6hp 4 stroke vibration

[simplystressed]

I have a 6hp 4 stroke mrcury and I notice it really vibrates on my boat at all speeds (worse at higher speeds it seems). Its too the point where it shakes the whole boat and my hand is numb from holding the tiller. Afterwards noticed one of the bolts was loose down by the release mechanism (1 of 4 that hold the casing together). Tightened that up and haven't tried it since not sure if that would help that much.

Boat is an 16' aluminum about 1300lbs. Pushes it to hull speed but needs to be at WOT to do so (around 5.8mph). Its fairly noisy but the vibration is the biggest concern.

Is there anything else to tighten on them (bushings etc) that will help? Maybe getting a different prop? Haven't measured rpm's at WOT yet though but saw other threads about a high thrust prop. Not sure if that would help with a 1300lb boat. Going to an 8hp would add lots of weight, so hoping I can improve this issue.

thanks in advance!

 

[simplystressed]

Re: 6hp 4 stroke vibration

Got the tach on her today and I got 4350 rpm at wot. That was with two people in the boat (which is typical). Do you think the high thrust prop would make sense and get me closed to the 5500-6000 range?

After tightening the casing it seemed to help a little with vibration, but its still bad....particularly on the tiller handle. If anyone has any suggestions that might help with the 6hp please let me know.

Thanks!

 

[pvanv]

Re: 6hp 4 stroke vibration

I assume you have the Tohatsu powerhead with Merc badging. You could try the 6-pitch prop (fits the 4/5/6 Tohatsu/Nissan). It's presently out of stock, but should be in stock in a few weeks. All 1-cylinder motors will shake a bit, especially near idle. Lightweight aluminum transoms can act like a sounding board in those situations, and seem to amplify the vibration. Check your rubber motor mounts. If the tilt/swivel bracket was loose, there could be a reason, such as a bad "donut" mount inside that swivel.

 

[simplystressed]

Re: 6hp 4 stroke vibration

I assume you have the Tohatsu powerhead with Merc badging. You could try the 6-pitch prop (fits the 4/5/6 Tohatsu/Nissan). It's presently out of stock, but should be in stock in a few weeks. All 1-cylinder motors will shake a bit, especially near idle. Lightweight aluminum transoms can act like a sounding board in those situations, and seem to amplify the vibration. Check your rubber motor mounts. If the tilt/swivel bracket was loose, there could be a reason, such as a bad "donut" mount inside that swivel.

Hi Paul yes its a tohatsu head. Is that the elephant ear prop?

It seems to vibrate more at higher speeds on the tiller...or buzzes.

What should I look for on the donuts? Are they much to replace?

Thanks.

 

[pvanv]

Re: 6hp 4 stroke vibration

No, that's not the HT prop... the EE prop is specifically for very heavy loads, but it might help a bit... might also slow down the motor, which might make the vibration worse. Is your prop bent at all? Even a slight ding could add vibration. Loose things can buzz around a lot, so make sure everything is snug. Typically those motors smooth out as the RPM goes up, so, without seeing/hearing it, I can't say for sure what your problem might be. If the tiller bushing is sloppy, the tiller could buzz around a bit. You can see the available props at http://www.tohatsu.com/accessories/prop.html

 

[simplystressed]

Re: 6hp 4 stroke vibration

No, that's not the HT prop... the EE prop is specifically for very heavy loads, but it might help a bit... might also slow down the motor, which might make the vibration worse. Is your prop bent at all? Even a slight ding could add vibration. Loose things can buzz around a lot, so make sure everything is snug. Typically those motors smooth out as the RPM goes up, so, without seeing/hearing it, I can't say for sure what your problem might be. If the tiller bushing is sloppy, the tiller could buzz around a bit. You can see the available props at http://www.tohatsu.com/accessories/prop.html

Here's some pics of the motor mounts (a bit of grease on there). The one bolt to the left of the grease nipple was loose.

The tiller handle bushing is definitely sloppy, when its down and I press on it it gives quite a bit. The two small bolts inside the cowling on the tiller are tight, not sure if it can be tightened more.

Is there a part # for the motor bushings and tiller bushings?

Everything else seems snug so maybe its the bushings.

The prop seems straight as far as I know.

 

[simplystressed]

Re: 6hp 4 stroke vibration

Another note: The motor is a long shaft and is sitting on a transom that is 17-18''. So its kind of in the middle of short/long territory.

Would it help if it was jacked up a bit?

 

[Sea Rider]

Re: 6hp 4 stroke vibration

Would help a bit if the boat is easy to plane at wot, as tail would have slight less drag against water flow, if non planeable, use at it is. If tiller has side's rubber bushings and are compressed, have too much slack, change for new ones as they act as shock/vibration absorvers.

Happy Boating

 

[TOHATSU GURU]

Re: 6hp 4 stroke vibration

Vibration is a relative thing. IE One guy who has one thinks in a vibrator, the next guy can't believe how smooth it is compared to something he had before. Basically all single cylinder engines vibrate. Aluminum hull boats seem to suffer the most. Try using a rubber pad between the engine and the transom to act as a dampener.

 

[simplystressed]

Re: 6hp 4 stroke vibration

Would help a bit if the boat is easy to plane at wot, as tail would have slight less drag against water flow, if non planeable, use at it is. If tiller has side's rubber bushings and are compressed, have too much slack, change for new ones as they act as shock/vibration absorvers.

Happy Boating

Definitely non-planable with the 6hp .

The tiller handle definitely has some play in it, when its fully down if I push on it it flexes considerably. Maybe I'll try and change em out.

