DIY engine mounts

[pandos]

Volvo branded ones are likely silly money.

A new set of 4 after-market mounts for that engine, though, can be had for £140 including shipping, perhaps less. That doesn't seem at all outrageous to me.

Where have you seen these?

 

[vyv_cox]

I would have thought that how soft or hard the elastic material would be is rather important to providing a good compromise between stopping excessive engine movement while limiting the transmission of vibration.

Very true. When my Yanmar 3GM30F was installed it vibrated quite markedly. There was a choice of engine mounts of different rubber hardness. I replaced the original aft ones with the alternatives, which was a considerable improvement.

 

[LittleSister]

Where have you seen these?

Novibrasyon Marin | Silent Anti-Vibration Marine Solutions
The '55 shore' set appears suitable for the 190kg (according to Google) Volvo MD21, unless the front and back weights are very different (in which case one might need the '45 shore' one end and the '65 shore' the other). (Spec on website says this range suitable for Volvos 9-70hp.) Price for set of 4 is €120, shipping to England €40, totalling just under £140 at current exchange rate.

Other brands and suppliers (including UK ones) available, very likely at similar or perhaps even lower prices.

 

[Klausen]

Try Febi Bilstein 04032

 

[pandos]

Well it's your choice

I know

 

[pandos]

But they were designed (or selected) by someone who knew the weight of the engine (and the difference between the weight of the front and the back if significant) and the amount of torque with which the engine could be loaded. (and perhaps how vibratory the engine is?)

I would have thought that how soft or hard the elastic material would be is rather important to providing a good compromise between stopping excessive engine movement while limiting the transmission of vibration.

The size and shape of the rubber is not in doubt. The metal parts are not in need of replacement. The only real question is the hardness of the replacement material.

It seems the hardness of the rubber is likely about 45. Most Polly bushes are made at about 60.. thus the initial question wondering if anyone has made their own from Polly...

 

[Klausen]

Motorlager Volvo Penta 2002 - Segeln-Forum

 

[Daydream believer]

Our Buka35 hp diesel in our launch was fitted when our local engineer installed the engine
Vibration was ridiculous. The mounts were very hard
I rang the manufacturer who sold us a smaller and far more flexible mounting. cost was not so expensive
Fitting it correctly made an amazing difference

 

[ducked]

But they were designed (or selected) by someone who knew the weight of the engine (and the difference between the weight of the front and the back if significant) and the amount of torque with which the engine could be loaded. (and perhaps how vibratory the engine is?)

I would have thought that how soft or hard the elastic material would be is rather important to providing a good compromise between stopping excessive engine movement while limiting the transmission of vibration.

If you were interested/concerned/convinced it mattered/could be bothered, and had sufficient access, you could probably measure the resonant frequency of the engine by rocking it manually, as can be done for vehicle suspension. There are apps that use the accelerometers built in to most smartphones to give T/D graphs and data, which could probably also measure vibration directly when the engine was in use, both on the engine, and elsewhere in the boat.

With incrementally applied cable ties, this might allow "tuning". Due to the shape of my engine mountings on the Skywing (a car, see linked post), I had to completely wrap the mounting with it removed, which meant that the cable ties were trapped between the mounting and the body (the mounting studs were long enough to allow this) , which, together with the fact that I didnt really think they would hold, meant I just put on as many as would fit.

(I only had white nylon ties so I blackened them with boot polish to make them less obvious at the 6-monthly inspections (ALL vehicle modifications are illegal in Taiwan) but if they were ever noticed nothing was ever said. Being effectively deaf, dumb and illiterate can be a great asset with this kind of thing)

From the picture, those mountings would allow ties to be applied incrementally, one pair at a time, without removal (assuming there is access) which could allow tuning (though a single pair might bust or deform).

Tuning of cast or carved elastomer mountings via material choice, (if a selection of resins is available) thickness, and incorporation of cast-in voids would also be possible but much, much more difficult, and seems unlikely to be worthwhile for a one-off.

