John Deere 3HP Engine Oil Seal Modification

By Bob McDowell

After restoring my 3HP John Deere hit-n-miss engine and getting it to run well, there seems to be a constant leak of oil around the seal at the magneto drive and crankcase cover. The felt seal that is used on the 3HP engine will sort-of work well, until it is saturated with oil, then it starts to drip down the side of the engine. I like a clean engine even though these engines are known to have a coat of oil somewhere on them. What I have been trying to come up with is a way to do a better seal around the magneto area between the magneto drive and the crankcase cover casting of my engine. I have come up with a way to modify the cover plate to take on a modern seal and prevent the oil from getting out from the crankcase. The photo shows the area where the felt seal and cover plate would normally go. I did some research and found a modern seal that fits the dimensional parameters I needed for this modification. I wanted to keep the original cover plate and felt seal in case I had to go back to the factory correct assembly sometime in the future. I purchased a really nice laser cut replacement cover plate to use for this modification. I had to machine out the clearance hole in the cover plate to allow a press fit of the new oil seal. I took several measurements of the centerline of the magneto to the top of the crank case cover gasket to make sure the new seal will be centered on the magneto drive gear when everything is assembled. The magneto drive gear has a flange on it that the original felt seal would ride on. I chucked the drive gear up in the lathe to true and smoothed out this flange so the new seal would ride on it and seal properly. After I bored the hole in the cover plate to the proper size, I press fit the new seal into the cover plate and centered it in the middle of the cover plate on each side. Here is a view of the original cover plate on the left and the new modified plate on the right. The gasket for the cover plate also needed to be enlarged to fit around the new seal. After fitting everything up I added a little sealent to the gaskets and made the final assembly. It all fits perfectly now.