1997 Challenger broke down...

[seadoosnipe]

Well, there are a few of you who know but I'm going to just get this out there, started as a thread, since I'm in the middle of a tear down.

My 787cc went down last July the 4th, just before riding downtown on the river to watch fireworks. When I got it home, I cleaned everything up and started to troubleshoot. Everything looked good. The motor is running about 138 to 140 psi in compression. Stumped, I didn't know where to go from there. I had just revamped my fuel system, rebuilt the carbs.

After breaking down the heads, I posted a couple pix up and asked some questions. Dennis aka DAWG asked me to check my TLCS drain line from the heads to the rear of the exhaust. I told him I did this once a year and they were always clean. Well, in the far back, at the exhaust, there is another calibrated fitting. This is where I had been breaking my hose from to blow on. So, I never blew on that fitting. Had I done this, I would have found it was stopped up.

He looked at my pix and told me my problem. He hit the nail on the head. The waterline was stopped up. I was washing my crankcase down with water.

Yesterday, I pulled the pistons. They were the orignal pistons so this is the first time this engine has ever been apart. I'm kinda happy about that. I measured the pistons and I was coming up with an average of 81.88 to 81.90. My cylinders were averaging 82.00 to 82.30. So, I'm thinking about re-ringing them and putting it back together and get one more season out of it. I just don't have the money to do a complete upper end (I broke, to many toys).

I got some pix of the pistons and cylinders I'm going to attach to this thread later tonight. Ya'll come take a look then. And please, don't rub it in my face that I'm not taking my OWN medicine. I know, I should not even attempt to re-use these old pistons. But, unless someone can send me a couple hundred bucks, I don't see anyother way.

I'll be looking for a response from the DAWG, since he hit the nail on the head for me.

I think this thread also proves, I'm just like any of you guys. I have the same problems you guys have. The best part, I've known where to find my answers since 2007!!!!!! :cheers:

 

[seadoosnipe]

Boxed up for sand blasting...!

Well, tonight I readied the motor for sand blasting tomorrow. Its a paid holiday at the plant so I'm going to use that time to get the motor blasted. This motor has been used primarily in salt water from the previous owner. I know it's the original motor because the wrist pin bearings were the original. The newer ones come caged so they are very easy to assemble.

I've siliconed all my ports because sand blasting will bounce off the rubbery material without scratching our gouging my bearing surfaces. I didn't take any pix of the motor after prep, but here are some from after I took out the crank and pistons.

These pix will show you the scratches and gouges in the pistons. They actually look worse than they are. The worse in my measurements of the pistons were about 81.46 of the piston and about 82.11 on the cylinder. I may still splurge for new pistons and cylinders.

But, I'm actually thinking about trying this to see how it works. This will give me more experience in giving our advice on the cylinders....

Look at the pix. You'll see the original needlel brearings and keepers. The bearings looked in great shape........

I got one more pix that I did not post and thats the brass gear of the rotary. I clearance is great but what I found interesting is for a motor this old, there were just some small scuff marks on the worm gear. Virtuall nothing to show, thought I could have gotten a close up I'm sure. I do attribute this clean engine due to my use of "full synthetic".....:cheers:

 

[Dr Honda]

Hi snipe,


I'm a little mixed right now. If I had a customer tell me they didn't have any extra $$$... depending on the jugs... I would just re-ring it, but I wouldn't put that back together for personal use.

if there isn't any scaring in the jugs... and no ridge or taper... at minimum, I would replace the pistons. The reason is... once you've overheated them to the point where th engine stops... there is a high chance of having a skirt failure.

If you do just a re-ring... I wouldn't hold WOT for very long.

keep us posted :cheers:

 

[seadoosnipe]

Rings...

Hi snipe,


I'm a little mixed right now. If I had a customer tell me they didn't have any extra $$$... depending on the jugs... I would just re-ring it, but I wouldn't put that back together for personal use.

if there isn't any scaring in the jugs... and no ridge or taper... at minimum, I would replace the pistons. The reason is... once you've overheated them to the point where th engine stops... there is a high chance of having a skirt failure.

