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2001 Seadoo Sportster LE. Just got it!

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I do have a wifi camera ordered for my jeep. It could be the first application for it. LOL.

I am just exploring ideas here, deciding if I need to invest into this sportster and keep it for another 5 years, or a challenger for another 5 years. If I decided putting another 2K into boat, I would like to spend it on the one I will keep at least for 5 years.
More room in the challenger is important to me according to the last 15-20 hours of my family boating experience this summer.


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Hey, before reinstalling those RAVES look ans see if you can see the piston move slightly and the rings staying still, this tells you the ring isn't seized in the ring land.

If I rock my motor back and forth from the PTO, I can see the piston move slightly before the ring begins moving b/c there's some clearance between the ring and the ring land, this tells me the ring isn't stuck to the piston.

I really can't tell from you photos if the piston discoloration is yellow and brown varnish deposits from probably more heat than cheap oil can withstand or if the aluminum piston skirt is scored/scuffed.
 
Here comes my evil thinking :-D : sell this sportster after the season and start looking for a 18' challenger at $6000 to $8000 range. And stick to it and do good maintenance on it if I am lucky to be able to get a decent one, then buy two rebuilt engines down the road if signs come up.

Sound like crazy? :drool5:

But man, jet boats are fun. Is asking for bigger my fault?:lol:

Look for a boat that has a 4-stoke engine and leave the 2-stroke world behind.
 
I thought the 2 strokes are easy to work on and the 4 strokes are real expensive to work on with all the EPA sensers and all that. Is this not true. What are the advantages and disadvantages for 4 stroke to 2 stroke.
 
Hey, before reinstalling those RAVES look ans see if you can see the piston move slightly and the rings staying still, this tells you the ring isn't seized in the ring land.

If I rock my motor back and forth from the PTO, I can see the piston move slightly before the ring begins moving b/c there's some clearance between the ring and the ring land, this tells me the ring isn't stuck to the piston.

I really can't tell from you photos if the piston discoloration is yellow and brown varnish deposits from probably more heat than cheap oil can withstand or if the aluminum piston skirt is scored/scuffed.

I will remove the RAVEs and take a look and pick with a long screw driver.

I was doing similar check this afternoon before I installed the raves, but not sure what I should be looking for.
I can see black stuff filling the gap between the ring and the ring land. I did use the screw driver try to "turn" one of the rings, but it won't move. Didn't do the axial way.
And when I was taking the pictures I don't think I saw the play.

Well looks like with RAVEs off, I will do more closer digging.

This is parting of boating. And I am enjoying it :-)



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Well, a second look at that piston photo and it still looks pretty ugly. Maybe the photo doesn't do it justice.

shuka, the 4-strokers are more durable due to the constant supply of lubrication in the crankcase that isn't being washed away by fuel. But you're absolutely right about them being considerably more expensive to replace once they're worn out. I don't see many worn out stern drive engines, near zero. Most suffer from neglect, such as cracked blocks from not winterizing them properly or neglecting crankcase oil changes and overheating from never servicing the stern drive and cooling system. Recreational users generally can't put that many hours on them in their lifetimes to wear them out, they can easily reach into the thousands of hours when well taken care of and properly stored compared to some 2-strokes lucky to reach a few hundred hours under the best of conditions. They're generally heavier and larger though, so the towing launching and hauling are more of a chore.

4-strokes typically use less fuel per HPhour as well, and with fuel injection they run like a top. Plenty of expensive parts though, sensors, injectors electric fuel pump and the added complexity these entail.
 
Look for a boat that has a 4-stoke engine and leave the 2-stroke world behind.

Is it because 4-stroke last longer with less maintenance? How come most of the seadoo jet boats for sale are 2-stroke?
Seadoo jet boat started 4-Stroke in 2004?

It looks like to get a 4-stroke jet boat, I need to prepare a 6-8 hours driving and pick up something from US. :-D
 
How deep the scored/scuffed lines normally are? like 0.005"?

Well scoring of the piston skirts doesn't necessarily guarantee death is here, ring seal is the most important metric of all b/c heat of gasses leaking past the piston rings can cause the lubricating oil to fail and once the lubricating oil cooks onto the side of the piston the chance of seizure increases, probably exponentially. If the oil film fails due to heat escaping from the combustion chamber and cokes the oil to the piston skirt then the clearance between the piston and cylinder is reduced at the same time as the oil film is compromised, combustion heat absorbed into the piston crown normally travels through the oil film and rings to be absorbed out into the iron cylinder walls.

