How much does your engine move on its mounts?

[contessaman]

So, some time ago I installed a new engine in my boat. I got a marine engineer to do the alignment for me, the shaft is perfectly in the centre of the tube when I slide back the rubber dripless seal. With the boat ashore the prop spins freely and the engine doesn't move at all when doing this. The flanges slide easily together and check out with a feeler gauge.
Boat in the water, rev the engine in neutral and it barely moves on the rubber mounts.
Stick it in gear and at tickover its not too bad, as soon as I increase the revs though it starts shaking on its mounts. I was expecting some rough and some sweet RPMs but it basically just gets proportionately worse with increasing RPM. The marine engineer thinks its fine. Indeed, if I close the engine room door and ignore it, you can barely feel any vibration through the boat and its a silent and sweet installation. But if I look at it, it seems bad to me. There's probably 1- 2 cm of movement at a decent cruise rpm of 2000. I can't help thinking that at the very least it won't be long before wires and connections start falling off the engine. My previous two yachts had similarly sized 4 cylinder diesels and didn't seem to move about so much.

How much movement is 'normal'?
What could the problem be?

Thanks

 

[Heckler]

So, some time ago I installed a new engine in my boat. I got a marine engineer to do the alignment for me, the shaft is perfectly in the centre of the tube when I slide back the rubber dripless seal. With the boat ashore the prop spins freely and the engine doesn't move at all when doing this. The flanges slide easily together and check out with a feeler gauge.
Boat in the water, rev the engine in neutral and it barely moves on the rubber mounts.
Stick it in gear and at tickover its not too bad, as soon as I increase the revs though it starts shaking on its mounts. I was expecting some rough and some sweet RPMs but it basically just gets proportionately worse with increasing RPM. The marine engineer thinks its fine. Indeed, if I close the engine room door and ignore it, you can barely feel any vibration through the boat and its a silent and sweet installation. But if I look at it, it seems bad to me. There's probably 1- 2 cm of movement at a decent cruise rpm of 2000. I can't help thinking that at the very least it won't be long before wires and connections start falling off the engine. My previous two yachts had similarly sized 4 cylinder diesels and didn't seem to move about so much.

How much movement is 'normal'?
What could the problem be?

Thanks

Has it always been like this or has it recently started! If recently started, sounds like an unbalanced prop. A crustacean found a new home?

 

[philld]

Propellor balance?

 

[contessaman]

Its a new installation and this is the first I've tried it so nothing to compare.
Prop is a brand new 3 blade fixed so I'd like to think its reasonably balanced.

Certainly a test will be when I come ashore in a few months, rig up a hosepipe and try it both prop on and off out the water. That will rule out prop imbalance and also see if its thrust pushing the engine out of alignment.

Was wondering if there's anything else I can try while I'm still afloat...

I'm a keen scuba diver but not keen enough to put my head under the water in my marina. Don't fancy a double ear infection and god knows what else!

 

[Heckler]

Its a new installation and this is the first I've tried it so nothing to compare.
Prop is a brand new 3 blade fixed so I'd like to think its reasonably balanced.

Certainly a test will be when I come ashore in a few months, rig up a hosepipe and try it both prop on and off out the water. That will rule out prop imbalance and also see if its thrust pushing the engine out of alignment.

Was wondering if there's anything else I can try while I'm still afloat...

I'm a keen scuba diver but not keen enough to put my head under the water in my marina. Don't fancy a double ear infection and god knows what else!

My md22 jiggles at low revs bu not much, in or out of gear, it smooths out as it revs. I have a circular rope cutter fitted which filled the gap between prop boss and cutlass bearing, about 6mm clearance, I found out that when motoring the engine moved under load and the rope cutter contacted the cutlass bearing and blocked waterflow to and from the volvo seal. It also made a noise! I solved the prob by fitting a 12mm spacer between the gearbox coupling and shaft. The moral? my engine can move up to 6mm when under thrust. I suspect an inbalance in your shaft or prop though but also check there is enough room for the prop!

 

[contessaman]

My md22 jiggles at low revs bu not much, in or out of gear, it smooths out as it revs. I have a circular rope cutter fitted which filled the gap between prop boss and cutlass bearing, about 6mm clearance, I found out that when motoring the engine moved under load and the rope cutter contacted the cutlass bearing and blocked waterflow to and from the volvo seal. It also made a noise! I solved the prob by fitting a 12mm spacer between the gearbox coupling and shaft. The moral? my engine can move up to 6mm when under thrust. I suspect an inbalance in your shaft or prop though but also check there is enough room for the prop!