If you do just a re-ring... I wouldn't hold WOT for very long.

keep us posted :cheers:

Yeah, I got a set of rings I was going to re-ring with. When this occured, I had been tubing with the boat all day. It ran great. We were stopped, swimming off the platform when we decided to go. When we left, I went WOT and that's when it bogged and shut down.

The motor never overheated in the sense that I lost cooling. What happened was while running, water was introduced into the crankcase. When it bogged and shut down, I got a tow to dock.

When I tested the compression at home, I was looking at good at 138 and 140.

My idea here is, I always make the recommendations of doing a minimum of piston and/or cylinder replacement or bore over. Here, with the measurements being what they are, I thought about putting it back together to see how it runs. I think this will give me a better idea of what these motors can take before doing what I"m doing, can be said that, "it's just not feasible".

I do have 2 spare 787's so, if I blow this one out, then I still have another one for rebuilding.

I have one new cylinder. I'm thinking I'll at a minimum, buy one more cylinder head to have a set match on them. I'm still undecided on the pistons. I may replace them. Still not 100% certain to the direction I'm going to take.

I've actually got all the internals pulled and engine together, here with me at work. I've got access to a sand blast cabinet so I'm going to do a paint job on it too...........

Thanks for the input Tony. I'll be checking into your idea and trying to weigh my final decision. At least, on the single engine Challenger, it's like a two hour job to pull the motor. So, it's not that big a deal to do this a few times for the experience.:cheers:

 

[Dennis]

pistons

I agree with DR. HONDA. The down side of using these pistons again is going to be the piston skirts. On the other hand, it would be interesting to see the results you would get (compression increases, etc.) by doing a bare minimum top end rebuild. Doing it is totally feasible....the question is how long will it last. I would use muriatic acid in order to remove any aluminum that might be stuck on the cylinder walls, ball hone the cylinders (don't worry about the little imperfections), sand the piston skirts smooth as possible, reassemble it, reinstall it and then let it eat!! We might be totally surprised at the results. The 787 is a tough old dawg (pun intended) and I've seen them go thru worse abuse and still live a long life.
Good Luck, DAWG

 

[voodoo]

I will be following this post as I have the same boat with similar trouble, 4 years ago I reworked my 650 powered GTX and used premium cylinder rework from fullbore with WSM molly coated pistons and it runs fine again except slight carb bug-a-boo.
My 787 is needing pistons resulting from overheating so I will wait to read about WSM comments, they seem to have a strong precense in the marine world, like wiseco in motorcycles.
Here is a question to those with 650 and 780 experience, my 780 needs everything for the shaft seal as father time rotted out the boot and all, I have a spare bearing/seal carrier for my 95 650 that fits right on the shaft and hull, besides regular greasing can anyone point to a reason it would be a bad idea to use the older style driveshaft seal?

 

[seadoosnipe]

Curious...

I agree with DR. HONDA. The down side of using these pistons again is going to be the piston skirts. On the other hand, it would be interesting to see the results you would get (compression increases, etc.) by doing a bare minimum top end rebuild. Doing it is totally feasible....the question is how long will it last. I would use muriatic acid in order to remove any aluminum that might be stuck on the cylinder walls, ball hone the cylinders (don't worry about the little imperfections), sand the piston skirts smooth as possible, reassemble it, reinstall it and then let it eat!! We might be totally surprised at the results. The 787 is a tough old dawg (pun intended) and I've seen them go thru worse abuse and still live a long life.
Good Luck, DAWG

That's what I'm wanting to find out too. You'll notice in the pix above, the wrist pin bearings are un-caged. Which means, this was the original motor. The ID plate is still on it too.

When I had the problem back in July, I got towed back in. I shut the motor down, did not run it again till I got home. Then, I did a compression and it was 138 and 140. So, that's when I started scratching my head.

