Vibration at fast idle.... 2100v

[jciscott]

I am still chasing that pesky vibration.... and found a new symptom.... there is a strong vibration ar 1500 - 1800 RPM in neutral...... what the heck ??

The boat idles super smooth, and runs as strong as ever.... but the whole boat shakes at those RPMs in neutral.... so... what all is spinning on the back end of the motor ??

Is the flywheel bolted to a shaft that goes into the transmission.... or is there some kind of a torque converter ??
What could be out of ballance on the back side of the motor ??

[spharis]

No converter. Did you pull plugs to see if any are starting to foul? Maybe you aren't getting spark.

[jciscott]

Planning on plug replacement.....

Thanks for the reply.... I had the plugs out early this sping ... they are not horrible, but probably should be replaced..... I was thinking of using a Platnium plug.... I think they old ones were RS12YC... Any thoughts ??

[dogbert]

My plugs and wires got replaced at 400 hrs. It could also be that you have a bad sparkplug wire. Also, check the distributor cap. Last time I had this issue, my distributor cap was toast.

[jciscott]

Marine cap & rotor... or Standard Chevy ??

Dogbert....
did you buy standard chevy or maring cap, rotor and wires ??
You say you had similar symptom.... was it smooth at idle, and still had plenty of power ??? I would have thought idle would have been rough... but most of my mechancial experience is on British sports Cars.... not a lot of V8 wrenching experience....

My water pump impeller had a catostrphic failure on Friday night... I did not replace it this spring, and it BLEW UP on Friday.... $30 at the Marina, and they had it in stock... WOW
I did the replacement in the water, what a pain the butt without good tools.... 10 min at home with air wrench, 1 1/2hours at the river.... oh well... next year we do a new one with the spring oil change......

[spharis]

You can use auto plugs and wires, but the engine manf. usually has a recommendation for the plugs. I usually get components from a 96 Camaro/Tahoe with a 5.7; it is going to depend on your engine though. O'reilly usually has the Marine ignition components. skidim.com carries tune up parts and ships quick too.

[dogbert]

Dogbert....
did you buy standard chevy or maring cap, rotor and wires ??
You say you had similar symptom.... was it smooth at idle, and still had plenty of power ??? I would have thought idle would have been rough... but most of my mechancial experience is on British sports Cars.... not a lot of V8 wrenching experience....

My water pump impeller had a catostrphic failure on Friday night... I did not replace it this spring, and it BLEW UP on Friday.... $30 at the Marina, and they had it in stock... WOW
I did the replacement in the water, what a pain the butt without good tools.... 10 min at home with air wrench, 1 1/2hours at the river.... oh well... next year we do a new one with the spring oil change......

My dealer did mine both times. The wires were part of a 400hr service package. I wanted them to do the once over. The distributor cap got replaced when it started running rough. It was under warranty at the time, but it looked pretty bad inside.

[jciscott]

did the tune-up....

I did the plugs, cap, rotor and wires.... it is smoother but still kinda shakes at 1600- 1800 RPM....
Based on the threads elsewhere, it sounds like this just may be normal.....

[dogbert]

You might want to check your prop next. If it has dings, then that's a possibility. So is a mis-aligned shaft.

[jciscott]

vibration

new acme 3 blade last year...... new strut..... checked shaft for straightness...

What I am puzzled about is the vibration in neutral..... at 1600 - 1800 RPM...
What is spinning that could be out of ballance....

[chpthril]

new acme 3 blade last year...... new strut..... checked shaft for straightness...

What I am puzzled about is the vibration in neutral..... at 1600 - 1800 RPM...
What is spinning that could be out of ballance....

There is some form of a coupler that links the crankshaft to the input shaft of the trans.

I know what the look like on an I/O and they can go bad. Dont know on and inboard.

[dogbert]

new acme 3 blade last year...... new strut..... checked shaft for straightness...

What I am puzzled about is the vibration in neutral..... at 1600 - 1800 RPM...
What is spinning that could be out of ballance....

Ok, I'm not sure how significant the vibration is, but every engine has a RPM range where harmonics will cause it to vibrate a little more. It's accentuated by the fact that the vibration is broadcast throughout the boat.

How bad is it?

[jciscott]

since the tune-up, it is much better, I am going to go with the natural harmonic thing... The big vibration under acceleration with heavy load is GONE with the new strut....... I put 12 hours on the boat last week... all is working good.....
We just crossed the 500 Hr mark... not bad in a PA boat.......
We have our big boating vacation coming up at Deep Creek Lake in MD... that will be the test... 5-6 hours per day for 7 days....