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93 XP died while on water - bent spark plug ground electrode (closed gap)

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airnewzealand15

airnewzealand15

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Hey all

I was going for a blast last night on my 93 XP 650cc. It was going along happily and then just died. I started it again no problem, went another 500m and it died. Repeated this once more, then died again and would not start. Got towed back to shore and found the rear spark plug ground electrode was bent and touching the centre electrode... not good.

final.jpg

The engine won't turn completely over by hand. The piston gets to the top of the rear chamber and then stops and won't go any further. Obviously it won't run correctly.

I'm suspecting its major, and I will need to pull the engine but any thoughts from you most knowledgeable people would be great.

Thanks heaps.
 
Well something either got in there and jammed the engine (possibly a snapped ring, but most likely a broken rod if the engine wont turn over fully. Take a screw driver and drop it in each cylinder. tap the top of the piston. It should feel solid. If you feel/sounds hollow, definatly a rod.

I would take the head off and take a look at the pistons/cylinders.
 
- BiRkS_ said:
Well something either got in there and jammed the engine (possibly a snapped ring, but most likely a broken rod if the engine wont turn over fully. Take a screw driver and drop it in each cylinder. tap the top of the piston. It should feel solid. If you feel/sounds hollow, definatly a rod.

I would take the head off and take a look at the pistons/cylinders.
Click to expand...

Thanks for this. Will pull the engine eventually and check it all out
 
hmm... could be a shot crank bearing. Take the head off, it's super easy and doesn't require any new gaskets to reassemble. It will give you a clearer picture of what's happening. Sounds like the piston came in contact with your plug.
 
Just depends on where the rollers went, but it usually means total meltdown. Crank, cyl, pistons, and prob a head. It can also get spit into the intake ports and wreck the cases, rotary valve, and rotary shaft.
 
I had a 580 that spit the needles from the crank end of the rod. Destroyed everything except one cylinder. got into the RV & wrecked the case as well.

Like the others have said, It's got come apart anyway, but just for grins, slip a long screw driver into the spark plug hole & rotate the crank by hand until the piston is about half way down. Then rotate the crank back & forth to see if there is any play between the crank rotation & the screwdriver moving up & down. There should none.
 
68ragtop said:
just for grins, slip a long screw driver into the spark plug hole & rotate the crank by hand until the piston is about half way down. Then rotate the crank back & forth to see if there is any play between the crank rotation & the screwdriver moving up & down. There should none.
Click to expand...

I took a video - better than me trying to describe it. It didn't feel like there was any play but the piston gets stuck at the top of the head. Have a look :-)
 
i'm thinking there's something in the cylinder getting wedged between the piston and head. may explain why the spark plug gap got pushed closed. other will chime in i'm sure.
 
Nice job with the video!! I really need to start using drop box. I have macs & other apple devices, but haven't tried it yet.

When you go back & forth, it didn't look like you had rod play, but is still hard to say because you weren't specifically checking that. regardless, you'll have to pull it apart & see. Not knowing your mechanical background, nobody here wants to force you into a rebuild on your own, but if your mechanically inclined, the 580-720's are easy machines to work on if you ask a lot of questions & don't assume anything.

Jammin is right, & No doubt you have damage in there, but the top of those pistons will help tell whats going on. something got in there that doesn't belong, & its a safe bet its another part of your engine, wether its a bearing, piston skirt, ring land, etc. I would remove the carburetor support bracket, the top cover & pull the head & show us what you find. Not going to hurt a thing at this point as it has to come apart anyway & it takes no special tools. Its not going to be pretty, but who knows, it might be rebuildable & parts for these are fairly inexpensive. But lets have a peak in there & see & start evaluating!
 
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68ragtop said:
Nice job with the video!! I really need to start using drop box. I have macs & other apple devices, but haven't tried it yet.
Click to expand...

Yup is a really great tool. I take the video on my iPhone, upload to the computer, drop it into dropbox, let it upload to the web and then post the link! Plus these days everything is full HD so you can really show detail in the video and good audio too for diagnosing problems.