 

[pandos]

Motorlager Volvo Penta 2002 - Segeln-Forum

The link in that thread has proved useful. It's a Turkish manufacturer so it may be problematic with delivery to Ireland but I am waiting for a quote..looks like about 300 euros for a set of heavy duty mounts...need to check that the bolting down arrangements are usable...

 

[ducked]

I think this is another one of those jobs on a boat that you can't scrimp on, considering the job they have to do

I think this is another one of those jobs on a boat that I could probably scrimp on, considering that I dont have a job to do.

 

[Tamar]

I think this is another one of those jobs on a boat that I could probably scrimp on, considering that I dont have a job to do.

Scrip away then. If you get it wrong say goodbye to your cutless bearing, stern gear and probably gearbox main bearing. Good luck

 

[ducked]

Scrip away then. If you get it wrong say goodbye to your cutless bearing, stern gear and probably gearbox main bearing. Good luck

Thanks. I dunno if I have an issue with my (presumably Yanmar, but possibly aftermarket) mounts since I've neither run the engine nor looked closely at them, but I suppose even if I dont have an issue, it might not do any harm to stiffen them up some with a few preventative cable ties, if geometry and access is as suitable as the OP's, shown above.

I assume the disastrous consequences you anticipate would be more likely to result from mounts that were too loose, than from those a bit stiffer than originally intended.

WHEN AND WHY SHOULD MARINE ENGINE MOUNTS BE REPLACED? - Ellebogen

Video showing excessive movement due to degraded mounts. Looks like the rubber or its bond to the bell has failed in tension (as had those on my car) Tethering with cable ties might restrain this. Its more difficult (probably not impossible) on this bell-shaped design, but much easier on the type shown in the linked detail video on elastomer failure, and the OP's

I dunno who installed the engine on my boat, but its a fair bet it wasn't Werner von Braun, or anyone who served out their apprenticeship at Vosper Thorneycroft, Rolls-Royce, etc

 

[ducked]

If you were interested/concerned/convinced it mattered/could be bothered, and had sufficient access, you could probably measure the resonant frequency of the engine by rocking it manually, as can be done for vehicle suspension. There are apps that use the accelerometers built in to most smartphones to give T/D graphs and data, which could probably also measure vibration directly when the engine was in use, both on the engine, and elsewhere in the boat.

With incrementally applied cable ties, this might allow "tuning". Due to the shape of my engine mountings on the Skywing (a car, see linked post), I had to completely wrap the mounting with it removed, which meant that the cable ties were trapped between the mounting and the body (the mounting studs were long enough to allow this) , which, together with the fact that I didnt really think they would hold, meant I just put on as many as would fit.

(I only had white nylon ties so I blackened them with boot polish to make them less obvious at the 6-monthly inspections (ALL vehicle modifications are illegal in Taiwan) but if they were ever noticed nothing was ever said. Being effectively deaf, dumb and illiterate can be a great asset with this kind of thing)

From the picture, those mountings would allow ties to be applied incrementally, one pair at a time, without removal (assuming there is access) which could allow tuning (though a single pair might bust or deform).

Tuning of cast or carved elastomer mountings via material choice, (if a selection of resins is available) thickness, and incorporation of cast-in voids would also be possible but much, much more difficult, and seems unlikely to be worthwhile for a one-off.

Autospeed Articles on rubber mounts etc

AutoSpeed - Designing Rubber Mounts

Measuring structure stiffness

AutoSpeed - Measuring the stiffness of structures by vibration testing

Car suspension tuning

AutoSpeed - Measuring wheel suspension rates

I looked at another app that was actually free, and available on both iPhone and Android, IIRC from Wartsila, for a possible student project that in practice I didn't manage to fit in to the schedule. IIRC it wasnt all that easy to use, though might have improved with practice. Can't find it now but there are a few others out there.

If for own use, with an IPhone, might be worth buying the app in the article

Vibration Version 2 and later