Dcoe soft mount vs hard mount

[golf02]

I know this subject has been debated in the past, but I don’t feel it’s been really studied. I am running dcoe 40’s on my 71, 292 cam, high compression, with the standard mods. The engine runs as smooth as I would expect. I have tried various different soft mount kits over the past 20 years with success for periods of time. The current setup is now showing its age and has developed leaks. I have always wondered if I should go to the dark side and run hard mount. Looking for some experience from other members.

[Son of Marty]

I've never seen or know of any car that runs weber style side drafts that use a soft mount, BMW never did on the ti's and tisa, if they were needed they would have used them. Just my opinion.

[halboyles]

14 minutes ago, Son of Marty said:

BMW never did on the ti's and tisa

That's correct!  BMW used Bakelite isolator spacers with paper gaskets.  The spacers were designed to isolate the carbs from the heat of the head, not provide any anti-vibration properties.

[jp5Touring]

Never seen anyone use the soft mounts in person. They do look problematic to me though.

I use just the paper gaskets on my 40 DCOE and know nothing about the Bakelite spacers.

They look interesting to me. Anyone use them and where does one find them at.

 

[AceAndrew]

To provide a data point, I've setup/speced 25-30ish DCOE combos and never needed to use vibration isolators.

 

Another note "phenolic spacer" as shown above can be made from various suitable materials.  I used a teflon-based material when developing the M20 DCOE manifolds.

 

 

[2002iii]

I have a set of ancient Borg Warner soft mounts on my dual 40's that work fine.they look like this:

 

I agree that you don't really need them, if your motor vibrates enough to need them you've got bigger issues.

[kbmb02]

There is thought that the harmonics of an M10 - beyond ‘simple’ shaking or vibration - are a reason for soft mounts (depending on application). Changing to a different type or material of engine mounts, for example, impacts the harmonics.

 

I’ll add this opinion: What BMW did on a stock-from-the-factory Ti and Tisa may not apply to M10 engines with aggressive camshafts, more compression, different carbs, out-of-tune and out-of-synch carbs, etc. Your results may vary. -KB

 

 

[Schon '02]

Here is the set up on my ‘73 with 45 DCOEs, Canon intake manifold and phenolic/Bakelite isolators. I’ve not had any issues with this set up in the four years that we’ve owned the car other than the Thackery (spring) washers (located under the Nyloc nuts).
 

The washers are intended to help with dampening vibration so are not fully compressed. However, there seems to be a fine line between under tightening (and leaking past the gaskets) and over tightening (eliminating any spring/dampening). And the washer is hardened spring steel so they will crack over time (as I found that mine had done). I’m tempted to remove them entirely for standard flat washers to see if there is any difference in engine performance. 

[visionaut]

I’ve been running a style like these for a long time. Rubber 40 DCOE spacers off a Mercedes 190SL.

 

Not as much vibration damping as a soft mount. But the rubber is much better than aluminum or Bakelite or Nylon, so it provides some vibe damping with the bigger cam. 

 

Tom

[cda951]

4 hours ago, kbmb02 said:

There is thought that the harmonics of an M10 - beyond ‘simple’ shaking or vibration - are a reason for soft mounts (depending on application). Changing to a different type or material of engine mounts, for example, impacts the harmonics.

 

I’ll add this opinion: What BMW did on a stock-from-the-factory Ti and Tisa may not apply to M10 engines with aggressive camshafts, more compression, different carbs, out-of-tune and out-of-synch carbs, etc. Your results may vary. -KB

 

 

 

This is an interesting discussion. My girlfriend and I have, among numerous other cars, a 1974 Jensen-Healey roadster with the Lotus 907 twin-cam 16V engine and Dellorto DHLA45 carbs (and a Getrag 235/5 CR dogleg 5-speed!), and in that world the soft mounts are a "must," and this is accepted as the gospel without argument from anyone as far as I can see. We have them installed simply because that is all my local Lotus parts supplier stocks! They work as designed with no air leaks, despite how unrefined the 907 mill is (it sure likes to rev, though!). 

 

I think one would have to do back to back testing to actually figure out whether fuel frothing in the float bowls is an actual issue, and if so then determine if the potential for air leaks is worth the compromise. On the other hand, the emulsion tubes of DCOEs or DHLAs are designed to "froth" the air-fuel mixture to aid atomization, so I suppose the harmonic nature of the individual engine is really the key here . . . .

[TobyB]

It would be trivial in this modern day and age to stick

a camera and light into a float bowl.

That wasn't true when I started.

 

When I get the green car back together, I'll try it.

 

I have used several different mount styles, and as long as they don't leak, they

all work.

How long your needle seat lasts may vary, however.

 

What IS real is slosh- over in corners, and I hesitate to say which direction

because I forget.  But a baffle over the jet stack on one side or the other really 

helps with bogging in hard cornering.  It's obvious when you look

at the way the well sits relative to the air correctors.

 

t

doesn't worry about it too much.

[Hans]

I had the O-ring style soft mounts for a while but threw them out. The O-rings crack, which I didnt realize, so spent hours trying to get it to run right. Paper gaskets work fine. I have the bakelite spacers that came with the CS motor but they push the webers out too far. The big hassle is getting the top and bottom nuts adjusted equally with the thackery washers - impossible to see down there much less use a feeler gauge. Not worth the effort in my experience but others will differ.

[golf02]

Ok well here’s what we have surmised so far. Soft mounting is possibly (more than likely) not needed. The consensus so far is to run the Bakelite spacers as they are an insulator. As a finicky engineer one thing bothers me. The longer the car runs the less effective the spacer becomes, at some point it will be the same temperature as the head, as it’s an insulator. At this point it becomes useless at the expense of having twice as many points of a vacuum leak (one seal on each side). Why not look for a conductor to act as a heat sink and radiate heat from the carb? I have seen heat shields. Thoughts?

 

[golf02]

And before some other engineer chimes in, yes I know a conductor (heat sink) will draw heat through the carb faster, but I am over thinking things and the effect at a steady state ( say after 1 hour of running)

[Tommy]

1 hour ago, golf02 said:

And before some other engineer chimes in, yes I know a conductor (heat sink) will draw heat through the carb faster, but I am over thinking things and the effect at a steady state ( say after 1 hour of running)

In this case head is the heat source, while carb acts as a sink cooling to the air. So the spacer as a resistance between does lower the carb temperature in steady state too.