Thumping sound when motoring ahead - worn cutlass bearing or engine mounts?

sebastiannr said:
Thank you for all the responses, it's amazing how much I learn through these forums.

As a follow up, I was able to dive down and take some pictures and check for play in the cutlass bearing yesterday. I couldn't feel any play in the bearing, but visually inspecting it was difficult.

I've noticed that the thumping occurs mostly after I've been in reverse, then go forward. So perhaps it's the prop blades not setting properly?

In the pictures you can see where paint has come off at the point of the crack on the p-bracket. There's no play in it so hopefully it's just the glass fibre sheathing that's cracked. Am I being reckless if I leave it until the next haul out (in October before we cross the Atlantic)?

http://i1347.photobucket.com/albums/p705/sebastiannr/IMGP0455_zpsd984bebd.jpg

http://i1347.photobucket.com/albums/p705/sebastiannr/IMGP0457_zpsf8bbf245.jpg

Anyway, thanks once again for all the input, invaluable as always.

N.B. Those shaft anodes are only 1 month old, is that normal corrosion or is there serious stray current somewhere?
Click to expand...

Usually an explanation when you see the whole picture. Your rope cutter and the first anode are (seriously) incorrectly installed. There should be a minimum of 15mm gap between the prop face and the P bracket and the same between the anode and the bracket. The noise you are hearing is the cutter and anode hitting the bracket as the engine moves 3 or 4mm back and forth when you go in and out of gear. The space is also necessary for water to flow in and out of the cutless bearing. Get it fixed soon as the bearings in the cutter will wear out and ruin the cutter. You need a 15mm gearbox spacer. See the chart on www.ropestripper.com to select the right one.
 
I have experienced a similar problem,every now and then at varying speeds there is an awful vibration which then turns into a rumbling sound and goes through the whole boat , the 1st time it happened I thought the boat was going to split in half it really is an awful sound/ feeling. it is definitely not coming from the engine or the gearbox, so it is from the shaft, either engine mounts, shaft alignment or cutless bearing I'm assuming, does anyone have any ideas/advice?
 
Our advice from many cutter and bearing installations is the bearing requires min 3.00mm gap for water to exit, and the worst case we have seen in terms of fore and aft shaft movement is 9 each way so the minimum gap we work on is 12.00mm this has been more than adequate on many boats. (9.00 for movement + 3.00)
The cutter and anode do look too close on this set up. Typical movement on small engines is 3-4mm 9.00 is an absolute worst case we have seen.
 
Aquabell27 said:
I have experienced a similar problem,every now and then at varying speeds there is an awful vibration which then turns into a rumbling sound and goes through the whole boat , the 1st time it happened I thought the boat was going to split in half it really is an awful sound/ feeling. it is definitely not coming from the engine or the gearbox, so it is from the shaft, either engine mounts, shaft alignment or cutless bearing I'm assuming, does anyone have any ideas/advice?
Click to expand...

Measure the clearance between bearing and shaft and look at where that clearance is, top/bottom/side (should be top)
For a new bearing on a 1" shaft you are looking at 0.13mm clearance, you can get noise/vibration when the clearance reaches 0.6mm which is the suggested change clearance.
 
I occasionally have a thumety-thumpety-theumpety which shakes the whole boat. From the fact that it invariably ends with a swooshing sound and an increase in boat speed, I am dead certain that it's the cone clutch (1GM10) failing to engage. Oddly enough, when it's happening it cannot be heard in the engine compartment. I can remove the top step and stick an ear in. Just normally diesel engine sounds. In the cockpit, thumpety-thumpety. Most odd. But I wonder if that's what you have too?
 
JumbleDuck said:
I occasionally have a thumety-thumpety-theumpety which shakes the whole boat. From the fact that it invariably ends with a swooshing sound and an increase in boat speed, I am dead certain that it's the cone clutch (1GM10) failing to engage. Oddly enough, when it's happening it cannot be heard in the engine compartment. I can remove the top step and stick an ear in. Just normally diesel engine sounds. In the cockpit, thumpety-thumpety. Most odd. But I wonder if that's what you have too?
Click to expand...


I see what you are saying but this doesn't end up with an increase in speed but I will check this just incase, many thanks
 
I used to have this kind of sound as well. It turned out to be the stainless steel bend at the top of the loop in the exhaust banging against the side of the lazerette just before it turns round to go out through the hull if you get what I mean.
 
I have the identical problem.
Terrible thumping / clonking on starting forwards when engine warm. Yanmar 3YM30 with KM2P-1 gearbox and autoprop.
After a huge amount of research I am convinced of the following:
1. The cone clutch is slipping on engaging forwards.
2. This makes the engine rock on its mounts
3. This makes the shaft bang on the stern tube
4. This makes it sound like it is coming from an unbalanced autoprop (but the autoprop is well serviced and looks fine).
I'm about to take the gearbox off and try to get it fixed.

http://www.ybw.com/forums/showthread.php?358222-Horrible-Clonking-from-Autoprop

BTW does anyone know how difficult it might be to do a DIY gearbox repair and cone lapping?
 
Last edited:
flat1 said:
4. This makes it sound like it is coming from an unbalanced autoprop (but the autoprop is well serviced and looks fine).
Click to expand...

That's very interesting. I was convinced it was my Autoprop. I've spoken to a couple of people who both said they experience the same phenomenon, but they didn't have autoprops.

I went in the water and watched it's action (from a safe distance) as my wife put the engine in forward and reverse, repeatedly. I could see no problem with the propeller, but then she said there was no banging this time whilst she was engaging the engine.

I have found that when the banging does happen, if keep the engine in slow revs for a little while, then slowly increase the revs, that sorts out the problem. I thought that pointed towards the prop, but could it also point towards a gear box issue?
 
