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oil leak odd color

Discussion in '308/328' started by bitsobrits, Jun 24, 2025.

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  1. bitsobrits

    bitsobrits Formula Junior
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    Nov 12, 2011
    740
    Omaha, NE area, US
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    Steve
    #1 bitsobrits, Jun 24, 2025
    Was investigating a minor oil leak that turned out to be from the left (front) cam belt drive sprocket. When I had replaced the outer bearings and seals a couple of years ago during an engine out clean and service, I had applied a bit of sealant to the drive sprockets at the outer ends before seating them and torquing the nut. But it appears the keyway didn't seal well. So while I think have the leak path addressed, what has me stumped is the color of the oil stain. It looks like more like rust. Any ideas?

    First photo shows the wet inner surface of the drive sprocket with the brown stain, which easily wiped off. Note there is no oil residue behind the sprocket, so not that seal.

    The second photo show the oil residue spray pattern inside the front belt cover from being flung off the sprocket, with the rust like stain that has me wondering. FWIW, I'm using Mobil 1 oil, and the engine when I first received it had affair amount of internal 'varnish' in the cam area.

    Ideas?
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  2. Anthony Rapuano

    Anthony Rapuano Karting

    Aug 16, 2022
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    Anthony V Rapuano, Jr.
    #2 Anthony Rapuano, Jun 25, 2025
    Hi Steve
    Perplexing. As you stated, there is no oil splatter/dripping on the back side of the cam drive gear/sprocket leading you to conclude that the seal is not at fault. In my thinking, then, the keyway can't be the pathway of the leak as the keyway is outside the seal. The only way the keyway would be the path of the leak would be if that cam drive seal was leaking, somehow getting onto the cam drive shaft, and then past the woodruff key out to the front of the pulley; all without leaving some sign of a leak on the back side of the pulley or on the engine block. Seems unlikely to me. You mention that you used some sealant on the cam drive shaft before torquing, but that the keyway didn't seal well. The woodruff key/keyway is simply a mechanical means to positively engage the pulley/cog with the shaft. They serve no sealing function that I am aware of. Could something be dripping down onto that cam drive sprocket from above and then be flung out onto the inside of the cam belt cover? Is the leak indeed oil? Could it be coolant? Also, what is that little rust-colored blob sitting on the block flange below the crank pulley? Is that a blob of sealant? It looks to be the same color as the residue around the cam drive pulley nut. Whatever the fluid is, and whatever the source, it does not appear to be getting onto the cam belt to any significant degree. Where's Brian when you need him?!
     
  3. Rifledriver

    Rifledriver Three Time F1 World Champ

    Apr 29, 2004
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    Brian Crall
    #3 Rifledriver, Jun 25, 2025
    A damaged shaft surface can allow oil between bearing and shaft. A pulley working on the shaft due to loose nut or bad key/slot will produce rust red steel powder.

    If it was mine I'd be taking it apart and not just staring at it.
     
  4. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Jan 11, 2001
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    Steve Magnusson
    #4 Steve Magnusson, Jun 25, 2025
    Last edited: Jun 25, 2025
    He's got a 1977 308 = has the early cam drive bearing/seal arrangement = can leak engine oil out the keyway path.

    The "rust" colored stuff could just be road clay/dirt that has become stuck in the wet oil film. In any case, it needs to be fixed as Brain indicated.
     
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  5. bitsobrits

    bitsobrits Formula Junior
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    Nov 12, 2011
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    Steve
    #5 bitsobrits, Jun 25, 2025
    I did remove the drive sprocket and cleaned/inspected everything, and didn't see damage or anything unusual. Virtually no oil on the belt, though I gave it a good clean anyway. Clearly there was oil in the key way groove. On re-installation I believe I did a better job of applying sealant (3 Bond 1211 this time) just before the sprocket was fully seated, with extra care in the keyway area. I'll see tomorrow after a test drive if I've got it whipped.

    I still find the color issue to be odd. I live on a rural seal-coat road, which while paved, can still be somewhat dusty in dry weather, and road dust easily kicks up into the engine compartment. But to my eye, that dust is more grey than brown. In any case, thanks for all the input.
     

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