piston wear?

[Toolanddiemaker]

Sorry to keep bothering everyone here but I wanted share my piston scoring pics because I was wondering if anyone new what causes this damage. The jugs are just as bad prob looking at oversize pistons these are 77.94 so 3.0685 with the boars being .004 over that. the rings were still intact and all circlips were good. there stamped 77.94 but they are so scored and messed up they micrometer out about -.010. I know new pistons and jugs are needed but I was wondering if the metal that made that scoring prob made it to the crankshaft? thanks!

 

[Dr Honda]

WOW... those are ugly. Scars that deep are from being seized up. Basically... they were stuck, and broke free. (repeatedly) It could have happened from using the wrong oil, or being overheated.

As far as "Is that material down in the crank?"... it's hard to say. In a 2-stroke, the air flow is going out the exhaust. But, if it came off the skirt, the flow would have run the fragments into the lower half, before entering the bypass ports, and being expelled.


If the crank in question is the old original crank... DO NOT TRY TO REUSE IT !! It won't last long with a new top-end.


Just for comparison... here's a Seadoo piston with over 400 hr's on it, using the right oils.

 

[68ragtop]

IMO, I feel that's one of the things with 2-strokes that gets overlooked with rebuilds & even general maintenance work. because a 2-strokes use ports directly in the cylinders, scoring & damage can come pretty easily from foreign objects, or from the piston itself from situations like doc mentions. Each time the piston is at TDC, the bottom of the cylinder is exposed & is in a vacuum. These small pieces can fall back into the case & will eventually make another lap into the cylinder. Some things will pass out the exhaust port, but some will get pinched & cause damage.

When 2-strokes have serious top end damage, you can pretty much bet the bank there is debris still in the case somewhere, at some level. I always cringe when I see top ends installed after damage without cleaning everything out, because scores in the new top end are coming sooner rather than later. It isn't possible too have an engine too clean when its assembled & if not, it will never have a chance to ever look like docs high hour example. No doubt that engine was maintained & as clean as a Church.

 

[Toolanddiemaker]

Ok thanks guys! I'll take the bottom end out and have a look. I was running seadoo 2 stroke oil given to me by the po I just bought the boat this summer so I only had it out a few times mabey 6 times oil was full when I bought it I just topped it off once. The other engine has perfect compression 150,150. This one was 145,135 so I thought I would check it out glad I did!! I'm thinking it was bad when I bought it wish I would have compression tested it on the spot but I didn't know anything about 2 stroke boats until I found this site and started learning from you guys!

 

[Coastiejoe]

I would think that is was bad when you bought it as well. Especially if you didn't hear new noises as compared to when you bought it.

Compression tests are a must do, but,,, if you don't know you don't know. I have been lucky in my past and bought skis with no test drive or a compression test. This was before I understood the importance. Thankfully they were all excellent.

Now I just buy new and sell mine.. LOL

Good luck with the lower end...

 

[Toolanddiemaker]

I would think that is was bad when you bought it as well. Especially if you didn't hear new noises as compared to when you bought it.

Compression tests are a must do, but,,, if you don't know you don't know. I have been lucky in my past and bought skis with no test drive or a compression test. This was before I understood the importance. Thankfully they were all excellent.

Now I just buy new and sell mine.. LOL

Good luck with the lower end...

Thanks! This has deifintly been a learning experience but I guess it will give me something to do this winter!

 

[Coastiejoe]

Fortunately you have the ability to service the engine yourself. Three HUGE bonuses, more affordable, know it is done right, and man will you learn a ton about your engines...

 

[grinditout]

I will never reuse an unwelded crank after a seizure, that is what you have there, make sure you rebuild your carbs and fuel system, was it just 1 cylinder?
Test, test, test.
Carbs are supposed to be rebuilt every couple years.
dump fuel tank.
Something leaned that cylinder or stopped the oil system.

 

[grinditout]

How many carbs?

Definately lean out, could have been from cases carbs, or oil.

I think oil.

 

[Toolanddiemaker]

How many carbs?

Definately lean out, could have been from cases carbs, or oil.

I think oil.

duel carbs that are out to Dr Honda for rebuild also converting to premix.Crank was shot metal chips everywere plus bad seals and up and down conecting rod play. everything is getting overhauled both engines fuel system, lines,ect.

no it was bolth cylinders.
thanks for they input!

 

[68ragtop]

duel carbs that are out to Dr Honda for rebuild also converting to premix.Crank was shot metal chips everywere plus bad seals and up and down conecting rod play. everything is getting overhauled both engines fuel system, lines,ect.

no it was bolth cylinders.
thanks for they input!

Are these 720 Engines? Personally I would repair the injection system & lines if they need it. They are pretty reliable & premix can wear your rotary valve assembly as its used to be being bathed in oil form the injection system.

(Just guessing 720's by the boat listed in your signiture.)

 

[Toolanddiemaker]

Are these 720 Engines? Personally I would repair the injection system & lines if they need it. They are pretty reliable & premix can wear your rotary valve assembly as its used to be being bathed in oil form the injection system.

(Just guessing 720's by the boat listed in your signiture.)

no there twin 657x engines. and Im keeping the lines to the rotary valve hooked up to the tank to constantly supply them with oil.
my buddy keeps telling me to keep the oil injection I guess his has never failed him but i just thought it would be one less thing to worry about!

 

[68ragtop]

no there twin 657x engines. and Im keeping the lines to the rotary valve hooked up to the tank to constantly supply them with oil.
my buddy keeps telling me to keep the oil injection I guess his has never failed him but i just thought it would be one less thing to worry about!

