Engine Mounts

Bewarethemoon

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So as some of you may have noticed I like a bit of R&D and I've been toying with designing engine mounts for my build for a couple of years now.

I think Hugh Ownings did a real nice job and there's not much to be improved upon, certainly not aesthetically, but I would still like to have a go at them myself.

Very recently I purchased a set of footrest mounts from Cognito Moto to go along with some Tarozzi rear sets I have. I went for the rubber bushing version because... well why not?

CognitoMotoMounts.jpgXS650Bushings.jpg

Can anybody see any obvious or not so obvious pitfalls of trying to incorporate a similar mounting point design into my engine mounts?

Daniel.
 
No comments or suggestions.... yet. Watching with interest.


View attachment 214796

I know twins are prone to excessive vibration and the XS650 more so than most so I wondered if this could potentially take the edge off a little?

I just thought I’d create a thread to open up a topic of conversation, bit of a think tank I suppose?

Daniel.
 
Not at all Daniel.
I have been wrestling with modifying the engine mounts on my punisher build. Much of the discussion in the Good Vibrations thread. Many great ideas and points given for consideration. My particular set up required me to modify my frame although my original intent had been to create the modifications without having to do that. The dampening that I settled on included the use of bushings similar to those you have posted. I will definitely be following your efforts with great interest.
 
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If my memory serves me correctly, when the Norton Commando was designed, they thought that they had to mount the swing arm to the engine and gearbox, rather than the main frame.
This was to prevent drive chain tension from deforming the rubber mounts.
They reckoned about two tons of tension on the chain in first gear.
Having said that, Suzuki's GT750 had a rubber mounted engine, and didn't seem to have any ill effects.
 
Yes I can see a problem. The rear of the motor will still be fixed rigidly. The front will be isolated on the rubbers, in time the rear motor mounts on the engine could crack. They crack on race bikes and sidecars. Those after market foot peg mounts are rubbish and dont last. Cast some eurothane ones and isolate the whole engine and you should be in a better position long term.
 
Yes I can see a problem. The rear of the motor will still be fixed rigidly. The front will be isolated on the rubbers, in time the rear motor mounts on the engine could crack. They crack on race bikes and sidecars. Those after market foot peg mounts are rubbish and dont last. Cast some eurothane ones and isolate the whole engine and you should be in a better position long term.
Could you open up the holes in the frame or engine case slightly to allow a rubber or eurothane top hat style bushing? I say it and sounds like opening it up could in the end cause it to Crack but I wonder if it's only a bit and every other mount point, perhaps minus the bottom most ends up isolated if it will hold up. Especially in a non race application?
 
The problem with anything like this is that you won't know what the problems are until you do it.

Signal has identified an issue unless you rubber mount all mounting points. Do this and you may then find that the vibrations are un-damped and could make the situation worse?
The choice of mounting material and size may well be able to overcome this?
I guess that the mounts would also have to be of sufficient size to withstand the vibrations; too small and the may well fall apart quite quickly.

You will also loose the rigidity that the motor gives to the frame.

I suspect you will never get it turbine smooth (unless you convert it to a Wankel engine) so an alternative may be to get the internal rotating components balanced. This won't eliminate the issue but should minimise it.
 
Try to find a principle drawing of the engine mounting system on the MZ 250 2 stroke single. Not as complex as Norton Isolastic system.
The idea is to let the engine pivot freely from an aft mount, and have rubber mount at the front, where the vibrations are caused by pistons and rods. On an XS that would require a bushed and free bottom bolt, rubber mounts on top of gearbox, at the cylinder head, and at the front. And ideally a very low balance factor, to keep the primary imbalance in the vertical plane.
 
Try to find a principle drawing of the engine mounting system on the MZ 250 2 stroke single. Not as complex as Norton Isolastic system.
The idea is to let the engine pivot freely from an aft mount, and have rubber mount at the front, where the vibrations are caused by pistons and rods. On an XS that would require a bushed and free bottom bolt, rubber mounts on top of gearbox, at the cylinder head, and at the front. And ideally a very low balance factor, to keep the primary imbalance in the vertical plane.
https://www.classicbikeguide.com/mz-es250-2/
1653305907380.png
 
Hard to argue with the classic lines.
View attachment 214832

:rolleyes:
Despite the design choises, MZ and Walther Kaaden got impressive results from very limited resources, back in the 60s. When Ernst Degner defected, and brought MZ tech and knowledge to Suzuki, the Suzuki 125 almost doubled its hp over a very short time period.
 
If my memory serves me correctly, when the Norton Commando was designed, they thought that they had to mount the swing arm to the engine and gearbox, rather than the main frame.
This was to prevent drive chain tension from deforming the rubber mounts.
They reckoned about two tons of tension on the chain in first gear.
Having said that, Suzuki's GT750 had a rubber mounted engine, and didn't seem to have any ill effects.
My GT750 engine is rubber mounted. Vibration is non existent except at 2500 ‘ish rpm when the handlebars get quite a buzz. Above and below that, silky smooth.
 
So as some of you may have noticed I like a bit of R&D and I've been toying with designing engine mounts for my build for a couple of years now.

I think Hugh Ownings did a real nice job and there's not much to be improved upon, certainly not aesthetically, but I would still like to have a go at them myself.

Very recently I purchased a set of footrest mounts from Cognito Moto to go along with some Tarozzi rear sets I have. I went for the rubber bushing version because... well why not?

View attachment 214793View attachment 214794

Can anybody see any obvious or not so obvious pitfalls of trying to incorporate a similar mounting point design into my engine mounts?

Daniel.

Hello Daniel
I also used Cognito Kit on my build, which is still in progress (The Welsh Flat Tracker Revival #86).
In my case the frame was modded to accept alternative Italian rear-sets; and the standard XS650 mounts were long gone. The existing sets were crap and replaced with the Cognito Kit. I had to re-modify the mounting points on the frame. I used the rubber mounts that came with the Cognito mounts; vibes are still there but massively reduced, and now tolerable.
The XS is a classic with inherent vibes of its type, a Honda CB750 or Suzuki GT750 Kettle it is not.
Ads.
 
Since we're putting ideas on the table. You seem to be thinking of rubber mounting the engine to isolate the vibes? But that will lose the engine contribution to frame stiffness. Another approach is improve the rubber mountings for the footpegs and handlebar - isolate the rider from the vibes.
 
Since we're putting ideas on the table. You seem to be thinking of rubber mounting the engine to isolate the vibes? But that will lose the engine contribution to frame stiffness. Another approach is improve the rubber mountings for the footpegs and handlebar - isolate the rider from the vibes.
Just what I did above Raymond. 😁
 
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