97 Challenger 787 motor blown 2nd time

[Hollymax0428]

Can't believe it. After all the dramas on my last post '97 Challenger slow... ' & rebuilding the top end of the motor.
Took the boat out last weekend, Saturday, running in the motor for around 2 hrs with brief periods of opening it up.
Sunday did 2-3 hrs not going too hard but using it for a bit of tube towing.

This weekend Saturday did similar, around 2-3 hrs towing the tube off and on, so hard for a start but then runing around 5,500 - 6,000 for fairly short periods.
Sunday did around 2 Hrs and every thing running fine then the motor cut out.
Fuel was low so turned onto reserve then went for another 10 minutes and motor cut out and wouldn't start again.

Checked the compression when I got home and MAG cylinder 150 psi, PTO cylinder 5 psi.

Last time the PTO cylinder was the good one & the MAG cylinder had the worst but both still had around 100 psi. Now one cylinder has virtually no compression.

Have no idea yet until I pull off the head and probably cylinders what has gone wrong. Motor wasn't showing anything or sounding wrong. Just cut out twice, prior to that was running well.

I checked the compression yesterday and was on 150 psi both cylinders.

Maybe the boat is jinxed :reddevil:

 

[Dr Honda]

Sorry to hear that you had problems. That sux.

Let us know what you find.

By any chance did you verify the oil injection? Did you verify the RAVE valves? Was this still on the tank of fuel with the extra oil in it?

 

[seadoosnipe]

Crank Bearings....

Can't believe it. After all the dramas on my last post '97 Challenger slow... ' & rebuilding the top end of the motor.
Took the boat out last weekend, Saturday, running in the motor for around 2 hrs with brief periods of opening it up.
Sunday did 2-3 hrs not going too hard but using it for a bit of tube towing.

This weekend Saturday did similar, around 2-3 hrs towing the tube off and on, so hard for a start but then runing around 5,500 - 6,000 for fairly short periods.
Sunday did around 2 Hrs and every thing running fine then the motor cut out.
Fuel was low so turned onto reserve then went for another 10 minutes and motor cut out and wouldn't start again.

Checked the compression when I got home and MAG cylinder 150 psi, PTO cylinder 5 psi.

Last time the PTO cylinder was the good one & the MAG cylinder had the worst but both still had around 100 psi. Now one cylinder has virtually no compression.

Have no idea yet until I pull off the head and probably cylinders what has gone wrong. Motor wasn't showing anything or sounding wrong. Just cut out twice, prior to that was running well.

I checked the compression yesterday and was on 150 psi both cylinders.

Maybe the boat is jinxed :reddevil:

First, you should go through a full tank of gas after a rebuild with a bit of extra oil added to help seat/wear your rings in place. You should not be going wide open until that full tank of gas has been used. Then, your ready to rip it up.

If you blew the top end first and did a repair without finding out why it blew, then yes, it's likely going to happen again. You have to find the "root cause" of why it blew in the first place.

If you blew the top end because you ran the carbs lean, then you can just rebuild the top end and re-tune the carbs to keep it from happening again. But, if you blew the top end with no visible cause, it's probably going to be caused by a bad bearing in your lower end.

So many times when I hear of someone wanting to do the top end, my advice was to go ahead and cut costs by getting a newly remanufactured motor, so it might take the guess work out of the equation.

Last year, a premium member (Gabwis {I think that was how it was spelled}) did the same thing. He blew his MAG cylinder so he decided to replace the pistons and cylinders. I suggested the motor. Shortly after doing this (which it was on the 97 Challenger) he blew the motor again. Because of the loss in his investment, he decided to get out of it and buy a regular outboard. A mechanic bought his Challenger and found the bad bearing.

Sorry to hear about your loss in your top end. The additional torque on the motor from tubing and running wide open after new pistons were installed, may have played a major role in the destruction, so I'm not saying that it's a bearing. Whenever you do an engine that has new pistons, you have to add extra oil and break the pistons in. The only exception to the break in is the injected motors. You just keep off WOT but no extra oil.

 

[Hollymax0428]

Dr. Honda...

I had checked the oil injection at the tank. I measured out both the fuel and oil tanks with exact graduations, and the oil tank was going through close to exactly 500 ml each 20 lt of fuel, so 40:1.
1st 80 lt of fuel I premixed an extra 2000 ml oil, to give 32:1. 2nd 80 lt of fuel I eased back on the oil so it would have been around 36:1.
I did check the RAV valves for clearance and took at bit more off with emery paper wrapped around the old piston, and the settings of the adjuster cap were flush with the top of the casing.