It blew me away when you asked that simple question because I honestly thought, "oh yeah, right, like he thinks I ain't checkin my water lines. I blow them out every year but the one you mentioned, I didn't realize had a calibrated fitting on the back of the exhaust pipe. I was pullling the hose off from the, what I thought was just a connection nipple cause you can't see it, back end and blowing from there forward. So, I was missing that fitting all together.

So, the total run time with the problem I had was about 3 to 5 minutes. I've measured the pistons in all 8 different directions and they are only thousandths off. It's not like the gouges are really that bad. They actually look worse in the photos than they really are.

I do have that spare 787 in my shop that I"ve considered interchanging heads with but like you said, I'll be taking a chance of seperating my compression if I don't do equally to both jugs.

The best part is, the upper end is easier to work with while it's still in the boat. So, I won't have to pull it out again.

I just finished sandblasting the engine casing, getting it ready for a primer coat. I used silicone on all my surfaces around the seals. I put it on yesterday. If anyone ever blasts their motor, the silicone will keep the sand grit from eating away at your mating surfaces. It repels the sand grit.

What's got me going on the motor outside a lack of funds right at this minute to rebuild is integrity. I'm sure you and many like us have come across a motor that was so indestructable, you had to take a hammer to it to break it. Well, I'm curious as to how well made these motors are and how it will run if I don't do a total upper end. I have another for a core if I need to replace it from blowing it. So, the casing is not the big deal.

I will have to order a set of wrist pin bearings at the minimum. I already have a complete gasket kit. I actually got a few gasket kits.

I think I'm going to evaluate it a little more before deciding. Tomorrow or Thrusday, I might hook up the laptop and ustream it. That way, those that are hanging around can watch. Not sure about what all I'll be doing when I get to Thursday though. I should have ustreamed it when I pushed my wrist pins out.............

Thanks for the input DAWG, I was waitin on ya.........:cheers:

 

[Dr Honda]

I guess I read it too quick. I thought that the hose was plugged, and the engine overheated to the point of shutting down. If you lost a gasket, or got a crack, and the water sprayed into the engine... that is different. As long as you got the crank bearings cleaned out quick so the water didn't start to pit them... then, a re-ring will bring it back to life.

BUT... the only other thing is... those pistons have a butt load of time on them if they are the originals. (so does the crank, seals, and rotary valve)

I guess the real question is... how much longer will it live before a skirt fails, or you loose a big end bearing?

You almost need to log the hours after the re-ring. :cheers:

 

[seadoosnipe]

I guess I read it too quick. I thought that the hose was plugged, and the engine overheated to the point of shutting down. If you lost a gasket, or got a crack, and the water sprayed into the engine... that is different. As long as you got the crank bearings cleaned out quick so the water didn't start to pit them... then, a re-ring will bring it back to life.

BUT... the only other thing is... those pistons have a butt load of time on them if they are the originals. (so does the crank, seals, and rotary valve)

I guess the real question is... how much longer will it live before a skirt fails, or you loose a big end bearing?

You almost need to log the hours after the re-ring. :cheers:

I see where everyone is going with this and it seems, everyone sees where I"m going.

Do you remember the old commercial where they took several engines, filled them with oil, then drained the oil out to see which engine ran the longest before burning up. That's kinda what I want to know.

Everyone has had one of those motors, whether it was a lawnmower, go-cart or motorcycle, that you could put through pure hell and not damage it. Well, I want to know what these motors can take and still run effectively.

The boat was used by a rich guy inland who had a condo on the Gulf. I don't think it was used on a regular basis every weekend. I was surprised when I removed the pistons, you can still see the markings 81.89 and the directional arrow AUS. So, how much run time does it take to wear that off the top of the cylinder.

I blasted the motor yesterday to get it ready for painting. I'm going to prime it today.

The pix above were with ,my cell, the pix I'm going to attach now, are with my camera. So, the quality should be much more improved.

