Volvo penta 5.7gsi engine vibrations at idle while in neutral

[Rick910]

Recently had a new engine installed. While during the last 10 hours of break-in my engine started vibrating at idle while in neutral. This vibration was not present during first 10 hours of break-in. You can feel the vibration throughout entire boat. Engine performs great otherwise. I installed aluminum 15.5x17 prop and at WOT its running about 4800-4850 RPM. The shop that installed it says thats normal for a big V8. all i know is that it did not do it initially.

 

[Scott Danforth]

welcome aboard

what year motor?

did you check plugs, do a balance test? if you have a dead cylinder it will show up more at idle.

 

[Rick910]

It's a 2001. New plugs. What's a balance test. This is a brand new motor. If it had a bad spark plug (dead cylinder) would it still perform at WOT? The intake manifold and carburetor are original.

 

[alldodge]

The shop that installed it says thats normal for a big V8.

Sorry to hear for you, but the guy that said that is either stupid or doesn't want anything to come back so they have to fix it. Something is either loose, bent or misfiring. Suggest start with the simple stuff. While the boat is idling, start pulling plug wires off one at a time and see if things change. If one is pulled and it doesn't change then that's the plug.

And a 5.7 isn't considered big, its a small block

 

[Maclin]

It could be some other component related to engine install, like coupler alignment, gimbal bearing condition, between the engine and the drive, and took a while to show up after the engine install.

 

[Maclin]

Oh yeah, and this is a truly insane thing for a real mechanic to say..."The shop that installed it says thats normal for a big V8."

 

[Rick910]

Thanks for the responses. This weekend I'll start of with the spark plug wires to see if I can isolate a dead cylinder. As for as the shop, they were the only volvo penta certified dealer. And -yes- it appears I'm getting the run-around. My problem is that any place I take it to will not look at to for at least 4 weeks. This all started back in April and I have yet to enjoy my boat on the water. Summer is running out. If its related to the install they should definitely fix it. If its not related to the install I'm definitely taking it else where.