Seadoosnipe...

I did the top end rebuild because it was low on compression, due to the cylinder water journals being full of sand & overheating and also having 720 pistons put in it when it was last rebuilt (approx 10 hrs before I bought the boat).

I guess the problem is I'm only assuming the bottom end was rebuilt, but when the cylinders were off, and from what I was told to expect it seemed OK.

I will try and pull off the head later today & see what has happened. I guess with no compression at all in one cylinder it will be major damage.

 

[Chester]

When you did the top end, did you also rebuild the carbs and pressure test the engine upon completion? Anytime the engine (or just the top end) is rebuilt, the engine MUST be pressure tested. No exceptions. Early in my professional career, I've only once just did a top end without at least disassembling the bottom end to re-seal and inspect the crankshaft. That engine failed and I had to do the job over again. That never happened again. On a PWC engine, there is no such thing as "just a top end rebuild". Seals wear out and if you don't know how to tell, ask.

Chester

 

[Hollymax0428]

thanks for the info Chester. I didn't do anything to the carbies or bottom end.
I did the top end up again after it supposedly had the whole motor rebuilt by a Jetski shop and I found that it had the wrong pistons in it.

When I pulled off both cylinders this time the one with no compression had the rings welded in on the exhust side and a hole around 3/4" in dia on top of the piston starting to blow through.

The other cylinder & piston looked fine.

My guess at this stage is no oil going into the cylinder even though it was using the correct amount through injection and I had extra oil in the fuel.

What I don't get is the motor was going fine to me right up till it stopped not showing any loss of power.

I guess I have to work out whether it is better to replace the motor. I just don't have any confidence in what has or hasn't been done to the motor before me.

 

[Dr Honda]

I think Chester is right on this one. if it was just stuck rings, I would say no/low oil. But... since there is a hole in the top... I would say it was running excessively lean. That could be the carbs, or a crank seal.

I'm in the same boat as Chester. Back in the day... I had a JS440 that lost 2 top ends because of bad crank seals. The first one let go because the engine was 7 years old, and I figured the crank was still OK... but when the second one let loose... I figured I needed the opinion of a pro. (this was back in the mid 80's when I was 16)

Since Your engine was suppose to have been rebuilt... the crank should have been new.

So the summery is... the engine wasn't rebuilt. The guy lost a top end because of a bad crank. (like you did) some shop pulled the bad parts... slapped in a set of pistons (that were wrong) and once it fired up... they last owner sold it.

Time for legal action if you have documentation of a "New" or "Remanufactured" engine.

 

[seadooya]

Not to throw fuel to the fire, and the fact, that none of us, mentioned to check the bottom end, on your other "thread", but with you finding 720 pistons on your first go around, that was an indication of, throwing the red flag.

With it ALL tore down, and cases/jugs look good, and no need for bore, just a hone, then you can gettaway with crank assy/pist kit...but doing the math, you'll save a few buks, or is it worth going reman. engine and getting a warranty?

 

[Hollymax0428]

That's what I'm now worried about. The motor condition as a whole.
The carbies were running the same as before. I will check the LSA screws but I'm sure at this stage they are the same as before the rebuild.

The part I don't get is what happened to the burnt piston, happen right at the very end, because the power and performance right up to that point seemed quite good. Motor wasn't missing or running rough, started easy.

Both Cylinders would need re-booring because the burnt piston has been rubbing on the bore and parts look like a strip about 1" wide of metal has actually built up on the cylinder but further down gouged into the cylinder.

The burnt piston & bore was extremely dry compared to the other one that was wet with oil/fuel.

 

[seadooya]

Anything runs awesome, when its "lean", until she pops. Set the LSA to 1-1/2, and HSA to, i believe, mag=0, pto=1/2.

 

[Hollymax0428]

thanks Seadooya. I'm pretty sure, but will check, that the LSA was 1-1/4 both sides (book says 1 + or - 1/4 turn) and HSA set to 0. I didn't change these settings after top end rebuild.

 

[Dr Honda]

Anything runs awesome, when its "lean", until she pops. Set the LSA to 1-1/2, and HSA to, i believe, mag=0, pto=1/2.

He's right. It will run very well as it is getting hot... but as soon as the crown of the piston hits about 1000F... it will liquefy. Aluminum doesn't have a nice "plastic" phase like steel.

It just hit me.... yes... you will need to check the crank... but did you set the squish band like I said??? (on the loose side) The SeaDoo head is a double dish design, and if the squish band is set too tight... the piston will melt down just like you described. Normally it's the PTO side, and that's why the PTO carb is set a little richer than the mag side. (helps it run cooler)

 

[Hollymax0428]

When you say lean, how lean on the screws would cause this in such a short time?

