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I was at a loose end yesterday and I used up some time making this. GTAR suggested it. I cut the center out of the support and welded in a pair of 3/8-16 nuts.
 

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Ed- yes, an old trick that comes in very handy if you don't happen to have a collection of the various length struts lying around. Particularly useful if you are doing an engine swap, early chassis to later, larger engine, etc.
I have achieved the same effect IIRC, by adding a section on the bottom and milling an elongated slot for the lower mtg. bolt in order to get some range of adjustment. This was to facilitate the installation of a twinspark (taller) motor into a GTV and achieve intake plenum/hood clearance. There is more elasticity (range of motion) in the Spica and later similarly designed Motronic rubber intake connectors than carb. mounts however.
I think yours is the better, more accessible option though.
 

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Nice, but why does it need to be adjustable?

Why not just cut it, install in place and work out how long it should be and then weld it at that length?
Pete
 

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Discussion Starter #4
Why not just cut it, install in place and work out how long it should be and then weld it at that length?
Pete
This way I made it ahead of time. The new carbs are not yet on hand.
 

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Richard Jemison
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WOW!

I was at a loose end yesterday and I used up some time making this. GTAR suggested it. I cut the center out of the support and welded in a pair of 3/8-16 nuts.
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Now the solid Carb mounts can stress the support rod.......................

Engineers... Stress sources for designers........
 

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Discussion Starter #7
Now the solid Carb mounts can stress the support rod.......................
If I adjust it right they will share the stress and increase the safety margin (against whatever bad thing might happen?)

Do you need a support rod with the solid mounts?
A couple of people (not Richard) recommended keeping it.
 

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I don't think a strut is necessary but I really like the adjustable feature. I wonder with the hard mounts if you should eliminate the rubber bushing...
The strut is very necessary with the standard system.
Pete
 

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Sorry, I should have been more specific: I don't think a strut is needed with SOLID mounts and could induce stresses if it is the wrong length. Ed solved that issue with the adjustable strut.

My only other objection to a strut is that it interferes with my fat fingers when I'm trying to reach back in that area to fiddle with the starter or the carb bell crank. Kind of a weak argument...
 

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Discussion Starter #11
So y'all think it is OK for the Webers to support the weight of the plenum and airbox ?
 

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Richard Jemison
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Support

Quote:
Do you need a support rod with the solid mounts?
A couple of people (not Richard) recommended keeping it.
(not Richard)
Really?

As already brought up, the "support rod should have a solid "bushing" to keep things stable and "control" the resonance of the carb and airbox weight so the ears on the carbs are lot the support mechanism. Same reason I would never use rubber o-ring type carb mounts.

Ed, give me the exact ID of the rod`s tube for the bush and I`ll make you one. I have the motor mounts to get width. Hole is 10mm but the width should be a close fit so the bolt locks the part in place.
 

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Discussion Starter #13 (Edited)
Ed, give me the exact ID of the rod`s tube for the bush and I`ll make you one. I have the motor mounts to get width. Hole is 10mm but the width should be a close fit so the bolt locks the part in place.
I will do that.

An extra consideration is this; The airbox hits the underside of the hood when the engine shakes. I have a piece of rubber glued to the hood in that place to stop it rattling. There must be some stress directed at the Webers when this happens. That is a reason why I think that I may need the support rod.

I pressed out the bushing and measured the OD with a micrometer, not a HF caliper! It is 1.341"
 

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Richard Jemison
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Fitting the engine in the automobile

An extra consideration is this; The airbox hits the underside of the hood when the engine shakes. I have a piece of rubber glued to the hood in that place to stop it rattling. There must be some stress directed at the Webers when this happens. That is a reason why I think that I may need the support rod.
Enginnering solution?

Actually what I suggest doing is supporting the engine and removing the driverside motor mount.
Remove the rubber part and cut the metal section vertically. Then weld the two halves together again so that the engine sits 1/8 to 3/16 lower at the motor mount.
The distance from the MM to the airbox should factor in a movement to the driverside by at least 1/4 to 3/8 inches as well as raising the airbox about 1/4 inch.

Then you are not adding stressors.

Anyway , that`s what I would do if I were an engineer.:x
 

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This is fun! For the rubber mounts, yes, the support IS necessary. As I learned years ago, and some Lotus owners (the honest ones) will attest, there IS a vibration element in solid Weber mounts. This had 4 cylinder Lotus engines running complex emulsion tubes in the 40 mm Webers. I do not remember who told me that the Weber side engine mount is located near dead "vibration node" in the 4 cylinder Alfa crank and attaching either a solid or bushed rod from there to the outboard side of the Webers reduces high frequency Weber vibration that requires trick (Lotus type) E tubes. Ok maybe or maybe not. However, this is real. Float paddles can wear quite quickly without a support rod. Below is the needle-seat paddle from a new float I replaced for a customer after one track session with solid Weber mounts and no support rod.
 

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This is fun! For the rubber mounts, yes, the support IS necessary. As I learned years ago, and some Lotus owners (the honest ones) will attest, there IS a vibration element in solid Weber mounts. This had 4 cylinder Lotus engines running complex emulsion tubes in the 40 mm Webers. I do not remember who told me that the Weber side engine mount is located near dead "vibration node" in the 4 cylinder Alfa crank and attaching either a solid or bushed rod from there to the outboard side of the Webers reduces high frequency Weber vibration that requires trick (Lotus type) E tubes. Ok maybe or maybe not. However, this is real. Float paddles can wear quite quickly without a support rod. Below is the needle-seat paddle from a new float I replaced for a customer after one track session with solid Weber mounts and no support rod.
I agree, this is fun and interesting. I am an engineer but far from an expert in vibration analysis so my comments are more seat-of-the pants than equations. I do have a fair amount of work experience manufacturing rubber mounts and such which I value far more than my degree. My argument regarding soft mounts verses hard mounts is that using rubber to attenuate vibrations is like juggling cats. There is little chance for success.