As for the motor problem? I've been a mechanic for so long that I realize that when a motor stops, you don't continue to try and run it. So, the motor never got a chance to over heat. It kills me when I see someone starting their car or whatever and hold down the start button till they drain the battery. I'm (thinking this to myself) wondering if they realize that if the motor does not start within a relative time of turning it over, it's not going to start.......:ack:

Look at these new pix. I'm still on the fence on what I"m going to do. If I choose to see how much abuse these motors will take, I stand the chance of being down a little while during the spring or early summer if something happens. But, at least I have the GTX the girls can tube behind.

I'm still open for opinions. Trying to make that decision on which way I want to go with it. Ya'll's input is probably what will sway me into what my next steps are.........:cheers:

 

[Dennis]

Pistons

Yo SNIPE,
I'm seeing little dings on the edge of the piston dome. Is the dome of the cylinder head also pitted? This pitting is not from wear. It's a sign that something has come apart and found it's way on top of the piston while the engine was running. Did you have a broken ring? Did a piece of RAVE break off? Crank or wrist pin bearing bad? I'd be doing all I could to find the cause of the pitting before I put the engine back together using the old parts.
DAWG

 

[voodoo]

I see the pock marks also and did not see this on my 95 650 but my sides looked like yours - skuffed in large areas making me think some tilting effect, my 97 780 has been hot enough to allow 35-40 degrees of the upper ring land to break off but I do not have these pock marks that I can see because I have not cleaned mine as well as you have here, carbon looking layer so I know mine was water and not a lean condition that melted my piston.

 

[seadoosnipe]

Yeah...

Yo SNIPE,
I'm seeing little dings on the edge of the piston dome. Is the dome of the cylinder head also pitted? This pitting is not from wear. It's a sign that something has come apart and found it's way on top of the piston while the engine was running. Did you have a broken ring? Did a piece of RAVE break off? Crank or wrist pin bearing bad? I'd be doing all I could to find the cause of the pitting before I put the engine back together using the old parts.
DAWG

Yeah, I saw them too but they don't look too bad. I don't know what it's from. I have a feeling that the old owner might have broken off a piece of the insulation of a bad plug. I've seen that happen before and ding up a piston top.

I've accounted for everything. Nothing is missing or broken. I'm not to sure I'm going to put it back together as is. The rings look nice, for the most part, the pistons look o.k., except for the scraps. The gouges really aren't that bad.

As much as I'd like to put it together to see what it will take, I'm not to sure that it's a good idea. I sand blasted the motor yesterday and just got a coat of primer on it tonight.

I didn't notice the dings in the piston until I wire brushed the carbon off. The head has no markings in it at all. Lest, I didn't notice any.

I'm going to take more pix tomorrow and we'll see if we can tell what caused it.

Thanks for eveyones help............:cheers:

 

[seadoosnipe]

Pistons...

When I first spotted the marks, I inspected the casing with my magnifying glass and didn't see any other signs of problems. With the caution you guys brought up, I'm going to go over them again. I didn't count my wrist pin bearings when I removed them. I think there is suppose to be 30, or is it 32. I'll look it up again. Anyway, with this original owner before me (4 years ago now), it's entirely possible this happened when he owned it.

I can tell you, just because you see some dings in a piston, doesn't mean destruction is imminent. That V6 motor I worked on last week, had a part of a spark plug that had broken off and beat the top of the piston a bit. Not bad, actually worse than the one on the 787cc. I took some emory cloth and smoothed it down and put it back together. Baby is still running like a champ.

I think the internal combustion engine will generally take a bit more of a beating than we most realize. I've decided to clean up what I have and go back together with it. If I get bad compression readings (which I'm gonna do while the engine is on my workbench), then I'll decide to take a different approach.

In using these parts over, I'lll want to get a full season out if it, then next off season, tear it down for a complete upper end rebuild. We'll also be documenting the damage from this teardown, to what we find next year. This will allow us to examine any changes that occured between now and next year.

