Spun Prop or Coupler?

[Scott in MN]

This seems to be a common question. Here is my scenario.

1980, Sea Ray SRV 225 with a Mercruiser 228.

I had been experiencing some overheating problems this year but only at high rpms. Still I had no problem getting up on plane and there was no slippage to the prop. I figured the overheating to be something with my impeller or thermostat so until I could address it I just cruised at lower rpms (<2000 rpm). Occasionally I would take it up to 4500 rpms but only for a few minutes as I watched the temp gauge slowly climb.

Last Saturday I went for a long cruise and as I approached the marina I brought it up to 4000 rpms for the final stretch. About two minutes into this I started hear noises in the back and then suddenly my engine raced. I immediately backed off the throttle and put it into neutral. I then noticed that my temp was higher than I would like and thought I smelled some burned rubber. I put it back into gear and started limping back to the marina at about idle speed. The temp came back down but the engine speed was no longer proportional to the boat speed. I could increase the rpms but I would not go any faster. There was slippage somewhere.

At first I figured I had spun the prop but after doing some more reading I'm wondering if it is my coupler. I'll do some tests this weekend but was wondering if this write up sounded like anything to you folks.

thank you

 

[Haut Medoc]

Re: Spun Prop or Coupler?

My guess is the coupler.....
You would not smell a spun hub.....
Get in there with a mirror & inspect the coupler area....
Couplers fail due to misalignment, you will need to find out where that problem is, (mounts, rotted transom).....

 

[jaxnjil]

Re: Spun Prop or Coupler?

above + a spun prop hub wouldnt cause you to loose raw cooling water but a spun coupler would

 

[John_S]

Re: Spun Prop or Coupler?

Check your rubber exhaust boots and flaps, especially if it turns out to be the prop hub.

 

[chiefalen]

Re: Spun Prop or Coupler?

Coupler.

But i think your overheating to this point was a t-stat not opening, impeller bad or clogged risers or flapper broke off or heat exchanger such as power steering cooler clogged.

Any of the Above could be why till the coupler went.

 

[Scott in MN]

Re: Spun Prop or Coupler?

Here is an update.

I was able to give the boat 30 minutes this morning. I put it in forward gear and stood on the prop to turn it counter clockwise. This turned the crankshaft as shown by the engine belts turning. I did this several revolutions and found no evidence of slippage.

I was hoping this would help pinpoint the problem but it didn't help.

Thoughts?

 

[chiefalen]

Re: Spun Prop or Coupler?

Yes it did help.

Maybe the clutch dog is starting to go. Slipped out of gear.

Rubber smell was the rubber hose connecting the exhaust tube.

When it started to overheat.

 

[Scott in MN]

Re: Spun Prop or Coupler?

Anything other than the coupler would be good news to me.

I remember last year when doing the shift cable I measured excessive movement (13 degrees) on the shift shaft going down into the lower unit. According to the manual this implies wear in the gear case shift spool assembly.

 

[Haut Medoc]

Re: Spun Prop or Coupler?

Anything other than the coupler would be good news to me.

I remember last year when doing the shift cable I measured excessive movement (13 degrees) on the shift shaft going down into the lower unit. According to the manual this implies wear in the gear case shift spool assembly.

True, but it is nearly impossible to get a drive out of gear while under load.....
A worn shift spool/crank will not force the drive out of gear under load....
I suspect you have two different issues.....
1) What kind of cooling system is this?....
Standard or closed cooled?......
The first thing that needs to be checked in any overheat scenario is the raw water impeller.....
First check for proper flow in, then restriction, (mans/risers) out.......
2) You need to pull the drive to check the impeller, at this time you can inspect the the input shaft splines & the coupler for signs of visible damage......
3) I don't think the test you performed for the prop/coupler is an accurate measure of their integrity.....
The most simple test would be to put on a new/different prop & see what results you get IN THE WATER.....
Until you start inspecting & performing tests, it is all conjecture.....

 

[Scott in MN]

Re: Spun Prop or Coupler?

I should wrap this thread up.

I ended up bringing in the prop to a shop to have them check it out. They went ahead and rebuilt it.

I also installed a new lower unit water pump. The old one had some of the impeller vanes turned the wrong way. I suspect it was improperly installed originally.

Boat has run great since I did these two things. I suspect the motor was overheating and the super hot exhaust contributed to prop rubber spinning.

 

[sethjon]

Re: Spun Prop or Coupler?

This seems to be a common question. Here is my scenario.

1980, Sea Ray SRV 225 with a Mercruiser 228.

I had been experiencing some overheating problems this year but only at high rpms. Still I had no problem getting up on plane and there was no slippage to the prop. I figured the overheating to be something with my impeller or thermostat so until I could address it I just cruised at lower rpms (<2000 rpm). Occasionally I would take it up to 4500 rpms but only for a few minutes as I watched the temp gauge slowly climb.

Last Saturday I went for a long cruise and as I approached the marina I brought it up to 4000 rpms for the final stretch. About two minutes into this I started hear noises in the back and then suddenly my engine raced. I immediately backed off the throttle and put it into neutral. I then noticed that my temp was higher than I would like and thought I smelled some burned rubber. I put it back into gear and started limping back to the marina at about idle speed. The temp came back down but the engine speed was no longer proportional to the boat speed. I could increase the rpms but I would not go any faster. There was slippage somewhere.

At first I figured I had spun the prop but after doing some more reading I'm wondering if it is my coupler. I'll do some tests this weekend but was wondering if this write up sounded like anything to you folks.

thank you

Any time you have a temp issue its not smart to bring it up to 4000 RPM. It doesn't take a lot of time running hot to cause lots of damage. And, to rely on a $25 temp gauge knowing there is a problem is beyond foolish.

 

[Scott in MN]

Re: Spun Prop or Coupler?

And, to rely on a $25 temp gauge knowing there is a problem is beyond foolish.

Yeah, whatever.

 

[JEC]

Re: Spun Prop or Coupler?

I had an issue similar to yours on a 5.7L Alpha I, Gen 2 setup but without the associated temp rise issue.

Marks were put on the prop, boat tested in water, and prop marks remained lined up pointing to a non-prop issue. At that point, engine pulled, found a blown coupler which was replaced.

Other threads on issue such as this have noted marking the prop and re-testing boat in water as part of the diagnostic workup. You got that taken care of by bringing your prop to a shop.

Anyone know how common it is to have a prop break down like this with an overheat? When I read the first part of this thread I thought this was going to be a blown coupler.