The following describes the OEM exhaust system as fitted to a 04 S4R (Desmoquattro), the system is similar on other S*R models.
The system consists of short 2-1 header pipes for the horizontal and vertical cylinders, a primary muffler/catalytic converter (hereafter referred to as the “Udder”), connecting pipes and two mufflers mounted one above the other in a “shotgun style assembly. System components are manufactured from stainless steel, with a nominal diameter of 40mm. Provision for the connection of gas analyser probes is made by bosses welded to each header pipe.
The system is EU3 compliant and meets the 93db noise level.
The udder is divided into two chambers with the catalytic honeycomb forming a passage between the two. Exhaust gas flow from each cylinder is collected in the first chamber and then flows to the second chamber via the catalytic converter finally exiting through two outlets, a muffler is connected to each outlet via an “S” shaped pipe. The joints between the under, pipes and mufflers are slip fit with the outer component being split to allow the pipe to compress down onto the inner component when a force is applied to circumference by a clamp.
The Outlet Chamber
The Catalytic Converter and Chamber Division Plate
The headers are mounted to the engine with three 6mm studs and copper nuts. (Fasteners used in exhaust systems are prone to seizing the use of copper nuts helps alleviate this problem). A thin metal gasket forms the joint between the header and the cylinder head.
The rest of the system is flexibly mounted, the udder to the engine via rubber isolated “dog bones” and the mufflers to the frame via an isolating bushing.
The joint between the udder and headers, is flexible to allow relative movement between the two, provision is made for both axial movement and misalignment.
The Horizontal Cylinder Header
Note that the header pipe has a ridge raised in its diameters just prior to the reduction in diameter. The rounded edge of the ridge forms a “ball”. The reduced diameter is a spigot that fits into an upset diameter in the udder pipe and determines the alignment between the components, a generous clearance between the spigot and the udder pipe allows some angular misalignment the ball and the header maintains a 360° contact between the components within the displacement angle afforded by the spigot clearance.
The Udder Connection
The Inserted Joint
A “V” shaped gasket riding on the spigot diameter, seals the annulus between the two pipes and accommodates misalignment by deforming into the irregular annulus formed by any such misalignment. The gasket also allows the pipes to move axially in relation to each other while maintaining an effective seal.
Operational Issues.
The hex on the copper exhaust nuts are stamped and i not very precise take care to ensure that the hexagon is firmly engaged with the tool before applying torque. Remove or cover the oil cooler prior to removing the front header nuts. It is easy to inadvertently damage the fins if precautions are not taken.
The header gasket is directional and should be fitted with the concave surface to the header. it is not necessary to use gasket sealant.
The studs should be coated with copper anti-seize compound prior to fitting the nuts.
The “V” gasket fits with the base of the V facing down stream, There is a school of thought that the V should face upstream the purpose being that the pressure of the exhaust forces the gasket into contact with the mating surfaces. This is probably based upon experience with fluid seals that seal better in on direction. The relatively low pressure of the exhaust and the low flexibility of the gasket make it unlikely that this is the design intent.
Leaks at this joint are not uncommon, backfiring being the symptom of a leak. In most cases the leak can be rectified by ensuring the joint alignment is as straight as possible. In some cases a sealant can be applied to the gasket and joint. The product recommended by Ducati is Holts Fire Paste. This hardens with the heat of the exhaust but is prone to disintegration when subjected to the vibration of the joint.
High temp silicon has also been reported as a successful treatment, however my own personal experience has shown it to be ineffective.
Wurth Assembly paste is reported as being effective over a long period of time.
Some after market udder replacement pipes have an insufficient spigot length and allow an angular misalignment in excess of the capability of the gasket to seal it.
