Engine Mount wear

[DAKA]

I am interested in your opinion of this please.

One of my engine mounts was showing signs of a crack in the rubber, I decided to change it before it got any worse.
Questions

Do all mounts wear like this ?
Does it show the shaft needs aligning ?
How much longer would it have gone before it cracked all the way through ?
What would have happened if it had have cracked all the way through ?

Ignore the wet antifreeze mark, note the crack starting under the 'Tre' of Trelleborge and wear ending just under 'g'

Would you ignore it or investigate further.


.

 

[MapisM]

It's very hard to give a sensible reply, 'cause you omit the most important thing: how old (age + hours of operation) is that?
Also, a couple of other things might be relevant: what about the other mounts? And the other engine?

 

[DAKA]

Good question
Other engine/mounts are in good condition.
Two on the front of the engine and two holding the rear/gearbox, this is one of the rear/gearbox mounts.
There has not been any noticeable vibration save in hard astern which I previously thought was cavitation.
I think the mount is 6 years old and about 430 hours.

 

[MapisM]

Other engine/mounts are in good condition.
I think the mount is 6 years old and about 430 hours.

Well, in this case, going back to your original questions:
1 - obviously no, according to your latest details;
2 - possibly, but you should have felt a noticeable difference in vibrations between the two engines, long before wearing the engine mount(s);
3 - no idea;
4 - a mess!

 

[MapisM]

There has not been any noticeable vibration save in hard astern which I previously thought was cavitation.

I missed this detail in my previous reply.
Ever tried that one engine at a time? At a guess, you'd feel the same vibrations.

 

[LittleShip]

Two points here...

1 That mount is past it's sell by date so you will need to change all of them.

2 You wont be able to check alignment of the shaft now you have removed it so when you replace the mounts it's time to re align the shaft (s)

Nobody can say how long the mounts will last it will depend on the type of boat, power of the engine, type of use ect ect.

Now you know that they seem to last about 400 hrs you may need to build it into your servicing regime.

Once the new mounts are fitted check the alignment again after 10 hrs or so.


ATB

Tom

 

[DAKA]

yes it was just the starboard engine that suffered astern cavitation a lot, I think it has stopped now the mount is fixed, I'll find out when the weather improves.

 

[rafiki_]

If specified correctly, and quality OK, mounts should last 10 years. Trelleborg are a good supplier. They can deteriorate quicker in a harsh environment, oil, excessive vibration etc.

There are some suppliers that you would not want to see.

Generally these engine mounts are "borrowed" from automotive applications, which are a nastier environment (greater thermal range, water soaking etc.), but mmore analysis is done with vehicles because of refinement needs and warranty costs.

 

[jfm]

In which direction is the load created by the engine's weight? Radial, i know, but in which direction relative to the crack?

 

[MapisM]

Right to left looking at the pic, I would guess.
Also interested to hear about it, though.

 

[hlb]

Well dont leave it till your stern gland comes adrift. The fire brigade make a hell of a mess of your cushions and carpets.

 

[DAKA]

In which direction is the load created by the engine's weight? Radial, i know, but in which direction relative to the crack?

MapisM guess is correct although I am bemused as to how he could tell.

The mount in question is the port side rear /gearbox of the starboard engine.

The shaft turns clockwise.

The underside bracket holding the mount as pictured came loose after a locking tab was not locked, when hard astern propulsion was used vibration could be felt which I incorrectly diagnosed as cavitation.

Now a lot of guessing on my part...........

Earlier in the season a Dinghy tacked in front of me and I had to use full astern, I believe this damaged the mount however I didnt notice this for several months.

Eventually I found the mount bracket nut loose, tightened it and noticed the wear crack in the rubber mount.
I have replaced the Mount bracket, the locking tab washers and the rubber mount that is worn.
I'll be honest I would like to leave it at that and get on with enjoying boating but I feel I have narrowly avoided a close shave so I am trying to learn as much as possible on engine mount wear/replacement schedules/alignment.

 

[Adrianwool]

Mounting trouble!

My surveyor found a problem we he surveyed my current boat prior to purchase, all engine mounts (eight in total) for my TAMD41B engines were replaced. In some cases mounting bolts 2 - 3 I think were sheared as well!. Yet this did not show up as excessive vbration etc on running. The spec for the mountings had changed, the original spec was for 16m bolts, this spec had been replaced with 18m bolts. To be fair the boat was 18 years old at the time of this work, a visual inspection of the old mounts showed no discernable deteriation in the rubber components, but I guess as they get older the rubber becomes less flexible. We could not account for the shearing in any way props and all underwater gear were fine, showing no signs of having struck any underwater object, engines run smoothly so no answer re the shearing. Volvo may know something of course, and this is why the beefed up the bolts sizes. In terms of when to replace such components I think the factor here has to be an annual inspection by your good self or engineer to check condition. In my view should be replaced as and when required , rather than on a 'time expired' basis.

 

[MapisM]

MapisM guess is correct although I am bemused as to how he could tell.

Did I win a cigar?