Is there a way of checking the bottom end seals with the cylinders off other than pull the bottom end apart.

Like Dr. Honda says, I'm leaning at this stage to the fact the motor was never done up apart from a honing, the wrong pistons put it and maybe new rings.

The Cylinder Gasket I put in was the thickest one (8 holes I think). Is that the squish gap you are talking about?

Also the HSA on the PTO side has no cap on, so just going by the other one that does have a cap, I thought the PTO HSA was set to 0, so giving a - 1/4 & + 1/4 turn if it had a cap on it. If you mean screwing in till hits 0 then at the moment it is 1/4 turn out.

 

[Dr Honda]

There isn't a good way to check the seals with the engine apart. When you do a leak down... you are checking more than just the seals... you are checking the engine as an assembly for leaks. But... a leak down test isn't an easy thing for a garage mechanic. You have to block off the intake and exh to pressurize the engine.

One other thing that came to mind is that even if the seals check out... the crank can be twisted, and the cylinder that melted could be seeing a little more timing. It's very common in the 3 cyl engines... but it can happen in the high output twins.

At this point... I wouldn't look for a problem... I would just do a full rebuild (with a new or rebuilt crank) and check everything as it goes back together.

As far as the carb needles... you don't need the caps. Lightly seat them, and adjust as needed.

a lean run can destroy a 2 stroke engine on the first run out. A 4 stroke is more tolerant of a lean run... but on a 2 stroke, it needs the fuel to get the oil to the top end, and to cool the piston crown. And, even though you have oil injection... without the fuel, it doesn't mix into the engine correctly. I know it sucks... but if you are into 2-strokes... you will eventually loose a top-end from a lean run. But since you had a hole... I would say you had detonation too. You should have heard it.

One last thing... were you running premium fuel? the 800 motor can't run on regular grade.

 

[Hollymax0428]

Thanks for the info Tony.
Again I'm pretty much resolved to doing a full rebuild myself (or having it done for me from Jetsports in QLD) because I don't have confidence in the remainder of the motor.
I've already spoken to a place to get the carbies redone in the next week or so. At this stage no one I can find wants to look at the motor for 6-8 weeks.

The fuel I have used is 91 RON which is our standard Unleaded and what I was told to use.
We also have 95 RON & 98 RON available.

So with the HSA adjustment on the PTO cylinder it should be out 1/2 turn from seated & the MAG cylinder HSA 0 turns seated?

What would detonation sound like? I didn't here anything abnormal.

 

[Dr Honda]

Thanks for the info Tony.
Again I'm pretty much resolved to doing a full rebuild myself (or having it done for me from Jetsports in QLD) because I don't have confidence in the remainder of the motor.
I've already spoken to a place to get the carbies redone in the next week or so. At this stage no one I can find wants to look at the motor for 6-8 weeks.

That sux. you should see what SBT charges to send a motor to OZ. They do a swap. They send you the rebuilt engine in a nice crate, and you send back your blown one.

The fuel I have used is 91 RON which is our standard Unleaded and what I was told to use.
We also have 95 RON & 98 RON available.

Yes... sort of. The 800 can run on "Regular" fuel... but when it gets on the ragged edge of a lean run... the "high test" fuel will help protect it since it's burrning slower, and the heat becomes less focused. (cheap insurance)

So with the HSA adjustment on the PTO cylinder it should be out 1/2 turn from seated & the MAG cylinder HSA 0 turns seated?

Yes. the PTO is normally the piston that will stick when it's hot, so a little more fuel will keep the heat in check.

What would detonation sound like? I didn't here anything abnormal.

Detonation will sound like marbles rattling around. Problem is... when it gets to the audible stage, it is at the pressure equivalent of hitting the tops of the pistons with a 2 Kg sledge hammer as hard as you can.

 

[Dr Honda]

here it is. it's $845 USD with a one year no fault warranty. You will have a hard time doing the rebuild for that price with having to buy a crank. Contact them for a shipping price.

http://www.sbtontheweb.com/Merchant...ode=40-107&Category_Code=40-1&Product_Count=5

 

[Hollymax0428]

OK thanks, I want to answer the other post you put up in a few minutes.

I can get an exchange motor in QLD, takes around 1-2 weeks turnaround for $1495 AUS so I should be pretty right, but I will look at that from SBT, which even with exchange rate would be similar or cheaper without knowing the freight cost and time.

The problem, which I should find out today, is that possibly the one in QLD did the last rebuild with wrong pistons which would realy surprise me.

