Outboard Motor Vibration in Neutral? | GTAMotorcycle.com

Outboard Motor Vibration in Neutral?

M

MaksTO

Well-known member
Hey all!

Friends and I just finished repairing an in-cockpit outboard engine well on our 25 foot sailboat. The mount was fully rotted away so we re-cored and rebuilt the fibreglass mount for the motor (which is a Tohatsu 6hp 4-stroke for those wondering).

I don't imagine anything is different with the engine as it's run great the last two summers with minimal maintenance. It always vibrated and I never really bothered to care, but I think it's become more noticeable since its now mounted to a structure that is solid, as opposed to soggy waterlogged wood with some gelcoat over it.

I don't have any issues running the engine so far (started from winter storage with just a few pulls :)), but the vibrations are a little annoying. Happens especially at idle, and was in neutral so I don't think it's a prop balance issue (though the prop has seen better days for sure).

Wondering if this is a normal thing for outboards? It's a single cylinder so wondering if this is just like owning a KLR thumper lol. Are these things usually mounted on a rubber surface? we are thinking of adding a small rubber pad on one side to keep it more secure as hand tightening the mounts still results in loosening over time.

Hoping some more experienced boat people can provide some advice!
 
MaksTO said:
Hey all!

Friends and I just finished repairing an in-cockpit outboard engine well on our 25 foot sailboat. The mount was fully rotted away so we re-cored and rebuilt the fibreglass mount for the motor (which is a Tohatsu 6hp 4-stroke for those wondering).

I don't imagine anything is different with the engine as it's run great the last two summers with minimal maintenance. It always vibrated and I never really bothered to care, but I think it's become more noticeable since its now mounted to a structure that is solid, as opposed to soggy waterlogged wood with some gelcoat over it.

I don't have any issues running the engine so far (started from winter storage with just a few pulls :)), but the vibrations are a little annoying. Happens especially at idle, and was in neutral so I don't think it's a prop balance issue (though the prop has seen better days for sure).

Wondering if this is a normal thing for outboards? It's a single cylinder so wondering if this is just like owning a KLR thumper lol. Are these things usually mounted on a rubber surface? we are thinking of adding a small rubber pad on one side to keep it more secure as hand tightening the mounts still results in loosening over time.

Hoping some more experienced boat people can provide some advice!
Click to expand...
You're probably right and the soggy mount was dampening vibration. Most outboards have the vibration isolation between the powerhead and the clamp. It will be hard to get much isolation while keeping a solid clamp. You may be able to put some rubber on top of the transom to help but you cant do much about the clamps without a bunch of work. The rubber has to be soft enough to squish with your fingers if you want it to do something useful.
 
Last edited:
Rubber mounts. Any rubber will do, but Sorbothane has a 95% absorption rate.
 
FullMotoJacket said:
Rubber mounts. Any rubber will do, but Sorbothane has a 95% absorption rate.
Click to expand...
Be careful with the marketing numbers. Isolation effectiveness depends on many things but most importantly proper loading. You need to get the correct psi to get the maximum isolation. Easiest way to do that is changing the size of pad or distribution plate to get the loading right. Under the clamps will have a ton of pressure and it will be hard to properly load isolation (and I would be concerned about motor wiggling loose). There are solutions but they need to be thought through so you don't lose the motor or waste your money.
 
Pretty normal with a single Cly 6hp . They tend to percolate a little . Going to a 9.9 2cly stops your problem but weighs more , costs double and burns more gas .
It’s a sailboat , uses the sails more .


Sent from my iPhone using GTAMotorcycle.com
 
Good to know vibrations are likely fine. I've had good luck with this motor and it's needed nothing but oil changes so far. We will likely put a rubber piece on the side where the screws go onto the transom mount and see if that helps even slightly.

Don't use the engine much except to get in and out of the dock / harbor so not too bothered, but wanted to make sure it's not something I should actually address.

Our long term goal (dream) is to go electric, but $10k on an electric system on a boat we paid $2k for doesn't really math out at the moment, though we would definitely bring it with us if we ever changed boats... Which I don't plan to do really - 25 feet is plenty for me and my needs.

Electric keeps getting pushed down the line as other repairs need to get done, so I think I will do with the Outboard what I do with my bike, which is to stop F'ing with it and run it as is. Maybe by the time we fix everything else going electric will drop in price haha :ROFLMAO:
 
timtune said:
The depth of knowledge here never ceases to amaze ( WTF is Sorbothane??)
Click to expand...
Here is a set of 30 durometer pads. Proper loading is 7-17 lbs each. Feels kind of like bubble gum but returns to original shape (unless you crush it horribly).

20240423-131223.jpg
 
Even putting a chunk of old yoga mat over where the engine drops on takes the drone out that is transferred to solid glass . Just make sure you have a safety line on the motor if you do anything other than screws to transome . ( good idea to alway have a safety string tied on) I watched two motors tread water briefly last yr lol .


Sent from my iPhone using GTAMotorcycle.com
 
crankcall said:
Even putting a chunk of old yoga mat over where the engine drops on takes the drone out that is transferred to solid glass . Just make sure you have a safety line on the motor if you do anything other than screws to transome . ( good idea to alway have a safety string tied on) I watched two motors tread water briefly last yr lol .