Did you change to a two bladed autoprop from a three bladed? I experience exactly the same symptoms described and was told it was cavitation.
 
sebastiannr said:
That's very interesting. I was convinced it was my Autoprop. I've spoken to a couple of people who both said they experience the same phenomenon, but they didn't have autoprops.

I went in the water and watched it's action (from a safe distance) as my wife put the engine in forward and reverse, repeatedly. I could see no problem with the propeller, but then she said there was no banging this time whilst she was engaging the engine.

I have found that when the banging does happen, if keep the engine in slow revs for a little while, then slowly increase the revs, that sorts out the problem. I thought that pointed towards the prop, but could it also point towards a gear box issue?
Click to expand...
Have you sorted out the cutter and anode positioning as suggested in post #21? If not you will still get the banging - nothing to do with the prop. What you describe is the shaft centralising at slow revs so no banging, and moving as soon as you go into gear or put load on causing the cutter to hit the P bracket.
 
Tranona said:
Have you sorted out the cutter and anode positioning as suggested in post #21? If not you will still get the banging - nothing to do with the prop. What you describe is the shaft centralising at slow revs so no banging, and moving as soon as you go into gear or put load on causing the cutter to hit the P bracket.
Click to expand...

In case you doubt what Tranona and H4 have said may I endorse their opinions entirely. You need more clearance! If it is not clear to you there are two reasons. 1. is that many clutches rely on a forward and aft movement of the shaft from forward to aft engagement regardless of thrust. 2. The thrust will reduce the clearance because the engine is being shoved forward on its bearers.
Add to this the fact that you have an autoprop. It is characteristic of these that if you engage forward gear and rev up it will take a few seconds for the blades to equalise and you have added to your problem. Sometimes with even the best installation of an autoprop it will always be that there is a little vibration until the blades equalise. Don't be concerned with this it's normal. It should not persist however and I agree the problem is lack of longitudinal clearance.
 
flat1 said:
I have the identical problem.
Terrible thumping / clonking on starting forwards when engine warm. Yanmar 3YM30 with KM2P-1 gearbox and autoprop.
After a huge amount of research I am convinced of the following:
1. The cone clutch is slipping on engaging forwards.
2. This makes the engine rock on its mounts
3. This makes the shaft bang on the stern tube
4. This makes it sound like it is coming from an unbalanced autoprop (but the autoprop is well serviced and looks fine).
I'm about to take the gearbox off and try to get it fixed.

http://www.ybw.com/forums/showthread.php?358222-Horrible-Clonking-from-Autoprop

BTW does anyone know how difficult it might be to do a DIY gearbox repair and cone lapping?
Click to expand...



Your problem does sound very similar to mine, I don't have an auto prop just a standard 4 blade, the boat was hauled out yesterday cutlass bearing is fine, 2mm of play at most, no wear on the rubber inside the cutless bearing so I'm assuming that would rule out engine alignment aswell, does your noise happen frequently or just every now and then? I have a Borg Warner v drive box with a ford mermaid 180hp
 
sebastiannr said:
Ok thanks for the advice.

I will jump in first thing tomorrow and reposition the anode. The cutter is a different matter though, I don't think it can be moved. Hopefully the anode will solve the problem.
Click to expand...
Please read post #21! Your cutter is NOT properly installed. I gave you a link to the installation instructions. It is not a question of moving it, but of moving the shaft back using the spacer I suggested. If you have not removed it, then it is almost certainly ruined by now as it is acting as a thrust bearing. The Delrin washers will almost certainly be worn away and the castings will be wearing. At least remove it completely before it does any more damage.
 
Tranona said:
Please read post #21! Your cutter is NOT properly installed. I gave you a link to the installation instructions. It is not a question of moving it, but of moving the shaft back using the spacer I suggested. If you have not removed it, then it is almost certainly ruined by now as it is acting as a thrust bearing. The Delrin washers will almost certainly be worn away and the castings will be wearing. At least remove it completely before it does any more damage.
Click to expand...

Again I completely agree. At least remove it and try again. It will be very easy to prove to yourself that this is the cause of your problem that way. If the problem persists you can always replace it can't you?
 
I totally see what you're both saying and I agree. I have removed the rope cutter now and will go for a little motor around shortly.

I am a bit confused about how else it could be installed though. Looking at the photo below, I don't think the holding block could be moved any further aft on the p-bracket, so there's no way to get more clearance. Also, if you look at the Spurs installation guide( http://haroldhayles.co.uk/spurs/install/26 ), they're not giving much clearance either.

http://s1347.photobucket.com/user/sebastiannr/media/IMGP0455_zpsd984bebd.jpg.html
 
Reading the installation guide I can see how you reach that conclusion. They indicate clearance is necessary but don't seem to quantify it. In practice when the thrust comes on in forward gear the engine mounts can allow the engine, shaft et al to move forward quite a lot. How much rather depends on the softness of the mounts, their condition and the thrust applied. No point in theorising though. You have done the right thing in removing it and moving the anode forward. Let us know how that works out. If it cures the problem you need to consider fitting a spacer between the gearbox flange and the shaft to increase clearance before refitting it. Either that or bin it......
 
Last edited:
You need 15mm clearance at least to allow water to come out of the cutless and for the fore and aft movement of the shaft when it goes into gear. Now I see that it is not a Stripper, but the principles are the same with the one you have. The problem is that whoever installed it just put it in the gap that is already there instead of either having a new longer shaft made or using a spacer between the gearbox coupling and the shaft to extend the shaft. You can use the spacers that are on the link i gave you.
 
You must log in or register to reply here.

Other threads that may be of interest

B
How does a tacho get RPM and engine-hours data, and how to fix faulty readings?
Replies
16
Views
459
Babylon
B

Share this page

Top