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what caused this, new motor blown?

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project_seadoo

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ill start off with how this all came about i brought a 96 seadoo xp 787 as a project, decided straight away to replace the motor
so i brought a recon exchange motor from jet sport QLD australia at a cost of 1750, had my carbies rebuilt at a cost of 500
i replaced all fuel lines and all other hose in the ski while i was at it, had new plugs welded in the exhaust while it was out as i didnt want problems later on, new wear ring and performance impeller in the jet unit.

took it easy for the first 5 hours with oil added to the fuel for the break in.
just before the easter long weekend here in australia i took the ski in for a service an tune so i wouldnt have any problems throughout the weekend
in the report from my mechanic he noted the rear cylndier (pto) was running rich an he adjusted the carbys
he also noted the bores in each cylinder looked perfect.
so i was very happy an set for the week end

we arrive at the river and the ski seems to be running great but would sometimes just die,i didnt think to much of it and kept ridng
the next day it was hard to start in the morning but was fine when warm but began to die at WOT by this stage the motors got around 8 hours on it
so i loaded it back on the trailer.

once i got home i decided to commpression test it mag side 153psi pto side 30psi
so i began to tear it down and heres the pics of what i found
and also a pic of the mag side still showing cross hatch on the bore
this engines at .25 over size, i shaved a bit of the raves for clearance even though its not needed till .50OS
as far as rebuilding this what would you guys do bore both cylinders to .50OS or just do the pto cylinder and the mag sides perfect?

now im wondering what caused the pto to fail? could it have been my mechanic adjusting the pto carb causing it to run lean?
any other possible causes?
would appreciate any help thanks guys
 

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definately a lean/heat problem. the smearing of the piston material is a dead give away of heat induced binding.At least it didnt destroy the cylinder. also could be a oil problem. in a lean condition it will usually destroy the ring land and or ring due to lean out or detonation.what oil are u using?
 
Dude.... you didn't Break the engine in all the way..... i did the exact same thing with my first SBT standard block.... i ran a quart of break in oil through the first tank , then after that i would ride it "normally" WOT for only a few seconds.... etc....occasionally mine would bog but no big deal right? wrong..... the bogging was happening because of too much stress on the new cylenders.... after 7 hours , my rear gave out... 55psi 120 in the front, origionally they where at 140...... basically the inproper break in procedure caused excess heat to the crank, and melted the rear seal..... allowed in extra air and wapow! done.....

Proper break in is as follows....

First Tank gets a jug of specially designed break in oil (from SBT) contains minerals that help seat the piston rings....

1st 30 minutes.... nothing but idle in the water
then 30 minute cool down.

2nd 30 minutes , up to 2000 rpms pulsating (idling around and nothing more than a high idle)
then cool down again

3rd 30 minutes, up to 4000 rpms pulsating (basically dragging a big a$$ wake around and barely getting on plane, but DO NOT let it redline if you try to get on plane!)
cool down again for 30 min
then do this again until you get it down to a half tank
then cool down.....

4th You can now run it up to 90% for the remainder of tank as long as you dont keep the throttle in one place for more than a couple seconds.... usually its good to do swerves and stuff in an open calm area.... but dont red line it! (basically anything over 6000 is dangerous)

Now the whole next tank you can only go up to 90% ... same as stage 4 ^^

after the second tank ,you can ride however you like , but you cannot run it wide open for more than a couple (2) seconds ... this is where the damage occurs if you keep on it....

After 10 hours of ride time you can run it at WOT as long as you want...... im still at 9.5 hours.... you just gotta make sure that you dont keep it wide open for more than like 5/10 seconds.... that causes a hell of alot of stress on a brand new block. ESPECIALLY one bored over.


Hope this helps in future cases.
 
Check the carb, the low speed screw should be 1-3/4 turns out. So note where the screw is(pic a point of reference), then count the turns in until it just bottoms out. Turning the screw leans it out, so if your less than 1-3/4 he was leaning it out, but you'll need to know how many turns in that will tell you how much he adjusted it. That cylinder was lean. Not sure WHY he would adjust a carb for being rich on an engine that is being broken in that just had a tank of pre-mix ran through it??? He should have waited for a full tank of clean (non pre-mix) gas to run through it. There was either no oil in the line, or an air leak. I fried 3 MAG pistons that weren't as bad as that. I found by pressure testing the engine that I had an air leak. All had around 5-6 hours on the rebuilds. You can just bore the one cylinder if the other one is good. Or if you really want them to match do both. Bummer dude, I can sympathize with you--it sucks! After the 3rd time I gave up paying someone to build my engines and I do it myself now.
 
Its twice as bad in aussie land.

