From what I've heard, unless the engine is essentially perfectly balanced, with solid mounts the carbs will shake themselves out of tune. Main cause for that is probably the super thick rubber on the engine mounts, which let the engine move even more. You could put solid engine mounts on it but that would shake the whole car instead and who knows what else.

 

unless the engine is essentially perfectly balanced, ....

An inline 4-cylinder engine is inherently imbalanced (*). So regardless of how well balanced the engine is and what sort of engine mounts you have, things are going to shake somewhat. The original-style carb isolators are probably more compliant than the solid ones + O rings, but if their rubber falls apart after 500 miles, you've got a problem.

The question comes down to: are the solid carb mounts that are cushioned with O rings compliant enough to protect the carbs from getting so shaken that their mounting ears fatigue off. I guess SamSteinig needs to hear from someone who has put a lot of road miles on a set of solid carb mounts; not someone who has used them on the track for a few laps.
==========================
(*) Here's Wikipedia's explanation:

straight-four engines have a secondary imbalance. This is caused by the acceleration/deceleration of the pistons during the top half of the crankshaft rotation being greater than that of the pistons in the bottom half of the crankshaft rotation (because the connecting rods are not infinitely long). As a result, two pistons are always accelerating faster in one direction, while the other two are accelerating more slowly in the other direction, which leads to a secondary dynamic imbalance that causes an up-and-down vibration at twice crankshaft speed. This imbalance is common among all piston engines, but the effect is particularly strong on inline-four because of the two pistons always moving together.

 

Since I restore a lot of Webers, I get really tired of this fix made necessary by solid mounts with Thackeray washers and "O" ring seals.

This was a decent pair of matched 45DCOE9's. Solid mounts work fine on the track where the engine is constantly at high rpm sucking plenty of A/F mix to keep the Webers cool. You also need a inlet side Weber support bar mounted to the dead vibration node near the center main bearing cap, usually the engine mount directly below. The PURPOSE of the rubber mounts is to act as insulators to avoid changing mixtures from heat moving to the Webers from the manifold, and isolators to isolate the Webers from variable frequency engine vibrations from normal 4 cylinder firing order imbalance.
On the street, the solid mounts can break Weber body castings from vibration as seen by many users.
The failure of todays insulator/isolator rubber mounts is caused by heat and rubber deterioration causing cracking. The NLA rubber mounts of times past were made by Pirelli and held up quite well. Today our good aftermarket Alfa parts suppliers must buy what's available at best cost to compete in the parts market.
There are suppliers of rubber mounts all over the globe. You might try other sources to see if ones mounts hold up better than others.
This is my opinion from my own experiences restoring Webers and using rubber mounts over many years.

 

Since I restore a lot of Webers, I get really tired of this fix made necessary by solid mounts with Thackeray washers and "O" ring seals.
View attachment 1762629
View attachment 1762630
This was a decent pair of matched 45DCOE9's. Solid mounts work fine on the track where the engine is constantly at high rpm sucking plenty of A/F mix to keep the Webers cool. You also need a inlet side Weber support bar mounted to the dead vibration node near the center main bearing cap, usually the engine mount directly below. The PURPOSE of the rubber mounts is to act as insulators to avoid changing mixtures from heat moving to the Webers from the manifold, and isolators to isolate the Webers from variable frequency engine vibrations from normal 4 cylinder firing order imbalance.
On the street, the solid mounts can break Weber body castings from vibration as seen by many users.
The failure of todays insulator/isolator rubber mounts is caused by heat and rubber deterioration causing cracking. The NLA rubber mounts of times past were made by Pirelli and held up quite well. Today our good aftermarket Alfa parts suppliers must buy what's available at best cost to compete in the parts market.
There are suppliers of rubber mounts all over the globe. You might try other sources to see if ones mounts hold up better than others.
This is my opinion from my own experiences restoring Webers and using rubber mounts over many years.

I am certain that other Alfa owners, particularly of the older models are like myself getting disillusioned with the quality of fit, finish and material quality of many of the “reproduction” parts being supplied by all of the suppliers.
Seals that don’t fit, cast and molded ABS parts that are weak, rough, misaligned and smell bad.
I have taken a much closer look at original parts needing replacing… more often opting for repair instead, even at more cost. At least they fit and will last another 50 years.

 

What he said^.....From experience, I would go with the soft mounts. I drove 20k miles with the solid mounts and they gave me nothing but problems. The o ring washer is not compliant enough and it is easy to distort it so that air gets in. Thackery washers are no help as you end up tightening them too much to get a seal and then they snap. The solid mounts will bounce you right out of adjustment and on several occasions the occasional carburetor screw/choke keeper etc.. I've been driving with soft mounts for about 5k miles and haven't experienced any problem with leaking and the carbs stay much more in tune for longer. If it helps, mine were sourced from Classic Alfa and I have not had a cracking problem whatsoever. Just my 2 cents

 

I drove 20k miles with the solid mounts and they gave me nothing but problems.

