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Author Topic:   Causes of Spun Hub

mrclean1 posted 06-17-2008 08:35 PM ET (US)
I have spun several [propeller] hubs on my 1998 Mercury 225 EFI for no reason. I never hit anything and was offshore every time [the hub spun]. I read somewhere that it could be due to a poppet valve that is bad. Can [a failure of a poppet valve] cause [a propeller hub to spin]?
deepwater posted 06-17-2008 09:30 PM ET (US)
The rubber hub in a prop is a large solid hunk of rubber squeezed and forced into the hub under lots of pressure. I have never heard of a poppet valve in a propeller. If you think you are spinning your hub mark the hub and rubber and go for a run. If it spins you will see it in the marks. If the marks don't move than its not your hub
sosmerc posted 06-17-2008 09:37 PM ET (US)
The poppet valve is an important part of your cooling system. If the poppet is not opening properly your engine may be running too hot. The excess heat from the exhaust passing through the prop CAN cause propeller hubs to fail.
jimh posted 06-17-2008 10:02 PM ET (US)
sosmerc--Thank you for linking those two seemingly unrelated events together. The relationship between lack of proper cooling due to a problem with the poppet valve and failure of the rubber propeller hub insert from excess heat in the exhaust makes perfect sense.
To the original poster: Do you have a temperature gauge on your Mercury 225 EFI motor? The engine running temperature when at high throttle settings ought to be quite low. On my 225-HP engine when running at higher engine speeds the cooling system removes so much heat that the cylinder head temperature drops to below 100-degrees-F.

mrclean1 posted 06-17-2008 10:25 PM ET (US)
Ther is no temp gauge for the motor, but it does always seem that it spins when on plane wich is usually after a long troll. This popett valve. Where exactly is this thing located? I might try changing it or rebuild it if possible. I never actually heard of it until tonite and have been around boats for years. As far as knowing wether or not my hub is spun or not, I've replaced 4 in the past year. I know, believe me. Thank you "Sea Tow"
To jimh: I posted a repair question about this same motor and you asked me to go to the repairs/mods discussion section. beings it's my first night on this site can you tell me where it is and how to get there? Thanks and again sorry for being a newbie at this, just not used to getting help from all you professionals, usually try and figure things out myself.
jimh posted 06-17-2008 10:36 PM ET (US)
The term poppet valve really refers to the shape of the valve, but in outboard motor discussions the term poppet valve is usually used to mean a valve in the outboard motor cooling system which operates in response to pressure.
In the cooling system there typically are two regulating valves which respond to different parameters. The thermostat is a valve that opens or closes in response to temperature. The poppet valve is a valve that opens or closes in response to pressure.
The usual operation of the cooling system is to include some mechanism for rapidly increasing the flow of cooling water to the power head when the engine speed increases. In Mercury motors this is often accomplished by a poppet valve. The poppet valve is located in the cooling system in such a manner that when engine speed increases, the corresponding increase in water pressure (in the water pump output stream) opens the poppet valve. The opening of the poppet valve directs more cooling water to the power head.
If the poppet valve does not function properly, the flow of cooling water will not be increased, and this may lead to the engine operating at a higher temperature.
Since all the engine exhaust passes through the propeller hub, if there is less flow of water the temperature of the exhaust passage will probably rise.
On some motors, for example on my Evinrude V6 225-HP motor, there is a separate water pick up on the gear case which feed additional water into the exhaust passage only--not to the water pump--in order to provide extra cooling to the exhaust passage just before the exhaust enters the propeller hub.
If you need advice on how to use the website, please post to the META-DISCUSSION. You can locate other discussion areas by navigating up one layer in the directory hierarchy, and also by using the JUMP TO pop-up below.

Tohsgib posted 06-17-2008 10:44 PM ET (US)
You guys are killing me on this one...Sure a hot motor might put the FINAL kiss on the hub but being under water I doubt it would do much before the engine puked from high temps. Hubs spin...plain and simple! The rubber eventually gives up the ghost and usually not at the right time. I have run a prop for 3 hours constsnt then all of a sudden it spins like I am neutral..had NOTHING to do with engine temp, it was just the right time. $45 and you are running again and a good reason to carry a spare.