Thanks, a useful insight. I left about a 15mm of shaft stuck out when I set it all up so that should be okay. Its 30mm diameter shaft.
The one thing I'm thinking - I retained the old Volvo half coupling and that had a big solid steel spacer, this then connects to the new r&d coupling, which goes to an adapter on the new techno drive transmission. The resultant is that all this gubbins between the gearbox flange and shaft must weigh at least 10kg, I guess if this is out of balance then that would cause my problem that gets worse not better with rpm. I could get a new slightly longer shaft and much smaller and simpler coupling... Its just this will cost hundreds and be a trial and error approach.

 

[Heckler]

Thanks, a useful insight. I left about a 15mm of shaft stuck out when I set it all up so that should be okay. Its 30mm diameter shaft.
The one thing I'm thinking - I retained the old Volvo half coupling and that had a big solid steel spacer, this then connects to the new r&d coupling, which goes to an adapter on the new techno drive transmission. The resultant is that all this gubbins between the gearbox flange and shaft must weigh at least 10kg, I guess if this is out of balance then that would cause my problem that gets worse not better with rpm. I could get a new slightly longer shaft and much smaller and simpler coupling... Its just this will cost hundreds and be a trial and error approach.

Ah, you might have hit the nail on the head.

 

[Tranona]

As Stu says +/- 6mm fore and aft movement as you go in and out of gear is normal so your 15mm between the bearing housing and front face of prop is fine.

You don't say whether the shaft is moving sideways or up and down when under load. if it does not that rules out imbalance of the shaft or prop (which is unlikely anyway). This gets back to the engine moving on its mounts. Well, that is what the mounts are for - to isolate the movement of the engine from the boat and the flexible coupling from the shaft.

I assume you chose the correct hardness for the mounts. If they are too soft the engine will move excessively, but in a way not a big issue if the coupling can absorb the movement and not transmit it to the shaft. However the R&D coupling is probably not flexible enough to handle excessive movement or misalignment. If the mounts are too hard then movement may be restricted and vibration might be transmitted to the hull and the shaft may show movement.

Not aware that your engine is known for excessive movement when running under load, but without having a direct comparison of a similar installation it is difficult to determine if yours is typical or not.

With regard to your coupling arrangements, the weight per se is probably not an issue - although 10kg does sound excessive. However, if it were my boat I would probably replace the whole lot with a Bullflex coupling direct to your new gearbox. You may well be able to fit one without changing the shaft. The advantage of this coupling is that it is softer than the R&D and it will tolerate up to 2 degrees misalignment - although of course best to get the alignment spot on. I had good success with this coupling with a very bouncy Yanmar 1GM attached to a fixed shaft (that is bearings at both ends of the stern tube).

Hope this helps.

 

[Heckler]

As Stu says +/- 6mm fore and aft movement as you go in and out of gear is normal so your 15mm between the bearing housing and front face of prop is fine.

You don't say whether the shaft is moving sideways or up and down when under load. if it does not that rules out imbalance of the shaft or prop (which is unlikely anyway). This gets back to the engine moving on its mounts. Well, that is what the mounts are for - to isolate the movement of the engine from the boat and the flexible coupling from the shaft.

I assume you chose the correct hardness for the mounts. If they are too soft the engine will move excessively, but in a way not a big issue if the coupling can absorb the movement and not transmit it to the shaft. However the R&D coupling is probably not flexible enough to handle excessive movement or misalignment. If the mounts are too hard then movement may be restricted and vibration might be transmitted to the hull and the shaft may show movement.

Not aware that your engine is known for excessive movement when running under load, but without having a direct comparison of a similar installation it is difficult to determine if yours is typical or not.

With regard to your coupling arrangements, the weight per se is probably not an issue - although 10kg does sound excessive. However, if it were my boat I would probably replace the whole lot with a Bullflex coupling direct to your new gearbox. You may well be able to fit one without changing the shaft. The advantage of this coupling is that it is softer than the R&D and it will tolerate up to 2 degrees misalignment - although of course best to get the alignment spot on. I had good success with this coupling with a very bouncy Yanmar 1GM attached to a fixed shaft (that is bearings at both ends of the stern tube).

