3d exhaust melt / scored cylinder

[johna56]

I have a 2004 3d with the 787. Supposedly had a rebuild winter before i bought it, very low hours since purchase - maybe 2 actual riding hours the more i think about it. T fitting in the exhaust melted and machine was choking off (poss from smoke?) after 10 minutes. Engine mount is also broken. During diagnosis, cooling water was flowing properly, compression was at 160 and 163lbs and all engine and exhaust temps seemed "normal". With the exhaust manifold off, independent dealer tech noted deep scoring in rear cylinder, recommending a rebuild. He thinks that oil getting into the cylinder caused the smoke choking off the engine. No cause for the melted exhaust T has been identified. Q1 - Does anyone with experience here have an idea about what caused the heat and melting? Q2 - Could a loose engine prevent water from cooling the exhaust somehow? Q3 - Does the scoring necessitate a rebuild if the compression is good? Q4 - Does a rebuild or reman replacement make sense if the cause for the melting isnt identified? Q5 - What can i sell a machine in this condition for? Is a $750 -$1000 sales price unrealistic? Im in North Jersey. Q6 - Can the cylinders be replaced without removing the deck? Q7 - Can the engine be removed through the access hole, or does the deck need to be removed?

Yes scrapping it is on the table. Just trying to do some research here. I cant find any posts answering my questions.

Thanks.

 

[mikidymac]

"He thinks that oil getting into the cylinder caused the smoke choking off the engine." This doesn't make any sense, it's a 2-stroke so it burns it's lubricating oil without oil it will seize.

Your compression numbers are perfect so I doubt you have any scoring of the cylinders.
Q1. THe only thing that will cause melting is a blockage in the cooling flow. the usual suspects are a sand blockage in the cooling line, the water valve on the muffler or and issue with the jet pump.
Q2. No.
Q3. I doubt you have scoring with the perfect compression numbers. But if it is scored yes you need to bore and fit new oversized pistons.
Q4. No, or it will happen again.
Q5. If it's in perfect condition $500 if not less.
Q6. Yes, just open the engine cover, but it's easier to pull the engine out.
Q7. Yes, should come right out the engine hatch.

 

[johna56]

Thanks for the reply. I saw and felt the scoring when the exhaust manifold was off. The jet pump pushes the cooling water through the exhaust? Im leaning toward a rebuild. My son has done 2 stroke rebuilds on his dirt bikes. Seems like another $600 is worth it (kit, engine mount and alignment tool) is prob worth it if i can confirm the heating issue is resolved.

 

[mikidymac]

It’s typically the water valve on the muffler that starves the exhaust of water.

There’s probably something else causing the cylinders to score. You would have had to get it really really hot to cause an issue. Even then once the exhaust coupler melts the exhaust in the hull chokes out the engine.

Seizure is typically caused by worn out cylinders, lack of fuel and/or lack of oil. Due to your good compression we can rule out worn cylinders which leaves lack of fuel and or oil.

How many hours on the ski?