454 bad vibration 1800rpm at dock

[454 boater]

please help 1990 36ft boat twin 454 d drive port 7.4 just got put in new last year grooms engines runs great will plain perfect however 4 guys have looked at it no one knows??
here is what it is doing ONLY AT DOCK NOT IN GEAR it starts vibrating at 1800 bad real BAD going away at 2000rpm and almost gone at 2200 runs great.. please help

[454 boater]

also meant to tell you all new plugs wires, cap , brand new carb, motor mounts look to be ok not loose..this boat drives great out on the water both motors run out great it's just that port motor vibration out of gear so we all know its not in shaft or trans, prop,, I would say we could rule those things out

[Stripermann2]

Hmmm. It's possible you have a balancer issue or flywheel issue. Perhaps under a load with tranny in gear, the vibration is compensated or lessened by the load.

[454 boater]

well i'm with you on that idea..
I changed the h bal.. on the front vibration still there
however the flywheel and f plate just came right off the old motor and right onto the new motor all in the boat day of install ?? I
was thinking if it was flywheel it would get worst and not go away in higher rpms. am I wrong?

[454 boater]

i'm sorry for adding but I did want to say the vibration is there even in gear at 1800rpms I just said out of gear at dock so I didn't get a lot of people to say oh your props or shaft. lol
it is the same in gear or out of gear 1800 bad bad vibration

[mikeandanne]

Is there some way to see the flex plate and fly wheel----sounds like a weight may have come off or the bolts are not torqued right--these engines are externally balanced so the plate and flywheel have to be keyed correctly--have a look if you can----this assuming the engine is timed and tuned ok----I believe you are always spinning the trans input shaft when engine is running so that could be something to look at---someone can correct me with that but just some ideas of where I would look---Mike

[k9th]

I was thinking if it was flywheel it would get worst and not go away in higher rpms. am I wrong?

With vibrations of any sort (which are basically objects oscillating at a certain frequency) you are dealing also with harmonics, which are basically points where the pattern will repeat the behavior. It will not necessarily get worse at higher RPM, depending on the wave length of the frequency, and may go away altogether until you hit the next harmonic frequency. If you knew the frequency, you could calculate the harmonics very precisely and determine where that will be.

[mikeandanne]

one more thing to add to my previous post---was the dowel pin in the crank when you installed the plate and wheel and are those parts from the same gen 454---keep in mind that you can do serious internal damage to an engine that is out of balance,for e.g..bearings,broken cranks etc----probably not what you want to hear---Mike

[454 boater]

wow a lot to take in the pin thing or dowel is some thing I can't say I remember where would it be at

also yes I can very easy get to the flywheel I could check them bolts
update today I re checked timing with two diff,,, timing guns and both said 8 bftd and the motor went to 4200 rpms like nothing ran great just that vibration at 1800

[rbcool]

Exhaust valve getting ready to implode!
RB