Speedster 657x engine locking up

[Alinvictor]

Hi,
I have a 95 speedster and last year I had to rebuild the engine after I found the engine with a hole in the top of one piston. The hole was very curios how it got there... It was about 1/4" in diameter and seemed like it was melted in the piston. Anyhow, I feeted the engine with new pistons and new ring. All seemed good, I started and took it on the water but 5 mins into the ride engine dies and locks that can't be cranked anymore. Pull to the shore on one engine, tried again the bad one and surprise.... It started in half of crank... Let it idle for 5 mins no issue... Back to cruising and engine locks again in 3 mins... I also observe this engine was running hotter then the other one but when I take the supply hose out I have a nice flow...All the test were done with the boat docked in the water so the pumps were immersed.
Any suggestion may help.
Thanks

 

[howie099]

Hole in piston is usually from over heating not getting enough gas. Did you clean/rebuild the carbs on that engine? Still might be over heating locking the engine.

 

[Sportster-2001-951C-Stock]

Hi Alin, does the engine feel hot at all? If cooling water is blocked for some reason it will feel hotter than normal and maybe no water coming from the tell-tale pisser. Also, likely you have a flush port on the jet pump transom adapter where water should be exiting the engine, this water is usually very warm to the touch but not hot enough to burn you.

Otherwise this might be a case of incorrect fit of piston to cylinder bore, there's surprisingly quite a bit of clearance normally or possibly even ring gap is too small causing the rings to bind, depending on the type of rings used you must always measure ring gap in cylinder at several locations and file the ring to obtain the recommendation.

Also consider, the cylinder ports must be properly chamfered to a reasonable radius otherwise the ring edge might snag on the edge of the port opening, and the piston ring ends must not be oriented towards inside of the cylinder ports (such as might happen if installing the piston backwards or the piston has no pin installed to keep the rings from spinning out of position)

If the pistons have seized, it's quite likely they have scored or will score the cylinder wall and/or leave puddles of molten aluminum smeared onto the cylinder wall which must be removed, I think you can see this by removing the head and carefully inspecting the cylinder wall.

Many times a small puddle of aluminum smeared on the cylinder can be effectively removed by using a bit of muriatic acid to clean away the aluminum without distorting the steel liner. You might also detect a ring sealing problem by measuring compression that's lower than normal.

If the piston is badly damaged such as a hole melted in the crown or along the length of of the skirt, there will be aluminum contamination in the crank case which will be in the rod and main bearings and cause them to fail as well. It's impossible to clean them effectively once they're contaminated, the crank must be disassembled and bearings replaced by an expert.

Lack of oil can also be a cause, most likely you are running additional oil by pre-mixing for the break-in (50:1 or more).

But the original damage you experienced was likely caused by a carburetion problem causing detonation which will melt the piston. It's also possible the carburetor is still running too lean causing piston overheating unless you rebuilt it and THROUGHLY cleaned the tiny passages? Sometimes this can be difficult due to very light corrosion inside the tiny passages.

Good quality fuel is very important to avoid detonation that will quickly damage an aluminum piston, the fuel must be absolutely fresh and I recommend no additives other than stabilizer in the case storage more than a month is necessary.

 

[Dr Honda]

If the hole was under the sparkplug... it was from high timing. If it was on the edge from the exhust port... it was from running lean. (and hot)

If your engine now is locking, but will crank when it cools... then...

1) the clearances in the pistons are too tight.
2) You are overheating
3) There is a lack of oil.


Either way... you will kill that engine if you continue to run it.

 

[wfo speedracer]

Pretty much when it locks up once it will continue to do so, the problem is not only not going away on its own it will get worse, tear it back down and see whats up.

 

[howie099]

20 years old only had a top end and its not right I vote get the full rebuild. You are just throwing money at it now. You have no idea on the hours on a 95' model.

 

[wfo speedracer]

Howie is pretty much right , the bottom ends on 657's are weak to start with.

