Broken engine mount bracket

[Gavlar1980]

Hi and good evening. I have a 33ft narrowboat with a Nanni 2.60 kc 15 hp engine. I have a current issue with constantly breaking one engine mount bracket which bolts to the engine in a L shape . I have had it welded and braced to support it but still has managed to snap. I have checked the number of threads on each mount and they seem even . The engine mounts seem ok but I’m by no means a expert.Any advice would be much appreciated . Many thanks 

[Movin' on]

Initial thought is to check the history and ensure they are the right brackets for the engine............

you don't say age/make of boat or age of engine which would help............

 

others will be along who know more than me - be patient.........

[Tracy D'arth]

Is the tickover too slow?

 

Does it crack in the same place every time?

Some Prima Perkins engines used to do this, the bracket was a poor design, also "L" shaped but once welded properly and triangle braced it was OK.

 

Watch the mounts on tickover and see if one or more seem to flex more than others.

Edited May 8, 2020 by Tracy D'arth

[Gavlar1980]

Hi the boat is a 1992 Allman boats. I assume the engine is the same age . It cracks it the same place every time. Had it braced with triangle either side but still snapped in the very same place. The engine mounts are r&d soft mounts if this helps 

[ditchcrawler]

42 minutes ago, Gavlar1980 said:

Hi and good evening. I have a 33ft narrowboat with a Nanni 2.60 kc 15 hp engine. I have a current issue with constantly breaking one engine mount bracket which bolts to the engine in a L shape . I have had it welded and braced to support it but still has managed to snap. I have checked the number of threads on each mount and they seem even . The engine mounts seem ok but I’m by no means a expert.Any advice would be much appreciated . Many thanks 

I don't know but is the number of threads important, is it possible that has put uneven loading on them and they should be adjusted somehow else.

[Movin' on]

I'm just throwing this out there - could it be the OTHER mount is putting a strain on the one that's breaking - have you tried to source 2 new ones and fitting them if they are simple and possibly generic have a look at OLD Range Rover V8 mounts they are like a solid rubber doughnut with a bolt/plate either side very simple but they have got me out of trouble before.......

I'm assuming these are flexible mounts?

A couple of photos are needed now I think? 

[Tracy D'arth]

If the gauge of the metal is thick enough and the welding good, it should not be breaking in the same place.

I would suspect that the metal has become brittle and that the arc welding has made it worse. Either get a new one fabricated and properly braced  or get the original welded and then fully annealed to remove the stress in the metal.

After any extensive welding, there will be considerable stress in the metal, annealing removes this.

JCB chassis are annealed overnight in a huge autoclave for this reason.

[BEngo]

Is there a separate thrust bearing between the stern tube and the engine? If there is, is it in good order? If the gearbox is taking the thrust, as many can, that then has to be transferred to the boat via the engine and gearbox mountings.

 

Has the engine been correctly aligned, and was this checked when the bracket was refitted? Misalignment causes vibration.  Vibration causes cracks.

 

Photos of the overall set up and of the mounts and brackets might help.

N

[Iain_S]

6 hours ago, Halsey said:

I'm just throwing this out there - could it be the OTHER mount is putting a strain on the one that's breaking - have you tried to source 2 new ones and fitting them if they are simple and possibly generic have a look at OLD Range Rover V8 mounts they are like a solid rubber doughnut with a bolt/plate either side very simple but they have got me out of trouble before.......

I'm assuming these are flexible mounts?

A couple of photos are needed now I think? 

^^^ This. We had a similar problem when we had a share in Copperkins and we went though a stage of fractured mounting brackets. The root problem was the nut under a bracket slackening off, resulting in the failure of the bracket on the other side of the engine.

[Eeyore]

Here are some images of my Nanni N2.60.

On the first image zoom in to see the repair to the front left mounting; similar to the OPs?

Also note that the front mounting bracket, as built, is quite a long way back; making the installation front heavy.

New heavier gauge brackets have been fabricated and fitted, and the engine mounted on stiff mounts. The gearbox is fitted with a centaflex coupling, and there is a separate thrust bearing on the shaft. Runs quite smoothly, but I'm monitoring the situation to see if it can or will break the new brackets.

The second image shows the engine reinstalled on new bearers, the thrust bearing is just visible at the bottom. Note the spacer blocks beneath the mountings to ensure the engine does not sit too high on the mounts.

Edited May 12, 2020 by Eeyore

[Gavlar1980]

Hi thanks for the images. That’s pretty much identical to my set up. And the repair is exactly what we done on the opposite side but still broke . I’m guessing it needs the engine alignment done. 
any idea on how this is done? 
many thanks Gavin 

[BEngo]

The objective is to get the centre line of the output gearbox exactly in  line with the tail shaft. If you know what you are doing and can think in  4 dimensions (pitch, yaw, heave,  sway) and their interactions as you move the engine  then it is easy.    For example, if you lift one side of the engine the gearbox centreline  may well move toward the side you have lifted, because many reduction box output centrelines are lower than the engine centreline.  The engine then needs to go bodily sideways to recentre on the shaft. Lift the front of the engine- the back of the gearbox will probably go down. And so on, so to describe how to do it would be a very long post.

 

Easiest way is to get  a man who knows in.  Lady aligners also exist.

 

N

[Gavlar1980]

Lol? that sounds like a good idea. Thanks a lot for the advice. Much appreciated 

[bizzard]

You can tell any unequally stressed mounts by '' Holding the mounts centre stud still, for this there should be flats for a spanner or hex socket for an Allen key on top. Whilst holding them still unscrew the top self locking nuts a long way up, DO NOT disturb the nuts underneath they are for final alignment.  When they are all slackened off  you should then see or feel with feeler gauges, or rock any movement on any of the mounts, unequal heights which will cause stress when those top nuts are tightened down.  Your engine bearers might not be perfectly true to each other either. one sloping a bit compared with the other perhaps. Once any discrepancies are known, then proper re-alignment proceedure can go ahead.

[Gavlar1980]

That’s sounds like super sound advice thanks, that completely makes sense and gives me something to work from. Much appreciated