3.0L Mercruiser I/O no thrust, engine revving smoothly

[Mikejr]

Took our Bayliner 175 with a 2005 Mercruiser 3.0 L I/O to the lake for the first run of the year after spring commissioning a few weeks ago. After embarassingly realizing it wasn't starting because I didn't tighten the battery nuts, the boat started up and we cruised smoothly away from the dock. After a minute or two of puttering along at about 1000 RPM, I pushed up to speed and did a short run on plane to other end of lake. We then did some more puttering through a shallow channel with some weeds etc and decided to turn around at it was getting increasingly weedy. After coming out of the weeds and pushing back up to power, the engine revved up, but no power or thrust to the prop. Back to idle, looked at the leg, adjusted trim all seemed normal. Went into neutral, then back to power and same result - engine revving, but no thrust.
I have not pulled the prop yet and will do that in the morning. One other data point - we had to remove the front engine mount last winter (the nuts on the underside of the mount had spun off and to actually tighten them, the mount had to come out). Is it possible we didn't get the alignment perfect and it's caused a problem?

thanks for any help you can share!

 

[Rick Stephens]

That sounds like either a coupler or a prop hub. coupler often snakes a bit when it goes and gives off burnt rubber smell. Couplers go from poor alignment as you noted prop hubs go from hanging up. Could be either.

 

[spoilsofwar]

I agree with Rick; prop hub or coupler are the likely suspects.

Was there any thrust in reverse?

 

[Scott Danforth]

If you were deep in weeds, were any wrapped around your prop?

In your case, I would lead to weeds around prop first, the either a hub or coupler.

 

[Bt Doctur]

One other data point - we had to remove the front engine mount last winter (the nuts on the underside of the mount had spun off and to actually tighten them, the mount had to come out). Is it possible we didn't get the alignment perfect and it's caused a problem?

If you removed the drive first, then did the work and checked the alignment ,No
If not YES

 

[Mikejr]

That sounds like either a coupler or a prop hub. coupler often snakes a bit when it goes and gives off burnt rubber smell. Couplers go from poor alignment as you noted prop hubs go from hanging up. Could be either.

Before I take to shop is there any way to confirm if hub or coupler? I have a spare prop, so easiest might be another trip to lake with new prop... Will try that tonight and also test reverse. But yes some thrust in reverse.

 

[Mikejr]

One other data point - we had to remove the front engine mount last winter (the nuts on the underside of the mount had spun off and to actually tighten them, the mount had to come out). Is it possible we didn't get the alignment perfect and it's caused a problem?

If you removed the drive first, then did the work and checked the alignment ,No
If not YES

BT - we held engine on a hoist and slipped front mount out and back in, so didn't take the leg off at all. Is getting alignment checked and adjusted an expensive job?

 

[Rick Stephens]

Ok,

So, you need to own an alignment bar. No possible way you achieved alignment with your method. Alignment is done by pulling the leg and using the bar to get it EXACTLY right. I pretty much am sure you burnt out the coupler because it was impossible to get good alignment the way you did it. There is no reason you cannot do the alignment yourself, should be done every year when you pull the leg for maintenance. Cost <$100 in a tool.

If you take it to the water you probably don't even have to take the boat off the trailer. Back in, lower the drive, power on and use a flashlight to watch the drive shaft behind the engine when you put it in gear. Probably mostly stops spinning. No use taking it off the trailer as you'll over heat the motor when the pump in the leg is no longer turning.

Rick