Engine mounts, rubber unstuck from steel frame. Yanmar 1gm10.

[niallw70]

Lightwave, wow your mounts look smart.... for now, but they are of the same design as old style Yanmar, will the rubber also not be susceptible to combination of diesel and moisture?
After much online browsing I think R&D offer best solution, but their direct replacement Yanmar mount 800-074 was too tall at 87mm minimum for my tiny engine bay. I'm going with their "Double acting mount 800-032" hopefully this will be flexible enough to avoid excessive vibration. Its a shorter mount with suitable bolt holes to match my bay.

 

[Lightwave395]

Lightwave, wow your mounts look smart.... for now, but they are of the same design as old style Yanmar, will the rubber also not be susceptible to combination of diesel and moisture?
After much online browsing I think R&D offer best solution, but their direct replacement Yanmar mount 800-074 was too tall at 87mm minimum for my tiny engine bay. I'm going with their "Double acting mount 800-032" hopefully this will be flexible enough to avoid excessive vibration. Its a shorter mount with suitable bolt holes to match my bay.

Time will tell ! My engine and it's mounts are well protected from diesel and moisture so hopefully they'll be fine. I too looked at R & D but there have been reports of these causing excessive vibration at low revs, although that didn't in itself put me off. Thus far mine are very smooth and I'm very happy with them

 

[JumbleDuck]

So what provides less vibration, flexible or fixed?

Generally speak, firmer mounts are worse if you pass through resonance.

Forgive a mathematical explanation. The magnitude of a rotating imbalance scales with frequency squared, since it's basically a centrifugal acceleration with magnitude m r omega^2, where omega is the rotational speed in radians per second.

Resonant frequency of a mass-spring system is sqrt(spring constant/mass) so if you make the spring constant higher you increase the resonant frequency. However, if you double (say) resonant frequency, the rotating imbalance forces will be four times as much and you end up with four times as much vibration.

Away from the resonant frequency the vibration is not too bad, so the answer is either to use hard enough mountings to avoid resonance altogether or to use such soft mountings that resonance happens at a low speed with low forces and therefore isn't too spectacular. That's why washing machine drums tend to have very, very soft suspension. There is always a rotating imbalance on spin, so by getting resonance out of the way at low speeds- typically 100rpm - the suspension can cope with 1000+ rpm spins.

For a boat engine, mounts which gave resonance at 300 - 400 rpm would certainly be better than at 1500 rpm.