 

[Alinvictor]

Hi,
I would like to take a minute to thank everyone on the site that put his efforts to answer. All the ideas are very good and thank you all for them. Attached you can see the pictures of the "melted" piston that made me open the engine.

Now here a bit more details: After I changed the pistons, rings and all the top end gaskets the engine started and is running fine idling or even at 3000rpm while boat is in the water. (I rarely run the engines on the water hose and that only for 1-2 mins during winterize.) Only when i take the boat to high speed in the water it takes about 3-5mins till the engine locks up and yes it gets hotter then the other one. When I say locks up i mean that it will not even crank. It just seize up and if i let it cool of it starts again. Obviously i only did this once till i realized what is going on and stop f..ing with it. I checked the water intake and it looks i got some pressure but I am a bit worried about it. when engine is idling and i disconnect the output water hose (1/2" hose) from the head i barely get any water coming out, but as soon i increase the rpm i get a nice pressurized stream of warm water... somewhere at about 100-120 degrees. Not to warm and not too cold.
Also i can run the engine in the water for as long as i want at 2500-3000rpm and no issues. Like i said just when i ask for his horses...lol
Hope i gave more info for you fellows to have a bright idea.
Thank you very much..
Alin

 

[Dr Honda]

I don't even have to read your description. From the pictures... you are running lean. (no sign of wash) Pure, and simple. In turn... you caused pre-ignition, and that's why you burnt a hole in the piston.

BUT... since it's glossy... there was plenty of oil.

So...........

The reason it's locking up now is that you are still lean, and the pistons are swelling. (too hot)

 

[Dr Honda]

Here's a pic to help illustrate.

Basically... as the cool, wet fuel enters the combustion chamber... it will "Wash" the piston crown of carbon. Your piston crowns are dead black... so there wasn't enough fuel to keep things clean. Personally, I think the picture is a little too clean compared to a Rotax engine... but you get the idea.

 

[howie099]

Did you go through the carbs fully to make sure the are clean the nothing is plugged up? Replaced rubbers, needle and seat as need be with mikuni parts? If this is dual engine boat steal the carbs for the other engine if it all runs fine you know the issue for sure.

 

[Sportster-2001-951C-Stock]

Running to lean will eat pistons. Are there no indications of being too lean, such as hesitation?

What else to say that hasn't been repeated I don't know..... except repeat; always tune 2-strokes to the rich side and other parameters such as stale fuel or too much ignition advance, the tuning process must avoid detonation (too much piston melting blowtorch-like heat destroys oil film). Here's an article instead, and read up on Gordon Jennings' tuning articles as well, he was a bonified expert.:

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

 

[Alinvictor]

Hi,
Once again i would like to thank everyone for your great support. I have been reading the service manuals on the timing adjustments and so on and I realized that i can f..it up more than I could expect. I am pretty handy on the engines (four stroke ones) works and understanding but i don't wanna catch my ears into the 2 stroke :willy_nilly:
Is there someone that you guys know in Trenton area (can also be anywhere between Philadelphia to NYC or close by areas) that I can bring the engine for a full professional tuneup? I would rather pay someone that have way more knowledge than me rather than getting the engine in a worst state. I figure Trenton cause there is where I have the boat on Delaware and I can take the engine out early in the morning, drive it for a tuneup and then mount it in the evening.
I would like to mention that I would rather f-up the engine than go to the dealers so please do not suggest that ...lol
I expect to pay for the tuneup (unless someone offers free help...:hurray: lol ) but i hate to pay their top $$$/hour when I know that behind they have mechanics that barely know how to use the screwdriver...

Respectfully,
Alin

 

[howie099]

I don't think a dealer would even look it. I bet you know more than there techs on 2 strokes. Someone here from the area has to know someone

 

[Sportster-2001-951C-Stock]

Maybe you can locate a ski using this motor that has low time and good compression, for pennies. Maybe even the carbs are good just needs refreshing?

Lots of nice spare parts too, all the electrics and exhaust even....

 

[Andy4k6]

Could this be failing / failed outer crank seals?

