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Oil spray blowing from primary chain filler vent hole

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  • Oil spray blowing from primary chain filler vent hole

    I took my East Coaster for its MOT this morning. It passed and seemed to be going very well as I rode it home. However, when I got home I noticed some oil spillage on the primary drive cover - LHS looking down from seat. It wasn't much and I wiped it off but when I started the bike I noticed a slight spray coming from the oil filler plug's vent. The level in the case is OK, only just weeping a little with the level plug is removed. I am wondering if this is a sign of trouble ahead. Is it likely there's a seal inside that is leaking and causing the case to become pressurised? I really haven't a clue what to think and hope someone on here may have come across this before and can advise.

  • #2
    Originally posted by djbgreeves View Post
    I took my East Coaster for its MOT this morning. It passed and seemed to be going very well as I rode it home. However, when I got home I noticed some oil spillage on the primary drive cover - LHS looking down from seat. It wasn't much and I wiped it off but when I started the bike I noticed a slight spray coming from the oil filler plug's vent. The level in the case is OK, only just weeping a little with the level plug is removed. I am wondering if this is a sign of trouble ahead. Is it likely there's a seal inside that is leaking and causing the case to become pressurised? I really haven't a clue what to think and hope someone on here may have come across this before and can advise.
    Firstly there should not be a vent hole in filler plug, and secondly there is a vent hole from inner chain case through gearbox casting that connects with a vertical drain hole in the carb recess. This can become blocked

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    • #3
      It sounds as though your drive-side oil seal is leaking pressure from the crank case. The seal lies behind the engine sprocket and is fairly cheap and easy to replace. You will need to remove the clutch and engine sprocket to get to it.
      John A - 268

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      • #4
        Originally posted by John-Boy View Post
        It sounds as though your drive-side oil seal is leaking pressure from the crank case. The seal lies behind the engine sprocket and is fairly cheap and easy to replace. You will need to remove the clutch and engine sprocket to get to it.
        The oil seal on a twin is NOT changeable from outside and involves splitting the crankcase. Most unlikely to be oil seal if engine starts and runs OK.

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        • #5
          'djbgreeves' was this info of use to you? As you have not yet replied to the the advice given. Have you found the problem?
          Last edited by John Wakefield; 01/08/2017, 05:54 PM.

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          • #6
            A short holiday has occupied me, so not looked at it again properly as yet. Hoping it's not a crank seal - running well is a good sign I guess. Then again, it hasn't sprayed oil out from there before and I haven't added any oil in, so something new is happening. Will post any discoveries as I find them. Thanks for comments.

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            • #7
              Back on the job - discovery

              After a period of idleness and holidays, I've finally set to trying to see what is behind the oil spray and decided to remove the cover and take a look. As soon as I undid the level plug around half a pint of petrol/oil mix spurted out. Removing the cover produced yet more. Unable to spot any obvious point of entry for petrol into the cover I decided to try starting it up. It fired up nicely and seemed to be running OK. Apart from some spray from the clutch no more oil appeared to be coming through. I'm now mystified on the cause. It did have a petrol leak a while back, since cured, but can't see a pathway in for petrol, although there must be one. I haven't spotted the vent hole JW refers to. I can only see the one that leads to the chain from under the carb. I'm wondering if I should do more than refit the cover, refill with oil and see if it happens again. Any suggestions?
              Attached Files

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              • #8
                The vent hole for chaincase is at 11 oclock position above clutch. I think that links to the drain hole in recess under carb, I suppose if carb flooded petrol could come back up from there, but as the c/case vent is higher up this should not happen. It should drain through the bottom. Very strange. its looking like a crankshaft oil seal but that would effect running. Sorry cant help further. Put it back and fill with correct amount of oil & see what happens

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                • #9
                  Thanks for quick reply John. My thinking is going along much the same lines - it's running well so unlikely be anything major and volume of petrol in the oil most likely from the carb leak. Can't see a vent for it to get in but I guess no harm in refilling the oil and see what happens next with a local test run.

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                  • #10
                    Chaincase breather problems

                    I had similar problems some time ago which I finally resolved, follow the link below.
                    Cheers Pete from the Antipodes

                    Greeves roadsters, e.g. Sports Twin and Single, Essex Twin, Fleetwing, Fleetmaster, Fleetstar Deluxe, East Coaster.

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                    • #11
                      Having removed the case and had a proper look I can't see an obvious source of the petrol but I can see that the primary chain is very slack and actually wearing the chain case. Having enjoyed a lengthy chat with JW this afternoon and picked up some useful hints, my plan is to order a new primary chain. I'll replace that refit the chain case and top up the oil. Fingers crossed that will solve it. I'll report back once it's done - maybe a little while.
                      Attached Files

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                      • #12
                        Might be worth fitting on of these from Villiers Services

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                        • #13
                          I think these tensioners only fit the singles (9E 32A 34A etc)

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                          • #14
                            New primary chain fitted

                            Having finally got all the necessary parts & special tools (thanks to Villiers Services) and, post holidays & other stuff, had the time to get to grips with it I have fitted a new Renolds primary chain - somewhat shorter than the sloppy stretched one I took off. I couldn't spot any signs of leakage around the seals and after refilling the chain case with oil, a quick blast round the block seems to suggest all could be well. Time will tell.

                            My thanks for all the helpful tips and advice received.

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