 

[Hollymax0428]

That sux. you should see what SBT charges to send a motor to OZ. They do a swap. They send you the rebuilt engine in a nice crate, and you send back your blown one.

In OZ they do it the other way round which is a pain. Send your motor then they either do it or send back another one.

Yes... sort of. The 800 can run on "Regular" fuel... but when it gets on the ragged edge of a lean run... the "high test" fuel will help protect it since it's burrning slower, and the heat becomes less focused. (cheap insurance).

Yes I wasn't sure, I see you have lower RON fuel than us. It will run fine or better on 95 RON fuel then? We only have 91, 95 or 98. I think yours starts at 87??

Yes. the PTO is normally the piston that will stick when it's hot, so a little more fuel will keep the heat in check.

OK so even 1/4 turn on the MAG and at least 1/2 turn out on the PTO HSA is better for lubrication. What about the LSA at least 1.5 turns out?

Detonation will sound like marbles rattling around. Problem is... when it gets to the audible stage, it is at the pressure equivalent of hitting the tops of the pistons with a 2 Kg sledge hammer as hard as you can.

Definitely didn't here any noise other than normal, to me anyway. The only thing was trying to restart when it died, it fired up for a brief moment running extremely rough (but that could be that just the one cylinder was firing) & it backfired a few times. Then eventually it wouldn't even start.

 

[Dr Honda]

You are on the Euro system. Your 95 RON is the same as our 87 (R+M)/2. (or close to it)

No... you don't want to open the screws too far, because you will foul plugs, and loose power... especially if the engine isn't peaking. But since you are having the engine totally rebuilt... get the carbs done too... then set the needles to the right point. Oh... since everything else was wrong... I would have the guy doing the rebuild verify the jetting, needle/seat size, and pop-off pressure. If he can't tell you what it should be... take them somewhere else.

 

[Dr Honda]

Just an FYI... Your jetting should be

142.5 main
70 Pilot
1 turn low
0 Turn High
27 to 39 pop-off
1.5 needle/seat

Personally... I would bump the mains to 145 so you don't have to worry about a lean run, or having to run the PTO high needle open more than the MAG.

 

[Hollymax0428]

You are on the Euro system. Your 95 RON is the same as our 87 (R+M)/2. (or close to it).

So does that mean locally on the Euro system/equivalent I should be running either 95 RON or 98 RON, not the 91 RON I was running.

No... you don't want to open the screws too far, because you will foul plugs, and loose power... especially if the engine isn't peaking. But since you are having the engine totally rebuilt... get the carbs done too... then set the needles to the right point. Oh... since everything else was wrong... I would have the guy doing the rebuild verify the jetting, needle/seat size, and pop-off pressure. If he can't tell you what it should be... take them somewhere else.

Thanks for that advice I will ask.

I have a 274 Page Workshop Manual I downloaded a while ago for Challenger/Sportster/Speedster that gives all the procedures & settings for pulling all the motor & pretty much the whole boat apart, but of course falls short of actual experience doing it. The only thing it is for a 96 model, mines 97 but everything looks the same.

I have spoken today to a local guy that seems to know a bit about Seadoo motors and was a Honda mechanic at a local dealership, now running his own business, and he's is going to have a look as well and give me a hand, plus I can forward on the info you have been giving me.

I don't know if he has the equipment/experience to test the carbies unless it is a similar procedure to motor cycles.

He knows how to do leak down tests on 2 stroke motors, has aboat and must do a bit of motor cycle racing, but I will watch what he is saying and doing just the same.

 

[Hollymax0428]

Just an FYI... Your jetting should be

142.5 main
70 Pilot
1 turn low
0 Turn High
27 to 39 pop-off
1.5 needle/seat

Personally... I would bump the mains to 145 so you don't have to worry about a lean run, or having to run the PTO high needle open more than the MAG.

Thanks for that.
I'm still a bit confused on the HSA settings.
MAG end should be 0 turns out, so seated, and the PTO end is 1/2 turn out from seated.

 

[Dr Honda]

Sorry... I meant 91 Ron is the same as 87 (R+M)/2. (95 R is 89r+m/2, and 98 R is 91 r+m/2) It's not really "Metric" it's just the system that the Euro counties adopted. RON is "Research Octane Number" and it is checked at 600 RPM in a variable compression engine. MON is "Motor Octane Number." it is a little more precise, but normally gives a lower number. (this is from the aviation industry) So... the USA uses an average of the 2 numbers. ([RON+MON]/2)

You can use you regular grade... but I would recommend at least your mid grade.

