OMC loud Clunking

cowlotter

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turned on boat this morning and i heard a clunk right as it cranked and it continued with the engine. its hard to hear at a low idle but its there in neutral as well as forward. didnt try reverse. it gets louder with rpm. it didnt sound like it was the engine so i took the outdrive off and gimbal and ujoints seem okay. nothing obvious by looking. any ideas what could be clunking. it was pretty loud and seemed very problematic i wouldnt not operate boat as such i could feel the vibration aswell in steering wheel when trying to get over 2k rpm the clunk would get bad ? any help appreciated
 

Scott Danforth

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it would help us if we knew what OMG outdrive you have.... over the 50 decades that OMG was in business prior to them going out of business decades ago, they made a few different drives...... and each one may have different problems....

so what drive do you have?
and have you been keeping up with the annual maintenance per the factory manual?
 

cowlotter

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it would help us if we knew what OMG outdrive you have.... over the 50 decades that OMG was in business prior to them going out of business decades ago, they made a few different drives...... and each one may have different problems....

so what drive do you have?
and have you been keeping up with the annual maintenance per the factory manual?

its a omc cobra 1987 on a 5.7. i have kept up with annual maintenance yes
 

Lou C

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If you pulled the drive off you can run the boat on the water hose by disconnecting the water feed hose at the thermostat housing and connecting a garden hose to that (may have to use a hose adapter). That way you can determine if the noise is coming from the engine or the drive. If its gone when the drive is off then you have to re-check the u joints....if they are ok, then it could be internal to the drive...if so...I'd remove the impeller housing so you can easily turn the driveshaft while someone shifts the shift rod into FWD, NEUTRAL and REVERSE to see if you get unusual noises when doing that.

If its coming from the engine you can use a mechanic's stethoscope to try to localize it.
 

cowlotter

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If you pulled the drive off you can run the boat on the water hose by disconnecting the water feed hose at the thermostat housing and connecting a garden hose to that (may have to use a hose adapter). That way you can determine if the noise is coming from the engine or the drive. If its gone when the drive is off then you have to re-check the u joints....if they are ok, then it could be internal to the drive...if so...I'd remove the impeller housing so you can easily turn the driveshaft while someone shifts the shift rod into FWD, NEUTRAL and REVERSE to see if you get unusual noises when doing that.

If its coming from the engine you can use a mechanic's stethoscope to try to localize it.

sounds good ill try and isolate it. what kind of adapter do i need to get the garden hose to hook into the thermostat housing?
 

Bondo

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sounds good ill try and isolate it. what kind of adapter do i need to get the garden hose to hook into the thermostat housing?

Ayuh,..... A short piece of the appropriate sized hose, 'n clamps,....

Whatever it takes,..... cob it together,.... build yer own adapter,.....
 

cowlotter

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Ayuh,..... A short piece of the appropriate sized hose, 'n clamps,....

Whatever it takes,..... cob it together,.... build yer own adapter,.....

can i just shove garden hose in the water inlet tube after the power steering cooler or how close to thermostat housing does hose have to be?
 

Lou C

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You could do that too just make sure it stays in place. As long as it feeds the thermo housing with water so the exhaust does not overheat. Don't want to burn up the rubber flappers at the top of the Y pipe and the rubber exhaust hoses.
 

Scott Danforth

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Duct tape is your friend

Annual inspection and maintenance includes checking the alignment
 

Scott Danforth

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well, with a cobra, its either the alignment, the u-joints, or the gimbal bearing as the most likely sources. after that its in two input bearings in the gear box itself.
 

cowlotter

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well, with a cobra, its either the alignment, the u-joints, or the gimbal bearing as the most likely sources. after that its in two input bearings in the gear box itself.

the gear box in the drive? is that in the upper or lower? alignment ujoints and gimbal seem good im going to reinstall drive and try and pinpoint noise on muffs
 

Scott Danforth

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Seam good?

What is the pattern on the alignment tool?

Did you spin the gimbal bearing with fingers? That will tell you the health of the bearing. It should feel smooth, and only take 2 fingers to turn

The u-joints should move freely, however may requre you to press out the crosses to check the bearings
 

cowlotter

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Seam good?

What is the pattern on the alignment tool?

Did you spin the gimbal bearing with fingers? That will tell you the health of the bearing. It should feel smooth, and only take 2 fingers to turn

The u-joints should move freely, however may requre you to press out the crosses to check the bearings

ran boat with the out drive attached. the noise is from the engine and much more pronounced without the outdrive off. its definitely a loud knocking or clunk. definitely internal and not something i can probably get into my self. im assuming an engine pull and internal work. what do you think and any recommendations appreciated
 

Scott Danforth

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with the drive off, you have half the work to pull the motor done. disconnect the cables, exhaust, fuel lines, remove the front motor mount bolts and transom shield bolts and lift the motor out. maybe a 30 minute process

any 1986-1995 5.7 from a truck out of a pull-a-part salvage yard would work. just change the core plugs for brass, and use marine head gaskets. you can be back on the water for under $500

or have your motor rebuilt and be back on the water for about $1700
 

cowlotter

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with the drive off, you have half the work to pull the motor done. disconnect the cables, exhaust, fuel lines, remove the front motor mount bolts and transom shield bolts and lift the motor out. maybe a 30 minute process

any 1986-1995 5.7 from a truck out of a pull-a-part salvage yard would work. just change the core plugs for brass, and use marine head gaskets. you can be back on the water for under $500

or have your motor rebuilt and be back on the water for about $1700

what do you think could be brokem? rod bearing or something?
 

Scott Danforth

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without pulling it apart, its a guess

could be valve train, could be broken piston, could be bearings.

either way, your motor is coming out.
 

cowlotter

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without pulling it apart, its a guess

could be valve train, could be broken piston, could be bearings.

either way, your motor is coming out.

what do you think about something like this? ill keep the truck block in mind, i dont think i want to rebuild the current one. its was a jasper rebuilt in 2012 and its already needing another. on this new half package though from michigan motorz what do you think? currently the onlly brand new parts on current engine are the fuel pump risers manifold and starter. which it looks like i could use those on this.
 

Scott Danforth

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You can build a brand new stroker motor for $4200. However its your money
 
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