As far as break in goes...everyone has an opinion. Mine is take it easy on the first tank, no full blast runs longer than 3 sec. I mix the gas with just a little bit of oil...125-1ish.

After the first tank...proper warm up then beat her like a red headed step child.

Mainly...its all about verying the throttle just dont run it at any rpm very long.

I agree...looks like an air leak. Id say oil issue, but your other cyl is fine. One thing many people overlook on the 787s...the PTO is what seals against the crank seal. If the PTO has pitting in that area, it would rip the seal fairly quickly. Thats the first place I'd look on a PTO cyl seize.
 
WOW... sounds like that mechanic owes you an engine. That piston crown tells me it was running lean.
 
DSchmidt54 said:
Dude.... you didn't Break the engine in all the way..... i did the exact same thing with my first SBT standard block.... i ran a quart of break in oil through the first tank , then after that i would ride it "normally" WOT for only a few seconds.... etc....occasionally mine would bog but no big deal right? wrong..... the bogging was happening because of too much stress on the new cylenders.... after 7 hours , my rear gave out... 55psi 120 in the front, origionally they where at 140...... basically the inproper break in procedure caused excess heat to the crank, and melted the rear seal..... allowed in extra air and wapow! done.....

Proper break in is as follows....

First Tank gets a jug of specially designed break in oil (from SBT) contains minerals that help seat the piston rings....

1st 30 minutes.... nothing but idle in the water
then 30 minute cool down.

2nd 30 minutes , up to 2000 rpms pulsating (idling around and nothing more than a high idle)
then cool down again

3rd 30 minutes, up to 4000 rpms pulsating (basically dragging a big a$$ wake around and barely getting on plane, but DO NOT let it redline if you try to get on plane!)
cool down again for 30 min
then do this again until you get it down to a half tank
then cool down.....

4th You can now run it up to 90% for the remainder of tank as long as you dont keep the throttle in one place for more than a couple seconds.... usually its good to do swerves and stuff in an open calm area.... but dont red line it! (basically anything over 6000 is dangerous)

Now the whole next tank you can only go up to 90% ... same as stage 4 ^^

after the second tank ,you can ride however you like , but you cannot run it wide open for more than a couple (2) seconds ... this is where the damage occurs if you keep on it....

After 10 hours of ride time you can run it at WOT as long as you want...... im still at 9.5 hours.... you just gotta make sure that you dont keep it wide open for more than like 5/10 seconds.... that causes a hell of alot of stress on a brand new block. ESPECIALLY one bored over.


Hope this helps in future cases.
Click to expand...

That is not why your engine failed I have taken rebuilt engines a beat the crap out of them less Than a hr after the rebuild. You had another issue if you melted a crank seal which I cant see happening in 7 hrs. 2 strokes are normally broken in after the first tank. I know I know but he said she said this is what it was. trust me you did not put too much load too soon and blow up a engine. Any bog or hesitation is not a good thing there is a reason for it just like the op had it shutting off on him thats usually a piston seizure causing it to die let it sit and it will fire back up.

Sent from my C771 using Tapatalk 2
 
Minnetonka4me said:
Its twice as bad in aussie land.

As far as break in goes...everyone has an opinion. Mine is take it easy on the first tank, no full blast runs longer than 3 sec. I mix the gas with just a little bit of oil...125-1ish.

After the first tank...proper warm up then beat her like a red headed step child.

Mainly...its all about verying the throttle just dont run it at any rpm very long.

I agree...looks like an air leak. Id say oil issue, but your other cyl is fine. One thing many people overlook on the 787s...the PTO is what seals against the crank seal. If the PTO has pitting in that area, it would rip the seal fairly quickly. Thats the first place I'd look on a PTO cyl seize.
Click to expand...

Exactly vary the throttle this is how I break in my engines. Also people who hold wot for minutes without chopping the throttle are just looking for a rebuild.

Sent from my C771 using Tapatalk 2
 
Well.........


There are a bunch of thoughts on proper break in... but I subscribe to the school of "Break it in HARD" !!! The islandia in my avatar saw full throttle once I gave it a good look-over, to make sure there were no leaks. Also.. when I was living in SoCal, and Racing SCORE... I would put a fresh top end in my bike... and go race.

Basically... if the engine is running right... running it hard, on a fresh rebuild will not cause it to melt. Overheating and running lean cause meltdown's.

I didn't read over all of this... but I saw something about a melted seal. If you lost a crank seal... that's why to top-end gave out. So... when they put the engine together... they probably didn't lube the seal, and it ran dry. I always grease the outer crank seals on assembly.

Anyway... If I read over it too fast, and missed something... sorry. (I'll look it over better tonight when I get out of my shop)
 
1) might be an issue with the mechanic's adjustments,

however..
I hate to throw the operator under the bus... but It has to be said..