Hope this helps.

Going to disagree with you here, 10kg is a lot of metal to be whirling around at one end of the shaft. I would assume/ that the new engine would have come with the correct mounts. Do we know what the engine is? Also the symptoms, no vibration in neutral but starts when in gear and increases with revs? Also a dripless seal, volvo seal? So can move a bit, I prefer solid couplings like on our AWBs with these seals.

 

[Tranona]

Going to disagree with you here, 10kg is a lot of metal to be whirling around at one end of the shaft. I would assume/ that the new engine would have come with the correct mounts. Do we know what the engine is? Also the symptoms, no vibration in neutral but starts when in gear and increases with revs? Also a dripless seal, volvo seal? So can move a bit, I prefer solid couplings like on our AWBs with these seals.

Doubt it weighs 10kgs and it is not whirling around the shaft but with the shaft and gearbox coupling so its weight is irrelevant unless it unbalances the shaft by being out of balance. A significant amount of that weight (the spacer and adaptor) is on the gearbox coupling, not the shaft and if that is properly indexed to the coupling should not affect balance. So the only bits on the shaft are the R&D and the half coupling which are nothing out of the ordinary.

I believe the engine is a Ford 1800 from the old Escort as often marinised by Lancing Marine. I don't know what shaft seal it has, but a Volvo seal would be OK if the flexible coupling is doing its job.

 

[fisherman]

I had a 4cyl ford with 200lb flywheel and PRM box. The point of balance was at the rear feet, and the engine gyrated about that point. It needed a raft extending back, with three sets of mounts, or at least the aft ones well aft where they had more purchase. The further fore and aft the mounts are the more effective they can be.
I often wonder if there could be a stabiliser bar like the old mini, somewhere at the top.

 

[contessaman]

So yep lancing /mermaid ford xld in the place of the knackered MD21. Finally all plumbed in and running a treat except this damned wobbling.

Chose the brand new r&d mounts on the advice of r&d themselves. They were the expensive sort that allow movement sideways but resist movement on the thrust line.

Previous md21 had no flexible coupling. I introduced an r&d one as part of my installation. I was of the understanding that since the shaft is only supported by the cutless bearing and gearbox it should either be no flexible coupling or the stiff r&d sort. Not a bullflex or similar. Shaft seal is indeed Volvo rubber type.

Holding a finger on the shaft reveals no wobble nor is any visible at the shaft seal when running in gear. Its not dripping. Also, if I get my dad to rev the engine I can't really see it moving forward on the mounts.

Regarding the heavy coupling, most of the weight IS on the shaft side of the flexi coupling NOT the gearbox side, the old Volvo half coupling is massive and this had a BIG spacer on it as part of the old rigid Volvo installation. I don't know why. ..

 

[contessaman]

I had a 4cyl ford with 200lb flywheel and PRM box. The point of balance was at the rear feet, and the engine gyrated about that point. It needed a raft extending back, with three sets of mounts, or at least the aft ones well aft where they had more purchase. The further fore and aft the mounts are the more effective they can be.
I often wonder if there could be a stabiliser bar like the old mini, somewhere at the top.

I had custom brackets made for the bow end of my engine so really my engine mounts are in the four corners of the engine so should be good on that front. Also, in neutral, the flywheel is still turning and the engine barely moves throughout the whole rev range. Think this little xld 1.8 doesn't weigh much more than just your flywheel!
Really its probably lighter than the perkie 4108 in my last boat and comparable to the watermota sea panther in the one before that. Me and a friend easily lifted it into the back of my wife's MPV .

 

[Tranona]

Regarding the heavy coupling, most of the weight IS on the shaft side of the flexi coupling NOT the gearbox side, the old Volvo half coupling is massive and this had a BIG spacer on it as part of the old rigid Volvo installation. I don't know why. ..

Ok, but the fact that the shaft is not moving suggests that the weight is a red herring. It is the engine that is moving and not the shaft, so the R&D and the engine mounts are doing their job by isolating the engine movements from both the shaft and the hull.

The movement fore and aft is on engaging and disengaging gear. Put a mark on the shaft just as it enters the seal and observe how far it moves forward when you engage gear.

 

[contessaman]

Ok, but the fact that the shaft is not moving suggests that the weight is a red herring. It is the engine that is moving and not the shaft, so the R&D and the engine mounts are doing their job by isolating the engine movements from both the shaft and the hull.

