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Author Topic:   What are the symptoms of a spun prop?

montauk madness posted 10-17-2003 06:43 PM ET (US)
I'm hoping you guys can help.
I have a 90HP Mercury 2S on my Montauk. It has a 19P s/s prop and up to now has been running great. I let a friend borrow it about a month ago (last time it was ran) and now I have a problem.
I can't get the boat up to speed w/out going way over max RPMs. Up to 6200+ (before problem 5500). Even then it's probably only going 3/4 of max MPH. If I trim it full in, it pulls dangerously to the side. Nothing looks damaged or bent.
Is the prop "spun"? I bought it earlier this year and it was reconditioned. I have a spare but due to weather have been unable to try it.
Any thoughts would be appreciated.
-Jeff

GeneNJ posted 10-17-2003 07:31 PM ET (US)
The one time I had a spun prop, the boat could not get on plane. Anything over 2k rpm and the boat slowed even more. Your symptoms don't match my experience with a 120hp Johnson on a 20' Center Console.
lhg posted 10-17-2003 07:38 PM ET (US)
Sounds like you do. Take off the prop, and look at the rubber hub from the back side. If it looks twisted, or torn and rough, it is definitely sheared.
It is very easy to shear a hub by driving a boat onto a bunk trailer. Sometimes they will just let go from age and use.
Jarhead posted 10-17-2003 08:27 PM ET (US)
Make a straight line on the hub to the housing with an indelible marker. Take a short spin and check to see if the mark between the housing and the hub still lines up. If not you've got a spun hub.
Ya, I know... Clear as mud. Hope you can understand my poor attempt at explaining the procedure...
brisboats posted 10-17-2003 08:54 PM ET (US)
Made sense to me Jarhead, and actually stirred a thought. What if we scawled a line that would last in the same way when the prop was installed from the beginning ? Then later this line could be checked if a spun prop was suspected. Kinda like the drag racers marking straight lines on their axles in order to check for twist later on. Just a thought.
Brian
jimh posted 10-17-2003 09:00 PM ET (US)
You can detect a spun hub just by looking for circular scratches on the portion of the hub that bears against the thrust washer. The splines on the shaft keep the thrust washer from slipping, so if the propeller has a spun hub it will become scratched as it rotates in relation to the thrust washer.
A Master Mercury Certified Mechanic with 25-years of experience explained this to me after he took a one-second glance at my propeller and declared it had a spun hub.
jimh posted 10-17-2003 09:02 PM ET (US)
Also, one way to get a spun hub is to have the propeller entangled in thick weeds. Perhaps you friend encountered that or something similar which caused the hub to spin.
Gene in NC posted 10-18-2003 04:38 AM ET (US)
Just pulled SS 13/19 that has been on '87 OMC 90 for at least six years of light saltwater use. Could be original. Small sliver of rubber 5/16 x 1 1/2 and very thin loose on the engine side. Looked like "flashing" from a casting. The grease was still there but it was black and had a "crumbly" apearance. None of the other indicators mentioned in the thread but still looks suspicious.
Pulled to replace with known good spare for performance test. Then pulled the cover and discoverd that perf prob "possibly" caused by one plug lead disconnected.
Easy to swap back and forth for operational test, but how determine incipient failure? Take to "trusted" prop shop?
montauk madness posted 10-24-2003 06:19 PM ET (US)
update:
Last weekend I set off to replace the prop with my spare and had to drain the water out of the boat before I could start. While doing so the engine/prop ran flawlessly. It never overevved and hit 5500 RPM at WOT (just as before). I guess I'll just have to keep my eye on it for awhile.
Thanks for your help.
-Jeff

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Author	Topic: What are the symptoms of a spun prop?
montauk madness	posted 10-17-2003 06:43 PM ET (US) I'm hoping you guys can help. I have a 90HP Mercury 2S on my Montauk. It has a 19P s/s prop and up to now has been running great. I let a friend borrow it about a month ago (last time it was ran) and now I have a problem. I can't get the boat up to speed w/out going way over max RPMs. Up to 6200+ (before problem 5500). Even then it's probably only going 3/4 of max MPH. If I trim it full in, it pulls dangerously to the side. Nothing looks damaged or bent. Is the prop "spun"? I bought it earlier this year and it was reconditioned. I have a spare but due to weather have been unable to try it. Any thoughts would be appreciated. -Jeff
GeneNJ	posted 10-17-2003 07:31 PM ET (US) The one time I had a spun prop, the boat could not get on plane. Anything over 2k rpm and the boat slowed even more. Your symptoms don't match my experience with a 120hp Johnson on a 20' Center Console.
lhg	posted 10-17-2003 07:38 PM ET (US) Sounds like you do. Take off the prop, and look at the rubber hub from the back side. If it looks twisted, or torn and rough, it is definitely sheared. It is very easy to shear a hub by driving a boat onto a bunk trailer. Sometimes they will just let go from age and use.
Jarhead	posted 10-17-2003 08:27 PM ET (US) Make a straight line on the hub to the housing with an indelible marker. Take a short spin and check to see if the mark between the housing and the hub still lines up. If not you've got a spun hub. Ya, I know... Clear as mud. Hope you can understand my poor attempt at explaining the procedure...
brisboats	posted 10-17-2003 08:54 PM ET (US) Made sense to me Jarhead, and actually stirred a thought. What if we scawled a line that would last in the same way when the prop was installed from the beginning ? Then later this line could be checked if a spun prop was suspected. Kinda like the drag racers marking straight lines on their axles in order to check for twist later on. Just a thought. Brian
jimh	posted 10-17-2003 09:00 PM ET (US) You can detect a spun hub just by looking for circular scratches on the portion of the hub that bears against the thrust washer. The splines on the shaft keep the thrust washer from slipping, so if the propeller has a spun hub it will become scratched as it rotates in relation to the thrust washer. A Master Mercury Certified Mechanic with 25-years of experience explained this to me after he took a one-second glance at my propeller and declared it had a spun hub.
jimh	posted 10-17-2003 09:02 PM ET (US) Also, one way to get a spun hub is to have the propeller entangled in thick weeds. Perhaps you friend encountered that or something similar which caused the hub to spin.
Gene in NC	posted 10-18-2003 04:38 AM ET (US) Just pulled SS 13/19 that has been on '87 OMC 90 for at least six years of light saltwater use. Could be original. Small sliver of rubber 5/16 x 1 1/2 and very thin loose on the engine side. Looked like "flashing" from a casting. The grease was still there but it was black and had a "crumbly" apearance. None of the other indicators mentioned in the thread but still looks suspicious. Pulled to replace with known good spare for performance test. Then pulled the cover and discoverd that perf prob "possibly" caused by one plug lead disconnected. Easy to swap back and forth for operational test, but how determine incipient failure? Take to "trusted" prop shop?
montauk madness	posted 10-24-2003 06:19 PM ET (US) update: Last weekend I set off to replace the prop with my spare and had to drain the water out of the boat before I could start. While doing so the engine/prop ran flawlessly. It never overevved and hit 5500 RPM at WOT (just as before). I guess I'll just have to keep my eye on it for awhile. Thanks for your help. -Jeff