Sent from my iPhone using GTAMotorcycle.com
Click to expand...
Yoga mat is actually genius! I will definitely try that.

Thankfully the hole in the cockpit well for the engine is smaller then the top of it, so even if it comes loose it wont go far. Might bang up our nice fiberglass job though...
 
MaksTO said:
Yoga mat is actually genius! I will definitely try that.

Thankfully the hole in the cockpit well for the engine is smaller then the top of it, so even if it comes loose it wont go far. Might bang up our nice fiberglass job though...
Click to expand...
How much room do you have? These want up to 60 psi (similar to yoga mat). You need almost 2" of extra room in the clamp to get them on both sides though. Unless the transom is really thin, you probably need a thinner solution. The thicker the isolator the more isolation you get assuming you maintain proper loading.

 
GreyGhost said:
How much room do you have? These want up to 60 psi (similar to yoga mat). You need almost 2" of extra room in the clamp to get them on both sides though. Unless the transom is really thin, you probably need a thinner solution. The thicker the isolator at the same pressure, the more isolation you get.

Click to expand...
Transom is quite wide. We have the fiberglass main section, and then marine ply painted and lightly glued to both sides as sacrificial pieces that we will replace every few years. We probably have half an inch to spare at this point for the motor mounting, so it would likely have to be a really thin piece of rubber, or we will just deal with the vibrations.
 
MaksTO said:
Transom is quite wide. We have the fiberglass main section, and then marine ply painted and lightly glued to both sides as sacrificial pieces that we will replace every few years. We probably have half an inch to spare at this point for the motor mounting, so it would likely have to be a really thin piece of rubber, or we will just deal with the vibrations.
Click to expand...
Next time you redo the plywood, put the yoga matt between the plywood and fibreglass and you are probably in good shape. I suspect directly under the clamps will be well over 60 psi.
 
Quick aside as well - has anyone ever done a mod to their outboard to prevent it from going up? We have it right in front of the rudder and if you throw it into reverse when its slightly up, it will be unlocked and shoot back into the rudder. Only happened once, but I am thinking it would be nice to just remove that feature where the motor is unlocked in forward gear, so that it's always locked in the down position. We have a keel in front, so grounding the motor isn't ever going to be a possibility.

From what I looked at, I'd have to disassemble the lower unit and remove the pin that runs down it which activates a latch that locks/unlocks the hinge. I don't know if it's worth the trouble removing it or cutting it down.
 
GreyGhost said:
Next time you redo the plywood, put the yoga matt between the plywood and fibreglass and you are probably in good shape. I suspect directly under the clamps will be well over 60 psi.
Click to expand...
Good idea! Might try that next time we remove the ply (though hopefully that isn't for a good long while).
 
MaksTO said:
Quick aside as well - has anyone ever done a mod to their outboard to prevent it from going up? We have it right in front of the rudder and if you throw it into reverse when its slightly up, it will be unlocked and shoot back into the rudder. Only happened once, but I am thinking it would be nice to just remove that feature where the motor is unlocked in forward gear, so that it's always locked in the down position. We have a keel in front, so grounding the motor isn't ever going to be a possibility.

From what I looked at, I'd have to disassemble the lower unit and remove the pin that runs down it which activates a latch that locks/unlocks the hinge. I don't know if it's worth the trouble removing it or cutting it down.
Click to expand...
Does it lock down or is it just relying on gravity/prop wash to keep it down? Most outboards I have touched lock up or in shallow draft position but most don't lock down (to maybe save the outboard if you hit something).
 
GreyGhost said:
Does it lock down or is it just relying on gravity/prop wash to keep it down? Most outboards I have touched lock up or in shallow draft position but most don't lock down (to maybe save the outboard if you hit something).
Click to expand...
It locks down when in reverse, otherwise it would pop up, but in forward (and I think neutral), it's unlocked. I am pretty sure its a safety feature in case you run into something, but it's not an issue I would run into on the sailboat.

Sometimes if we move forward at a few knots, and I quickly pop the gear into reverse, the water flowing over the prop will push the engine up just enough that it frees from the locking mechanism, causing it to fly up in reverse.

I might look at it again and see if there's some other piece I can remove to keep the lock engaged at all times. It would just be a small quality of life improvement as it's one less thing to think about when getting into the mooring.
 
My 6hp Suzuki locks down, I need to push a release to tip it up , I’m surprised your Tohatsu is not similar. Do you pull the motor off when sailing ?
I would not sandwich the foam between the ply and transom, you still need the plywood fastened somehow and those fasteners will transmit vibration . If you ‘wrap’ a thin foam over where the motor sits like a saddle you have better insulation all around .
When you rebuild it next use PVC trim boards from Homodepot instead of plywood . Stays white , looks nice , lasts about 1000yrs . Use a 2” spade bit and make small indentation where the screws wind down so they have a fixed home .
Which boat is it ? Not many had a well in front of the rudder . Most went behind , except those frenchys that put a well behind the keel in the cabin ( not handy)


Sent from my iPhone using GTAMotorcycle.com
 
You must log in or register to reply here.

Back
Top Bottom