454 vibrating and breaking starter bolts

[Trevordakid]

I have a stingray 698zp with a rebuilt 454 in it with low hours. When I accelerate and as the rpm’s come down it vibrates at 2300rpm-3000rpm and then it seems to smooth out. It is also breaking starter bolts. I can get about 5 starts on new bolts before it breaks them again. It will also vibrate in neutral. Any feedback or information would be greatly appreciated.

 

[Scott Danforth]

The vibration is something seriously out of balance

The bolts breaking is most likely a result the weight of the starter if you have a direct drive starter and your vibration or you have 2 plug wires swapped

Who did the rebuild?
Whas the motor aligned properly when the motor was replaced?
Stock rebuild balance or did you pay for a balance job?
New damper or original reused?
New coupler or original reused?
Have you verified the firing order?
Have you done a power balance test?

Even a stock 454 should run smooth enough to balance a coin on edge in top of the motor. If you have a vibration as bad as you state, you have an issue

 

[Lou C]

The starter bolts can break if they are the wrong length (too long) and the old direct drive starters usually had a brace on the front to stabilize it. The bolts you use must match whatever starter you are using.

 

[Trevordakid]

The vibration is something seriously out of balance

The bolts breaking is most likely a result the weight of the starter if you have a direct drive starter and your vibration or you have 2 plug wires swapped

Who did the rebuild?
Whas the motor aligned properly when the motor was replaced?
Stock rebuild balance or did you pay for a balance job?
New damper or original reused?
New coupler or original reused?
Have you verified the firing order?
Have you done a power balance test?

Even a stock 454 should run smooth enough to balance a coin on edge in top of the motor. If you have a vibration as bad as you state, you have an issue

Awesome I’ll double check all of those tomorrow!!! The rebuild was professionally done by a shop.I believe it is original dampener and reused coupler. I pulled the motor and took the fly wheel off and noticed it was a little warped but I’m not sure if it’s enough to cause harm. I’ll post a pic.

 

[Trevordakid]

The starter bolts can break if they are the wrong length (too long) and the old direct drive starters usually had a brace on the front to stabilize it. The bolts you use must match whatever starter you are using.

Thank you for the input I ordered that starter bracket.

 

[Lou C]

If Merc doesn’t sell it any longer check Summit Racing or Jegs
It’s actually a GM part

 

[Scott Danforth]

Awesome I’ll double check all of those tomorrow!!! The rebuild was professionally done by a shop.I believe it is original dampener and reused coupler. I pulled the motor and took the fly wheel off and noticed it was a little warped but I’m not sure if it’s enough to cause harm. I’ll post a pic.

look at your receipt. what did you pay for? a balance job is an additional $700+ charge

regarding your damper. use a piston stop and a degree wheel. verify that the damper ring hasnt slipped.

the flywheel ring gear is fine. you would not feel that dent. if it bothers you, get a new ring gear from your local parts store and swap it.

who did the installation? and was the motor aligned properly? hint: if the drive was left on, it wasnt aligned

 

[Trevordakid]

look at your receipt. what did you pay for? a balance job is an additional $700+ charge

regarding your damper. use a piston stop and a degree wheel. verify that the damper ring hasnt slipped.

the flywheel ring gear is fine. you would not feel that dent. if it bothers you, get a new ring gear from your local parts store and swap it.

who did the installation? and was the motor aligned properly? hint: if the drive was left on, it wasnt aligned

Allison marine service. The motor was actually just a motor swap 88-97 454 motor. Gonna put the motor back in today without the outdrive on and start it to see if the shaking stops.

 

[Scott Danforth]

the pre 90 motor is a Mark IV block with 2-piece RMS
the 1996 and later motor is a Gen VI motor with a 2-piece RMS

you should have gotten a new damper with the gen VI motor.

 

[flashback]

the pre 90 motor is a Mark IV block with 2-piece RMS
the 1996 and later motor is a Gen VI motor with a 2-piece RMS

you should have gotten a new damper with the gen VI motor.

Just curious, but why is the damper different?

 

[Scott Danforth]

Just curious, but why is the damper different?

timing marks in different locations

 

[alldodge]

Allison marine service. The motor was actually just a motor swap 88-97 454 motor. Gonna put the motor back in today without the outdrive on and start it to see if the shaking stops.

My guess you need a different flywheel and that's where the vibration is coming from

 

[Trevordakid]

My guess you need a different flywheel and that's where the vibration is coming from

Motor was running smooth when I got it back but after about 50hrs it started vibrating. I put the flywheel back on and am putting the motor back in the boat and gonna get a different dampener.

 

[Lou C]

If it was smooth when you got it back think of what could have changed…could there be an engine miss, cracked distributor cap, high tension lead with too much resistance etc. First I’d go thru it like auto shop 101 tune up…The balancer slipping is possible but not super likely…

 

[Trevordakid]

If it was smooth when you got it back think of what could have changed…could there be an engine miss, cracked distributor cap, high tension lead with too much resistance etc. First I’d go thru it like auto shop 101 tune up…The balancer slipping is possible but not super likely…

Sweet thank you. I’ll go through everything tomorrow and see if anything pops up I will keep y’all updated with what I find. I appreciate everyone help very much!!!

 

[stresspoint]

guessing you have a miss fire , possibly a lead , plug or dizzy cap, starters can struggle when trying to crank when a cylinder is not firing.

 

[tank1949]

Thank you for the input I ordered that starter bracket.

MC have very strong motor mounts that do not allow vibrations to be seen unless something is very bad. I suggest pulling plug wire and listening to drop in RPMs. Just an idea...

 

[Trevordakid]

Sooooo after further investigation. I believe that someone may have switched the balancer on the left with the one on the right.

 

[Trevordakid]

I got a 454 gm mercruiser or whatever u call it. Older model Mark IV 454 I believe. I bought recently and it has been shaking around 3500 rpm. I have looked at the harmonic balancer and noticed it does not have a weight on the inside. Do all 454s have weights in the harmonic balancer. Picture on the left is what I have on it now and the picture on the right is what I’m referring to. Could this be the cause of the vibration? Any feedback helps

 

[kenny nunez]

The un counter weighted balancer is probably from a small block engine that are internally balanced. A good thing that you found the problem.
I had that exact engine and I remember the balancer along with the countered flywheel.