Vibration Increases with RPM 454 Mag MPI based 468
 

Hey everyone!

I have one that is stumping me.

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Excalibur 27x7
454 Mag MPI based 468
Merctrans
TRS Drive

I picked up a boat and noticed it has a vibration, during sea trials I expected it to be the u joint going to the drive.

I got it home and realized that the vibration is NOT in the drive. So I started by checking out the engine out, making sure that the timing was not off, making sure that I was firing on all cyl., etc. engine is running well and is pretty smooth at idle for a choppy cam.

What I have is a vibration that gets worse with speed through 3000 RPMs, literally rattling the floor. Way worse than say a race car with solid motor mounts.

Correct me if I am wrong, all 454s are externally balanced? That means that the proper flywheel must be used otherwise we will have issues.

Before I rip the drive, engine, and gear out to verify this, is there anything else I could check? Any of you all run into this problem before?

Thanks!

Flywheel and damper should be weighted

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I would probably first get an alignment tool and pull the drive and check it out.....
Actually i would first check the motor mounts to make sure its all tight...then check alignment. Then check the U-joint on the drive... If neither of those figure it out then start looking at motor parts like the flywheel or harmonic balancer etc..
Have you also checked for bent blades on the prop?

Check the prop shaft to see if it's bent.

Thanks for your thoughts. I've checked the mounts, and will do so again. I at first suspected it was the u-joint when I sea trialed the boat, however with the Merctrans and TRS drive the u-joint is not spinning when in neutral. hence why I am leaning towards balancer and flywheel. Boat in neutral, prop NOT spinning, (drive has no moving parts in it) rev it up and the vibration gets worse. Hence my thoughts on the flywheel and balancer. I just wanted to check myself before I start pulling things. Do the driveplates come apart and cause vibration?

Thanks all!

Sorry, for some reason it didn't register in my head when i read your post! MY bad....yeah i think unfortunately you need to investigate the balancer and flywheel for sure. I cant think of anything else that would make it shake that bad other then someone stabbing in a replacement piston/rod combo that's WAY off in weight compared to what came out...

Years ago I had the balance ring move on a balancer once. It started one weekend when I noticed a slight vibration, but wasn't weekend ending type vibration. I forgot about it and the next time I took it out, it got worse. On my shifter trim, I noticed screws (that were loose in the holes anyway) backing out on their own. Taking a wild guess, I pulled the balancer and compared it to one I had laying around. The timing mark was off.
I read somewhere if the balancer was in front of a leaking crank seal the oil will swell the rubber and cause ring movement. I'm my case it wasn't leaking or oily, but I had no idea on the history of the motor or it's balancer. The rubber did look weird though.
Made me cringe to think what the crank was feeling a 3500.... lol

Balancer is a quick easy check, I'll pull it and see!

You should not have to pull it to see. Big Block dampers are notoriously a very hard press fit onto the crankshaft and you might get into more trouble than you think by pulling it.

Stupid question but have you asked the previous owner about it ?? If nothing else maybe just verify that it has been that way for a while or if something else was changed that might have caused the problem.

What does it do if you go past 3000 rpm ??

With the different ages/generations of the boat and motor...I would check part numbers on balancer and flywheel.
Along with the separation/slippage like mentioned on the balancer.
Wonder if older parts on newer engine are not matching correctly.
My first WILD guess...
good luck