Oil leaks are never a pleasant thing to deal with. One ounce of oil can look like a gallon once it has circulated around your engine, making a complete mess and creating a very aggravating work environment. Last month, we explained how to replace the side cover gasket. This month, we want to expand on that and explain how to replace a leaking PTO seal, and stop leaks at the valve chamber.
Before starting an oil seal leak, take note of which seal you need. There are two seals for the raPTOr engine, depending on the crankshaft in your engine. Both are the same on the outside diameter, but have much different inside diameters. The Briggs part number 495307 is for the crank with the 1.00” PTO bearing, and the 393812 is for the .785 crank. If you aren’t sure which you need, get help before proceeding. I like to have the repair parts in hand before I start disassembly. To begin, drain the oil and remove the side cover as explained in last month’s article. Hopefully we have a clean engine to begin with. However, if this is a field repair, clean everything with brake cleaner before starting. I want to stress again the need to be very cautious not to allow any dirt to enter the engine, as well as not to disturb the internals of the engine. Remember, we are here to cure the problem, not create more.
Once the cover is off the engine, take a socket or other blunt object and drive the seal out of the cover. Use caution if using a screwdriver or other sharp object as this can nick the seal bore and start another leak. To install the new seal, lay the cover flat on a solid bench or table and place the seal into position. Use a solid piece of flat steel to drive the seal into the cover. Be sure to use something that covers as much of the seal as possible, as this reduces the risk of deforming or bending the seal. Once it is flush in the seal bore, take a socket turned upside down and gently bump the seal down about 1/8” below the outer edge of the cover. Pay attention and make sure it is not cocked in the bore. Before installing the cover, always lubricate the inside of the seal with oil. Using last month’s article as your guide, replace the cover, add oil, and you are finished.
A sometimes-overlooked source of oil leaks is the crankcase breather. To access it, we must remove the tank and carburetor. Just like previously stated, always clean the affected area before opening the engine; dirt is for racing, not lubrication.
There are several reasons we have leaks in this area. One of the more common is the bottom edge of the block where the chamber seals. Over time, due to removal of the valve springs, and working inside the chamber, a burred edge forms on the gasket surface. Take a small smooth file; lay across the gasket surface, and after a couple short smooth strokes, the burr should be removed. Check your work and repeat if necessary.
The materials the breather assembly is made from cause another issue. The thin metal cannot withstand repeated tightening of the bolts without some deformation around the mounting holes. If you see this, replacement is the best option.
Speaking of replacement, this brings up another issue. A few years ago, Briggs changed the breather assembly design and shape. I used to see a higher rate of leaks with the new style breather, but I have found a method that seems to pretty much eliminate any leakage issues associated with the breather assembly itself. Before I install the breather, I take it to my bench vise and squeeze the top and bottom of the breather assembly to crimp the rolled edges a bit more. It doesn’t take a lot of pressure. Just tighten securely, flip it over, repeat, and you are done.
Anytime you are working with the breather, always use two good gaskets and use flat washers to spread the torque of the mounting screws.
Hopefully this sheds some light and helps you correct an issue you may be having. Always use care and good judgment, and if you aren’t sure or comfortable with something, don’t be afraid to ask for help.
See you next month.