53.jpg




we arrive at the river and the ski seems to be running great but would sometimes just die,i didnt think to much of it and kept ridng

2)if the operator experiences multiple shutdowns and keeps riding... well,,, the operator is shooting himself in the foot.

Not quite sure why you brought it back for a tune, if it was running spot on. and then ignored issues when it wasn't...

so... I'm not sure why in the hell you kept riding it if it kept stopping, you SHOULD have limped it to the ramp and THEN brought it to the mechanic after the first, or at the very least, the 2nd time it failed on you... you might have saved the engine.

but really... I gotta know...

why would you take it for a tune when its running right, then ignore issues when its not... ?
 
Spimothy Leary said:
1) might be an issue with the mechanic's adjustments,

however..
I hate to throw the operator under the bus... but It has to be said..

53.jpg




we arrive at the river and the ski seems to be running great but would sometimes just die,i didnt think to much of it and kept ridng

2)if the operator experiences multiple shutdowns and keeps riding... well,,, the operator is shooting himself in the foot.

Not quite sure why you brought it back for a tune, if it was running spot on. and then ignored issues when it wasn't...

so... I'm not sure why in the hell you kept riding it if it kept stopping, you SHOULD have limped it to the ramp and THEN brought it to the mechanic after the first, or at the very least, the 2nd time it failed on you... you might have saved the engine.

but really... I gotta know...

why would you take it for a tune when its running right, then ignore issues when its not... ?
Click to expand...


the reason i took it in for a tune was because as per the break in procdure from jet sport says that the carbies must be set 1/4 turn richer the factory specs and there break in time was 5 hours of varried riding with no wot runs
so i took it in to have the carbies set to factory specs and for a good check over to make sure i wouldnt have any problems

i know i should have stopped riding when it shut off the first time, there was around 5 of us riding my ski through out the day i asked every one to take it easy an it seemed like they did
yes im probally at fault but whats happened has happend
 
just a bit of an update i pulled the whole motor from the ski last night, and noticed a big air bubble in the oil injection line running to the rear cylinder. i think i found my problem. but the next question is howd it get there and if the oil pump was working corretly shouldnt it of pumped the air though ?
i know for a fact there was no air in either of the lines before i took it out, i never ran it low on oil either, the lowest the tank was would have been 1/2 full
there was also a small air bubble in the line going to the mag cylinder just arftet the oil pump.

how often do these pumps fail ? and is there anyway to check them?
it looks like ill be running premix from now on, dont want to risk it again

ill be sending by my cylinders out to be rebored to keep them even, hopefully i can get away with going to .50 oversize so ill hold off buying new pistons till i know. can any one recomend a good brand? wsm? the bottom end of the engine looks to be in good shape ill give it a good clean out and start putting it all back together


as for the break in like its already been mentioned everyone has diffrent thoughts on it, i followed what i had been giving by jetsport witch was 5 hours easy riding with varried throttle and oil added to the fuel.

thanks for the help so far, i really appreciate it
 
Depending on how the oil line was run, it is quite possible to get an air bubble in the line, this happens after the engine is shut down. Some oil in the line drips out the oil injection port and is replaced by a small air bubble. I saw this quite often with my GS. The bubble wasn't huge, but it was there.
 
Last edited by a moderator:
i have contacted them, and they want me to send the engine back the them for inspection, buy thats 100 shipping to them and if they say it was due to running lean i dont have any warrenty and ill have to pay return shipping back to me at another 100
so im really torn as to what to do
 
Robj said:
Depending on how the oil line was run, it is quite possible to get an air bubble in the line, this happens after the engine is shut down. Some oil in the line drips out the oil injection port and is replaced by a small air bubble. I saw this quite often with my GS. The bubble wasn't huge, but it was there.
Click to expand...

do you think this could have been the cause? i trying cranking the motor to see if the oil pump would pulse but it didnt look like it was doing anything at all?
 
I would be more concerned about what the pump does. If you crank it over and hold the pump wide open you should see the bubble move through the line. If it doesn't then the pump or check valve is faulty. My guess is the oil pump had nothing to do with the failure.
 
Oil pumps rarely fail. Usually air bubbles come from pressed in fitting that has broke loose, or a check valve not working correctly. hook a line to the nipples going into the intake. You should be able to blow but not suck.

And just to be the first one that says it...thats what she said.
 
Robj said:
I would be more concerned about what the pump does. If you crank it over and hold the pump wide open you should see the bubble move through the line. If it doesn't then the pump or check valve is faulty. My guess is the oil pump had nothing to do with the failure.
Click to expand...

thats exactly what i did cranking it and holding the pump wide open, the same way youd do it if bleeding the oil system
but it did not pulse at all, the air bubble never moved.
 
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