Forums, Engine, Gearbox, Stern Gear, etc, New prop shaft but still vibrating

GlennG at 15/05/2012 09:18:36
Have fitted a new prop shaft, Tuffnell bearing and PSS seal. Have an Aquadrive thrust bearing/CV joint between the engine and prop shaft. Have a 3 year old 13.5 × 13 × 3 prop which is suffering from a bit of de-zincification but is sound. Engine is a 2GM20.

The engine revs to about 2700 max, indicating that it’s propped about right.

I’m quite disappointed that there’s still a fair amount of vibration when cruising at ‘normal’ revs, say 2300.

The old prop shaft was only 3 years old but needed to be replaced as it was clearly worn at both ends. I know that the stuffing box may have been a bit in need of stripping down, but I thought it was odd that the wear on the bearing end appeared a bit uneven. I need to measure how ‘circular’ the wear was, but it seems to be more on one side than another.

Ideas?

St Paddy at 08/06/2012 07:50:58
Hi
First thing to check is the Aquadrive, It has to be square to the stern tube. you will need to made a jig or borrow one. You cannot get it right with a tape measure.
Then you need to be sure the shaft is straight, as you say the wear needs to be true to the shaft. you need a lathe or rollers and a clock (dial indicator)
The prop balance is a funny one I did a dynamic balance on mine to within 2 milligrams and a prop manufacture would say that was over the top, that said it was 12grams out from new. I would say yours will be ok. Again when you have the shaft on rollers fit the prop and see if it wants to rotate. Sand of the back of the heavy blade
While it’s all apart check the engine mounts as well. Oil and fuel will rot them, on the Volvo you can buy the rubber part only, they unbolt to dismantle
The rudder will flutter in the prop wash and make a noise as the lower bearing is stainless against stainless. The later boats had a nylon bearing in there, and I have fitted one to mine.
The tufnol bearing will always wear the shaft. I made three for St Paddy then gave up machined out the stern tube and made a fancy bronze one with a thick wall cutlass bearing and pressure fed that from the engine to keep it water lubricated.

St Paddy at 08/06/2012 07:55:40
Last thing, the prop de-zincing is due to the fact that the Aquadrive is insulatiing it from the main annode. Mine used to be ok and I dismantled it, re-greased it and assembled with new boots and then It would not conduct, either that or I have paint in the clamp.