I think this will be a very good experience that I can pass along to the members of the forum.

Oh, for the crank, all tests outlined in the shop manual have been done. The only thing I have left is a pressure test..............:cheers:

 

[seadoosnipe]

Painting....

Well, I got two coats of primer on the engine. I'm deciding on what my top coat should be. I already have a two part Polyurethane paint that is jet black (glossy) but if I want to make it orginal, I'll have to go out and buy some white.

I looked over the pistons again. Though I think I"m still wanting to go with these, just to see for how much longer the enigne will hold up, I did want to take into account the comments from Dr. HOnda and DAWG.

I noticed where those dings are on the surface, it actually hit it hard enough that it reduced the clearance of the ring groove. They both still fit, but that closure on the pistons groove is a bit concerning. I did take some more pix, this time with a real camera. In one pix, you'll notice where I drive the piston up to the top, right before the ring pops out of the cylinder........:cheers:

 

[voodoo]

I did not read it correctly when you said you cleaned up the dings before you put it together, I see the piston in the hole and I think this will be a place for hot burn-away unless you smooth off the high spots with some 100 sandpaper, I have put diesel back like this after sanding and they still run the tractor in a narrow rpm band, with the wide rpm band we have in watercraft I would be cautious of detonation.

 

[Dennis]

Piston

I don't think that this piston is gonna come flying apart if you use it but I would definitely take a small file and create some more clearance for the ring in the bad area of the groove.
DAWG

 

[Dr Honda]

Looks like a sparkplug shattered in the jug.

I would take a jewelers file, and smooth out the high spots... and make sure the clearance in the ringland is proper. If it's too tight, the ring can stick.

A note on pre-ignition. It can happen, but on a 2 stroke... the corrected compression ratio is so low... it's hard for it to happen. I would however, run the squish band a little on the large side. I would set it to the top of the spec at 1.6mm.

 

[Chester]

To start with, you might want to find out why there was water in the crankcase. The only reason that drain hose is there is to drain the cylinder water jackets when the engine is not running. Even if you plugged off the drain hose from the cylinders, water should not ever enter the crankcase and it would not cause the engine to overheat. Did you tow it without plugging the water inlet hose from the pump?
You didn't mention the piston to cylinder wall clearance as this will give you a positive way to determine if you need new pistons or not. Measure the piston skirt at 25mm up from the bottom (perpendicular to the piston pin). Then measure the cylinder bore 16mm from the top of the cylinder (also perpendicular to the pin axis). The difference between the two measurements is your piston to cylinder wall clearance. The maximum clearance is .008". If you have more than .008", the piston will "rock" in the bore until it eventually breaks off the skirt. Also, a piston that is too loose has a greatly reduced ability to transfer heat from the piston to the cylinder wall and will expand faster than the cylinder causing it to seize if you go WOT on a cold engine (like a cold seizure). Please post your clearance.
As you can see, a compression test is a very poor indicator of piston and cylinder wall condition. The only way to know the true condition is to pull the head off to look at the cylinders and pull the RAVE valves off to inspect the pistons. I've seen pistons with worse damage that gave good compression readings many times.
Your rings are bad as your pistons show a lot of blow-by. This could be another reason for your seizure. When you get that much blow-by past the rings, combustion will burn the film of oil off the pistons and cylinders.

Chester

 

[seadoosnipe]

Kinda waitin on you, what took you so long?....

