280dp vibrations

[txkingfisher]

I just bought a 21' lafitte skiff. 1984 AQAD30 diesel 280DP outdrive A8 props.

It has a "bad vibration" as it's comming up on step, but once it planes out the vibration completely stops.

I havent seen the boat yet. I work offshore and sent my dad to look it over and buy it with my cash while I'm out.

I'm planning on checking for water in the bellows and the condition of the u-joints. The forward wheel has a ding in it and I'm probably going to put a new set of props on it anyway but I don't think thats where the vibration is comming from. I will also check the runout on the prop shafts. I have plenty of experience with inboards but zero experience with outdrives. How do I check the engine alignment? Does it matter that much with the u-joints between the engine and outdrive? Is there some other obvious place I should start looking besides u-joints, alignment, wheels, bent shafts?

Just trying to get a leg up on what I will be up against when I tear into this thing on wednesday.....

 

[bruceb58]

Re: 280dp vibrations

Could be the props especially if one has a good size ding in it. I have also seen props that have been repaired poorly that are way out of balance and or the pitch is way out. Probably more noticable on a duo prop. I would also make sure that both props are both A8s.

While it is a very good idea to pull the upper gear case and inspect the u-joints, you could do a quick test on the muffs and just turn the drive to both sides and listen for the u-joint noise.

 

[jerryjerry05]

Re: 280dp vibrations

You don't have to worry about allignment on that outfit.Merc and OMC need to worry about that.Sounds like u-joints or possible drive shaft bearings in the bellhousing. Check the u-joints.If they are ok take top gearcase off and check driveshaft shaft endplay (wiggle it) Jerry

 

[KnottyBuoyz]

Re: 280dp vibrations

We've spent the last 5 yrs trying to diagnose a similar problem with a 290 DP. This was our first boat with this type and we thought we had problems with timing, tuning, carb, you name it. The boat was sluggings, noisy and vibrated. After eliminating the issues above, as I gained some knowledge of these things, began to think it was props. With the help of DonS on here and a few others we decided to go to B5's from the original B6's. Things improved a lot but still noisy (cavitation). Yesterday I installed a new set of B4's and the boat came alive!!! It jumps up on plane with little effort, cruises quietly (no more u-joint grumbling) and it just seems happier. It's a little slower but appears to be running more effortlessly. The downside is it seems to be less responsive at slow speeds so you have to be ready to give it some throttle.

So basically if you eliminate the dings & balance issues you might want to find a shop that has a test set of screws and try out the various sizes to see if that eliminates the issue.

 

[txkingfisher]

Re: 280dp vibrations

Thanks for the advice guys. I feel much more prepared for battle now!

 

[Don S]

Re: 280dp vibrations

Might want to look the engine over also. Turbo and injectors. I've had the 31's shake a lot if the turbo was slow kicking in, or the injectors were missfiring.
While the 30's had different injectors than the 31, they are still the 4 cyl diesels and they can have a vibration zone.