L150XTRT runs great on land but not water!

[JDWOODBURN33]

Thanks @townsends I will be taking it apart tonight to get a sense of where it stands. I can get the parts by 7/2 so thats not too bad. I like the idea to see if there are any concerns in the low compression head before opening up the side thats good.

Yeah I agree the guy just wanted to get out of there as fast as possible. He probably laughed all the way home with my $125 bucks. But at least I have the next step in my trouble shooting.

Cross your fingers for me!

[JDWOODBURN33]

Hey gents first let me say thank you to all who have shared wisdom and offered advise. Lol now to the good stuff

Got the head off and the bolts on the bad cylinders had alot of corrosion.
Screenshot_20200630-203246_Gallery.jpg
The cylinders are clean. The dust in the middle cylinder I assume is from the bad gasket when I pulled it off. I turned the crank to see inside the bottom cylinder and I didn't notice anything standing out that was bad. There is no scaring or visual signs of damage. A little oil in the bottom which I think is normal for a two stroke. A little bit of carbon but I don't know too much looks like.
Screenshot_20200630-203305_Gallery.jpgScreenshot_20200630-203256_Gallery.jpgScreenshot_20200630-203320_Gallery.jpgScreenshot_20200630-203329_Gallery.jpg

Anyone see anything I should be concerned about?
What signs should I be on the lookout for?
Any tests I could do before putting it back together?

Oh and for those wondering I only broke off one bolt. Ill be drilling that out tomorrow YAY ME!

[TownsendsFJR1300]

Feel free to wipe put any "dust", etc that may have fell in when disassembling(it wasn't there when running) and looking at it now, doesn't help..


Carbon wise, pretty darn clean for a 25 year old motor (don't see any issues there).


Get the block and head surfaces super clean. I'd also run a tap/ bolt thru all block holes to rid corrosion for an accurate torque reading for re-assembly).

And importantly, scrape out, remove all corrosion in the water jackets both in the block and head (under the smaller, lighter cover). Kinda surprised there wasn't more...


Putting a straight edge across the block and head wouldn't hurt either...


On any of the cylinders, can you catch, with a fingernail, any scoring?

.

[99yam40]

that bolt in the pic looks like it pulled some threads

[amahaork]

It is so good you doing it yourself. I would be very cautious to run tap in block. easy to do it wrong and create mess with it. always a compromise.

[amahaork]

some stuff for you

[JDWOODBURN33]

The screw was covered in a dust (assuming gasket particles and corrosion). From what I felt tonight there was not scaring on the cylinder walls. Is there anything I can clean the pistons and cylinders with, carb cleaner?

I will clean up the old gaskets and get a better look tomorrow.

[Bluefish]

Very important to straight edge the heads, they will usually be warped I think the max is 3 thousand of an inch. you can bring them back to specs by placing head on a piece of glass with wet & dry sand paper and sand down doing a figure eight patten. Also, you should put some flat washers on the head bolts and ck that they will hold when torqued down, and install helicoids as needed.

[JDWOODBURN33]

So I got the gasket off and its in one piece. Could this still cause low compression?
Screenshot_20200701-121212_Gallery.jpg
Cleaned up the faces everything looks good.
Screenshot_20200701-121237_Gallery.jpg
I did find this spot in the cylinder. My finger nail doesn't catch on it but it does look like some scratching
Screenshot_20200701-121220_Gallery.jpg

[99yam40]

does the other low compression cylinder look like that too?
looks to me like piston leaving some aluminum on the cylinder, may have bugered up the rings lands and grabbed the rings

it would be interesting to figure out which oil lines were disconnected

I have seen a few weed eater 2 strokes run without oil, and they had piston and cylinder damage after they were run till they died

[JDWOODBURN33]

No the other cylinder has no scoring. I have no idea which oil lines were off but when I removed the heads there was oil in the bottom of all 3 cylinders. So I assume they have been getting oil. I ended up wetting a rag with carb cleaner and wiped down the inside of the cylinders and the piston heads. From what I can gauge the pistons rings are still operational, they all have very little movement.

2 day shipping for the new gaskets. I guess i was kind of hoping the gasket would look worse so I would get a better feeling of that being the root for the low compression.

[TownsendsFJR1300]

That scoring isn't, of course helping with compression..

It's hard to look close up at the head gasket pic's (via computer) re the head gasket.

You'll have the cost of parts invested to see if the compression comes up enough to be usable.
That or tear down, machine block, new piston, etc so I'd continue on the path your on for now..


If you looked at the side of that piston, via the exhaust port, would give you a better idea of the damage to that piston/rings.

I'd re-assemble and check on compression again once assembled..

As 99Yam posted, I see that type of damage to a two stroke somewhat often (repairing them). I currently have a blower (25cc maybe) compression was 90 PSI, wouldn't start/run.
Too small to scope, I pulled the muffler and peeked. Same damage as yours, but much worse. Pulled it apart, severe scoring all the way around, piston and cylinder.. Had another parts machine, swapped cylinder/head(one piece) and piston/rod. Compression went to 170 and it's now running again. How it even had 90 PSI was amazing..


.


.

[panasonic]

Do you have th means to measure them cylinders? If the engine is still on the boat you could possibly bring it to a machine shop and they could measure the bores right in the parking lot...only take a few minutes for them to do.

[amahaork]

bring block to shop. I recommend to stay with Yamaha piston, even it is only +0.5, contrary to Wiseco piston offer +0.25. beauty of Yamaha rings are designed for plateau finish cylinder walls (if your shop can master it). it's ok to bore only one cylinder, and light hone (if your shop can master it) all other cylinders for new standard size Yamaha rings.

[99yam40]

That scoring isn't, of course helping with compression..

It's hard to look close up at the head gasket pic's (via computer) re the head gasket.

You'll have the cost of parts invested to see if the compression comes up enough to be usable.
That or tear down, machine block, new piston, etc so I'd continue on the path your on for now..


If you looked at the side of that piston, via the exhaust port, would give you a better idea of the damage to that piston/rings.

I'd re-assemble and check on compression again once assembled..

As 99Yam posted, I see that type of damage to a two stroke somewhat often (repairing them). I currently have a blower (25cc maybe) compression was 90 PSI, wouldn't start/run.
Too small to scope, I pulled the muffler and peeked. Same damage as yours, but much worse. Pulled it apart, severe scoring all the way around, piston and cylinder.. Had another parts machine, swapped cylinder/head(one piece) and piston/rod. Compression went to 170 and it's now running again. How it even had 90 PSI was amazing..


.


.

I had a small 2 stroke leaf blower that was less than a year old brought to me to work on that had low compression(less than 100) that would not start.
I pulled it apart and found the rings stuck with carbon.
I was able to get the rings off with out breaking then and cleaned them and the ring lands on the piston , put it back together and it started and ran great.
I am not sure what oil he was using or how much he was mixing in the gas, but it carboned up quickly.

if OP would have pressurized the cylinder with compressed air like doing a leak down test would have said if it was a head gasket leaking into another cylinder and coming out the other plug hole.
too late now