The Stovebolt Site Forums The Shop Area Engine Shop Pesky oil leaks

About a month ago, I installed a completely rebuilt '59 235 in my '49 3100. Ever since then, I've been chasing pesky oil leaks which are starting to wear me out. I've read a ton of information on this forum, which has helped, but she still leaks! :mad: If I run the engine for 10 to 15 minutes, I get 1 to 2 teaspoons of oil on the garage floor the following morning. It seems like I should be able to do better than this with a new engine and new gaskets.

The source of the leak appears to be in two places. The first is several spots along the lower side of the pushrod cover gasket. Look carefully and you can see the trail of oil. I used 3M gasket sealer on both sides of the gasket and the bolts, so I don't understand why it is leaking. Maybe I didn't goop it up enough? Should I cut the cover off and start over or just accept the fact that 235 engines will leak? The cover is glued on there pretty good, so I'm not sure how to get it off.

The second leak is from the crankcase vent tube. The vent tube is a real mystery. I can't understand why it would leak at the vent tube. You can see that I used a bead of 3M sealer here, as well, but it still seems to seep oil.

Any advice would be appreciated.

The gasket looks squashed out which means over tightening. The original bolts in a GMC had a Phillips head as well as a hex. They were meant to be tightened with a screw driver only. Chev may have had slotted screw driver heads. Before I install a push rod cover, I put as straight edge to the cover and see if the sealing ridge is straight. I also check the bolt holes. If they are not flat, I lay a small ball pein hammer in the hole and tap it until the hole is straight. Most covers are bowed from being overtightened at some time in their life. Straightening them is a rather tedious job, but it can be done. I prefer to use a sealer that becomes rather hard such as Permatex Super high tack #97 against the block. I then use screws to locate the gasket the gasket until it is stuck to the block. I then apply a sealer that remains flexible like Permatex No 3 on the cover and the gasket. I then remove the bolts, put the cover in place and tighten the screws with a screw driver or nut driver. The vent tube is a press fit and probably leaks because it is distorted a little. I think you need to pull it out and try again. What you are doing now is like trying to patch a hole in a boat from the inside of the boat with bubble gum. I would pull it back out, clean the two mating surfaces absolutely clean and apply something like Permatex no 1 to both surfaces. http://www.permatex.com/products/Automotive/automotive_gasketing/gasket_sealants.htm

For the pushrod cover, I had the same problem. I finally gave up and used RTV with no gasket. That was the fix. If you do that you have to make sure to circle all the bolt holes.

The vent is a mystery. If the vent is plugged, I suppose the pressure could build up. Also I wonder if the engine is overfull.

I'm happy to report that my new pushrod gasket is drip tight! No more oil leaks!

Getting the old gasket off was a royal pain in the keaster, but I'm glad I bit the bullet. I installed a new cork gasket using a cement sealer called Gasgacinch. This product was recommended to me by a couple of old mechanics I know. I also straightened the cover as described above, which may have been the problem. It turns out the vent tube was not leaking after all. It appeared to be leaking, but the real source of the leak was the pushrod cover located behind the vent tube.

The first gasket I installed was the pressed paper variety, and I cemented it in place with a product called "Super Weatherstrip and Gasket Adhesive" by 3M. I'm not suggesting this is a bad product, but the gasket leaked in several spots even though I know I installed it with care. Perhaps I over-torqued the original fasteners, but I started at 6.5 ft-lbs, just like the book says, and worked my way up to 10 ft-lbs.