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Dreaded no compression on #1 cylinder

Darryl Humby

Member
Messages
3
Reaction score
0
Points
10
Boat Make
Yamaha
Year
2001
Boat Model
LS
Boat Length
20
Hey guys..
On my last outing I noticed my port engine had lost power. Upon further inspection I happened to look down into the plug hole as I was about to attach my compresion gauge when I saw an actual hole about the size of a dime in the centre of my piston...
I removed the top end cover of the motor and checked the cylinder bore for any damage but I got lucky and the bore is not harmed or marked at all.. The numbers 010-826 are marked on the piston but I can't seem to figure out if it's a standard size piston or not. Anyone have any idea if it's standard or oversized? Trying to find out so I know what parts to order to rebuild. Sorry for long post ...
 

Darryl Humby

Member
Messages
3
Reaction score
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Points
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Boat Make
Yamaha
Year
2001
Boat Model
LS
Boat Length
20
Just found the number 100 engraved on the intake side of the piston.. if that helps thanks for any input!
 

Mainah

Jetboaters Admiral
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Location
Chapin, SC
Boat Make
Yamaha
Year
2016
Boat Model
Limited S
Boat Length
24
I would find a local jetski salvage/repair guy. The skis and boats share the same engines. The salvage skis guys are usually quicker and cheaper with plenty of goid used parts on hand. You could also call SBT. Keep in momd that something caused the failure. Could be the carb needs adjusted/rebuilt, not getting enough oil, or things have gotten sloppy lower in the engine allowing the piston to raise too high.

Good luck.
 

4x15mph

Jetboaters Captain
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Location
Downingtown, PA
Boat Make
Yamaha
Year
2001
Boat Model
LS
Boat Length
19
I would wrap up the top end and send it to fullboreonline.com. Ask for a bore/hone and new pistons to match. I am not against SBT personally but given how much everyone else is against SBT, realize you will have trouble selling the boat when you do decide to move on.

That said, before you do anything, you need to figure out why you overheated and burned a hole in the piston. It sounds lean which could be the carbs or the head gasket/leak. Either way, don't do anything with the pistons until you figure out what caused the problem. I think this is why a lot of people think SBT is to blame personally when it is really their fault for not really fixing their issue.

I sent my carbs out to jetskisolutions and they are literally brand new.
 

Darryl Humby

Member
Messages
3
Reaction score
0
Points
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Boat Make
Yamaha
Year
2001
Boat Model
LS
Boat Length
20
4x15mph I am looking into fullbore online and was thinking it would be best to send the cylinders to them and get a bore job done with matching pistons. After some research they seem to be a popular choice for rebuilds...
I checked out the carb associated with #1 cylinder and found the small filter in the carb almost completely blocked with debris and a tiny hole in the clear diapharm as well... I don't think the previous owner did much if any maintenance on the engines.. So I'm leaning toward tearing jnto my starboard motor carbs and do some compression tests while im at it... any experience with fullbore online yourself?
 

4x15mph

Jetboaters Captain
Messages
1,453
Reaction score
755
Points
217
Location
Downingtown, PA
Boat Make
Yamaha
Year
2001
Boat Model
LS
Boat Length
19
@Darryl Humby good plan and I like that you are seeing some evidence of a problem (e.g. carbs). I do have experience with Fullboreonline personally as I used them in September and was very happy with the service. I did have a bit of a debacle and delay with them turning it around in the 7-10 days that they advertise since they said my shipping box had another name on it and was "pending" up until I called them to straighten out the issue. I accepted the explanation and they stayed in communication with me after that point. I rebuilt the engine when it arrived and it went real well but the proof will be this next season when I water test, etc. FYI, I went with fullbore's premium kit which included better pistons

After I rebuilt my engine, I then found I had a leak in the other engine's carb rack. I have built carb racks on 3 occasions and this is the 2nd time I was having the same leak. I new it was time to get the carbs rebuilt and professionally restored. In speaking with jetskisolutions they "vat stripped all casting pieces, glass bead blasted, flat surfaces resurfaced flat again, including round check valve seats.
individually recoated, etc.. when it all comes together with genuine Japanese parts, there are no leaks.....ever. New shaft seals are installed as well."

I have not installed the new carb rack and will do so when the new season starts. I may be sending the other rack but I will do that after I am satisfied with how this rack turned out.

Pic of pistons installed (moly coated) along with a pic of the newly rebuilt carbs (in the shipping box... nicely packed).

Glad to see you working on your LS. You will love it

IMG_2415.JPG IMG_2525.JPG
 
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