Any little thing that increases friction can throw off this thermal balance to a point where no oil can continue providing a lubricating film and combustion gasses sneaking past the rings can cause the sides of the piston to become soft and at risk of thermal runaway. Throw in a thermal runaway event and the side of the piston becomes molten, blows out and smears on the inside of the cylinder quickly causing seizure (molten piston sticks to cylinder).

This (seizure) will eventually happen to every 2-stroke engine as the ability of the rings to prevent combustion gasses from escaping decays over a period of time, hundreds of hours of operation in some cases depending on the thermal capabilities, construction method, amount of heat generated (by running hard) and overall design of the engine. The 951 is quite the Ferrari of small 2-strokes, IMO.

In the case of lower performance engines such as small antique outboards (951 doesn't qualify) I have on occasion removed fairly scored pistons and cleaned them up using solvent and sandpaper, used muriatic acid to dissolve the aluminum dotted up and down inside the cylinder walls and installed new rings with a light hone to the cylinders using emery cloth.

I guess the point is, IF you experience a ring or piston seizure due to a heat related failure there's a good chance you may find pieces of broken piston begin bouncing around in the crankcase, and from there the damage possibly snowballs into a broken piston rod liable to punch holes through the engine case. But, so what?

I don't know what that coking is I see on your piston skirt but if that's oil varnish and were to begin decomposing due to heat it could "ball up" and cause the piston to bind in the cylinder.

Scoring of the piston along with coking of the oil and low compression are all indicators of the eventual root causes of failure every 2-stroke will naturally experience, it's only a question of when, not if, and the only way to avoid this is by rebuilding before it happens.

Unfortunately the cases are expensive, in good condition possibly worth up to $500?

On the plus side, now you're using XPS-2 there's a slim chance some of that coking may actually be cleaned away, but I wouldn't hold my breath waiting for that to happen.
 
Thanks Sportster. This write up is exactly what i am looking for. I am one of those "know why", "know how" people.
You know what, I definitely has spent more time on this forum than the time on the boat! Not sure how many times more. I only go out boating about every other weekend if weather is good, and only a couple of hours on the boat, and rest of time play with kids in the park. But I learned a lot of from this forum and enjoyed.

I probably will buy a top end gasket set, just wanted to see what is inside the engine. knowing it will be a waste because I may just open it and put it back if I didn't find a blue crab in it. :-D
 
Back to you trailer runaway, sometimes a lean mixture causes this (in every case I know), and so it's important to understand the root cause of a lean-running cylinder. There could be a maintenance issue with one or both carbs being partially plugged with gum and debris in the small internal low speed passages thus restricting fuel delivery at small throttle angles, or:

If one of the outer crankshaft seals was leaking air into the crankcase as the crankshaft is rotating the mixture would go lean. Often when I've found leaking crankshaft seals the unloaded engine had an unstable idle, one moment the idle would be smooth and even and the next moment it would begin to lean runaway. By adding fuel, I could control runaway but then often the idle would become too rich during times when the seal wasn't leaking. It becomes impossible to adjust for a stable idle mixture when the seals are leaking badly. Also, I could see wetness of oil/fuel mixture around the seal on the outside of the crankcase as some of the mixture is respirated outward, around the seal.
 
One more question mark in my mind, just wanted to be clarified:

If I just changed the top end and increased the compression to 150PSI. It will fix the "heat transfer/balance" problem which is good, and helped the lubrication too.
But is it going to increase the stress to the bottom end which was OK with 120PSI, and fail at 150PSI? Or this 30PSI is minor for the bottom end to take.?
 
Back to you trailer runaway, sometimes a lean mixture causes this (in every case I know), and so it's important to understand the root cause of a lean-running cylinder. There could be a maintenance issue with one or both carbs being partially plugged with gum and debris in the small internal low speed passages thus restricting fuel delivery at small throttle angles, or:
I always wanted to do carb rebuilt, and I already bought the kit last winter! Probably I should just do it? Or I need to play with the low speed / high speed setting screw first? What do you think?

