View Full Version : Vibrations & rubber mounts

kemis - n/a
27-Sep-07, 08:58 AM
Have a question about Vibrations & rubber mounts. If I understand this correct their is 3 kind of mounting.

1. Rubber mounts on the engine.

2. Rubber mounts on the engine and use a lower pully and Flexible Coupling to the engine.

3. Rubber mounts on the frame.

Nr 1 get you a very small engine installation, but I have some problem with the belt that moves a lot on the left side seen from back, see picture nr 2, specally on low rpm. Maby only the belt that is to lose!? This solution give me the easyes and smallest installation but it i safe to do like this?

Nr 2 seams to be a very nice solution but take a lot of space. Need to place the engine atleast 30 cm forward to have space for the lower shaft and the coupling. Probobly the best solution but I do not like to lose so much space. Have 10 mm space to the duct today. Is this enough for this kind of mount?

Nr 3 Here both engine, frame and the fun moves and maby the fun can hit the dukt and I need mor space betwean fun and dukt.

I have made solution 1, se picture but is this a correct way to do? It is on a crusing craft not racing.

As you can se on the picture the installation is very small. Only 35 cm from the duct and out.

Very interested to see how other have done this.





profqwerty - n/a
27-Sep-07, 02:21 PM
The engineering looks ok to me - some nice welds there! As long as that top sq tube is thick walled it should be ok... (although I'm not qualified to say that!)

hoverchaps - n/a
27-Sep-07, 05:43 PM
Sorry to dapen things but if you rubber mount the motor as you have as you load the belt the rubber hounts will stretch and the shafts will go uot of line and belt jump. You need to solid mount the motor then rubber mount the whole assembly.

Jamie Lewendon - n/a
27-Sep-07, 05:52 PM
I agree with Duncs (shocking I know) As the engine is free to move around, the shafts will not stay in line, the belt will then come off.


kemis - n/a
27-Sep-07, 09:39 PM
Has not happend yet but their is a small movment on the belt.

If you have rubber mounts on the frame. Is their not a problem that the fan hits the duct? Or need to have extra space to the duct. Hav locked on many picture but I have not seen any that have rubber mount their frame to the dukt.

I flexible coupling is probobly the best solution but it need so much space.


profqwerty - n/a
28-Sep-07, 06:11 AM
I used to use the engine inverted with a gearbox. the frame was bolted to the duct/hull, and the engine rubber mounted onto the frame.

There was a small amount of movement in the fan, so i left about 10mm at the top, and 5mm at the bottom clearance (as the centre of the fan was above the mounts, it rotated upwards slightly (but only slightly)).

The main issues were at certian speeds (low ones) there was resobnance in the engine caiusing the whole thing to move obviously.

If the blades scrape the duct, they just wear the duct/themselves till the fit!

tonybroad - n/a
28-Sep-07, 08:13 AM

sorry to bring bad news, i once had a problem with the first craft i built which had the engine rubber mounted a similar way to yours

the belt tension under load pulled the engine upwards in the mounts making the belt slack and also putting the shafts out of alignment

the belt would either jump or ride off the bottom pulley

one way of overcoming this might be to put some form of tie-rod from your engine plate to the frame which will allow the engine to vibrate in the mounts but will not let it pull upwards

good luck


kemis - n/a
28-Sep-07, 09:22 AM

The problems is in low speeds for me that you called "resobnance in the engine caiusing the whole thing to move obviously". It is then the belt moving litle to much.

Probobly the ruber mount still is hard enough to hold for load but this problem would probobly come soon to when the rubber mount gets little softer.

Their is probobly not a god answer like. This is wrong. You shall do like this...

The rubber mount I use is made for this engine 4 cycle, 2 cyl, wight aso and work very well. Allmost no vigration to the hull!

If I change the 4 rubber mount on the engine to 6 like on the picture it my work? It is only the fun movement I was I litle worried for.

Dust dust dust and alot of sanding! http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif

Have done litle more now. This picture is one years old.