Auto, Car, Truck seals, gaskets, leaks, diagnosis, repair

What seals and gaskets do

Your engine has many fluids and gasses at high pressure running through it. Many of these are behind moving shafts, or flow through passages in cast parts bolted together.

TYPES OF SEALS

SHAFT SEALS

Examples: Front and rear crankshaft seals (also called front and rear main seals)
Camshaft and auxillary shaft seals (overhead cam motors)
Water pump seals
Transmission/rear axle or transaxle (front wheel drive) input and output seals
Wheel bearing and axle grease or oil seals

All the above seals have a spinning shaft going through them with a liquid or lubricant on the other side of them. By design they will leak a very small amount of liquid: thus it is normal for there to be a little oil around the crank seal after a year or so of driving.

That's one reason you should keep your engine clean!

There are two types of seals common today. The first, and most common, is the rubber lip seal. The second, older, and less common is the paraffin rope seal.

THE LIP SEAL

Lip seals have a circular piece of rubber inside a metal ring. The rubber ring is flattened, and slanted toward the liquid it seals in. Thus, when installing a lip seal the lip must always slant TOWARDS the liquid it is sealing.
The lip seal, especially larger ones, will often have a tiny coil spring formed into a circle. This presses the seal against the shaft. That's another way to tell which way the seal goes in: this spring is on the liquid side!

Rope Seals

The rope seal has been around for centuries: it is basically a piece of specially treated (with graphite for one thing)piece of rope which fits in a groove cut in a housing which surrounds the rotating shaft. There is a close tolerance between the shaft and the housing, and the rope is fitted tightly in its groove. Because the rope is soaked with fluid, it has little friction on the shaft. Because the tolerance is tight and the liquid isn't under extreme high pressure, very little liquid is lost (a teaspoon per year or less).

Rope seals are a pain to install, and are often messed up by the inexperienced. The only reason they still are out there is they MAY last a bit longer. They aren't made of RUBBER!!

CYLINDER HEAD VALVE STEM SEALS

Valve stem seals seal two ways: they keep manifold vacuum and exhaust from leaking to the crankcase, and (more importantly) they keep oil from being sucked past the valve stem.
Bad valve stem seals will cause oil smoking on engine startup which goes away after running for awhile.

INJECTOR SEALS

There are seals around your fuel injectors: they can leak vacuum or leak fuel

PCV System Seals

PCV SYSTEM SEALS

These grommets can cause oil leaks from blowby and can allow dirt to get sucked into your engine. Usually in the valve cover, they should be pliable and make a good seal around the PCV valve and fresh air inlet.pcv

O-RING SEALS

Used extensively. Some are in a circular groove on one surface which mashes against a flat surface on another piece: the o-ring seals a hole going between two pieces. An o-ring you can easily see like that is on the bottom of a spin on oil filter!

Other o-rings are used around a pipe to seal it where it goes into a socket. Some o-ring fittings move around in their sockets as part of normal operation. Example: some power steering line fittings, Ford A/C lines.

GASKETS

At their simplest a gasket can be a cut out piece of craft paper (like a grocery bag!)
At their most complex they can be multilayer composite structures designed to shift and slide with heat expansion and contraction, while still sealing in thousands of pounds of pressure.

The purpose of all gaskets is the same: to seal the join between two mechanical pieces, preventing the leaking of fluids or gasses at this join area.

Gaskets are used all over a car. Common ones are:

COVER AND PAN GASKETS

These gaskets seal sheet metal covers to large cast units, like valve covers, oil pans. They tend to be cork, rubberized cork, or rubber. These gaskets are usually 1/8 inch (1.5 mm) thick: they must take up the irregularities and deformations of the sheet metal cover.

CASTING TO CASTING GASKETS

Thinner than cover gaskets, these seal one machined casting surface to another. Examples are manifold gaskets, head gaskets, water pump to block gaskets. Head gaskets are usually multilayered composits. Manifold gaskets often are also. The water pump is one area you may find the old paper gasket, alnog with the thermostat housing, and many other locations.

THE OLD GERMAN ENGINEERS SAID NEEDING A GASKET IS A SIGN OF SHODDY MANUFACTURE!

Indeed, many places use no gasket: aircooled VW/Porsche engines have no head gaskets. Many cars have no exhaust gaskets, even no exhaust manifold gaskets!

Other areas use a thin, stays-soft sealer between 2 well machined surfaces, but no gasket.

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Thank you for visiting the ECONOMECHANIX WEB SITE. Please feel free to comment. We also serve the surrounding communities of Alachua, High Springs, Hawthorne, and Newberry! Gainesville has been my home since 1974, and I've loved Gvl and the Gators since I came here in the fall of 1974 to attend the University of Florida. I loved it so much I stayed and opened my car repair business. Originally it was out of the back of a 1963 Chevrolet wagon, but in 1977 a fellow mechanic and I opened an auto repair shop with actual walls, etc. I stayed in the same location for 26 years, and recently moved my operation to property I bought 15 miles east of Gainesville. I am doing most all the repairs myself now, having reduced my overhead from $1500 per month to practically nothing. I do work by appointment only. I mostly work only on my established customers cars, but I will occasionally take on new clients. E-mail me and I will either make arrangements to look at your car, or I will recommend you to someone who will.

George G. Scott, Jr.

Automotive Seals and Gaskets