To start with, you might want to find out why there was water in the crankcase. The only reason that drain hose is there is to drain the cylinder water jackets when the engine is not running. Even if you plugged off the drain hose from the cylinders, water should not ever enter the crankcase and it would not cause the engine to overheat. Did you tow it without plugging the water inlet hose from the pump?
You didn't mention the piston to cylinder wall clearance as this will give you a positive way to determine if you need new pistons or not. Measure the piston skirt at 25mm up from the bottom (perpendicular to the piston pin). Then measure the cylinder bore 16mm from the top of the cylinder (also perpendicular to the pin axis). The difference between the two measurements is your piston to cylinder wall clearance. The maximum clearance is .008". If you have more than .008", the piston will "rock" in the bore until it eventually breaks off the skirt. Also, a piston that is too loose has a greatly reduced ability to transfer heat from the piston to the cylinder wall and will expand faster than the cylinder causing it to seize if you go WOT on a cold engine (like a cold seizure). Please post your clearance.
As you can see, a compression test is a very poor indicator of piston and cylinder wall condition. The only way to know the true condition is to pull the head off to look at the cylinders and pull the RAVE valves off to inspect the pistons. I've seen pistons with worse damage that gave good compression readings many times.
Your rings are bad as your pistons show a lot of blow-by. This could be another reason for your seizure. When you get that much blow-by past the rings, combustion will burn the film of oil off the pistons and cylinders.

Chester

Well, I was waitin on you to pop in. I almost sent you email to your home address.....:rofl:

No, ... you are completly right. But, I had wondered if that was plugged, could it build more pressure on the cooling water system since the calibrated fittings allow a restriction in flow so you maintain your enigne full of water.

I thought I had posted the vid in the forum but see I did not. It's still on my laptop.

WHen I had taken down the engine, the exhaust manifold at the MAG cylinder had breached the gasket. You could see the lower end of the gasket had been blowing a good bit of water in during a full power run..

That was where the water entered the bottom end but I did find it curious that DAWG made the comment and when I checked it, it was in fact, stopped up.

I want to put the engine back together without doing a full upper end rebuild. Just out of curiosity as to how much these motors can take. You know, we've all had a motor of some sort that you could set on fire, fill the gas tank with sugar and the damn thing still run. SO, curious as to how much these motors can take. I have a spare 787 in case a connecting rod blows through the casing, but I honestly don't think it'll happen.

The pix actually look worse than they truly are. The measurements are really close. Just a rew thousandths off between the cylinder and heads. SO, because I have the spare parts, I don't mind seeing what this motor can take.

I've already got a cylinder replacment for the one with the broken exhasut manifold bolt in case I can't easy get it out using my easyouts....

Chester, outside the water leak at the Mag side of the exhaust manifold, do you forsee any other problems I should look at?

BTW, the motor never ran hot. I idled around and when I stepped up to plane, that's when I had a reduced power, like bogging, then I pulled the throttel back and shut down.. Found comprression was good.

What's your opinion? It did not run hot. It did not lock or seize the mtor. Got it home and it ran fine, tested compression, it was good.

 

[seadoosnipe]

Measurements...?

To start with, you might want to find out why there was water in the crankcase. The only reason that drain hose is there is to drain the cylinder water jackets when the engine is not running. Even if you plugged off the drain hose from the cylinders, water should not ever enter the crankcase and it would not cause the engine to overheat. Did you tow it without plugging the water inlet hose from the pump?
You didn't mention the piston to cylinder wall clearance as this will give you a positive way to determine if you need new pistons or not. Measure the piston skirt at 25mm up from the bottom (perpendicular to the piston pin). Then measure the cylinder bore 16mm from the top of the cylinder (also perpendicular to the pin axis). The difference between the two measurements is your piston to cylinder wall clearance. The maximum clearance is .008". If you have more than .008", the piston will "rock" in the bore until it eventually breaks off the skirt. Also, a piston that is too loose has a greatly reduced ability to transfer heat from the piston to the cylinder wall and will expand faster than the cylinder causing it to seize if you go WOT on a cold engine (like a cold seizure). Please post your clearance.
As you can see, a compression test is a very poor indicator of piston and cylinder wall condition. The only way to know the true condition is to pull the head off to look at the cylinders and pull the RAVE valves off to inspect the pistons. I've seen pistons with worse damage that gave good compression readings many times.
Your rings are bad as your pistons show a lot of blow-by. This could be another reason for your seizure. When you get that much blow-by past the rings, combustion will burn the film of oil off the pistons and cylinders.

