Vibration when underway

[Glasplyer]

Haven't had this boat long. Posted another question about my sterndrive. Sorry to be redundant. Wanted to post this different under a different subject.

When idling this 302 sounds great! Everyone that has witnessed this gem comments about how good the engine sounds. Smooth and strong. Does just fine at 3 -5 mph (heading out of the boat haven...no wave zone)...then went i accelerate ...you can feel vibration...not enough to shake anything off the table...but a perceptible vibration. I am wanting to pull my sterndrive and look at the ujoint or ??? any thoughts. I'm not particularly mechanically adept but want to correct the problem before it becomes major.

 

[180shabah]

Re: Vibration when underway

Anything that spins is a possibility. What does the prop look like? chunks missing? dinged or bent blades?

 

[chiefalen]

Re: Vibration when underway

You got the dog house open/off, does the motor shake, sound different?

Your motor getting hot at the same time?

What else is going on with the gauges, oil pressure change, temp gauge going up, rpm's are at what?

What year is this boat?

It''s a 8 cylinder?

You smell anything burning, hear anything whining?

 

[Glasplyer]

Re: Vibration when underway

Anything that spins is a possibility. What does the prop look like? chunks missing? dinged or bent blades?

The blades actually look pretty good. It is aluminum and some paint chipped but the blades do not look too bad.

 

[Don S]

Re: Vibration when underway

If you just got the boat and haven't had the drive off yet, it's time.
Check the gimbal bearing, ujoints, and alignment. There should be no water or heavy rust inside the bellows. Bent prop shaft or a tweaked blade on the prop sill also do it. You can't always see a bad prop, have it checked.

 

[Glasplyer]

Re: Vibration when underway

You got the dog house open/off, does the motor shake, sound different?

Your motor getting hot at the same time?

What else is going on with the gauges, oil pressure change, temp gauge going up, rpm's are at what?

What year is this boat?

It''s a 8 cylinder?

You smell anything burning, hear anything whining?

Engine runs remarkably cool...at 3000rpm....when i get her to sea the temp runs up to 200F you can see the thermostat open up...it drops to a steady 150F. Oil pressure runs at about 70 lbs gauge shows 80 lbs max.

The engine is a 302 mercruiser model 888 in a 1975 21 ft glasply.

No smells mothing burning no whining. It is pretty noisy revd up...but the doghouse is sorely missing insulation. Nothing but what i would call normal engine...friends (several) have said it really sounds good for as old as it is.



Oil pressure

 

[Glasplyer]

Re: Vibration when underway

If you just got the boat and haven't had the drive off yet, it's time.
Check the gimbal bearing, ujoints, and alignment. There should be no water or heavy rust inside the bellows. Bent prop shaft or a tweaked blade on the prop sill also do it. You can't always see a bad prop, have it checked.

Thanks for the input. Was hoping i wouldn't have to go that far...i'm an old hospital and school administrator...not too mechanically adept but am not above giving it a try. Have been looking for a manual that would give me explicit insts (a 'how to') and have purchased a Clymer. It gives general information but not specific and not sure which sterndrive i have. Here are some pics...could you give me some idea? This is a 1975 mercruiser model 888 Glasply (mentioned and engine picd above). Don't know if it is a mercruiser one or ????

 

[chiefalen]

Re: Vibration when underway

Alright see why i asked about the temp, and gauges.

Don't run it anymore.

Change out the impeller. Change out the t-stat.

Than run it. If it goes anywhere near 200 again shut it down.

I'll bet you have a bad impeller and i hope thats all it is.

post after you do those 2 things how it runs.

 

[Don S]

Re: Vibration when underway

Here is a link where you can download the oem manual. It's 1 GB (not MB) so give it an hour or so to download. Depending you your ISP abilities.
http://www-alt.mercurymarine.com/mnetdata/SERVICE/CRUISER/Servmanl/02/cover.pdf

If that isn't step by step enough, then you need to find a mechanic. Boats may be toys, but they are also mechanical things that get dipped in the water and need maintenance.