Been there, done that. You saved me from writing the exact same thing.

I had a Lotus Elan with solid mounts and did not have a problem

Ditto.

 

Thanks Gordon and gmjohns!

I trust your opinions and experience. I do have the inlet Weber support bar in place. I want to inspect the bushing at the base of the bar to see if it's worn and possibly causing wiggle. I emailed Kevin at EB Spares (UK) to see if the rubber mounts they have are from a better source than Centerline. Will check with Classic Alfa as well.

 

I wonder if you could get slightly longer studs and put like a 1/4" rubber gasket cut like an original one over top of the O-ring. That would give you a little bit of that thermal barrier and should theoretically allow it just a little bit of wiggle room for vibrations to eliminate or at the very least lower the chance of snapping the carburettor body.

 

Your physics is correct. More flexible stuff between carb and manifold means more vibration damping.

But that extra 1/4" might push your air cleaner too close to the RH inner fender. It would also require lengthening and changing the angle of the support strut.

 

My duetto has had rubber mounts from Centerline on it for over a decade with no problems.
Yes, I have the carb support plate and the support arm on all my cars.
My GTV has them as well.
The only issue I did have with them is one of the studs was only finger tight from the factory.
It worked loose and caused a vacuum leak.
I put thread lock on it and snugged it back in place and it has been fine since.

 

I'm using thwacker washers and the "thick plastic" mounts from Redline
but I used "nyloc" stainless nuts because I was worried about the nuts backing out.
And yes it made it hard to mount the air filters.

 

I had a Lotus Elan with solid mounts and did not have a problem for over 30 years with them. However, do not use thackery washers on the top studs. Use thackery washers on the bottom and cup washers with rubber grommets on the top. This helps with compliance. Do not put rubber grommets on the bottom as dripping gas will dissolve them. Tighten the thackery washers as per their spec on the distance between the coils. Use nylock nuts to prevent loosening.
All said I think the rubber mounts are superior.

 

Tony, was your manifold cast as part of the head? On those Lotus engines you can use gasket paper Weber gaskets, bolting the Webers directly to the runner. Webers so mounted do not suffer broken castings on that Lotus head. The Lotus Webers used special emulsion tubes to compensate for high speed vibration and engine vibration fuel emulsion. FUN!

 

Interesting discussion. Just picked up a Spider with Webers. All my experience has been with injected Alfas, so this will be fun learning. I noticed they are mounted directly to the manifold - no rubber. I didn't even realize this was a thing - thought they always used rubber.

I have no idea how well thought out the current engine set up is. PO said he could never get the carbs right, but did drive it about a year ago until the trans locked in second. It will need to be gone through with a good eye and suspicion of everything. Looks like I will be investigating a rubber mount set up with strut (I know that is a critical part)

Thanks guys for the education!
Mark

 

I noticed they are mounted directly to the manifold - no rubber.

Wow, really?! Oh my...

 

You never know what a PO could do. This car is an S2 but has S3 tail lights grafted to the rear, and who-knows-what seats installed (they don't look bad actually). It's really a collection of parts in the shape of a car.

 

The Lotus Webers used special emulsion tubes to compensate for high speed vibration and engine vibration fuel emulsion. FUN! ,

Gordon I have put together Webers from My Elan Coupe and Bobs Lotus 23. The Elan had plain old F16 and The 23 had F15s.

If you buy solid mounts and they come with grooves for "O" rings and spring washers toss the "O" rings and "Thackery" washers and fill the grooves with epoxy and sand smooth when cured. Use paper gaskets on both sides of the mounts.

Cars have run with Webers on solid mounts as long as Webers have been available.

Vibration problems are unfounded. The rubber mounts just add to complexity.

 

........When you are stupid you don`t know it; only those around you are distressed.

 

Any experience with these?

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I agree with rubber being the best solution, if you got one or two cars. Maybe you are happy to change the mounts every five years or so as it keeps you busy. But having more cars I always search for solutions that won't keep me busy anymore....

 

Any experience with these?

I agree with rubber being the best solution, if you got one or two cars. Maybe you are happy to change the mounts every five years or so as it keeps you busy. But having more cars I always search for solutions that won't keep me busy anymore....

They work pretty well.
But what exactly are your concerns? In comparison to yearly oil changes or valve clearance checks a quick rubber replacement all 5 years (if that's really the case) seems no big deal.

 

I've studied those and decided that WHEN (not if) the rubber fails, replacing the aftermarket version is less costly. These do seem a good racers solution...