Tohsgib posted 06-17-2008 10:47 PM ET (US)
HOLD UP! I am sorry for my last post...you have replaced 4 hubs this YEAR???? Something is seriously wrong. If your engine was getting that hot, after 4 props I think you would have chunked a piston.
mrclean1 posted 06-17-2008 10:59 PM ET (US)
Since the increase of the water pressure from the water pump opens the poppet valve, could I be safe in saying the that the water pump may be weak or old and not creating enough presure to open the poppet vavle? If this might be the case should I change the water pump assembly without changing the poppet vavle. Should the poppet vavle be changed on a yearly basis as the water pump? If so, where is it located, to change it?? I can't even find it in my repair manual.
mrclean1 posted 06-17-2008 11:17 PM ET (US)
Well Mr. tohsgib, you would think so, I don't have a temp gauge for it, just an idot light. Darn ting always ran like a top until this year and started missing on 3 cylinders. Refer to repair section if you can help me out on that one.
Bella con23 posted 06-17-2008 11:31 PM ET (US)
Prior to my purchasing "Bella", my neighbor, the prior owner of my boat, was complaining of the same spun hub condition. Every time he brought it out of the marina and cracked the throttle open, the prop hub would let go and he would idle it back to the marina.
He arranged to have a mercury representative come down to the dock and check out the outboard. This rep had checked out everything from prop pitch to downloading the computer error messages.
His conclusion was the poppet valve was not opening correctly allowing hot gasses to flow around the hub and the pitch of the propeller being questionably to steep for this 23 footer was enough to break the hub bond.
My neighbor sold it to me with corrections to the poppet valve made and myself changing the prop to a Rev. 4 and 2" less pitch, I have not had a problem in two years of ownership.
Joe
Tohsgib posted 06-17-2008 11:37 PM ET (US)
Honestly that is the 1st time i have EVER heard of that situation...anything is possible so the best of luck to you. I would then change/check the poppet valve(s) which on that Merc is not a big deal to get to. Try it on an older V4 OMC...Geez!
Tom W Clark posted 06-18-2008 12:39 AM ET (US)
Hot exhaust gases is a very commonly reported cause of a spun prop, especially the Mercury Flo-Torq hub which use a plastic (DuPont Delrin) hub insert, which seems to turn brittle and fractures.
I have never had this happen to me but I have heard it repeated enough that I now give it credence and I have seen several disintegrated Flo-Torq Hub inserts.
deepwater posted 06-20-2008 05:50 AM ET (US)
this is the first i have heard of a poppet valve on an outboard motor,,the only thing opening before was the thermostat,, i do have a poppet valve on my hot water boiler
Tohsgib posted 06-20-2008 10:04 AM ET (US)
Not sure if ALL outboards have them but most do, especially higher HP.

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Author	Topic: Causes of Spun Hub
mrclean1	posted 06-17-2008 08:35 PM ET (US) I have spun several [propeller] hubs on my 1998 Mercury 225 EFI for no reason. I never hit anything and was offshore every time [the hub spun]. I read somewhere that it could be due to a poppet valve that is bad. Can [a failure of a poppet valve] cause [a propeller hub to spin]?
deepwater	posted 06-17-2008 09:30 PM ET (US) The rubber hub in a prop is a large solid hunk of rubber squeezed and forced into the hub under lots of pressure. I have never heard of a poppet valve in a propeller. If you think you are spinning your hub mark the hub and rubber and go for a run. If it spins you will see it in the marks. If the marks don't move than its not your hub
sosmerc	posted 06-17-2008 09:37 PM ET (US) The poppet valve is an important part of your cooling system. If the poppet is not opening properly your engine may be running too hot. The excess heat from the exhaust passing through the prop CAN cause propeller hubs to fail.
jimh	posted 06-17-2008 10:02 PM ET (US) sosmerc--Thank you for linking those two seemingly unrelated events together. The relationship between lack of proper cooling due to a problem with the poppet valve and failure of the rubber propeller hub insert from excess heat in the exhaust makes perfect sense. To the original poster: Do you have a temperature gauge on your Mercury 225 EFI motor? The engine running temperature when at high throttle settings ought to be quite low. On my 225-HP engine when running at higher engine speeds the cooling system removes so much heat that the cylinder head temperature drops to below 100-degrees-F.
mrclean1	posted 06-17-2008 10:25 PM ET (US) Ther is no temp gauge for the motor, but it does always seem that it spins when on plane wich is usually after a long troll. This popett valve. Where exactly is this thing located? I might try changing it or rebuild it if possible. I never actually heard of it until tonite and have been around boats for years. As far as knowing wether or not my hub is spun or not, I've replaced 4 in the past year. I know, believe me. Thank you "Sea Tow" To jimh: I posted a repair question about this same motor and you asked me to go to the repairs/mods discussion section. beings it's my first night on this site can you tell me where it is and how to get there? Thanks and again sorry for being a newbie at this, just not used to getting help from all you professionals, usually try and figure things out myself.