Andy

 

[Sportster-2001-951C-Stock]

Did you go through the carbs fully to make sure the are clean the nothing is plugged up? Replaced rubbers, needle and seat as need be with mikuni parts? If this is dual engine boat steal the carbs for the other engine if it all runs fine you know the issue for sure.

And keep the original meetering springs b/c they are the correct ones. Also the original jets will be correct orifice size.

Could just be the thimble-style fuel filters in the carbs are clogged and need cleaning, but clean every passage and blow them out with carburetor cleaner and compressed air, remove mixture needles to get the gunk out and carefully run a wire through each small passage to get everything clean, maybe get a bucket of carb cleaner and leave the unassembled carbs in overnight (no rubber pieces or o-rings) and get 'em clean of all corrosion.

Or you could buy new carbs, many posts about multiple cleanings and still too lean due to corrosion in the tiny passages changes the calibration too much.

Once you get this engine running right then do the other engine too, those carbs will have the same problem in not too long.

May as well take care of it yourself else it'll just continue being a headache trying to get eomeone else to do it for you at a reasonable price and hassle of dragging it somewhere so they can charge you for screwing it up and spend your money. The more of it you do yourself the better off you'll be, takes time and patience yes, some people have more money than time of patience, they just go buy new boats at $90k.

 

[Sportster-2001-951C-Stock]

Could this be failing / failed outer crank seals?

Andy

Absolutely, and this is another reason why doing just a top end doesn't work out b/c it's treating a symptom and not the root cause.

Also, I can testify leaking crank seals can cause a seizure at higher power loads, I've experienced this several times myself. The reason I know 100% what caused this for me is when seals were leaking I could never get the idle mixture tuned in, it would be too rich one moment then too lean the next moment as I kept backing the idle mixture needle out far enough to idle with the leaky seals. Sometimes when the seals weren't leaking it was too rich to idle, choking on excess fuel and the next moment when the leak would occur it would be too lean so I had to open the needles and constantly crack the throttle to add air and clear out excess fuel. Pop new crank seals in and idle was perfect again, idle mix screw worked as intended.

Or do a WOT pull knowing there were leaky seals and stick a piston due to lean out. You can kind of compensate by going richer with the high speed mixture but it sucks b/c it has to be way on the rich side otherwise it can go too lean and usually you can feel it hesitate when that happens or it makes more power and runs like a raped ape just before it sticks.

 

[howie099]

You can leak down the engine. On the 95s and lower you don't know the hours so it could have a few hundred or 50 u don't know. Most seadoos unless you have like under 100 hours it was just a few years on a rebuild a top end never lasts long. The bottom goes next. The other makers the bottoms seem to do better with just too ends but seadoos make high hp for small displacement. I did my 97 Yamaha gp1200 top end like 8 years ago and it's still going strong but I knew it was the carbs that were messed up on it.

 

[Sportster-2001-951C-Stock]

You can leak down the engine. On the 95s and lower you don't know the hours so it could have a few hundred or 50 u don't know. Most seadoos unless you have like under 100 hours it was just a few years on a rebuild a top end never lasts long. The bottom goes next. The other makers the bottoms seem to do better with just too ends but seadoos make high hp for small displacement. I did my 97 Yamaha gp1200 top end like 8 years ago and it's still going strong but I knew it was the carbs that were messed up on it.

Exactly. And over the years while the rubber lip seals harden due to drying out the rubber compound the bearings gain slop and allow the crank to move around, reducing the chances crank seals will keep air from entering the crankcase. Sometimes you can see the fuel/oil mist spitting out around the seal as the engine is running.

Shoot some carb cleaner at the seal or drop some motor oil on it and if the idle changes, this tells you the seal is leaking.

 

[Alinvictor]

Thank you all.... You guys convinced me to go for it... At the end I may f...it up but at least i know it was me and no other... lol I was just afraid with all the timing setup using the angle disk and so on... but it's worth to give it a shoot. :cheers: