A rant about Diaphragms
It is rare that I would dare to disagree with Snowbum, the guy is an encyclopaedia of knowledge of all things BMW.
However, there is one topic on which I think Snowbum talks though his hat, that topic is generally the topic of Bing carburettor parts and specifically Snowbum’s opinion that death, doom and destruction will result from the use of non OEM parts in Bing Carbs.
In fact, Snowbum’s beliefs on the topic of where to buy Bing parts includes not buying them from Bing themselves, only from BMW according to Snowbum.
Let’s analyse that a little:
Aside from BMW motorcycles the largest “consumer” use for Bing carburettors is in aviation. Before any part goes into any component that becomes part of an aeroplane that part is subjected to rigorous testing and the manufacturer must supply the aviation authorities with a “supply chain assurance” to the effect that all parts will meet the specification without deviation and that all replacement parts are fit for purpose – in fact the manufacturer, even one the size of Bing, faces oblivion in the courts if any part of this sentence is found to be untrue.
Now I have never, ever, bought parts from Bing USA, or any other “Bing direct” outlet, however I would do so without a moment’s hesitation not only because of Bing’s supply chain assurance, but also because I figure that they want to stay in business and are unlikely to sell sub-standard parts.
The second area of Snowbum’s objection to non-OEM Bing parts is the dreaded area of diaphragms, Snowbum says that no replacement diaphragm should be used other than the original.
Why?
Most of Snowbum’s strongly held opinions are backed up with his test results and good solid reasons why he holds a particular view. For Snowbum he is very sparse on reasons for his preferences in regards to Bings.
Again Why?
Use of non-OEM diaphragms – the reality.
The slide actuated by a diaphragm is in effect a vacuum engine, due to the design of the diaphragm itself the material has to have quite a drastic (and noticeable I’d suggest) stiffness in order to offer any real opposition to movement. The height to which the slide rises for a given vacuum is determined not by the stiffness of the diaphragm material but by the resistance of the spring fitted to the slide internal.
Could two slides of differing material thickness rise to different heights for a given amount of vacuum – not on your life, they will raise to the same height, the only thing that might vary is the speed at which they do so, and then you will not notice it anyway.
To re-cap.
1. The design the diaphragm is such that the material stiffness (or lack therof) will not impede operation
2. Carburettors (theoretically) fitted with diaphragms of different construction may well rise (or fall) at different rates but will ultimately rise to the same height as the slide height is mediated by the spring, not the diaphragm. To the extent that two different slides might rise or fall at different rates, for practical purposes you will never notice.
3. In respect to other Bing parts, I have never bought from Bing Agency but I can think of no rational reason that a Bing part, made by Bing and sold through a Bing Agency (for use in aircraft no less) will be any less well made than a Bing Part delivered to BMW and then sold to the user.
4. I have purchased a number of non Bing parts, including float needle and seat, jets and slide needles. I have also fitted both Stromberg and Motobins diaphragms – I have never had a problem.
So why the almost religious fervour to buy OEM.
Well, firstly Snowbum says that only OEM parts are the correct parts, that carries weight.
I suspect that the usual scenario plays out like this - Someone buys non-oem parts and has a problem when they put them into the carbs, they pull the carbs apart again (and probably fix the underlying problem) and put it back together with OEM parts – the problem has gone away so it must have been those danged non-OEM parts.
When it is said and done a carb is a simple device and usually it either works or it does not. Usually when it doesn’t work it is because either air or fuel is not going where it should, in the quantities it should. If you get the impression that I think 99.9% of carb problems are fixed by careful methodical cleaning, you are right.
Even with precision components such as jets I rarely actually buy a new jet, If I think that I need a different sized jet I will drill it to size – an investment a long time ago in a set of metric “number drills” pays for itself again and again. If a jet is too big, solder it closed and re-drill.
Rant continues next post
Topic: A rant about Diaphragms (and other carb stuff) (Read 2704 times)