Chester

I did several measurements but not in the way you described. I'm going to give that a try to see what the difference is. I know your history so, I'm fairly certain that what you say, I can take to the bank. I'll def let you know what I come up with.

I"m trying to stay with all my original parts. The casing is a must, I know the bottom end is a cut to match surface. But, I have several cylinders and a few pistons.

I"m on the verge of doing a one over bore but just so damn curious as to how much these engines can take. Kinda like an experiment.

I'll do the measurements as you describe and post my results.....thanks for posting those measurement directions. The ones I did were just the standard 4 point measure.

:cheers:

Oh, BTW, .... I got the motor spray painted a really nice, pretty white. The thing looks brand new again.....:hurray:

 

[seadoosnipe]

Measurements....?

Well Chester, with your idea on taking measurements from your locations, I was able to get a more stable measurement to give me a better idea. It also made much more sense to pull from there.

I only had time before going to work, to do one piston.

The results? I measured 3 or 4 times, to get the best average......:ack: now I can't find my pocket notepad. I must have left it on my workbench. I'll post them tomorrow. But, all my measurements came up a few thousandths less than the .008" that you quoted.

I'll repost tomorrow and also, get the measurements on the MAG. Kinda made me feel like I got a chance in getting this together the way it is.

I've also started on the other 787cc I have so in the event, this one doesn't hold up, I'll already have a head start on putting another engine together

Thanks for the pointers on the measurements...........:cheers:

 

[Chester]

By looking at the pistons, it was most likely was a seizure that shut engine down. I've had customers of mine experience a seizure at WOT and, by the time they coast to a stop, restart the engine and it runs like nothing is wrong. Then, unfortunately, they run it again at WOT causing the engine to seize again. After repeating this a few time, the engine will fail to start.
I once had a customer with a GP1200 (3 cylinder) that experienced an engine shut down (seizure). When he restarted the engine, it was low on power so he held the throttle wide open to try to "clear it out". Big mistake! A con-rod broke, punched a big hole in the cases and trashed the cylinder and the head.

Chester

 

[seadoosnipe]

By looking at the pistons, it was most likely was a seizure that shut engine down. I've had customers of mine experience a seizure at WOT and, by the time they coast to a stop, restart the engine and it runs like nothing is wrong. Then, unfortunately, they run it again at WOT causing the engine to seize again. After repeating this a few time, the engine will fail to start.
I once had a customer with a GP1200 (3 cylinder) that experienced an engine shut down (seizure). When he restarted the engine, it was low on power so he held the throttle wide open to try to "clear it out". Big mistake! A con-rod broke, punched a big hole in the cases and trashed the cylinder and the head.

Chester

It might have but outside the scuff marks, there are no other signs that there might have been a problem developing. The compression is good, the bearings (connecting rods) look good, the domes were clean and spark plugs were good. It is the original motor. I was able to determine that.

As for running, the boat had run good all day. Then after being shut down for a while, we went to leave. When I went WOT, that's when I felt and heard the bog. I started to back off then it shut down. A boat came by right when I opened the engine cover. He towed us back to dock (yes, hose pinched.). When I got it home, checked the plugs and compression, looked good. So, I ran and flushed it.

Then, I took it back to the river and after launching, I eased into the throttle and felt the bog, dropped the throttle and put it back on the trailer. I probably made it about 1/4 mile out from the dock. When I got it home, I pulled the motor.

I'm still not 100% certain whether or not to do the top end. I'm going to look into the crank bearings to see if I can determine if one or more of them might be bad. There is just no obvious signs of it having a problem outside the results showing on the sides of the pistons. They both are scuffed on the down side of the piston, gravity side down.

I'll decide what I'm going to do this coming week, I'll let you know.....Thanks for your help!........:cheers: