How do these pistons look?

[schwab16]

I have the exhaust off to replace a starter, and took a peek at the pistons. I'm pretty new to diagnosing engines, so was hoping someone could give some insight.

Looks like the front piston is in better condition than the rear. I wasn't able to check compression recently due to the bad starter (ski has been sitting for 4 years). I was hoping I didn't need to do a top end, but after seeing the pistons, thinking one might be due? Is it worth putting the exhaust back on and testing compression, or just go for a rebuild?

Thanks for taking a look!

 

[schicks]

You can test compression with exhaust off. Is motor in ski still? Could just be water ingestion scuffing.

 

[john zigler]

Looks like you have some pretty good scoring. Do I see a crack? (2nd pic?) Try to feel with your finger nail. If that is a crack, you NEED pistons for sure.

 

[te4250]

Looks like you have some pretty good scoring. Do I see a crack? (2nd pic?) Try to feel with your finger nail. If that is a crack, you NEED pistons for sure.

Good call it definitely looks like a crack from here lol, yeah probably gonna want to do top end before pieces of that piston take out your bottom end

 

[schwab16]

Looks like you have some pretty good scoring. Do I see a crack? (2nd pic?) Try to feel with your finger nail. If that is a crack, you NEED pistons for sure.

Thanks for the response! Wow yeah that picture does look like a crack. I just went back and checked the piston, when I ran my finger on it I couldn't feel a crack. I took a picture after and it looks to just have been oil, looks like it smeared.

So even if that isn't a crack, is the scoring a sign for a rebuild? Also just for my knowledge, is the scoring the black vertical smears, or is it just the vertical scratches?

 

[Big Kahuna]

you got to pull the cylinder to tell, your only seeing about 20% of the pistons. Do a compression check.

 

[schwab16]

You can test compression with exhaust off. Is motor in ski still? Could just be water ingestion scuffing.

The motor is still in the ski, but I still have to get a starter, so probably at least a week out until I could test. If I test compression without the exhaust should I expect the reading to be any different? Thanks!

 

[schwab16]

you got to pull the cylinder to tell, your only seeing about 20% of the pistons. Do a compression check.

Gotcha, that makes sense. Once I get my starter I will check the compression. Probably will just pull the cylinders in the meantime. Thanks!

 

[schwab16]

Update on the engine situation. I was hoping to get some more information, as I'm still unsure of diagnosing some of the engine stuff.

So the pistons were definitely if rough shape, especially the rear piston. Looks like it melted in the middle and also had some material breaking off from the top, see in the picture below.

They were both pretty stuck on the rods, but got them off. I'm concerned about the rods. Seems to be some discoloration.. Does that mean they are bad and I need to replace the crank? I'm going to open up the cases when I get some time, but wondering if this is enough to know the rods are bad? Thanks!

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[Quinc]

I would spend the 200$ for a new sbt from @JetManiac and replace everything. New seals too.

 

[schwab16]

I would spend the 200$ for a new sbt from @JetManiac and replace everything. New seals too.

I ended up grabbing a 62t to drop in my SN. Thinking in the future once I have some more money I will go ahead and do the full rebuild on the 650.

Sent from my Pixel 3 XL using Tapatalk

 

[Quinc]

If it is a 650 it is not worth the cost of the crank. You can buy a fully assembled ready to go 650 in the for sale section for less than the crank cost.

 

[MiNDRiVE]

Images in the post from the 13th won't display but I'm curious to see them.

 

[bored&stroked]

650?!?!? If you had said that we would have said the pistons look terrible and tiny.

 

[schwab16]

650?!?!? If you had said that we would have said the pistons look terrible and tiny.

Lol! Not only were they tiny, the one piston was cooked. Very excited to drop in a 62t, should be here tomorrow!

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[schwab16]

Images in the post from the 13th won't display but I'm curious to see them.

Huh, yeah not sure why the link broke. I can add the pics of the crank here later today.

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