Last Updated:  01/30/11

Oil Leaks - by James Drumm

Disclaimer! Thinking back 50 years has it's faults, so be prepared for inaccuracies, but some things were done so often as to seem crystal clear in my mind. 

No oil leak was ever encountered at the front pulley, not sure why, but if mains are even half decent and crank pulley hub is not damaged or plugged up with permatex or some such around seal surface, there is no reason for an oil leak there. The timing gear cover is subject to error with gaskets, as well as distortion from over zealous screw tightening, the screw and gasket surfaces should be carefully pounded flat and true. 

We had a square iron plate about an inch thick that was real handy as a check surface, as well as using it for an anvil with the timing gear cover edge "hung" on it to pound on. Dad would soak all cork gaskets in water for several hours, and use a wee dab of any sort of permatex to hold them in place, but also used string from a chicken mash sack to tie gaskets in place through bolt holes. As tiny as that string was it would not hinder a screw. Pliable paper gaskets now are much better now, as is silicone that can be liberally massaged onto the gasket first, but tighten screws gently, and let the silicone set before a bit of tightening. Over tightening screws always leads to distortion and leaks, "just enough" is sufficient. 

I never saw an oil pan leak, and we never used anything on those gaskets, but today I would use silicone and wipe the edges after setting screws. Don't use so much that you squeeze gobs inside, it can plug things up.  Seems like we had a nasty cam plug leak once behind the flywheel, can't remember which engine, but easy to confuse with a main bearing leak.  All freeze plugs I set with loctite these days, any grade, as it remains set! I still pound them tight but like to see loctite all around the mating edge. Rear main leaks are more often damaged pan gaskets than the bearing itself, but look for a gob of gasket sealer in the drain-back groove and hole into crankcase. Permatex #2 was great at flaking off a chunk when it gets hard, and any obstruction in the gravity path will back up oil and cause leak into clutch housing. Never saw a main loose enough to leak, but it's possible.  

Transmission front leaks are confused with main leaks too, but personally I would choose a sealed bearing for the trans input shaft today just because its easy and permanent seal.   The side covers on the pushrods are a nasty plate to get straight.  Always warped, seems like, but the same routine with straightening and silicone will work.  Any leakage from valve cover gasket should be prime suspect of too much oil on top. These gaskets on valve covers should be thick enough, (check that cover will go down to head without gasket, check for "bent down" around rocker studs)  Oil delivery tube to the rocker arms always had a restriction orifice somewhere in system, but varied from 29 to 40's, it needs very little flow, but continuous. 

Lack of oil may be caused by cam bearing wear, or a plugged tube, but too much is more common. Worn valve guides will suck a lot of oil, most any good guide and valve stem will not show oil consumption at all. Plugged up pushrod holes will back up oil and even fill the valve cover, but lets assume these are all clean and not sledged up.  Leaving the engine run after driving and removing the valve cover will sometimes be an unpleasant surprise if it is half full of hot oil! It should never back up to fill cover. I saw many that did.

Rear transmission leaks can be invisible, and appear in rear end when the filler plug is opened. Don't confuse the issue with filling cold, and checking hot, or on a slope, either. When this occurs you are in for a nasty bit of front driveshaft bushing and seal replacement, and a new universal joint driveshaft bushing as well. Never had a problem with the 29 that had a 31 engine, but the 36  must have had an out of balance driveshaft that caused that to occur over and over. It was true and straight ok, we checked that, but a seal and bushing was good for about 25 thousand miles max. The 29 truck went on forever with no leak. 

There are various seal arrangements for the driveshaft over the years, patented aftermarket stuff, some good, some not. Do not be tempted to use a sealed rear transmission bearing, as that is the source of universal joint lube oil.  Rear end leaks I don't remember ever happened. Can't even remember if there are seals at the axle, but something must have worked right. I know if you happen to miss tightening one of the taper screws that retain the pinion bearing, it will fall out and will run a stream! 

I am a full believer in modern lubricants! Solves most problems that were unsolvable originally. There are high temp wheel bearing greases that any old seal will keep in place, and a bright blue grease from Std Oil will stand 600 F without melting. Synthetics are great, oils can be chosen to conquer any condition, but we also have piston rings to end all consumption available.  Even a set of plain cast iron pistons, I suspect, would use no oil with a second groove full circle ring installed.  <end>