 

I still do not understand why Alfa Romeos have this problem. There are thousands of Mk1 Cortinas with Webers hanging on their non-crossflow engines, Mk2 Cortinas crossflow engines, Lotus engines, Escorts BDAs, English Pinto engines, Ferrari 365GT4s, Lamborghini Countachs, Sunbeam Talbots, single seater race cars (juniors, formula 2, pacifics ... but they are race engines) ... Chrysler Avengers with BRM engines ...

The way these threads read there should be a market for replica carb bodies to be sold in the hundreds per week. Also if the Alfa market is so big why not make the rubber replacements properly ...

But yes the solution above has taken modern concepts and applied them to this old Alfa problem. Nice
Pete

 

Also if the Alfa market is so big why not make the rubber replacements properly ...

And if the Alfa market is so big why not make ALL reproduction parts properly?

Yet, we know that reproduction parts manufacturers do NOT make parts with the same quality as the OE parts. Particularly rubber parts. So it shouldn't be a surprise that repro carb mounts sometimes split after only 500 mi.

 

When I was a young teenager, and later when racing myself, I was surrounded by these carbs. My brotherinlaw rallied Escorts with 1600 crossflow engines and ran road cars with hotted up engines ... assume side drought carbs.

Classic race meets had close to every car with these carbs ... no issues.

Classic car shows, hundreds of side draught carbs in just clean road cars ... and this is just New Zealsnd and Australia.

Never ever heard of this being a problem before this site. Is it because our carbs are now getting old and work hardening so running a Mk1 or Mk2 Lotus Cortina is now going to become an issue? We're lucky that Alfa designed in a solution ... the Cortina owners are in trouble!
Pete

 

I modified some solid mounts so that both the manifold side and Weber side used regular paper gaskets. Then used a cold air box with support bar to the engine mounts. I think Richard Jemison also does this with race Webers. No issues driving, but sitting in traffic, manifold heat migrated to the Webers and changed mixture enough to give me rough acceleration and an idle that drops off to a stall. Next idea was to cast the insulator / isolators of a thermo plastic for some insulation against heat transfer, again using gaskets. Haven't had time to try that yet. I was thinking of a glass fiber plastic for durability. This might be a 2023 solution.
Just a thought.
The problem with repo Weber bodies is all the slightly different body variations used. 40 or 45 mm? 2 or 3 progression holes? Notched or plain butterfly plates or maybe plates with holes? Here we would be reengineering Weber bodies, and the Spanish Weber builders have already been-there-done-that. It gets COSTLY!
As usual, only my opinion from my own experiences over time.

 

The solid mounts, when used according to the instructions, do provide some degree of heat barrier: there is no direct metal to metal contact. There are two small gaps, on either side of the mount, that are bridged by a oring. The Lotus twincam used a similar arrangement: the carbs were not bolted directly to the head but had thin spacers between carbs and head with orings on each face.

The challenge is to maintain this gap while at the same time keeping the orings tight enough to avoid vacuum leaks.

 

Down draught carbs use an isolator gasket that is like 10mm thick. I assume that is to help with heat transfer. Wonder if they would work for side draughts
Pete

 

Working on it.

 

Oddly, I never had a rubber, oe or aftermarket, fail in service. They were often dead when I acquired a car, typically sitting somewhere unloved for decades.

A couple of thoughts….

Whenever I’ve worked on a carbed Alfa, I take time to ensure the support structure is fully supporting the intake assembly. There is always a fresh bushing at the bottom of the rod. I check to ensure there is a slight upward tension on the intake assembly. Not accusing anyone, but I’ve come behind people that simply reassembled things, not checking that the dimensions and loads are where they need to be.

Secondly, vibration is a dark art. That various engines seem to work fine with solid mounts is irrelevant to other engines.

On my Mooney, the original engine was prohibited from operating between 2,300 - 2,450 RPM. An identical-appearing engine used on just a few-years later, same manufacturer, airplane had no such limitation. The difference? Crankshaft design. Not visible to a casual observer.

An oil refinery I used to sell to was having pipe breakage problems. Famous vibration analysis company quoted a bunch of money to fix. Refinery accepted lower quote from another company. All kinds of straps, supports, X-rays later, Breakage continued. Refinery hired the high-price guy. He shows up and tells the crew to fill the vertical supports with sand.

Problem solved.

 

Pneumatic-hydraulic hammering Don. Took Alfa years to fix it on the cracking GTA oil pump pick up bells. Some of the stuff that ruins Weber bodies only apply to some 4 cylinder engines. Not all of them.

 

Seems there is a fix for the heat transfer at least

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Don't look as if they would limit vibration

 

My webers were sourced from a Lotus so I didn't have a support rod. I made one from a piece of "all thread", bent as needed thus it has no bushing at either end and is adjustable for an exact fit. I have never had a problem with the rubber mounts.