Small vibration, rattling noise. Any ideas?

[ckraker]

Working on a 99 4.3. Just got it last fall. I have already done a TON of work on the engine a including head gaskets. I just replaced the raw water pump. I've had the lower unit off several times working on various things. I bought an alignment tool to ensure a good alignment. I think I'm almost sea Worthy.... But i can't seem to figure out a vibration that is quite evident at idle. I even hear some rattling that seems like it's coming from the rear of the engine. I would have guessed that it was the gimbal bearing but, when i had it apart the bearing seemed ok to me. Any thoughts on what else it might be? Motor mount bolts are all tight. Thanks all!

 

[GA_Boater]

Probably the shutters making their normal noise. Does it go away as revs are increased?

 

[ckraker]

Well.......i know that's not the case. There are no shutters installed. But the vibration does go away under load.

 

[achris]

Well.......i know that's not the case. There are no shutters installed.

Suggest you get some installed, lest you want an engine with a belly full of seawater.

But the vibration does go away under load.

Pull the drive, stuff a hose up the water inlet on the bell housing and see if the vibration is gone. If it is, then it's the gimbal bearing, unis, or something in the drive. If the vibration is still there, I'd first be looking for those missing shutters, then think about a loose flywheel or engine coupler...

Chris........

 

[ckraker]

Coupler . The motor might have to come out again. Is there a way that i can check the coupler without taking anything apart? I hate assuming.

 

[QBhoy]

How are the UJ’s ?

 

[achris]

Coupler . The motor might have to come out again. Is there a way that i can check the coupler without taking anything apart? I hate assuming.

If you have the space, and can get your hand down there. Pull the drive and then see if you can move the coupler by hand. (Just because you can't doesn't mean it's not the problem. )

Pulling the engine's no big deal, and if you do find that the vibration is still there with the drive off, then it's a sure bet the engine will need to come out anyway... But do the test first, drive off, hose in the bell housing, start her up...

Chris........

 

[ckraker]

How are the UJ’s ?

Joints were both replaced when i had it apart.

 

[ckraker]

If you have the space, and can get your hand down there. Pull the drive and then see if you can move the coupler by hand. (Just because you can't doesn't mean it's not the problem. )

Pulling the engine's no big deal, and if you do find that the vibration is still there with the drive off, then it's a sure bet the engine will need to come out anyway... But do the test first, drive off, hose in the bell housing, start her up...

Chris........

Will do. Can't believe i didn't even think to look at the coupler with the engine out!

 

[QBhoy]

Is this on the trailer running on the hose just or does it also happen in the water ?

 

[ckraker]

Both, why? What you thinking it could be?

 

[TunaFish389]

I have a few rattles.. Found the board under top of transom (where the fold back seats/engine cover screw down) to be loose on outer edges.. I can put my hand under there and stop the noise. It was concerning but now I will fix eventually.

 

[tank1949]

Your boat is around 20 years old. It my have wood rot causing sagging in the mounting. Hammer on the inside of transom and listen for hollow sound. Don't pay a marine surveyor. Do it yourself! With muffs on, have a friend increase throttle and watch and see if any of the 4 motor mounts move. That motor shoudn't move if mounts are tight. Are the rocker arms making noise? You may not have adjusted them correctly or they need adjustment (20 years old?) See if pullies on front of motor move of shake. If you can gain access, examine bellhousing lower inspection plate to determine if you have loose bolts. May need a mirror on long pole. If loose they will rattle. With OD off, check gimbal bearings and u-joints. Gimbal bearing should NOT move inside its keeper or retainer. Then check alignment. Have a friend bump starter (w/o power to ignition) so that flywheel has rotated 180 degrees. Now check alignment again. If loose coupler or flywheel the alignment tool should not fit easily. Good luck!

 

[ckraker]

I keep hearing about loose flywheels..... Is that a common issue with these. The mounts and transom are very solid so i don't think that is an issue. "Gimbal bearing should not move"..... Now we are onto something. With my alignment tool installed i could move the tool up down or left right with some persuasion. Is that not normal??

 

[achris]

.... "Gimbal bearing should not move"..... Now we are onto something. With my alignment tool installed i could move the tool up down or left right with some persuasion. Is that not normal??

Normal if the tool isn't pushed all the way in and is outside the coupler. Have a look at a video I did called 'Understanding gimbal bearings', or something like that. Links to my videos at the bottom of my signature.

Chris...........

 

[ckraker]

Chris... Thanks a ton. That video was awesome. Wish there were more people like you posting things!!!

 

[QBhoy]

Both, why? What you thinking it could be?

Was wondering if it only happens in gear ? If so perhaps the prop.

Other slight thought I had was a cylinder not firing right ?

 

[QBhoy]

Both, why? What you thinking it could be?

Just remembered also why I asked. It was if the drive was perhaps tilted up when the vibration happens.

 

[ckraker]

In neutral. So prop is not the issue.
it happens with trim all the way down, too. Could be a cylinder misfire....

 

[QBhoy]

In neutral. So prop is not the issue.
it happens with trim all the way down, too. Could be a cylinder misfire....

Yeah. Maybe worth having a look at ignition and fuel system. Could be lucky. Good luck.