty head pipe, stock silencer, dual stage boyseen reeds, running a 280 main jet on the stock carb.

 

[scotj77]

dude it sounds like you have done everything right. as long as you are leaktesting your motor upon assembly. I would put it back together. new base gasket and anneal the head gasket. leak test it and then start looking for the problem. I am pretty sure it isn't in the topend or crank from what you have told me

 

[JBRoc01blaster]

Could it be possible that the contact with the cold snow caused the jug to contract as the piston was still hot and fully expanded ? Is there any scoring or black marks on the side of the piston and piston skirt ?

 

[scotj77]

Could it be possible that the contact with the cold snow caused the jug to contract as the piston was still hot and fully expanded ? Is there any scoring or black marks on the side of the piston and piston skirt ?

I looked pretty clean no scoring on that piston that you can see anywhere.... there aren't any signs of overheating.

 

[Indread]

Thanks for all the input, as Scottj77 said there is no signs of over heating that I could find, no black spots or score marks in the cylinder or on the piston. Im leaning towards what Scottj77 had said back on page 1 about it maybe being a casting flaw that fell out. I cant really explain how the head has damage and not the piston any other way. Hopefully in a couple weeks when I can afford to get my head recut, I can put her back together and rip around again.

P.S
Thanks again for all the help everyone, I'd like to wish all of you that of chimed in to my thread a belated Merry Christmas.

 

[Blaaster]

I have seen the piston wash effect on a motor that picked up a bit of water through the air filter.

Water will produce a cooler and somewhat leaner charge, maybe a lump of snow got sucked in.

The blemish in the head baffles me!