Itinerant Air-Cooled

asiab3 wrote:

sped372 wrote:I read a lot of lamenting about the one-piece style clamps, but I reluctantly went BACK to trying one after multiple unsuccessful attempts at fixing a leak with the two-piece style. So far it's holding well. To me, I see no reason why it shouldn't work... whether the "diameter" is shrinking as a result of two halves coming closer together or a circumference shrinking the net effect is the same. It's collapsing! That collapse gets transferred to a squish/pinch by the angle of the flange and conical washer underneath. Sure was easier getting it positioned vs. the two-piece style right next to the mustache bar, too.

The problem with the"squish" you mentioned is the complete sealing of the system requires two pipes to seal together. The squish only seals the donut gasket to the heat exchanger, it does not seal anything to the muffler flange.

Oh, but I think it does! Factory diagrams show the single-piece clamp on the buses, they must have been "ok" originally.



Follow my logic, which I think checks out (please forgive my crude section diagram):



The radial clamp provided by the (purple) circumferential shrinkage serves two purposes. First, it directly crushes the donut, providing a seal to the HE tube at interface 'A' in my diagram. Secondly, because the muffler flange and washer are tapered, a portion of the radial force becomes a clamping force pulling the donut into the muffler flange and sealing it at interface 'B' in my diagram. It's the taper that's key.

I pondered this quite a bit while the road debris was raining down into my eyes and I think this makes sense.

Excellent diagram! Where is that scan from, though? My Bentley shows the two-piece clamps, tilted on their side with the nuts running parallel to the floor. This is what I see, but the diagram shows bug and bus mufflers...




EDIT: Oops that is from my bug book. I'll see what my bus manual says when I get to the car today.

My issue with the cheap modern donut clamps (unless you have NOS VW clamps?) is that they lack the inner curve of your mauve semi-circle. Every one-piece clamp I have seen is flatter (though appears round on the outside) and crushes the donut down radially. If you have orange-arrow-force at B, and a corresponding normal force on the opposite edge (red washer) then the gasket itself will do all the radial crushing you need, without needing to be crushed down by the clamp. When I used NOS asbestos gaskets, they were cracked by the one-piece clamps, and leaked all day and all night.




Now, if the clamps and gaskets matched, it might have been fine. But I do not think VW would have engineered the tapered muffler flange and matching washer if they could have gotten away with a glorified hose clamp that just exhibits force on the "A" joint.

Nice diagrams, again!
Robbie

As long as the 'hose clamp' contacts the washer and the tapered portion of the muffler flange, you're gonna get clamp. The normal force has to act perpendicular to the tapered surface. The clamp needs to clear the donut and act on the flange and washer.

sped372 wrote:The clamp needs to clear the donut and act on the flange and washer.

This is where I've had trouble with the one-piece clamps; they always crush the gasket and don't grab the washer/flange. Where did you get yours, and do you have a brand name?

I believe this is where I got mine but am not 100% sure.
http://www.autohausaz.com/pn/211251269A