New Gaskets To Slow Down Leaks

By Stephen Kassis

Replacing engine or transmission gaskets in your old car is mandatory when doing a restoration. But what about the old car that isn’t being restored or the driver vehicle with lots of miles since it was restored? No matter when it occurs, leaks are never welcome. Sometimes leaks that seem to be a major problem might be easily fixed by replacing an old gasket or two.

Determining where the leak is coming from is the first step. This requires a little detective work in some cases, but it is worth the effort. Try wiping down the affected area with solvent to clean off excess oil. Run the car down the street for a few miles or take it on a short trip and check again. You should be able to see a fresh track of oil then follow it back to the source.

Engine oil leaks are some of the most worrisome in a car. They can indicate loose main bearings, bad rear main seal or even a bad oil pan gasket. However, one of the most common engine leaks is not any of those. A bad valve cover gasket can cause oil leaks that can appear to be from major problem areas, yet it is one of the easiest to fix.

A valve cover gasket on early six cylinder engines is very simple to replace. Try tightening the valve cover bolts to see if the leaks disappear. If not, the gasket should be replaced. Remove the valve cover gasket and clean the cylinder head surface with lacquer thinner or similar solvent. Be sure the surface is clean of any oil residue and dry thoroughly. Test fit the new gasket dry first. This will insure that you have the correct gasket for your application.

Once the surface is clean and dry, put a thin coat of silicone (or other gasket sealer) on the surface of the head and the bottom of the gasket. Install the gasket and let set up for several hours. Put a thin coat of grease on the top surface of the gasket, install the valve cover and tighten down. By using grease on the top surface, it allows the valve cover to be removed and replaced easily for valve maintenance. If the valve cover gasket is thick, like the originals, oil will be retained inside the edge of the gasket. On 1934-1953 engines, don’t forget to replace the rubber grommets on the valve cover studs.

Push Rod covers on six cylinder engines are another problem area for gasket leaks. This gasket is also easy to replace and like the valve cover gasket, can cause phantom oil leak symptoms. Unlike the valve cover, this gasket should be glued on both sides – no grease used here. Early 194, 206 & 216 engines also have cork seals around the spark plug holes. These gaskets do not require sealer as they should fit tightly around the spark plug holes in the push rod cover.

Oil pan gaskets can be replaced with the engine in the vehicle. However, the specific procedure can change from vehicle to vehicle. Most early six cylinder oil pans will require the removal of the steering tie rod which is directly below the oil pan. If your engine is 1940 or newer, the rear main bearing rope seal should be checked for leaking. If this is the source of the leaks, now is the best time to fix it. In order to completely replace the rope seal, the crankshaft must be lowered by loosening the main bearings. Special tools are available to pull and install the rope seal through the upper part of the block. The rope seal must be trimmed to length for proper fit.

Prior to 1940, there was no rear main seal in Chevrolet engines. If these engines are leaking oil at the rear main, it is likely due to one of two things: either the rear main bearing is loose or the oil return hole is plugged and should be cleaned.

Either of these situations will require removal of the oil pan and rear main bearing cap. Use Plastigauge to check clearance on the main bearings. Ideal clearance for main bearings is .0015″ to .002″. If shims are still available, remove .001″ shim from each side to get proper clearance. If clearance is beyond .004″, leaks are possible as too much oil can pass by the bearing surface and overload the return hole.

The second reason for the rear main bearing to leak is a plugged return hole in the main bearing cap. With the main cap removed, check to see that there is a completely clear return hole. If sludge has blocked the return hole, spray B-12 Chemtool or similar carburetor cleaner to clean out the passage.

Installing the oil pan gasket should be done on the block, not the pan. After cleaning off the old gasket material from the block and pan, flatten out any irregularities in the oil pan mounting surface. The end of pan gaskets that are straight strips of cork should be coiled up to help them conform to the curved mounting surface. Coil the strips into an aerosol paint lid and let set for several hours. Check the fit of the long gaskets on the block. Once confirmed, glue the surface on the block and the mating surface of the gasket with silicone (or other gasket sealer). Install the long gaskets after they are slightly tacky. Check the fit on the end of pan gaskets and trim as necessary. Install the end of pan gaskets making sure to put a small dab of sealer in the corners where this gasket meets the long gaskets. Put a light coat of grease on the surface of the gaskets that will mate to the pan.

Alignment pins are helpful when mounting an oil pan under a car. They are easy to make out of four 1/4-20 x 1″ screws. Simply cut the head off of these screws and screw them by hand – two on each side, front & rear – in the block. As you put the pan in place, these pins will help keep the pan straight. On dipper system engines be sure to check the alignment of oil troughs and nozzles when mounting the pan. This is critical to having proper oiling of connecting rods.

While holding the pan in place, start several of the oil pan screws on each side. Remove the aligning pins once several of the pan bolts are in place. Make sure all screws and bolts are started before tightening everything and snug down evenly.

Many of the early six cylinder engines have a special bracket to hold the oil line that goes to the dash gauge. There is also a special bracket on some of the early engines for oil breather/oil fill tube. Both of these require longer screws that go into the oil pan and extend through for the bracket and nut. When installing your oil pan, don’€™t forget these two longer screws.

When it comes to transmissions, the most common leak area is at the back of the transmission – the closed driveline U-joint gaskets. 1954 and earlier cars & 1/2 ton pickups had a torque tube enclosed driveline. Where this tube connects to the back of the transmission is often leaking. To replace this gasket set requires disassembly of the universal joint.

Remove the four bolts (6 bolts on Powerglide models) that hold the U-joint collar to the back of the transmission. Put a container under it on the floor to catch gear oil that should drip when the ball is slid back. Slide the collar back as far as it will go on the torque tube. CAUTION: Support the torque tube with a floor jack as it is under stress from the weight of the car on the springs. The tube will drop with force if not supported properly.

For proper adjustment and installation of the U-joint gasket set, refer to the article Universal Ball Housing Adjustment