Logo
FULL SITE MENU

Vibration

I

insp140

New member
"Hi all, I'm new to this b

"Hi all, I'm new to this board and need some help.I have a 2004 baha 26'er with a merc. 5.7 250hp in/out bravo 3 drive. On a recent outing i noticed a vibration at low speeds, [between 5-10 knots,the whole boat will vibrate]. this vibration will stop at higher speeds. I checked the props and found some small nicks. could these make the boat vibrate? Please help, shaking all over!}"
 
How many hours are on the moto

How many hours are on the motor and outdrive and when was the last time that both were serviced?? I would hit all of the grease fittings and see if it improves.. When lubing the Gimbal bearing Have the engine at idle ( the fitting should be on the side of the transom ).. Also look at the prop and see if it is out of round or if there is a wobble.
 
"the engine and drive are both

"the engine and drive are both professionly maitained and serviced in the spring, april. I don't know the hours because my clock stopped working. I just came back from testing the boat again and the vibrations are also felt when the engine is in neutral. worse vibs are between 1000-1200rpm. could it be a bad spark-plug."
 
"You should have been given se

"You should have been given service receipts that detail what maintenance has been performed. That info. would tell you if the spark plugs have ever been changed. One bad spark plug would cause the engine to shake but w/a V-8, I don't think it would cause the whole boat to shake violently. Prop or shaft damage is more likely the culprit. Have them inspected."
 
"Tom,

You can change the

"Tom,

You can change the plugs and test again but im thinking something along the lines of Gimbal bearing or u-joints, I just had to replace mine the other day and I had about the same symptoms that you do.. I am not sure which one was causing the vibration but I figured while in there I would replace both along with some other stuff that Guy and some other people on this site recommended.."
 
"by the way my vibration would

"by the way my vibration would change when I adjusted the trim, you might want to try that and also turning the wheel.. see if that changes the vibration at all."
 
"Thanks for info, i'm goin

"Thanks for info, i'm going to take your advice and start with the plugs.I'll be back to let you guys how i made out. Tom"
 
"just came from changing plugs

"just came from changing plugs, same vibs, had the mariner pull boat to examine props and shaft. all good. mechanic test drove the boat and determined it may be plug wires or compression in one cylinder. Going back on wednesday to test compression and change wires. will post results, thanks again. Tom"
 
Tom:

How did the old plugs

Tom:

How did the old plugs look as for color? Any individual plug(s) appear different than the others? That may indicate which cylinder(s) were problematic.
 
"It's the props. You'

"It's the props. You're getting cavitation on plane off. For some reason the cavitation will always go away as rpms increase.

Pull the props and get them reconditioned, and the problem will go away.

Jeff

PS: If it was plugs, the problem would INCREASE with engine speed!"
 
"After reading Guy G's rep

"After reading Guy G's reply i went and cheaked the plugs and low and behold one of the plugs looks very clean, like the plugs not firing. I did'nt check the plugs when i pulled them. So my next step is to find out why! I'm going to start by finding that clean plug and testing the wire,{ohms test} and look at the cap. Should be the answer to my problem. Will post my findings. Thank you Guy, you just saved me a trip to the mechanic and $$$$$$. Tom"
 
"Tom;
If you had one plug not

"Tom;
If you had one plug not firing, it would be black and sooty/oily from not firing; not clean.
You don't say if its carbed or EFI, but if it's EFI this could be caused by a bad/dirty or unplugged injector.
Rod"
 
Tom & Rod:

Clean plug;

Tom & Rod:

Clean plug; could the intake valve be not opening? A few years back my B-in-law had a 350 in his new van when the engine started shaking pretty hard but not noisy. Turned out to be a broken pushrod on the intake valve.
 
"My 350 is a carb, all plugs w

"My 350 is a carb, all plugs were black except 1, which was clean, and the way the engine is running, i'm leaning towards Guy's anaylsis. Either a broken pushrod or stuck valve. I gave up and brought the boat to the mechanic. I'm past doing these type of repairs. I will let you know what they found. Tom"
 
"By the way, i put in new plug

"By the way, i put in new plugs, tested the wires and cap, same results. Pulled the plugs again and still one plug was clean. #5cyl. Rod, is it correct to think when you HAVE a black/sooty plug that it is caused by a burn?, and a clean plug from not firing? Tom"
 
"Tom;
Usually when one cyl is

"Tom;
Usually when one cyl is not firing (or occasionally firing) the plug will get black and dirty from the incompletely burned air/gas mixture.
When a plug is firing properly with the correct mixture (not rich, not lean), it will develop a light tan color; but this takes some time to develop. A new set of plugs is not likely to take on any color immediately unless the mixture is way out of whack.
Being as it is carbed, I would have to agree that it could be a collapsed intake lifter, pushrod, or broken rocker arm.
Did you run a compression test?
If #5 has very low compression for some reason that would account for vibration.

Rod"
 
"No on the compression test. I

"No on the compression test. Is it possible then that i have to rich of a mixture,{hence the black/sooty plugs} and that #5cyl. which is clean, is still not firing."
 
"Finally got an answer from th

"Finally got an answer from the marina, 1cyl. had no compression while two other cyl's had low compression [135 psi], all on the same side of engine. They told me the valves were tuliping. They said the gas is probably cauing this to happen, [ethanol}. Are'nt these engines made to run on 10%ethanol? Could anyone explain to me what really is causing this. This engine is still under warranty and it looks like i'm in for a fight! This marina has been servicing this engine, spring/winter. Could this be a warranty issus or could} a bad tune-up cause this to happen? NO BOAT TOM!!"
 
"Call Mercruiser about this. T

"Call Mercruiser about this. Tell them who has been servicing it and ask if the gas can actually do this. Usually, it's from water getting into the cylinder(s), IIRC."
 
Back
Top