Slant rear main and oil pan saga and fix

Slant 6 Engines

  1. Naplm00

    Naplm00 Well-Known Member

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    Since I have owned my car for a few years the oil pan and rear main have always been trouble. From minor to serious leaks and back again, its been a HUGE pain in the ass.


    Bought the car and the leak was minor but annoying from the rear main only. I suspected an original rear seal as all of the hardware was original and seemingly untouched. I dove in and pulled the pan and rear main with the engine in the car. With a crane wasn't hard and just needed a 1/2in ujoint socket.


    Crank was pitted on the seal land from rust, replaced it with a rubber Felpro BS40240 crank seal kit and a Felpro OS 12705 C-1 pan gasket set. Leaked worse from before from the crank seal. I knew a new crank was needed.


    Found Doug Dutra was less than a hour from my home. He had the parts and even offered to rebuild the engine, seemed like a no brainer. I go it back from him and was leaking from the pan now and then Doug’s house burned down and he couldn't help me getting it right. Almost a year later its was still pissing and I had to relocate the car to Las Vegas in August.


    The 11 hour drive in desert heat wasn’t kind, the rear main was now leaking and the pan was too.


    Doug squared us up and I wish him the best.


    Now in an HOA rental, I couldn’t pull the motor to fix it. Asked around for a few months and landed on a local old school shop that had done slants before and BB mopar work. Had the car for a week and put in a new felpro main and pan gasket. Drove it home…leaking again. Towed it back, they tightened up the pan bolts and ran it, no leaks. Drove it home and it pissed a quart outside of my house and covered the underside in oil.


    Im fed up, going to set the car on fire.


    Do a ton of research, im going to give it one more go with a new rear main and pan seal, at home wit the garage door shut.


    Using an engine lift bar : 1000 lb. Capacity Engine Support Bar


    I crank up the engine, remove the center link, mounts and get to work. I removed the pan, old RTV, seal retainer and main seal. Cleaned it loke the virgin mary would eat off it. Scraped the block with a carbide, perfectly flat and degreased. Let it drip for two days and then degreased again.


    I then turned my attention to the seal retainer. Using a granite block and emory paper I flattened the face that touches the block and checked with a straightedge. Test fit the retainer without a seal and looked for land alignment with a bore scope and tiny mirror. Cleaned it to look like NOS.


    Oil pan was wire wheeled on all sealing surfaces and then flattened on a neighbors anvil with a finishing hammer.


    Using this bore snake https://www.amazon.com/dp/B01N1YPNZY/?tag=fabo03-20 I cleaned the backside of the crank and groove. Then using a cut up rag soaked in brake cleaner I degreased the same area on the far side of the block , under the crank with a sneaky pete and shredded rags to get it as clean as I could. https://www.amazon.com/dp/B0002SRCJW/?tag=fabo03-20 . I would soak the rags in brake cleaner then drag them through the sealing land with the sneaky pete.

    Air compressor to blow out any fuzz from back there

    I used the fastfish single piece viton rear main seal. Product Page

    Comes as one piece, you cut it, then insert it with greased lips and sealant on the backside. I ONLY use black right stuff, regular RTV is garbage in comparison.

    Greased the lips and spread sealant on the backside of the seal. Using one had to feed the flexible seal and the other to pull on the fan rotating the engine to feed the seal into the block side. Purposely over feeding it by about an inch so the seal cut was inside the block side above the midplane of the crank diameter. Put a dab of black right stuff on the end and forced it up to meet the other half of the seal.


    Using the small fat L shaped side seals from the felpro rear main kit I basted them in right stuff and inserted them into the rear crank seal retainer.

    Basted the back edge of the seal with more black right stuff and put some in the seal retainer. Also on the now laser flat faces of the crank seal retainer. Torqued to 30ft lbs. I then cleaned the block sealing area where the little ends of the side seal stuck out and glued them down with superglue, so they would not move during pan install.


    With the pan on the bench, I put right stuff on both sides of the cork rails and the rear pull through rubber seal that goes over the crank retainer. I also put sealant on the front and back faces of the front rubber seal that pulls though the timing cover, extra where the cork transitions to the rubber. Putting it in place making sure that the rubber and cock doesn’t squirm out from all the sealant. Torquing from the center out


    Now I let it cure for another two days. Filled with oil and heat cycled it twice…no leaks.


    Thank god. The fastfish seal while expensive is very high quality, recommended
     
    Last edited: Oct 13, 2021 at 4:43 PM
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    • my68barracuda

      my68barracuda Well-Known Member

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      Good for you that you got it fixed. I have built three slants and using the FelPro two piece rear seal, good judgement on cleanliness and alignment and RTV have never had a rear seal leak.
      I will add that on the very first slant I had oil leaking where it looked like a rear seal leak. Had that engine out twice, then figured out it was oil wicking up and out of the aluminum rear seal retainer bolts. On this block those two bolts were drilled through on the crankcase. Put RTV on the threads and capped the drilled through holes with RTV and no more leaks. I have built that practice into the slants that I have put together.
       
    • Naplm00

      Naplm00 Well-Known Member

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      I did also coat the bolts the ARP thread selant, forgot to mention that ! thanks !

      id suggest you take a look at the fastfinsh the back profile is so much more appropriate than the felpro /opinion
       
    • volaredon

      volaredon Well-Known Member

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      I do not believe in RTV or "right stuff" as it may be called..... if I use anything its proper gaskets, and either Aviation shellac, (a "Permatex brand product), Indian Head or Weatherstrip adhesive just enough to hold things in place and minimal RTV type products at gasket joints/corners.
       
    • Naplm00

      Naplm00 Well-Known Member

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      I have been in the same boat before but with three separate failures on this assembly, one by literally the guy who wrote the book, something had to be done. All the parts here were factory type replacements.

      Right stuff: Permatex® the Right Stuff® Gasket Maker – BLACK

      is different than standard RTV, it has zero cure time required and is quite a bit thicker. anywhere where you use black/grey/red/blue RTV, i use this instead. Copper RTV is the one exception that i dont replace it if called for by a manufacurer. its also much tackier, like a glue and less like as silicone
       
      Last edited: Oct 13, 2021 at 4:57 PM
    • volaredon

      volaredon Well-Known Member

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      Yeah, I have used them/ "right stuff" and various RTVs/ but don't like to if I don't absolutely have to.
      Even on things like diff covers, if there is a cut gasket available I prefer to use it in place of "gasket in a tube"
       
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