25 HP Yamaha outboard won't turn over but pistons aren't siezed ?? Lower unit ??

[beads8]

My 2003 25 HP Yamaha O/B stopped abruptly with a thud almost like I had hit something in the lake. I took off the cylinder head to inspect the pistons/cylinders and they are clean and smooth. The piston actually move freely about a 1/4 inch but will not move any further. It almost feels like it would if the motor was in gear when I try to turn it over with the starter or pull rope even though it is in neutral, the and prop will spin. I can put it in gear where the prop locks in and when I turn the prop the shaft moves the pistons the 1/4" or so. Any ideas what to look for? does this sound like a lower unit issue?
Thanks in advance for any advice!
Beads

 

[kfa4303]

Re: 25 HP Yamaha outboard won't turn over but pistons aren't siezed ?? Lower unit ??

Hi beads. I'm no Yami pro, but it does sound like a lower unit issue. I would try to drop the lower unit then rotate the flywheel. You can also try cycling through the gears with the LU removed as well.

 

[99yam40]

Re: 25 HP Yamaha outboard won't turn over but pistons aren't siezed ?? Lower unit ??

dropping lower unit would be the easiest way to eliminate the possible locked up drive shaft.

If it still will not turn with lower off, then look for a mechanical device the keeps motor from being started while in gear.

Some of the manual start motors had these, but electric start did not from what I understand

 

[beads8]

Re: 25 HP Yamaha outboard won't turn over but pistons aren't siezed ?? Lower unit ??

My 2003 25 HP Yamaha O/B stopped abruptly with a thud almost like I had hit something in the lake. I took off the cylinder head to inspect the pistons/cylinders and they are clean and smooth. The piston actually move freely about a 1/4 inch but will not move any further. It almost feels like it would if the motor was in gear when I try to turn it over with the starter or pull rope even though it is in neutral, the and prop will spin. I can put it in gear where the prop locks in and when I turn the prop the shaft moves the pistons the 1/4" or so. Any ideas what to look for? does this sound like a lower unit issue?
Thanks in advance for any advice!
Beads

I am finally going to get a chance to look at the motor today. The more I think about it logically, I don't think the lower unit is the problem because the prop will spin freely when in neutral and locks in in forward and reverse. The flywheel/drive shaft has the same feel no matter what status the gears are in...1/2" movement of the pistons and a "bottoming out" feeling when it stops. Does anyone know if there is a mechanical device designed to lock the flywheel if it's in gear that could have slipped or broke? This is an electric start and the starter does engage when in neutral...

 

[kfa4303]

Re: 25 HP Yamaha outboard won't turn over but pistons aren't siezed ?? Lower unit ??

Hello again beads. While I don't know of any special tool, you may try removing the spark plugs which should allow you to rotate the flywheel much more easily. If it doesn't help, I suspect you may have a serious issue withing the power head. With the plugs removed, you can also try spraying lube, such as Deep Creep into the cylinders to help free up the pistons. Btw is the motor a 2-stroke or 4-stroke? Was it starved of oil during the failure perhaps?

 

[beads8]

Re: 25 HP Yamaha outboard won't turn over but pistons aren't siezed ?? Lower unit ??

Hello again beads. While I don't know of any special tool, you may try removing the spark plugs which should allow you to rotate the flywheel much more easily. If it doesn't help, I suspect you may have a serious issue withing the power head. With the plugs removed, you can also try spraying lube, such as Deep Creep into the cylinders to help free up the pistons. Btw is the motor a 2-stroke or 4-stroke? Was it starved of oil during the failure perhaps?

I wasn't looking for a special tool, but rather a mechanical switch that is on the drive that may have come loose or broke, causing a safety feature or something to prevent it from starting in gear.
My first thought was that it seized up, and pulling the spark plugs and then the head was the first thing I did. The cylinders and piston show no wear and move freely back and forth about 1/2"...until whatever is preventing the drive shaft from moving stops them. So I've confirmed it is not an issue with overheating or being oil starved and seizing up. IT is a 2 stroke.
Thanks

 

[99yam40]

Re: 25 HP Yamaha outboard won't turn over but pistons aren't siezed ?? Lower unit ??

If you would post your motors model # when you ask questions about a motor, then others could look at a parts break down to see if there was such a device on your motor

 

[beads8]

Re: 25 HP Yamaha outboard won't turn over but pistons aren't siezed ?? Lower unit ??

Well I found the problem. A tooth broke off of the forward gear and was lodged preventing any movement. There was plenty of gear lube in the gear case and no shavings to speak of in the lube, so I'm not sure what would have caused it to break unless it was just defective and finally stressed enough to break.
Anyone know a good source for these parts? Just a quick look on-line before writing this didn't reveal very many places to order from....some stuff on e-bay but shipping from Singapore :-(.
By the way: Yamaha Model #C25ELRU
Serial #695 L-560352

 

[beads8]

Re: 25 HP Yamaha outboard won't turn over but pistons aren't siezed ?? Lower unit ??

Found the parts at boats dot net

 

[Pas Bon]

Re: 25 HP Yamaha outboard won't turn over but pistons aren't siezed ?? Lower unit ??

glad you got it resolved!