scootz
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| posted on 15/7/13 at 11:25 AM |
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Engine Vibration Damping
I've noticed in more and more build diaries that engines are being solidly mounted to chassis - paricularly bike engines.
Is there a particular reason for this shift away from using traditional damping techniques, or are we just becoming a more 'hardcore'
bunch!? 
It's Evolution Baby!
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40inches
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| posted on 15/7/13 at 11:35 AM |
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Can't help, but I would be interested in the answer. The high frequency vibration gets a little uncomfortable around 4000rpm, and
has caused fractures in the header to silencer link pipe. 
I have considered fitting wishbone poly mounts on the cradle.
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MikeRJ
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| posted on 15/7/13 at 11:42 AM |
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For a competition vehicle it may make sense, but it's madness for a road car.
[Edited on 15/7/13 by MikeRJ]
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Slimy38
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| posted on 15/7/13 at 11:42 AM |
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Bike engines are solid mounted in their native habitat, I don't think I've ever seen a rubber mounted engine in a bike.
One reason that springs to mind is that car engines 'sit' on their mountings, whereas with most bike fixings being side mounted the rubber
mount would be in a sheer position and may not last long. I guess you could solid fix a hanger of some kind and then use a more standard mount? Or as
mentioned, use poly mounts on the cradle rather than the engine?
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40inches
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| posted on 15/7/13 at 11:50 AM |
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quote:
Originally posted by Slimy38
Bike engines are solid mounted in their native habitat, I don't think I've ever seen a rubber mounted engine in a bike.
One reason that springs to mind is that car engines 'sit' on their mountings, whereas with most bike fixings being side mounted the rubber
mount would be in a sheer position and may not last long. I guess you could solid fix a hanger of some kind and then use a more standard mount? Or as
mentioned, use poly mounts on the cradle rather than the engine?
True, except my ZX9R is rubber mounted on the top rear mountings, don't know if the other mountings are, on the bike.
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v8kid
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| posted on 15/7/13 at 12:11 PM |
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it makes the gearchange more positive - no need for rubber mounts on gearchange.
one chap in our club had a middie zetec and the gearchange was fine in the garage or when tootling around - boot it and it would jump out of gear and
baulk. solid mounting cured it
You'd be surprised how quickly the sales people at B&Q try and assist you after ignoring you for the past 15 minutes when you try and start a
chainsaw
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coyoteboy
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| posted on 15/7/13 at 01:23 PM |
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It depends on your engineering and choice of compromises surely? There's no right answer, there's a right answer for certain situations.
If you have gear cables you can happily rigid mount the lever and not the engine/box, if you have gear rods you probably can't get away with
rigid mounting one end but not the other, but maybe.
There's really only 2 reasons for rigid mounting an engine/box. 1) To use it as a structural member to add rigidity or to replace a structural
part 2) to make your life easier (debatable) not having to use more parts and rubber mounts. IMO if you're not going to be using it as a
structural member, there's few other real reasons to rigid mount it. Unless you like the vibrations :-)
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sdh2903
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| posted on 15/7/13 at 03:26 PM |
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Out of interest what would people use to dampen cradle mounts as its on my winter to do list?. I have gear cable so can get away with a bit of engine
movement. Polybushes aren't very good at dampening so what else, thick rubber washers? metalastic bushes?
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theprisioner
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| posted on 15/7/13 at 06:41 PM |
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My J15, Puma 1.7 engine is virtually solidly mounted only mutualistic concentric bushes in four places. It has a bugger of a resonance at 2500 that is
driving me to distraction on the road. Tomorrow I am attacking one end of the engine installing some rubber pads to see if that helps.
http://sylvabuild.blogspot.com/
http://austin7special.blogspot.co.uk/
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40inches
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| posted on 16/7/13 at 08:21 AM |
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Doing a Google search brings up the fact that Mac#1 bike engine cradles are mounted using what look like wishbone poly mounts.
Wonder what the softest Shore hardness Polyurethane is available in?
It appears that Polyurethane is available in a greater range of hardness than rubber.
Chart
[Edited on 16-7-13 by 40inches]
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baz-R
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| posted on 16/7/13 at 04:57 PM |
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why not just make an engine sub frame then mount this to the chassis with some firm rubber mounts? like car engine users use
it will kill the vibes but not move about too much
or posibbly a metalastic bush?
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MikeRJ
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| posted on 20/7/13 at 09:55 AM |
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quote:
Originally posted by Slimy38
Bike engines are solid mounted in their native habitat, I don't think I've ever seen a rubber mounted engine in a bike.
Quite a few modern bikes have rubber engine mountings now (even Harleys driven by big bad accountants!), but sports bikes often use the engine as a
stressed member so have to be solidly mounted.
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coyoteboy
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| posted on 24/7/13 at 05:45 PM |
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quote:
Originally posted by theprisioner
My J15, Puma 1.7 engine is virtually solidly mounted only mutualistic concentric bushes in four places. It has a bugger of a resonance at 2500 that is
driving me to distraction on the road. Tomorrow I am attacking one end of the engine installing some rubber pads to see if that helps.
Attack both ends, rigid one end and flexi the other will stress the engine and tend towards warping the block under load.
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Mr Whippy
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| posted on 24/7/13 at 06:51 PM |
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I mind trying solid mounting a 2.8 v6 cologne in my JBA falcon, was truly awful, like sitting in a giant blender. I fitted soft diesel transit mounts
instead and you couldn't even feel the engine running. For a road car it's a terrible idea.
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theprisioner
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| posted on 24/7/13 at 07:27 PM |
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Your right, both ends now done, what a difference:
http://sylvabuild.blogspot.co.uk/2013/07/road-trials.html
http://sylvabuild.blogspot.com/
http://austin7special.blogspot.co.uk/
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