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Fixing a rear main leak

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  • Engine: Fixing a rear main leak


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    When I pulled the head on my 186 c.i. engine I found it bored .040 over sized. When I looked down the back cylinder I saw a deep gouge about 1/16" deep and 3/4" wide in the cylinder wall. The wrist pin had come loose and the pin shifted to one side and gouged up the wall. Took it to a good automotive machine shop who used to work on these vintage engines and they bored it out and installed a sleeve for me. We had the whole block then bored to .060. Checked the crank and one rod journal was a bit out of round and the rear main was pitted somewhat so the crank got .020 on the rod journals and .015 on the mains. However they could not get in to the rear main seal area and it too was pitted real bad. That explained all the oil sprayed along the entire bottom of the drive line. So how do you fix that.
    Well here was my solution and it worked. I chucked the crank up in my big old Barnes lathe with a 4 jaw and got it centered as close as possible, less than 1/2 thou. supported the other end with a live center. I took a slight skim gut off with a parting tool washed it real clean with lacquer thinners and brushed on a thin layer of JB Weld. Let it harden over night and then tried to turn it round with a parting tool. I kept cutting trough to bare metal and the JB Weld kept pealing out of the pits. So after several tries like this I decided I would need to cut through the pits to good metal to make it work. So I took off about 1/16" and then re-applied the JB Weld. This time I was able to bring it down to stock size and leave perfect surface for the seal. I polished it with some crocus cloth around a square file and assembled the crank in the block. When I torqued the bearings down I couldn't turn the crank so back to the machine shop that had turned the crank and they found a high spot about .005" in the rear bearing journal of the block so they line bored it for me. So now it has everything new in it front to back. All bearings, timing gears, lifters, valve guides, valves, oil pump. pistons, wrist pins etc.
    So here is a picture of the crank in the lathe how I repaired it. I once used to sell JB Weld and had many discussions with factory reps on it's usefulness and have tested it on various projects in the past. Now that I have had it running for several hours she is bone dry. One nice thing about this repair is that it will never pit again.
    Last edited by njonkman; 12-04-2012, 06:13 AM.