 

[simplystressed]

Re: 6hp 4 stroke vibration

Vibration is a relative thing. IE One guy who has one thinks in a vibrator, the next guy can't believe how smooth it is compared to something he had before. Basically all single cylinder engines vibrate. Aluminum hull boats seem to suffer the most. Try using a rubber pad between the engine and the transom to act as a dampener.

Its the higher rpms that are bugging me. From what I'm seeing, I don't think it should be vibrating that much at wot. I realize they do at lower rpms which doesn't bother me so far. I posted the rpm, was wondering if I drop to the 6 pitch if it would help with that?

I tried just steering with the main motor while the 6hp was running, and I could feel the vibration even through the main tiller handle.

I can try the rubber pad and see if that helps at all. Maybe I'll try to get a video and post it up here.

Is there a way to check those rubber bushing on the shaft housing and the tiller handle for wear?

 

[Sea Rider]

Re: 6hp 4 stroke vibration

Is there a way to check those rubber bushing on the shaft housing and the tiller handle for wear?

Place tiller at horizontal position, with engine in forward check lateral play while moving tiller sideways, if excesive dead play, rubber bushings are compressed. Will see more play while moving tiller sideways if wing nut is excesively pressing inside friction plate, If tiller doesn't drop by itself from a vertical to it's working position leave as it is, probably will need to disassemble carb to work properly, remove tiller stopper, throttle cable linkage, lot of work involved.

Happy Boating

 

[simplystressed]

Re: 6hp 4 stroke vibration

Place tiller at horizontal position, with engine in forward check lateral play while moving tiller sideways, if excesive dead play, rubber bushings are compressed. Will see more play while moving tiller sideways if wing nut is excesively pressing inside friction plate, If tiller doesn't drop by itself from a vertical to it's working position leave as it is, probably will need to disassemble carb to work properly, remove tiller stopper, throttle cable linkage, lot of work involved.

Happy Boating

I'll give that a try and report back. What would you suggest for rubber padding for the transom?

 

[simplystressed]

Re: 6hp 4 stroke vibration

I had a chance to go to the marina and check out a new 6hp and inspect the bushings. It seemed much tighter on the new on when I was moving the motor side to side. I did notice that the steering was much harder to turn on the new one. I played with the adjustment screw and it loosened up.

On mine, even when the steering adjustment screw is as tight as it can go, I can move the tiller easily. I suspect this is adding to the vibration and why I can't tighten up the steering.

I took the screw out and there is a washer and spring in there. Everything looked ok.

How can I fix the steering tensioner? Does the band need to be replaced? Is that a warranty item?

Here's a video of my motor shaking the mounts:

Here's a video of the tiller handle:

 

[pvanv]

Re: 6hp 4 stroke vibration

Some idiot has overtightened the steering tensioner and damaged it. It is NOT a steering lock, but a friction control. I would replace the friction parts, and probably do the bushings. The operator error that wrecked the steering tensioner is not a warranty item, but the bushings, if bad, would be. The tiller bushing seems normal. As Elvin noted, the vibration is a relative thing, and yours may not be unusual. Did you test the new 6 hp motor by running it on your boat?

 

[simplystressed]

Re: 6hp 4 stroke vibration

Some idiot has overtightened the steering tensioner and damaged it. It is NOT a steering lock, but a friction control. I would replace the friction parts, and probably do the bushings. The operator error that wrecked the steering tensioner is not a warranty item, but the bushings, if bad, would be. The tiller bushing seems normal. As Elvin noted, the vibration is a relative thing, and yours may not be unusual. Did you test the new 6 hp motor by running it on your boat?

Nope I didn't just looked at it in the store. It wobbled quite a bit also when the steering tensioner was loose. So I'm suspecting if I replace this tensioner and snug it (not overtighten) it should help firm it up.

 

[simplystressed]

Re: 6hp 4 stroke vibration

Some idiot has overtightened the steering tensioner and damaged it. It is NOT a steering lock, but a friction control. I would replace the friction parts, and probably do the bushings. The operator error that wrecked the steering tensioner is not a warranty item, but the bushings, if bad, would be. The tiller bushing seems normal. As Elvin noted, the vibration is a relative thing, and yours may not be unusual. Did you test the new 6 hp motor by running it on your boat?

I took the back housing off and bent back the steering tensioner. As suspected it was too loose. The bushings looked good.

Now the tensioner keeps things in place much, much better.

Also put some rubber sheets between the transom and motor and it has made a big improvement for the vibration! So a combo of fixing the tensioner and adding a bit of cushioning on the transom has made it much more tolerable.

Thanks again for the tips pvanv!

 

[JOSEPHC]

Re: 6hp 4 stroke vibration

As I posted earlier, have same problem with 2002 6hp 4str nissan..excessive vibration especially at low rpm.
One fix that I did seemed to help for secondary vibration and the annoying tick, tick of metal on metal where the thrust rod impacts on the swival bracket is to slip a piece of atomotive fuel hose over the thrust rod. This allows the motor to run alot more quiet but does not help dampen the primary vibration very much.
Would be interested in any ideas for effective rubber pads to use between motor and transom...thanks

 

[TOHATSU GURU]

Re: 6hp 4 stroke vibration

The rubber pads are available commercially from any boat dealer. They are called Moeller Transom Pads.

 

[simplystressed]

Re: 6hp 4 stroke vibration

You could also go to a flooring place and get some strips or higher grade linoleum or fiber floor (thicker/softer). Probably much cheaper than those pads and quite durable. Stack a couple ontop of each other. Check the material out it would probably be pretty cheap for a small sheet.

Of course be certain that it doesn't interfere with ensuring the motor is securely fastened to transom.

I'll check out the thrust rod tip.