Gaskets for exhaust systems

From the 1930s to the 1960s, joints on Harley-Davidson exhaust systems had no gaskets ex works. Exhaust pipe collectors of Knuckle- and Flatheads are inserted into the cylinders and cylinder heads, on the cylinder head of Panhead and Ironhead Sportster they fit over a connecting stub, all the individual pipes fitting precisely into each other and the mufflers onto the pipes. A few clamps and brackets complete the assembly and the gasket-free exhaust system is ready. Of course, this kind of tubular system only works well as long as the joints fit together without play and the material wear caused by vibration (friction!) remains low.

In practice, it is useless to overly tighten the clamps around the exhaust pipe. The 5/16" bolts are not designed for high torques and then even lose their clamping force. They lose further tension under the effect of heat. It is much better to tighten them with normal torque and retighten them more often. Sounds like a lot of unwanted work, but works better in the end.

With the Shovel engine came the exhaust gasket, i.e. the one between tube flange and cylinder head. And with the exhaust tube gasket came the problems. While the European competition was still struggling with union nuts and ripped-out fine threads, the guys north of Okinawa had devised a fairly simple manifold fastening system with two stud bolts, a flange to pull over and a crush seal. Why the factory in Milwaukee then came up in 1966 with a flange that was welded to the collector tube and that is only held in the cylinder head by a single 5/16" bolt, will remain an eternal mystery. Also why the gasket was under the flange instead of at the end of the tube inside the cylinder head. In any case, this design always causes a furrowed brow among Shovel fans, because it hardly ever seals properly. Sorry, Harley ...

The improvement came with the Evo: a two hole flange, two stud bolts in the cylinder head, a crush gasket and that was it. And the system works the same way for the V-Rod, Twin Cams and Milwaukee Eight models.