 

[chiefalen]

Re: Vibration when underway

Doesn't it say mercury right on the motor, i see it in your pic.

 

[ringmaster]

Re: Vibration when underway

take a look at the prop pic agian. it looks like the prop isnt all the way on. the nut isnt frar enough on the shaft.

 

[bolo78910]

Re: Vibration when underway

take a look at the prop pic agian. it looks like the prop isnt all the way on. the nut isnt frar enough on the shaft.

good catch that prop ie way off shouldn't be that much space . loose prop or the wrong prop, that could be your vibrating problem,

 

[ringmaster]

Re: Vibration when underway

for some reason that was the first thing that poped out to me. maybe cause i always check mine before i take it out.

 

[Glasplyer]

Re: Vibration when underway

Doesn't it say mercury right on the motor, i see it in your pic.

ayup...says mercruiser on the engine...

 

[Glasplyer]

Re: Vibration when underway

take a look at the prop pic agian. it looks like the prop isnt all the way on. the nut isnt frar enough on the shaft.

Good eye! I did take the nut loose in an attempt to take the prop off. Wanted to identify by sn or ???. When at sea....the boat does terrible. At 3000 RPM we are barely doing 10 mPH (confirmed by GPS). So wanted to check pitch and work on that problem as well!

Any thoughts on a prop puller...i am hesitant to buy one for upwards of hundreds of $$$$$! Do not have a torch to heat. This prop was not taken off by the previous owner (obviously) in years! Wanted to grease the spline and shafts as part of my winterizing as well.

Thanks for your input!

 

[chiefalen]

Re: Vibration when underway

Sir: that is a good setup motor and out drive wise.

However as with anything, age can and will require, that the motor and drive be serviced bye experts.

You are very fortunate to be near one in WA.

If i were in you shoes and near him i would contact him.

Don S would be one of a very few that i would let work on any of my stuff.

Don't know how mush it would cost, but at least you would know that it was done right.

I wish you luck, in all your endeavors.

 

[JustJason]

Re: Vibration when underway

you don't need a prop puller..... all you need is a wrench, a hammer..... and a 2X4.....
leave the drive in neutral. wedge the 2X4 in between the prop and the gearcase, and you'll be able to get the nut off that way. (or if you have the tool... I just use my impact. both of my cordless ones have enough guts to spin it)
after you get the nut off.... if you can't just pull the prop by hand, well put the 2X4 behind the prop and start hammering. start with the wood on 1 vane of the prop and give it a thwack, then move it to another vane..... so on, and so forth.
you still should pull the drive as per Don's advice. But the drive will be easier to pull and reinstall with the prop off.

 

[Haut Medoc]

Re: Vibration when underway

I prefer to put some thing under the prop to get the prop nut off, but you can wedge a piece of wood, once you have the nut off, tilt the drive up & spray some kroil or PB blaster down into the splines & let it soak for a bit, over night if possible.....
Then do what Jason says to remove it....
I coat the splines with anti-sieze.....
I have the exact same 888 set-up, even the heater.....
You really should pull the prop & have it checked & pull the drive to check the ujoints & gimbal bearing as well as check alignment as Don S suggests....
I run a 14.25 x 17 stainless.....
Too bad you aren't a little closer, I'd have it up & running in no time.....

 

[Glasplyer]

Re: Vibration when underway

Excellent advice. Think i'll go ahead and get that prop off and perhaps get a better one. But as you and Haut Medoc suggest...i'll get someone that knows what they are doing to pull and check the joints, alignment, etc.

I think you are all on to something. The nut on the prop was actually (in my opinion, too loose) easy to remove. When pulling on the prop to see how loose it might be on the splines i felt some play (although the prop was 'froze' on the splines). Could be that it was never (years ago?) tightened to torque specs. You would think that would cause some vibration...particularly at higher speeds with that prop turning more rapidly. As mentioned earlier, you do not feel the vibration at idle...or in neutral.

Thanks again for the help!

 

[180shabah]

Re: Vibration when underway

Loose prop will absolutely cause vibration.