I am keen to take the head off myself and take a look. I am just working on getting my "new" 97 GSX cleaned up and sold and then I will attach my lovely dead XP. Its a shame, that XP was the first jetski I have owned - I stripped all the ugly stickers, recovered the seat, got new decals for it, put down new floor mats, polished it up, replaced the engine mounts... rode it for less than 10 hours max... and it decides to blow up on me. HOW RUDE lol
 
Who knows, maybe you'll get lucky & just need a cylinder head, piston & ring kit, hone the cylinders & clean out the block. Never know.
Of course you'll have to figure out why it failed so it doesn't happen again.

Seems like most piston failures however, leave some sort of damage in the cylinder walls that require replacemnt or boring.

Pull it apart & cross your fingers!

On the drop box, who hosts the video? Is that apple, or some other thrid party? Can you control the files after they are published?
I would like to try that out.
 
97GtxMan1687 said:
In my house B O A T
Means bust out another thousand. Haha it's always something


Sent from my iPhone using Tapatalk
Click to expand...

you have a house boat? that would be expensive..... :D :D just kidding.....

As long as were talking about technology too, I recently added taptalk to my phone, but it wants me to log into a facebook, or twitter account. So i didn't go any further with it.
Do you have to have some sort of social media account to use it?
 
68ragtop said:
On the drop box, who hosts the video? Is that apple, or some other thrid party? Can you control the files after they are published?
Click to expand...

Dropbox is a third party company. Any uploaded to dropbox is on their servers, so nothing to do with apple. You can easily remove files from dropbox so yes you have full control :-)

With the tapatalk app, it asks you to sign into a twitter, Facebook or email account just so it can save your forum settings somewhere. So if you have Facebook or twitter just go ahead and log in to that.
 
You might be lucky I could be wrong. Its possible a chunk of the piston hit it instead of bearing parts.

Did head bolts break off in the cylinders?
 
I have been informed by my south african friend that the head bolt are just the bolts that hold down the whole head (duh lol) so to answer the question - they are all perfectly fine :-)
 
Tonka is asking about the head bolt taps looking like they have something stuck in them. Is that some sort of fluid or something?

Here is my guess. I think your machine was running a bit lean. The part that is broke is the top ring land, & if you notice, its broken off in front of the exhaust port. That is the hottest part of the piston, what happens is the piston will distort & expand in that area causing the area to get weakened & beat up. Then it will break off. It looks to me like you shut it down right away. That is the least amount of damage I have seen from that type of failure. The bad news is, you will need to split the case & clean it out completely. its amazing how much of the debris will be in the bottom of the case & everywhere else. Its also probably likely that it got into the Rotary valve, but maybe not, & if so its hopefully minimal damage. To be honest, this is pretty minimal damage so far considering....

But, IMO, you have a lean condition that needs to be addressed, could be plugged fuel filters in the carb/s crank seal/s, maybe bad fuel. The Mag side looks borderline. The finger nail marks of clean area on the dome is where the fuel/air come in & cool the piston. As those areas get smaller, its an indication that the piston is getting hotter & things are going to get tight in there.

I have some pictures from an engine I did a few years ago, were I caught a piston that was about to loose its ring lands. I'll see if I can post them a bit later.

68RT
 
Found some pictures. These are from an engine I rebuilt a few years ago. It went lean & broke the ring land much like yours did. While its hard to see in the picture, the "good" piston had very little wash on it. it was running pretty hot.

The piston on the right side, while intact was a ticking time bomb. It was already overheated, expanded & was having clearance issues. On the piston picture you can see where the ring groove was actually getting pinched as the land was hammered out of shape. In my opinion, this is the first stage, before failure. This piston was doomed & would have suffered the same fate as the other side. Point of no return!
 

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Now this picture is why I am not a fan of doing just the top end after a piston failure. While the damage is very localized & at first glance would seem like like an easy fix, it takes just a second for the fragments to be located throughout the case & even into the intake system.

This is the bottom half of the case, untouched after I opened it up. Install just the top end, & all this debris is headed back upstairs & through the newly installed top end.
 

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thanks heaps for posting these - most helpful! In a few weeks I will get on to pulling the engine out and taking things to bits. I have a jetski mechanic buddy who does most of my hard stuff and he'll be back in a few weeks. I shall post some pics of the damage below the pistons etc.

Thanks again!
 
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