1979 5.7 mercruiser bad vibration when running

[Blujay96]

Ok so for starters this is a 1979 slickcraft. When I bought to boat it had no motor in it. The motor I have is out of a 1979 truck. It came with the external pars of the motor, such as manafolds, intake, carb, mounts, flywheel, etc. I got everything hooked up on th motor. The outdrive is off of the boat right now. I hooked water up to the inlet and got the motor started today. The problem is there is a bad vibration that get worse the higher rpm is. The motor has new plugs, wires. What could be some things to check on. One of my friends thinks it could be I fouled the plugs getting it started. What are your guys thoughts. Thanks for the help.

 

[HT32BSX115]

Re: 1979 5.7 mercruiser bad vibration when running

Ok so for starters this is a 1979 slickcraft. When I bought to boat it had no motor in it. The motor I have is out of a 1979 truck. It came with the external pars of the motor, such as manafolds, intake, carb, mounts, flywheel, etc. I got everything hooked up on th motor. The outdrive is off of the boat right now. I hooked water up to the inlet and got the motor started today. The problem is there is a bad vibration that get worse the higher rpm is. The motor has new plugs, wires. What could be some things to check on. One of my friends thinks it could be I fouled the plugs getting it started. What are your guys thoughts. Thanks for the help.

Howdy,


Well, since you have the drive off, I would say that yes, it might be a fouled plug or 2, or maybe you have a couple of plug wires switched.

 

[86 century]

Re: 1979 5.7 mercruiser bad vibration when running

The one thing that comes to mind is are you sure it is a 350.
On the off hand chance its a 400 when you put the neutral balance flywheel on from the stock eng you put her out of balance.

 

[Blujay96]

Re: 1979 5.7 mercruiser bad vibration when running

I will check the wires and replace the plugs. The casting numbers called it out to be a 350.

 

[86 century]

Re: 1979 5.7 mercruiser bad vibration when running

It still possible it has a 400 crank if it was made into a 383.
Have someone check the old flywheel or flex plate.

 

[Bondo]

Re: 1979 5.7 mercruiser bad vibration when running

Ok so for starters this is a 1979 slickcraft. When I bought to boat it had no motor in it. The motor I have is out of a 1979 truck. It came with the external pars of the motor, such as manafolds, intake, carb, mounts, flywheel, etc. I got everything hooked up on th motor. The outdrive is off of the boat right now. I hooked water up to the inlet and got the motor started today. The problem is there is a bad vibration that get worse the higher rpm is. The motor has new plugs, wires. What could be some things to check on. One of my friends thinks it could be I fouled the plugs getting it started. What are your guys thoughts. Thanks for the help.

Ayuh,.... My 1st guesses are, the firin' order, is outa order, or it's got a dead cylinder, 'n it's skippin'...