The big factor to me is the fact that rubber's attenuation capacity varies with temperature, aging, the base polymer, fillers, cure systems, extenders and a dizzying array of additives, yada, yada, yada.

I make a product used in science experiments that consists of two rubber balls that look, feel and smell the same. One bounces like a super ball and the other has zero rebound.


What's my point? Three (as any good sermon should):

1) If you allow me to relate the rebounding ability to frequency attenuation (they are related) then it is obvious from the video that two seemingly identical rubber materials will have vastly different characteristics. And guess what? Specialty, "engineered" polymers are a lot more expensive than your basic rubber. So, who here thinks that the material that was originally specified in 1955 (or whenever these mounts were designed) is the same material 60 years later? Not me... And if not, the chance that this rubber is attenuating the frequency that the carbs require is as likely as me attending Claude Lemieux's birthday party (obscure hockey reference...).

2) What isn't addressed in the video is that if you heat (or cool) the sad ball (no, I didn't name them and no, that's not me in the video) it will bounce much like the happy ball. This has to do with the glass transition temperature of the rubber which, at room temp absorbs a tremendous amount of energy. Point being that attenuation will vary with temperature. So what might work when the motor is cold will not necessarily work at motor temperature...

[2a) As the rubber mounts are heated and cooled over time they do what? They harden. Changes in hardness = changes in frequency attenuation.]

3) Manufacturing rubber mounts is no simple, inexpensive task. In addition to having the machinery and knowledge you need stamping dies and rubber molds. A cheap set will cost about $50,000. So there are likely only a few in the world that make these. And since they are all aftermarket, there is no governing body (ie, Alfa Romeo, Lotus, etc) that holds the manufacturer to the design requirements of the drawing (assuming they even have the drawings). Just like the happy and sad balls, they can look, feel, smell and taste the same but will perform vastly different in the field.

Solid mounts, OTOH, can be made by just about anyone with a decent mill and the skill to run it. Their main performance criteria is dimensional fit and if they don't we the consumer will know that as soon as we try to install them.

I have used (and do use) rubber mounts and have had little trouble with them. They are not evil. But I don't think they do anything to attenuate vibrations, I do know that they won't last as long as solid mounts and there is literally pennies different in cost between rubber mounts and solid mounts...

Oh yea, did I say I really liked the idea of using an adjustable strut with a solid bushing...
 

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Discussion Starter #17
Below is the needle-seat paddle from a new float I replaced for a customer after one track session with solid Weber mounts and no support rod.
Do you think that my adjustable support rod with a solid bushing is a "correct" installation with solid adapters?
 

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The rubber diagnostics just above are accurate Ed. I just made a second run of square cut Veloce sump to goose-neck gaskets as these are periodically in short supply. My first lot of 25 went to Dean Russell at Trail Auto, and sold out, builders called me for more. The second batch was for 50, but befor I got them to Dean, i had sold 15. These required a material analysis as gprocket mentions, for compressive strength cold and hot, from an original that might be 20 years old now. Then the NEW material had to be able to live in hot and cold engine oil for many years. The MATERIAL wasnt cheap.
So... YES, I KNOW the support rod is necessary. However it would seem that it needs some elasticity to damp SOME vibration. You can probably "adjust" the degree of damping by tensioning your support rod with the adjustment against the solid mount Webers and the soft silent block in the bottom of the rod.
Dandy... Then just HOW is the float eating vibration measured, AND what is acceptable? We know, with soft rubber Weber mounts, and a rod with a rubber bush, that in STREET use float paddle wear in minimal over time. We know many use solid mounts on the track, with or without a support rod, and seem to have no issues with E tubes, or float wear. Then we also have those with both running issues on the track or street (E tubes?) with solid mounts, AND I see periodic ruined floats on solid Weber mount engines.
Lotus tried some variations, and came up with funny E tubes. Float wear? none mentioned. One Lotus owner modified his head-manifolld combination in a race car to use Alfa rubber soft mounts and he uses regular E-tubes, and has no float wear, though he DOES use a rubber bushed support rod like Alfa. He performed this modification after air leaks in the Lotus Weber / manifold "O" ring type mount failed, and cost him an engine.
Solid Weber mounts do work, but always? Maybe not. We know if you use soft mounts you MUST use a support rod. We know that with solid mounts some, not all, suffer float and mixture issues. Would a support rod help? It might. So in my opinion it is worth a try. It seems a solid Weber mount AND soft mount in the rod end would also be worth a try with variable tension from your adjustable rod. You can also try it with the bush replaced with a solid aluminum bush in the support rod end.
It was a short question, but a long answer.
As always, just my opinion.
 

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Discussion Starter #19
I may be interested in trying alternate methods of carb support +and measuring the vibration at the Webers with an accelerometer. Do you guys think that vibrations at all frequencies are equally bad or should I be focused on a particular frequency range?
 

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For me, the answer is "I don't know." because some floats are worn quickly, while others are not, using solid Weber mounts. Also some run poorly with E tube issues, while others are fine.
It seems some vibration frequencies are harmless and others quite harmful. I don't know which is which, or how to identify them other than by problems they cause. Unfortunately, thats pretty much after-the-fact. Probably also the reason I have stayed with the rubber mounts where I've had no problems.
 
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