Hi,
I've heard that automobile engines (VW etc) in the past were sealed without using a gasket, ie, used a metal-to-metal contact with bolts etc. I was wondering if anyone could point me in the right direction to obtain more information. I would appreciate it.
Abhinav
If you are refering to the sealing surface between the crank case halfs, they were sealed with a sealant like permatex, as were Corvairs and ww2 aircraft engines. If you are refering to seals as in crankshaft seals, some engines used felt (chysler), rope(most everone), wire- looked like solder wire(Mack trucks). or nothing except a spiral groove (called a windback) Rootes engines. I'm sure there are many other ways to seal or not.
In automotive use you tend to always see gaskets for reliability and ease of assembly. in esoteric automitive applications, you can see things like metal - metal joints for cylinder heads, etc. But they are rare, and don't really have to seal the pressure for very long, so the seal doesn't have to be perfect. They often use rather tricky spigots, or threaded joints, and are always hard to assemble. A really good cylinder seal, using metal - metal valve - seat seal and ring - cylinder wall seal, leaks by about 3%. So it would hold your 70PSI, but not for long...
Another metal-metal joint that comes to mind is the whole idea of hydraulic AN joints - they use a precise 37 deg taper on a male and female joint to seal up to a few thousand PSI rather well. I regard the normal automitive bubble flares as a gasketed joint - the bubble deforms to create the seal and is only marginally reusable.
Brian
Not sure what you are sealing (face seal like block or metal tube or valve type) but there are many examples of metal to metal seals. Valves have been mentioned, but the flare tube fitting is metal to metal, ferrel tube fitting sare metal to metal, in plumbing - you can get ground joint uinions and there are more if given time to think a bit more. To get a better seal on valves and the ground joints (plumbing), you use lapping compound to get the mating surfaces to have the exact same profile (they are exact as one surface is grinding the other surface so any imperfection is ground into the other surface). This method was used when doing a valve job on automotive cylinder heads (maybe still is as I've never personally rebuilt a head). My dad showed me a tool one day that was designed specifically for lapping valves for the Model-T. I assume back then, this was part of a normal PM.
bb
Still done....same tool.
Valves seal well due to precise machining...and orientation.
The higher the pressure in the cylinder, the tighter the seal (valve) is pushed against it's sealing surface.
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