If one of the outer crankshaft seals was leaking air into the crankcase as the crankshaft is rotating the mixture would go lean. Often when I've found leaking crankshaft seals the unloaded engine had an unstable idle, one moment the idle would be smooth and even and the next moment it would begin to lean runaway. By adding fuel, I could control runaway but then often the idle would become too rich during times when the seal wasn't leaking. It becomes impossible to adjust for a stable idle mixture when the seals are leaking badly. Also, I could see wetness of oil/fuel mixture around the seal on the outside of the crankcase as some of the mixture is respirated outward, around the seal.
The boat idle has always been smooth and stable this season after the first time I adjusted it to 1300RPM in the water in my first trip out. And I normal stop a few times out in the lake and restart always no problem. Does this tell us some good news :-)
 
How come most of the seadoo jet boats for sale are 2-stroke?

I think b/c people don't understand a 2-stroke and they don't want to spend time or money maintaining it, they just want to splash and ride, turn the key and go. Besides, owning a large heavy boat is the best excuse ever, for buying a new pickup truck to haul it.
 
I always wanted to do carb rebuilt, and I already bought the kit last winter! Probably I should just do it? Or I need to play with the low speed / high speed setting screw first? What do you think?


The boat idle has always been smooth and stable this season after the first time I adjusted it to 1300RPM in the water in my first trip out. And I normal stop a few times out in the lake and restart always no problem. Does this tell us some good news :-)

I would start by checking the low speed mixture adjustment, you may find the PO didn't set them correctly. If they are set correctly, then open them 1/8 turn more and see if the runaway is gone. It sounds like your motor is on the edge of lean runaway, and this tendency even if seals are a little leaky will only be noticed when there's no load (on trailer out of water).

But, the 951 is famous for runaway and not really famous for leaky crank seals, or is this an unreported hidden flaw of the 951? I dunno, but seals do wear out, I've seen this on other motors with my own eyes.

It really would be somewhat of a shame to see your cases ruined if it blew up, now b/c these motors are no longer in production parts will become progressively scarce.
 
I would start by checking the low speed mixture adjustment, you may find the PO didn't set them correctly. If they are set correctly, then open them 1/8 turn more and see if the runaway is gone. It sounds like your motor is on the edge of lean runaway, and this tendency even if seals are a little leaky will only be noticed when there's no load (on trailer out of water).

But, the 951 is famous for runaway and not really famous for leaky crank seals, or is this an unreported hidden flaw of the 951? I dunno, but seals do wear out, I've seen this on other motors with my own eyes.

It really would be somewhat of a shame to see your cases ruined if it blew up, now b/c these motors are no longer in production parts will become progressively scarce.

Well one step at a time. I will fix the trailer run away first, which won't blew up the engine, right?


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One more question mark in my mind, just wanted to be clarified:

If I just changed the top end and increased the compression to 150PSI. It will fix the "heat transfer/balance" problem which is good, and helped the lubrication too.
But is it going to increase the stress to the bottom end which was OK with 120PSI, and fail at 150PSI? Or this 30PSI is minor for the bottom end to take.?

I think 150psi is too much unless you are willing to use better fuel, Seadoo found this themselves and lowered the compression to 130 b/c they knew people would fill their tanks using regular fuel.

120psi really isn't that bad but you're doing this test after placing some oil in the cylinders so it may not be an accurate measurement. I would rather see you measure before shooting it with oil, even if after running the engine briefly.

We have a "junkyard" area of boats here where people bring their old boat for our disposal, and we sell some parts like engines and drives off of them for local people who want to repair their boat, or sometimes we offer a customer a choice of used parts for our repairs.

Long story short, even though we fog these motors before dragging the boat out to the yard where it may set for a couple of years before someone wants to buy the engine, I usually find the cold compression on these after sitting unused in the yard is often near the low end of acceptable, or cylinder balance can be more than 10psi until after starting and running them for 10 minutes or so. It's not b/c the engine is worn or damaged, it's b/c there may have been some light corrosion on the exhaust valve seats or perhaps in the cylinder, which compromises the initial compression results slightly. Almost always, the compression and balance come right back to normal levels after a 10~15 minute bench run. We won't sell a motor as a good running motor unless first we at least bench run it and measure compression.
 