It sounds like you may have found the right person to help you. Someone who has been a mechanic for a while and knows 2-strokes. The Rotax engine has some things to watch for... but anyone who has played with 2 strokes will know what to watch for.

As far as the carbs... no they are totally different than motorcycle carbs, but they are not complected. The cleaning process, and checking the jet sizes will be easy for a mechanic. The only thing that MUST... WITHOUT FAIL... be checked is the pop-off pressure, and that is not something that a motorcycle carb would need. But the tool needed to check the pop-off pressure can be made with a simple pressure gauge from the hardware store. (there is a thread above on building the gauge, and how to use it)

And finally... The jetting.

SeaDooya suggested that you run the high needle on the PTO carb open a little. That is good advice, even though it's not the spec for your boat.

Here's the deal... On the early 800 motor, they ran a 147.5 main jet, and all was happy in the world. But the EPA (smog police) came down on the 2-stroke world. SeaDoo then changed to a 142.5 main jet to make them happy. (it was just enough fuel to keep from melting the pistons) Shortly after that, the hot sit-down skis would stick the PTO piston if any mods were done. So it became normal practice (and the factory spec) to open the PTO high needle to help cool that jug.

The reason I suggested to go one size bigger (2.5) on the main, is so you don't melt down again.

Now... in my boat... it was also neutered by the EPA. So, one of the first things I did (when rebuilding the carbs) was to rejet to the pre-EPA specs. My boat runs cool and strong. Also, I was going to shave the head on my engine, and I knew that I would need the extra fuel to keep from melting things.

 

[Hollymax0428]

Sorry... I meant 91 Ron is the same as 87 (R+M)/2. (95 R is 89r+m/2, and 98 R is 91 r+m/2) It's not really "Metric" it's just the system that the Euro counties adopted. RON is "Research Octane Number" and it is checked at 600 RPM in a variable compression engine. MON is "Motor Octane Number." it is a little more precise, but normally gives a lower number. (this is from the aviation industry) So... the USA uses an average of the 2 numbers. ([RON+MON]/2)

You can use you regular grade... but I would recommend at least your mid grade.

OK the mid grade 95 RON it is. Interesting my son kept saying "do you think we should run the 95 premium fuel to get better power". I was thinking, being a 2 stroke it wouldn't mix with the oil properly, so I've still got a lot to learn.

It sounds like you may have found the right person to help you. Someone who has been a mechanic for a while and knows 2-strokes. The Rotax engine has some things to watch for... but anyone who has played with 2 strokes will know what to watch for.

As far as the carbs... no they are totally different than motorcycle carbs, but they are not complected. The cleaning process, and checking the jet sizes will be easy for a mechanic. The only thing that MUST... WITHOUT FAIL... be checked is the pop-off pressure, and that is not something that a motorcycle carb would need. But the tool needed to check the pop-off pressure can be made with a simple pressure gauge from the hardware store. (there is a thread above on building the gauge, and how to use it).

OK I will definitely make sure he can and does do that or I will take them to someone who can.

And finally... The jetting.

SeaDooya suggested that you run the high needle on the PTO carb open a little. That is good advice, even though it's not the spec for your boat.

Here's the deal... On the early 800 motor, they ran a 147.5 main jet, and all was happy in the world. But the EPA (smog police) came down on the 2-stroke world. SeaDoo then changed to a 142.5 main jet to make them happy. (it was just enough fuel to keep from melting the pistons) Shortly after that, the hot sit-down skis would stick the PTO piston if any mods were done. So it became normal practice (and the factory spec) to open the PTO high needle to help cool that jug.

The reason I suggested to go one size bigger (2.5) on the main, is so you don't melt down again.

Yes I would definitely rather have some insurance.

Now... in my boat... it was also neutered by the EPA. So, one of the first things I did (when rebuilding the carbs) was to rejet to the pre-EPA specs. My boat runs cool and strong. Also, I was going to shave the head on my engine, and I knew that I would need the extra fuel to keep from melting things.

So if I went back to 147.5 that's too big?
Am I better to just go to the 145 you are suggesting?
I would say the carbies have never been touched so it's going to be a couple of weeks before getting anything going again so I want to get a carby rebuild kit. I'm assuming the jets come in it, or do they need to be purchased seperately?

Thanks all what you are explaining all makes sense to me & I can see why the new piston would have been running lean & melted. Old pistons without compression didn't have the issue & I was probably too hasty putting it back together without doing further checks, so this time around, if it works out with this mechanic guy (who also goes to the same lake with his boat) & I should get some onsite/onwater service.