New to forum, vibration Volvo 280 with 350 V8

[MrLabGuy]

New to me 1983 Sunrunner 18.5' bowrider with Volvo Penta 280 outdrive and 350 Chevy V8. The boat is real clean and has very low hours. Engine looks new and everything works. Problem is a pretty significant vibration at about 2,500-3,500 RPM and the boat seems to lack some top end. Just replaced the 15/19 prop thinking it was the problem but only helped slightly. Engine runs perfectly. Where should I start to look and can a shop diagnose this without putting it in the water?<br /><br />Thanks in advance.

 

[Don S]

Re: New to forum, vibration Volvo 280 with 350 V8

On an 83, I would be worried about bad ujoints. Perhaps due to water in the bellows. <br />Second would be a bent prop shaft.

 

[MrLabGuy]

Re: New to forum, vibration Volvo 280 with 350 V8

Thanks for the fast reply...Is there any way to test the u-joints without taking them out? I assume there are two. Prop seems to spin without any wobble but I will take a closer look at the shaft at a higher RMP.

 

[bigbrownbuku]

Re: New to forum, vibration Volvo 280 with 350 V8

could also be bad steering fork bushes. simple to chage if you are going in to do the u joints its not much more effort to change the bushes and shaft seal. how much side to side play does the drive have?

 

[MrLabGuy]

Re: New to forum, vibration Volvo 280 with 350 V8

I'm also reading it could be the Gimbel bearing. What is the best test to isolate the vibration? Tomorrow I'll run the boat and try in gear, neutral, load and no load. What should I be looking for?

 

[bigbrownbuku]

Re: New to forum, vibration Volvo 280 with 350 V8

find a nice wide flat area of water and do some lock to lock turns. you will hear it if it is bad crosses/gimbal(it will grumble quite loudly from the area behind the engine). back on the trailer grab your drive by the back and just rock it side to side, how far does the helmet move? does the seal on the fork pin where it enters the top of the transom plate look damaged.<br />check your propshaft like don mentioned also. remove the prop and set up a stack with a pen or similar, perpindicular almost touching a flat point near the propshaft end then just spin it by hand taking note of distance to pen. its important the drive stays motionless during this test.