Shaft knocking noise

[DJB]

I have just had my Carver Riviera 1985 hauled out because of a knocking noise at 1500 revs from the port side shaft.
On inspection the cutlass bearing is in good order and the shaft seems loose nearer the engine. I would appreciate
your thoughts please.
Engine is VP MD2040 and gearbox MS15A

 

[longjohnsilver]

What do you mean by loose near the engine?
My guess is either engine alignment issues or an unbalanced prop.

 

[DJB]

I mean under the boat at the engine end as opposed to the propeller end..
Many thanks

 

[kashurst]

Engine mounts delaminated.?

 

[alandalus11]

Gearbox.

 

[bigshineybike]

Engine mounts delaminated.?

I've had a look at DJB's boat, fairly certainly Engine mounts. The rubber has gone soft and sticky to the extent that the upper metal frame is in contact with the lower fixing plate.
Initially it just looked like the shaft was sitting a little low in the shaft log. a crowbar allowed me to lift the engine easily off the rubber mount.
The part number on the rear mounts is 838262 a quick google seems to suggest they will cost in the region of one to two hundred pounds EACH.
does that sound reasonable?

This surely means the engine is not properly aligned. How closely aligned must the engine be given its got rubber mounts and a flexible coupling between output shaft and propellor shaft?

 

[kashurst]

try these guys for new engine mounts: Volvo Penta 2003 engine mount - if that's the right part a lot cheaper.
If the engine mounts have delaminated the engine will be bouncing about - hence the knocking noises.
The shafts must be pretty well aligned. It's not hard just takes patience and time.

Disconnect the gearbox drive flange - you will need to do this anyway to change the mounts. Give the shaft a good clean between the stuffing box and the coupling. Push/wind the shaft backwards about an inch away from the flange . Initially just by eye re-align the engine to the shaft - then slide the prop coupling up to the gearbox flange- there may well be a concentric internal lip - adjust up/down, left right until the lip can engage into the flange. Push the shaft up as far as it will go and put some feeler gauges in any gap(s) and measure the gap. Put the bolts back in but not tight, they are there to keep the shaft and gearbox flamge rotating together for now. Rotate the shaft @ 90 degrees and again look for gaps with feeler gauges. Rotate again and check/measure. Then small adjustments on the mounts until there is no gap. regardless of the rotation of the shaft. Then tighten up the coupling/flange bolts. If there is a flexible mount in the middle - same process.
Sometimes its dead easy sometimes it will require lots of swearing.

 

[bigshineybike]

Kashurst, the link to partforengines, Brilliant thanks.
also the description sounds right. just missing the need for a skeleton made of rubber and armour plating for elbows.

 

[AndieMac]

try these guys for new engine mounts: Volvo Penta 2003 engine mount - if that's the right part a lot cheaper.
If the engine mounts have delaminated the engine will be bouncing about - hence the knocking noises.
The shafts must be pretty well aligned. It's not hard just takes patience and time.

Disconnect the gearbox drive flange - you will need to do this anyway to change the mounts. Give the shaft a good clean between the stuffing box and the coupling. Push/wind the shaft backwards about an inch away from the flange . Initially just by eye re-align the engine to the shaft - then slide the prop coupling up to the gearbox flange- there may well be a concentric internal lip - adjust up/down, left right until the lip can engage into the flange. Push the shaft up as far as it will go and put some feeler gauges in any gap(s) and measure the gap. Put the bolts back in but not tight, they are there to keep the shaft and gearbox flamge rotating together for now. Rotate the shaft @ 90 degrees and again look for gaps with feeler gauges. Rotate again and check/measure. Then small adjustments on the mounts until there is no gap. regardless of the rotation of the shaft. Then tighten up the coupling/flange bolts. If there is a flexible mount in the middle - same process.
Sometimes its dead easy sometimes it will require lots of swearing.

Good advice K.

Flexible couplings will compensate for small errors, up to 5 thou, of gearbox to shaft misalignment, but as I found out recently, a previous “mechanic” had not re-tightened the GB side flex coupling bolts which were less than finger tight, resulting in a 20 thou lateral shaft movement just behind the coupling and the subsequent extra vibrations through the boat.

 

[AndieMac]

Kashurst, the link to partforengines, Brilliant thanks.
also the description sounds right. just missing the need for a skeleton made of rubber and armour plating for elbows.

Good luck with the project, I for one would like to see and read about progress during the job if you could be bothered taking pics and commenting. Engine mount replacement and shaft alignment issues and processes is something many need to consider and understand.

 

[DJB]

Thank you for all the above comments and advice. Most helpful.

 

[Seastoke]

Thank you for all the above comments and advice. Most helpful.

Try robush vibrating solutions, ask for Tony he knows Volvo inside out.

 

[vas]

since none mentioned it and with the danger of repeating the obvious, the whole exercise that kashurst elaborately explained has to be done in the water, not on the hard with hull possibly flexing a bit and moving about.

 

[AndieMac]

since none mentioned it and with the danger of repeating the obvious, the whole exercise that kashurst elaborately explained has to be done in the water, not on the hard with hull possibly flexing a bit and moving about.

Indeed, good point Vas.
GRP or timber construction in the water, but steel can be done on the hard.

 

[bigshineybike]

Given that the propellor shaft is only supported in the rubber cutlass bearing. what should we consider is the correct height at the gearbox end of the shaft?
Im assuming the shaft will be bending due to gravity at the engine end.
In this particular installation the shaft log doesn't give any support.
I was considering using a wooden block and wedges between the hull and the coupling to gently jack the propshaft so it is centered in the shaft log . We will then set the engine using its new mounts to align with the prop shaft flange both radially and axially.
When the engine starts or is running it will naturally wobble about but the flexible coupling will allow for that along with some natural flex in the long propellor shaft?

 

[kashurst]

The shaft should be supported by the cutlass bearing in the p bracket at the prop end and a similar bearing where the shaft goes into the hull. Some boats don't have that and rely on the stern gland assembly to support the shaft at the engine end. When you undo the coupling the shaft shouldn't just drop or move at all. Once you have changed the engine mounts align the engine to the shafts resting position. The shaft when running should not bounce about at all unless it is bent. Ps gravity won't bend a prop shaft

 

[bigshineybike]

Kashurst I agree with everything you say and it's a helpful comment.
I did a bit more looking around and found this video that sort of confirms my thoughts on the shaft dropping and how it needs to be centred in the stern tube.
In the Carver installation we are discussing there is also a Rand D marine, flexible coupling.
I have been looking at their installation instructions. they allow .25 mm out of alignment. but also caution about the clearance of the bolt heads.
I had noticed that in DJBs installation the bolt heads are making light contact with the flange which needs to be addressed as this will be another source of noise.

 

[kashurst]

Thats a good video - explains exactly what is needed. If the boat we are talking about is out of the water great - do that! If it is in the water the stern tube or log may have a bearing in it so the shaft won't move up or down. If not the seal assembly or stuffing box will keep it in place pretty well. The tubes are pretty stiff. If you are concerned about the shaft loading the stuffing box and dont know if there is a bearing in the shaft log, I would put some pieces of wood or packing to just take the shaftw eight and lift it a smidge (i.e - sod all).

 

[SimonD]

I did this job some while ago with an engine that turned out to be well out of position. Instead of the rubber tube used in the video, I had made up a top hat shaped sleeve to fit exactly in the stern tube with a hole slightly larger that the shaft. This centred the shaft in the stern tube while allowing it to be rotated to check it was true once aligned with the gearbox flange.