Vibrating chair effect - Merc 140 - SOLVED. THANKS...

[fishnfiend]

Update - Thanks to Don S., Rodbolt and Bondo, I found the likely culprit for this problem. Both U-joint crosses had washboard wear on at least two of the posts. New U-joints going in. Gentlemen, you saved me $$ and headaches. Thank you.


Original problem:
1986 Mercruiser 140. Motor runs great at all rpms. Gimble bearing is smooth. Coupler splines are well greased and seem tight. Ujoints rattle slightly in sharp turns on the muffs, but seem OK for now. Motor does not seem to vibrate more than expected.<br /><br />The problem is that it seems that every vibration of the energetic 4 banger gets transmitted directly to the boat. You can feel the thing run through the floor and in your butt in the seat.<br /><br />It seems that the motor mounts are not doing any insulating of the natural vibration coming from the inline 4 (haven't seen one yet that doesn't vibrate some...). <br /><br /> Has anyone replaced the rubber bushings in front and rear mounts, and did it make a difference? <br /><br /> Second question, does a person have to pull the motor to replace the rear mounts? <br /><br />Found this info on Aftermarket.com about rear motor mounts on the Mercruiser 3.0:<br /><br />3) The rubber mounts are pressed into th bell housing (flywheel cover) of the Mercruiser and are the live rubber insulation for vibration in the motor transmitting into the boat. <br /><br />4) If the rubber fails in the motor mount, the motor will fall onto the mounting tabs which pertrude forward from the inner transom plate on the transom and the entire boat would feel like a vibrateing chair .<br /><br /><br />Thanks for any information. This board is most awsome for covering topics not addressed in the manuals (I have both factory and Seloc).

 

[Don S]

Re: Vibrating chair effect - Merc 140

Re: Vibrating chair effect - Merc 140

The rubber mounts are probably not the cause of your vibration. That would be either an ugly prop, bad gimbal bearin, bad ujoints, or bent prop shaft.<br />My first thoughts would be to pull the drive and check for water in the ujoint bellows which will destroy ujoints, and gimbal bearings.

 

[fishnfiend]

Re: Vibrating chair effect - Merc 140

Re: Vibrating chair effect - Merc 140

Thanks for responding, Don. Brand new prop. Prop shaft spins true. Gimble bearing has no rough spots, turns smooth. Engine alignment checked out OK. U joints are a maybe, but the sensation in the boat seems very much engine-related - you feel every rev. It feels like the motor is hard welded to the hull. <br /><br />I do have new u-joints that I will install soon. Had the drive off last weekend - unjoints were dry and pretty loosie goosie but seemed intact - no sign of water intrusion fortunately.

 

[Don S]

Re: Vibrating chair effect - Merc 140

Re: Vibrating chair effect - Merc 140

If the ujoints are real loose feeling but still feel smooth, I would bet they are bad. They have fooled me more times than I want to admit to.<br />When you take them apart, I would bet you find grooves from the needle bearings in a couple of the bearings.<br />Let us know what you find.

 

[rodbolt]

Re: Vibrating chair effect - Merc 140

Re: Vibrating chair effect - Merc 140

I am with DonS<br /> pop them apart and see if they have washboard marks on the cross's.<br /> if not you may have mount issues but with the 4 banger its rare unlesss the front mount stringer is getting soft.

 

[Bondo]

Re: Vibrating chair effect - Merc 140

Re: Vibrating chair effect - Merc 140

Engine alignment checked out OK.

If the rear motor mounts were Bad,..........<br />The Alignment would be Way Off,........<br /><br />Change your U-Joints............

 

[fishnfiend]

Re: Vibrating chair effect - Merc 140

Re: Vibrating chair effect - Merc 140

U-joints will be my next attack, then. I probably did misread them. They certainly are loose. Hope to tear into them this weekend. Will report back with results (though have to take a trip and may not get back on the water for awhile.). <br /><br />Phoenix summers turn rubber into charcoal. One of the first things I do with a used (land) vehicle is go through and replace all of the heat-cooked rubber. Maybe the Mercruiser rubber mount bushings are small enough and enclosed enough so they're not affected as much. In any event, if the experienced ones say u-joints are more likely, then I'll definitely start there.<br /><br />The front stringer seems solid enough. When I bought the boat though, the lag screws holding the motor mount to the stringer had stripped out and were completely loose (previous owner had tried to tighten them by adding popsicle sticks into the holes). I swapped the screws out for bolts with washers and locknuts and cinched them down good. They are tight now.<br /><br />Thanks gentlemen. I'll post results of ujoint inspection this weekend.

 

[fishnfiend]

Re: Vibrating chair effect - Merc 140 - SOLVED. THANKS...

U-joints definitely worn. New ones going in. Thanks Don S., Rodbolt, and Bondo.