Well one step at a time. I will fix the trailer run away first, which won't blew up the engine, right?


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Yes, I suspect you just need to add a little fuel, it's slightly lean. Rebuilding the carbs isn't absolutely necessary if throttle response is crisp without hesitation. You don't know the history of when they were last rebuilt, the PO may have done them recently.

But rebuilding them would give you the opportunity to replace the Tempo fuel lines, it's a well established fact those gray lines are responsible for contaminating the carbs eventually. My thimble filters had traces of Tempo contamination in them, the PTO carb filter was about half full of Tempo trash.
 
120psi really isn't that bad but you're doing this test after placing some oil in the cylinders so it may not be an accurate measurement. I would rather see you measure before shooting it with oil, even if after running the engine briefly.

This is what I did in the afternoon.
After I installed the clean RAVEs. I add some oil into the cylinder. Then did a compression test. I tried both long screw adapter and short screw on the compression test kit. They both give same measurement. And today is the highest I ever get. Both cylinders are over 120 and once hit 125.
Then I started the engine, it ran at 3500RPM for 15 seconds, very loud as usual. After I shut off the engine the head was warm not hot. So I did a compression test right away. Still 120PSI at both.
Does this answer your question about reading after engine run briefly?


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Checklist:
Quick hot restarts after sitting heat soaking for 10 minutes? - Check
No lean hesitation during acceleration or operating at low speeds around low wake zones? - Check
Jabbing the throttles to cruise RPM the engine catches and revs without delay and sputtering, doesn't fall on it's face and quit? Check

Sounds to me like it's running correctly, so rebuilding the carbs is unnecessary IMO. If I was installing a reman engine or doing a top end then I'd pull them apart for thorough cleaning, new filters and needle/seat set + maybe metering diaphragm and definitely replace the Tempo fuel lines.
 
This is what I did in the afternoon.
After I installed the clean RAVEs. I add some oil into the cylinder. Then did a compression test. I tried both long screw adapter and short screw on the compression test kit. They both give same measurement. And today is the highest I ever get. Both cylinders are over 120 and once hit 125.
Then I started the engine, it ran at 3500RPM for 15 seconds, very loud as usual. After I shut off the engine the head was warm not hot. So I did a compression test right away. Still 120PSI at both.
Does this answer your question about reading after engine run briefly?


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If you allowed it to set for a few days after fogging and measured more than 120, that's reasonable I think. But measuring while there's unusual amounts of oil in the cylinders is cheating.

I'd prefer to see the compression after running before shooting it with oil. If both cylinders are the same and blowing 120psi then the rings are sealing pretty well I think.

If one cylinder blows 120 and the other blows 100 then there's a problem.

Probably this weekend I will clean the RAVEs and measure compression before and after running. I didn't oil it this time at end of day, so the first measurement will be worst case.

I'm surprised you didn't see a noticeable difference between the long and short threaded adapter.
 
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Look for a boat that has a 4-stoke engine and leave the 2-stroke world behind.

4-Tec seems to be too expensive from what I can find. My budget so far is not more than $8500. Plus the BOAT $1000 in my mind. :-D

Looks like still 2-stroke for me. Maybe a house boat when I retire :-D


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If you allowed it to set for a few days after fogging and measured more than 120, that's reasonable I think. But measuring while there's unusual amounts of oil in the cylinders is cheating.

I'd prefer to see the compression after running before shooting it with oil. If both cylinders are the same and blowing 120psi then the rings are sealing pretty well I think.

If one cylinder blows 120 and the other blows 100 then there's a problem.

Probably this weekend I will clean the RAVEs and measure compression before and after running. I didn't oil it this time at end of day, so the first measurement will be worst case.

I'm surprised you didn't see a noticeable difference between the long and short threaded adapter.

I will sit tight for a few days. And get my experiment top end gasket ordered, about $70. Even I have fullbore do the rebuild, I still want to see what does it look like before the rebuild.


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I will sit tight for a few days. And get my experiment top end gasket ordered, about $70. Even I have fullbore do the rebuild, I still want to see what does it look like before the rebuild.


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$70.00 for that head gasket? Ouch, I see complete top end kits with everything for $225-$250 (I'm not trying to encourage you to do that :) ) but it would allow you to tear it down far enough to actually see the full extent of the wear and damage.
 
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