jimh	posted 06-17-2008 10:36 PM ET (US) The term poppet valve really refers to the shape of the valve, but in outboard motor discussions the term poppet valve is usually used to mean a valve in the outboard motor cooling system which operates in response to pressure. In the cooling system there typically are two regulating valves which respond to different parameters. The thermostat is a valve that opens or closes in response to temperature. The poppet valve is a valve that opens or closes in response to pressure. The usual operation of the cooling system is to include some mechanism for rapidly increasing the flow of cooling water to the power head when the engine speed increases. In Mercury motors this is often accomplished by a poppet valve. The poppet valve is located in the cooling system in such a manner that when engine speed increases, the corresponding increase in water pressure (in the water pump output stream) opens the poppet valve. The opening of the poppet valve directs more cooling water to the power head. If the poppet valve does not function properly, the flow of cooling water will not be increased, and this may lead to the engine operating at a higher temperature. Since all the engine exhaust passes through the propeller hub, if there is less flow of water the temperature of the exhaust passage will probably rise. On some motors, for example on my Evinrude V6 225-HP motor, there is a separate water pick up on the gear case which feed additional water into the exhaust passage only--not to the water pump--in order to provide extra cooling to the exhaust passage just before the exhaust enters the propeller hub. If you need advice on how to use the website, please post to the META-DISCUSSION. You can locate other discussion areas by navigating up one layer in the directory hierarchy, and also by using the JUMP TO pop-up below.
Tohsgib	posted 06-17-2008 10:44 PM ET (US) You guys are killing me on this one...Sure a hot motor might put the FINAL kiss on the hub but being under water I doubt it would do much before the engine puked from high temps. Hubs spin...plain and simple! The rubber eventually gives up the ghost and usually not at the right time. I have run a prop for 3 hours constsnt then all of a sudden it spins like I am neutral..had NOTHING to do with engine temp, it was just the right time. $45 and you are running again and a good reason to carry a spare.
Tohsgib	posted 06-17-2008 10:47 PM ET (US) HOLD UP! I am sorry for my last post...you have replaced 4 hubs this YEAR???? Something is seriously wrong. If your engine was getting that hot, after 4 props I think you would have chunked a piston.
mrclean1	posted 06-17-2008 10:59 PM ET (US) Since the increase of the water pressure from the water pump opens the poppet valve, could I be safe in saying the that the water pump may be weak or old and not creating enough presure to open the poppet vavle? If this might be the case should I change the water pump assembly without changing the poppet vavle. Should the poppet vavle be changed on a yearly basis as the water pump? If so, where is it located, to change it?? I can't even find it in my repair manual.
mrclean1	posted 06-17-2008 11:17 PM ET (US) Well Mr. tohsgib, you would think so, I don't have a temp gauge for it, just an idot light. Darn ting always ran like a top until this year and started missing on 3 cylinders. Refer to repair section if you can help me out on that one.
Bella con23	posted 06-17-2008 11:31 PM ET (US) Prior to my purchasing "Bella", my neighbor, the prior owner of my boat, was complaining of the same spun hub condition. Every time he brought it out of the marina and cracked the throttle open, the prop hub would let go and he would idle it back to the marina. He arranged to have a mercury representative come down to the dock and check out the outboard. This rep had checked out everything from prop pitch to downloading the computer error messages. His conclusion was the poppet valve was not opening correctly allowing hot gasses to flow around the hub and the pitch of the propeller being questionably to steep for this 23 footer was enough to break the hub bond. My neighbor sold it to me with corrections to the poppet valve made and myself changing the prop to a Rev. 4 and 2" less pitch, I have not had a problem in two years of ownership. Joe
Tohsgib	posted 06-17-2008 11:37 PM ET (US) Honestly that is the 1st time i have EVER heard of that situation...anything is possible so the best of luck to you. I would then change/check the poppet valve(s) which on that Merc is not a big deal to get to. Try it on an older V4 OMC...Geez!
Tom W Clark	posted 06-18-2008 12:39 AM ET (US) Hot exhaust gases is a very commonly reported cause of a spun prop, especially the Mercury Flo-Torq hub which use a plastic (DuPont Delrin) hub insert, which seems to turn brittle and fractures. I have never had this happen to me but I have heard it repeated enough that I now give it credence and I have seen several disintegrated Flo-Torq Hub inserts.
deepwater	posted 06-20-2008 05:50 AM ET (US) this is the first i have heard of a poppet valve on an outboard motor,,the only thing opening before was the thermostat,, i do have a poppet valve on my hot water boiler
Tohsgib	posted 06-20-2008 10:04 AM ET (US) Not sure if ALL outboards have them but most do, especially higher HP.