The movement fore and aft is on engaging and disengaging gear. Put a mark on the shaft just as it enters the seal and observe how far it moves forward when you engage gear.

Good plan will do that and I'll report back....

 

[2Tizwoz]

The MD7B in the video moves in the same way as mine. With increased revs it smooths out. The saildrive permits a lot of movement.

 

[contessaman]

The MD7B in the video moves in the same way as mine. With increased revs it smooths out. The saildrive permits a lot of movement.

Oh! Well mine is about on a par with that at higher Rpm and barely moves at lower rpm.
Maybe I'm worrying over nothing. But my 2 previous boats had similar sized 4 cylinder diesels (perk 4108 and w.m. seapanther) and they didn't move much at all.

I was at the boat yesterday and marked my shaft where it emerges from the shaft seal with permanent marker. I made observations in neutral, in gear at idle, then at 1000, 1200, 1500 and 1800 rpm (by which time the engine is moving worryingly) and the shaft and engine combine IS NOT moving forward a measurable amount. Perhaps 1mm at the most from 1800 rpm in fwd to 1800 rpm in reverse, so those expensive r&d mounts I fitted are doing their job well.

I've come to thinking the problem has been caused by my inserting a flexible coupling in the drive train.
These engine mounts resist thrust very well but allow movement up and down. If I get in the engine room (easier said than done at 6'2" !!!) And straddle the gearbox I can easily grab it (the gearbox) and lift it or depress it an inch in either direction.

I was thinking that with the engine thus mounted, plus the flexible coupling, plus the floating shaft with flexible seal, that as soon as it spins its getting a tiny bit off centre, then the centrifugal force pulls it out even more on the flexibility if the system, and the problem becomes ever worse. The fact that my coupling weighs a ton is possibly making it worse. I think with the boat ashore I can take the prop off, slide the shaft back and remove the r&d coupling from the system to test it. If that was the culprit then order a new linger shaft and lower mass half coupling at the same time.

Any other thoughts or observations based on my latest findings?

 

[Brent Swain]

Yanmar mounts are so soft that engines have been known to break them all, leaving the engine rolling around in the boat , and bashing a hole in the hull. One Canadian boat was quickly sunk that way ,off the Great Barrier Reef several years ago, being rescued in the nick of time by a helicopter. If you have that kind of mounts, get rid of them. Perkos are far safer .
The softer the mounts, the quieter, but the more dangerous. I'll take a bit more noise, for the safety.

 

[Heckler]

Oh! Well mine is about on a par with that at higher Rpm and barely moves at lower rpm.
Maybe I'm worrying over nothing. But my 2 previous boats had similar sized 4 cylinder diesels (perk 4108 and w.m. seapanther) and they didn't move much at all.

I was at the boat yesterday and marked my shaft where it emerges from the shaft seal with permanent marker. I made observations in neutral, in gear at idle, then at 1000, 1200, 1500 and 1800 rpm (by which time the engine is moving worryingly) and the shaft and engine combine IS NOT moving forward a measurable amount. Perhaps 1mm at the most from 1800 rpm in fwd to 1800 rpm in reverse, so those expensive r&d mounts I fitted are doing their job well.

I've come to thinking the problem has been caused by my inserting a flexible coupling in the drive train.
These engine mounts resist thrust very well but allow movement up and down. If I get in the engine room (easier said than done at 6'2" !!!) And straddle the gearbox I can easily grab it (the gearbox) and lift it or depress it an inch in either direction.

I was thinking that with the engine thus mounted, plus the flexible coupling, plus the floating shaft with flexible seal, that as soon as it spins its getting a tiny bit off centre, then the centrifugal force pulls it out even more on the flexibility if the system, and the problem becomes ever worse. The fact that my coupling weighs a ton is possibly making it worse. I think with the boat ashore I can take the prop off, slide the shaft back and remove the r&d coupling from the system to test it. If that was the culprit then order a new linger shaft and lower mass half coupling at the same time.

Any other thoughts or observations based on my latest findings?[/QUOTE
As my original post the big coupling. 10kilos you said?

 

[Daydream believer]

I'm a keen scuba diver but not keen enough to put my head under the water in my marina. Don't fancy a double ear infection and god knows what else!

If you did it with the engine running a single ear infection would be a whole lot worse:encouragement: