What's up with my piston? What's considered a normal/safe mark?

[Roseand]

So I rebuilt my engine last winter. New crank, new pistons, absolutely everything including brand new parts for a very rebuild, etc. Last season i ran it pretty hard with a 4 to 1 pump gas to race gas at 180 psi. I believe I got 5 gallons of oil in last season, so 200 gallons of fuel/60+ hours of ride time. I was comfortable enough with my tuning that I'd endup doing 15 second+ WOT runs, shutoff the ski immediately, and read the plugs. I also checked the compression multiple times during the season and it stayed at 180 psi. Soooo my cylinders look pretty much perfect. No marks that will grab your fingernail. Only marks are near the exhaust ports and they look like other cylinders I've seen.
I just sent my cylinders off but didn't take a look at my pistons until today. The exhaust side on both of my pistons look pretty good! They're almost perfectly smooth(there's marks, but normal ones) . My rear pistons intake side looks pretty good too(small marks, but I don't think there's anything abnormal) . Then there's the front intake side piston.... It has a bunch of small scratches which don't seem like anything to worry about. Then there's one large mark. It's not a deep score, but you can feel it with your fingernail. Is that possibly a mark that happened during break in? Or did I have a small seizure that didn't affect my compression? I was running dual cooling so my motor never over heated.. I don't think that mark is affecting anything though, but I'm not 100% positive.

Besides just my case, what is normal to see on a piston? Are some marks caused from the first time running a ski after a fresh rebuild?

Here's some pics: I think my piston wash is fine.

 

[Quinc]

Engine running to cool and the pistons heated up and expanded faster then the cylinder?

 

[restosud]

something went though it.

 

[Roseand]

something went though it.

Cylinder is fine. And the mark isn't real deep.

 

[DAG]

The cylinders harder than the piston bro

 

[Roseand]

I'm not stupid. I realize that. Other piston's intake side has similar marks just not as deep.

 

[restosud]

Cylinder is fine. And the mark isn't real deep.

yeah and?
a spec of something got wedged and eventually found it's way out.no big deal.

 

[kevbo]

It got a little tight at some point, it is extremely common on watercraft. Not a problem unless it pinches the rings. When it does you will experience a high speed shutdown.

 

[Pro-pulsion]

^^ Yup, seems to be a common occurrence with aftermarket pistons such as Wiseco. They like to be warmed up before put under hard riding otherwise they expand too quickly compared to the block. Sometimes you will see guys fire up their skis out of the water and let them idle for 10-15 seconds...or what seems to us to be way to long out of the water lol...but they do it because it helps the block heat up quickly and save potential piston lock-up when they unload and go. Most ramps are busy and people don't want to wait on us to warm up our skis before we leave, they just want us out of there so a minor warm up on the trailer allows us to drop and rock. It is a much less likely scenario to see this with oem pistons because they are cast and a bit more material than the forged after market versions so they take longer to expand. If you are not finding any real depth to the marks then they should be fine. I have even polished pistons with 800 grit wet sand to smooth out slightly more noticeable marks, give a little swirl with the paper all around the skirts and it helps retain a tiny extra bit of oil on them...same concept as cross hatching in the cylinders, gives a place for oil to cling to.

 

[CRJ]

Yep something went through it but cleared out. Its common with how thin of an intake most of us use. The rest and the piston wash looks great. why did you send it out with it in clean running shape?

 

[Roseand]

Yep something went through it but cleared out. Its common with how thin of an intake most of us use. The rest and the piston wash looks great. why did you send it out with it in clean running shape?

Yeah I don't think it's anything to worry about! I just saw it and was a little surprised.

I'm getting them ported, that's why I sent em out.

 

[Roseand]

Just found this. I rebuilt it with oem seals and it passed a leak down test by a mile. I oiled and greased the crap out of my bendix too.. So I'm wondering if this is from a crankcase leak or just from all the original grease. It's kind of sludgy in places compared to just straight/smooth oil. Thoughts?

 

[CRJ]

i bet its a mix of both. and leakdown test has nothing to do with flywheel cover sealing, so water and oil will cause that. and seal will let a little oil past, as its how the seal is lubricated, and for the hrs you put on its not shocking, but that is more than id expect to see. Id do seals while you have it apart, their cheap from JM

 

[Roseand]

I rebuilt it freeken last season and I tested a leak down test without the flywheel cover on to make sure the seals were good. I know some of it is from the grease on the bendix but some of it might be oil too. I'm just surprised, I used everything OEM, built it right, etc. My old setup lasted 20 years before it blew up lol.
70 hours is enough to cause issues? Doesn't seem right to me IMO.
Either way I'm doing a leakdown test what I put my cylinders and stuff back on. It's just disappointing if i gotta replace a seal already.

 

[Roseand]

After closer inspection it looks like it's just the grease and another lubricant I used on the bendix. It does not smell like two stroke oil. There's a runny liquid in there too but it looks like it's the lanolin fluid film stuff I soaked my bendix in.. I soaked it for days in that stuff and also greased all necessary parts of the bendix and starter. Also greased the crank seals when I put em in. In the flywheel area I was pretty liberal with grease and stuff so there's a good chance it's just that. There was zero water in there as well. And the flywheel was very clean too.

 

[Dartman]

make sure you have the pistons glass beaded
you don't want any of that black on the piston
have cylinder honed
not a flex hone
use rigid hone just a little to be sure of no high spots on the wall
front cover mess is more than likely from the soaked bendix slinging all about

 

[Jakobi86]

Coming from a snowmobile background and rebuilding multiple engines, I'd say your Pistons probably at one point expanded a little faster than te cylinders. More than likely it was one of the first start ups. See this all the time with sleds. That's why I always hear cycle them after rebuild a few times and always let them warm up before getting on it. You have to be careful with heat cycling and new rings/walls because you want to get a few heat cycles into the engine before a hard run but at the same time the only way to properly seat rings is under a load. Not running on the stand or out of water. So you see it's a compromise between running the engine between a few heat/cool down cycles but not too much that you glaze over the cross hatch and end the break in period. Hope this makes sense


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