Flexible Engine mountings and vibrations

[Theo]

After my engine (BMC1.5) was rebuilt at Calcutt we decided to quieten it down by installing it on flexible mountings.  Picture of the ones that we now have below.

 

Irritatingly, revs at tick-over hit resonance.  Of course I can adjust tickover but if I do it might be faster or slower than is reasonable.  Is there any way I can adjust this type to increase damping so that the resonance curve is less peaky?

 

[Bee]

I don't think so but I would put a bigger, thicker washer under the left hand nut and then just check all the rest of the bolts. Might find that a bit of looseness has crept in and something is actually vibrating.

[MtB]

You can probably change the resonant frequency by tightening down two diagonally opposite mountings by a turn or two and adjusting UP the opposite two mounts by the same number of turns.

 

This will (or should!) keep the engine in the same place but will pre-stress the mounts and raise the resonant frequency. Might even get rid of it totally.

[IanD]

1 hour ago, MtB said:

You can probably change the resonant frequency by tightening down two diagonally opposite mountings by a turn or two and adjusting UP the opposite two mounts by the same number of turns.

 

This will (or should!) keep the engine in the same place but will pre-stress the mounts and raise the resonant frequency. Might even get rid of it totally.

That's not what happens, you end up with two different resonant frequencies for diagonal rocking in the two directions, one higher and one lower than before the adjustment. Might help things or might make it worse... 😉

 

(and if the rocking mode is side to side it'll probably make no difference)

[Theo]

I have increased the tick-over out of the resonant frequency.  I'll see what happens on the way up to Kingswood junction.  (Up Hatton just in time!)

 

I'll try the various tightening methods when I am not in a rush.