The main lines that keep the RV gear cavity filled are a must. I am guessing thats what you are reffering too? I was talking about the injection lines. The main RV oil lines keep the crank & RV shaft happy, but the injection lines keep the valve happy. All of the injection oil makes a few laps around the valve on its way into the bottom of the case. It will still get oil running premix, just not as directly.

What did you find was your failure?

 

[grinditout]

I agree with keeping the oil system, find new pumps and gear {usually ebay about a $100 to $120 if you wait around}and filters and lines and dump old oil and clean out, I know it is an investment but it will pay off in less oil expense, I believe it only runs at 100:1 at idle.
There is a test in the book for the oil pump, but I just would not skimp there.

 

[Toolanddiemaker]

The main lines that keep the RV gear cavity filled are a must. I am guessing thats what you are reffering too? I was talking about the injection lines. The main RV oil lines keep the crank & RV shaft happy, but the injection lines keep the valve happy. All of the injection oil makes a few laps around the valve on its way into the bottom of the case. It will still get oil running premix, just not as directly.

What did you find was your failure?

Yes thats what i was reffering to but I didnt think about valve so it has the chance of running somewhat dry without they injection lines? What goes on with premix only machines wouldnt they run into issues if that was the case? I'm new to all of this so i'm a little confused but i get that keeping the valve prop lubed is important.

I wish I knew what caused it! they other Engine was runing great with 150,150 compression so I'm not sure if fuel lines were an issue but the carbs did have that grey fuel line running between them but the rest of the fuel lines are black. I checked out the grey line and it wasn't that bad but its going to be replaced along with the rest of the lines there pretty ugly and moldy! could have been a bad crank seal I took it apart at the shop and some of the guys said the seals didnt look that good.

 

[grinditout]

I would say this , I saw one this summer that looked exactly like that and it was due to the oil line coming off in 1 cylinder the other 2 were fine.

shoot a picture of the rv cover from the intake manifold side, so I can see which cover they used there are 2 different ones and the back side to see scoring.

 

[grinditout]

Also when he gets your carbs he can see what is in the baskets, I would pull the tank and clean it out, I know the other engine is in the way but you have a lift and a garage, it would be the smart thing to do, it would also make it easier to access all the fuel lines and filters, oil tank probably will have to come out to, get some pincers for the lines from harbor freight, they have some that are styled like the factory c style, also good to have two in the boat in case you have to get towed, and to understand how and where to apply them in that event.

 

[Toolanddiemaker]

Also when he gets your carbs he can see what is in the baskets, I would pull the tank and clean it out, I know the other engine is in the way but you have a lift and a garage, it would be the smart thing to do, it would also make it easier to access all the fuel lines and filters, oil tank probably will have to come out to, get some pincers for the lines from harbor freight, they have some that are styled like the factory c style, also good to have two in the boat in case you have to get towed, and to understand how and where to apply them in that event.

Here is that pic u wanted to see and yes I agree with u on cleaning the tank I actually pulled they other engine out already to clean up the bildge it's a disaster and it's funny you recommend those harbor freight pincers I have about 20 of those in my toolbox they work great cheap to thanks for they advice

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[grinditout]

Take gas tank to car wash with hot water to wash out.
I did one in the driveeay with a pressure washer but next time I will pony up the 1.25 to keep from poluting my own space.
I will look at the pictures tomorrow, on my desktop.

 

[grinditout]

Send pictures of the cover, it is what is sandwiched in all that from, both sides, and both sides of that rotary valve in your fingers.

 

[Toolanddiemaker]

Send pictures of the cover, it is what is sandwiched in all that from, both sides, and both sides of that rotary valve in your fingers.

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[grinditout]

I would probably replace the valve, looks like it sat up for a long time at some point.
let me see the other side of the cover.
can you feel any ridges withe your fingernail in that first picture?
From what I can see, the rv side of the case and block look normal.
Rv valve does not,but that was not the problem though.

 

[Sportster-2001-951C-Stock]

Sorry to keep bothering everyone here but I wanted share my piston scoring pics because I was wondering if anyone new what causes this damage. The jugs are just as bad prob looking at oversize pistons these are 77.94 so 3.0685 with the boars being .004 over that. the rings were still intact and all circlips were good. there stamped 77.94 but they are so scored and messed up they micrometer out about -.010. I know new pistons and jugs are needed but I was wondering if the metal that made that scoring prob made it to the crankshaft? thanks!

View attachment 23114 View attachment 23115

Could be a wide variety of things to cause that, I agree it probably suffered several partial seizures over a period of time and there's probably aluminum still melted onto the cylinder walls if it got hot enough, but that's just my speculation and won't buy you a coffee.

http://www.off-road.com/dirtbike/tech/dirt-bike-tech-twostroke-seizure-52428.html

 

[Toolanddiemaker]

I would probably replace the valve, looks like it sat up for a long time at some point.
let me see the other side of the cover.
can you feel any ridges withe your fingernail in that first picture?
From what I can see, the rv side of the case and block look normal.
Rv valve does not,but that was not the problem though.

Yep I do feel ridges,is this the other side of the cover your talking about?

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[Toolanddiemaker]

Could be a wide variety of things to cause that, I agree it probably suffered several partial seizures over a period of time and there's probably aluminum still melted onto the cylinder walls if it got hot enough, but that's just my speculation and won't buy you a coffee.

http://www.off-road.com/dirtbike/tech/dirt-bike-tech-twostroke-seizure-52428.html

Yea the cylinder walls were a mess also!

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