Alpha One Knocking Sound in Stern Drive / Engine overheats at idle speed

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rctownes

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Aug 12, 2012
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5
I have an Alpha One I/O. I have a sharp knocking sound in the stern drive that changes with engine RPM but is constant whether boat is in neutral or drive/reverse. When sitting idle for more than a few minutes engint temp climbs to the point of pegging out the temp guage. Increasing RPM's caused temp to return to normal.

My first suspect was the water pump in the lower. But it really sounds like the noise is located in the upper. I took off the top cover and observed the drive gear / driven gear while the engine is runnign and they seem to be normal. Ther. The drive gear / driven gear seem to be working together normally. The nut on the end of the universal joint assembly doesn't seem to be knocking onthe drive shaft.

Lastly, when I took off the top cover I noticed there is no ring around the bearing at the top of the drive shaft. According to the diagram there should be a ring and a shim and o-ring but mine has only the bearing. I have never had the cover off before and have had the boat for two years and about 20 trips to the lake? Could the missing ring be allowing the drive shaft to move around and causing something to wear?

Any ideas or suggestions apreciated.
 
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itsacrazyasian

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Jul 15, 2012
Messages
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Re: Alpha One Knocking Sound in Stern Drive / Engine overheats at idle speed

The race, the metal sleeve that the bearing rollers would ride in is pressed into the top cover. Look on the underside of it. You'll see it.

Have you tried to pinpoint the noise with a stethoscope or screwdriver?

I'm not even close to being an expert. I only know about your bearing concern since i have my alpha one apart to reseal right now.

btw, how are the u joints? Does it only overheat at idle? The lower splits easily. I would drop it down and have a look at the water pump at the very least.
 
ktbarrentine

ktbarrentine

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Re: Alpha One Knocking Sound in Stern Drive / Engine overheats at idle speed

Your temp problems are definitely impeller replacement time symptoms. When was the last time you replaced the impeller? two years and 20 trips to the lake is long enough!!
The knocking noise sounds tremendously like u-joints. When you pull your drive to do the impeller, you can give a good check-up on the u-joints, while you are performing all the other annual preventive maintenance that should be done on the drive related components. Best of luck and keep us posted! Also, you need to provide more details on your equipment: Year, serial number of the drive, engine type and serial number, age of the equipment, maintenance history. it will help in the long run.
 
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RenkenII

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Jun 13, 2011
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Re: Alpha One Knocking Sound in Stern Drive / Engine overheats at idle speed

Agree with the u-joints. Mine were good when I put the drive on this spring, but now I get a rythmic knock when hard-over to either side - another winter project I guess! Can't say enough about the impeller maintenance either. Just do it.
 
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rctownes

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Re: Alpha One Knocking Sound in Stern Drive / Engine overheats at idle speed

UPDATE: thanks for the replies and sorry it took so long for me to get back, but other issues have kept me away.

I finally got a chance to do a little work on the boat this week. Took the bottom unit off, ran the engine, still the knocking noise, so that eliminates the impeller. (although I plan to replace while I have it apart anyway). Took the upperr part of the drive unit off, engine runs quiet so I have isolated the general area of the noise.

The U-Joints look OK, no obvious wear. Not really sure how to tell from a visual inspection. They seem to sit tight and not have any noticeable play. The knocking sound was pretty consistent whether I was turning or not, so maybe not the u-joint.

what I did notice when I looked under the top cover again was that there is a tooth missing on the driven gear (the gear at the top of the vertical shaft that drives the lower unit and that interacts at a 90 degree angle with the drive gear at the end of the drive/u-joint shaft assembly). I would imagine a missing tooth in that gear would possibly cause the "knocking" sound and maybe explain why the impeller wasn't functioning optimally. Obviously this is something taht must be repaired regardless. Maybe that will be the source of the knocking. (fingers crossed)

Thoughts??
 
ktbarrentine

ktbarrentine

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Re: Alpha One Knocking Sound in Stern Drive / Engine overheats at idle speed

rctownes said:
UPDATE: thanks for the replies and sorry it took so long for me to get back, but other issues have kept me away.

I finally got a chance to do a little work on the boat this week. Took the bottom unit off, ran the engine, still the knocking noise, so that eliminates the impeller. (although I plan to replace while I have it apart anyway). Took the upperr part of the drive unit off, engine runs quiet so I have isolated the general area of the noise.

The U-Joints look OK, no obvious wear. Not really sure how to tell from a visual inspection. They seem to sit tight and not have any noticeable play. The knocking sound was pretty consistent whether I was turning or not, so maybe not the u-joint.

what I did notice when I looked under the top cover again was that there is a tooth missing on the driven gear (the gear at the top of the vertical shaft that drives the lower unit and that interacts at a 90 degree angle with the drive gear at the end of the drive/u-joint shaft assembly). I would imagine a missing tooth in that gear would possibly cause the "knocking" sound and maybe explain why the impeller wasn't functioning optimally. Obviously this is something taht must be repaired regardless. Maybe that will be the source of the knocking. (fingers crossed)

Thoughts??
Click to expand...

OK...let me get this straight... you took off your "lower" and ran your engine with just the upper in place? What did you use for oil in the upper assembly while you were running the engine? What did you use for water supply to the engine if the lower was off? If you drained the oil to remove the lower, then you drained oil out of the upper. If this is the case, it somehow does not surprise me that there is a chipped tooth in your upper.... and, this surely would be a cause of a knocking noise. From the sounds of things, you have serious issues with your drive. Have you considered a replacement? What was the quality and quantity of the oil that you drained out?

(I also just re-read your first post and find it quite interesting that you ran your engine and drive with the top cap removed from the drive.....again..... not surprised at all now that there is broken tooth in the upper)
 
nola mike

nola mike

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5,786
Re: Alpha One Knocking Sound in Stern Drive / Engine overheats at idle speed

Sounds like your lower unit is hosed. Esp if you ran it without oil. Is your prop turning in gear? Try running with the lower unit removed and make sure the knock is gone. Also, you haven't eliminated the impeller as the source of the overheat.
 
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