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Crankcase oil seal leaks

Discussion in 'Norton Commando Motorcycles (Classic)' started by pierodn, Mar 25, 2019.

  1. pierodn


    Nov 10, 2012
    Hi All.
    The cranckase oil seal leaks trough the cranckshaft.
    I have changed with a new one, but it leaks too.
    Someone supply a tighter oil seal?.
    Other sugestions will be apreciated.
  2. Onder


    May 11, 2010
    My seal on the DS leaks. Ive tried three seals. They were installed with great care but to no avail. Having a dry belt drive it is just not what
    one would want. If you have a stock setup you would never know it is leaking.
    I run the Jim Comstock breather valve which should really eliminate leaking.
    I dont know, a multi lip seal of some kind? You tell me!
  3. lazyeye6


    Feb 28, 2014
    After installing the Comstock breather and a new DS oil seal I still had leakage. Then I found that the leakage was from the lower mounting bolt of the inner primary case. I re-installed those bolts using a gasket sealing compound on the threads and, voila, no more leakage at all..
  4. pierodn


    Nov 10, 2012
    Mine leaks from oil seal!
  5. texasSlick

    texasSlick VIP MEMBER

    Jan 2, 2013
    Leakage with a new seal is usually caused by a rough, scored, or out of round crankshaft seal journal.

    Excessive play in the main bearings, either due to a worn crankshaft journal, excessive clearance in the main bearing outer race to case, or simply a worn out main bearing can also be a factor.

    Time Warp and Deets55 like this.
  6. Time Warp

    Time Warp .......back to the 70's. VIP MEMBER

    Dec 3, 2012
    The best one is folk who drag the bearings or inners off the journal without heat expanding them (and that is only a hot air gun) and put gall scores in the seal surface which is minimal as is, scored and you are all but stuck with seepage under the seal lip.
  7. pierodn


    Nov 10, 2012
    I understand, but this is not the my case.
    The engine is on the stand without primary transmission cases with oil seal in view.
    I have drained the old oil and fit the new one.
    After five days, without started the bike or turned the cranckshaft, the oil seal has began to leak.
    I understand that after the first days the oil was gone from tank in the sump.
    So, if the oil seal leaks with the bike on the stand i can understand that the crankshaft journal is worn and i need a tighter oil seal.

    Last edited: Mar 26, 2019
  8. Chris

    Chris VIP MEMBER

    Jan 21, 2008
    Hi Pierodn
    My crankshaft oil seal leak turned out to be porous cases. Had them coated.
  9. kommando


    May 7, 2005
    Seals with a steel OD can leak on the OD, rubber on the OD has a better chance of sealing but a sealent on the OD is even better, steel or rubber will benefit.
    concours likes this.
  10. concours

    concours VIP MEMBER

    Dec 29, 2011
    Yamabond 4
  11. Time Warp

    Time Warp .......back to the 70's. VIP MEMBER

    Dec 3, 2012
    Is it that obvious ?
    Time to wipe it down and a application of talcum powder to see the path for sure ?

    Even rubber bodied oil seals I use Wellseal applied to both surfaces and left the suggested 5 minutes (at least) before installation.

    No doubt the seals used are the same item which came from where ?

    If it leaks that badly between the lip and seal and the seal is the right one there would have to be a defect of some sort surely (Is there a X ring or labyrinth seal available I do not know)

    Worse case (Not that I have given it any thought and it is the early morning) if the journal was compromised in some way that was not reversible, maybe a Speedi-Sleeve could be used for a repair somehow.
  12. dynodave


    May 28, 2003
    How many people/mechanics that change a main bearing on the DS...afterwords polish off the hundreds of microscopic or bigger scratches made on the sealing surface of the crank?
    + Yes, wicking loctite on metal bodied seals.
  13. acadian

    acadian VIP MEMBER

    Mar 5, 2010
  14. Onder


    May 11, 2010
    Well I can see it is the speedy sleeve is among my future tasks...
  15. Chris Zet

    Chris Zet

    Aug 14, 2009
    Hi Piero,

    i am once bitten, twice shy on this problem/thread......

    do you have inspected your timings side or did you a general service on the parts in the timing side on your bike lately/last years?

    my bike had a blown crankshaft oilseal on the timing side and i didn`t know about that kind of problem....

    drove me almost crazy!!!!

    i tried and tried and tried to fix the problem on different ways from checking the piston rings, making new breathing routes with pcv-valves and so and so on.......

    My crankcase was pumbed up with oil and the oil went through the driveside oilseal [as through the tachometer drive].
    As you describe your problem.

    Do an oil pressure test.

    when the pressure isn`t right:

    don`t hesitate to service your timing side:

    service the oilpump....put in a new oilpump sealing [NMT272] ....put in a new crankshaft oilseal [#048023......#21 for 1972 Commandos] and a new points oilseal.....check your timing chain adjustment [you MUST use the intermediate shaft support plate tool]
    and check the slipper .... this is done in a few hours and you get peace of mind for several years!

    if this isn`t the problem:

    put in a pcv-valve [i get me one from NYC Norton...this is top of the notch!!!]


    get an oversize oilseal for the drive side [there is for sure a company near your place who can make an oversize oilseal for your dimensions]

    hope it helps and you get your problem solved!

  16. DogT


    Jan 20, 2009
    I've had the bolts of the primary side mounting studs leak into the primary also. I replaced the bolts with studs and nuts. The lower nut I had to grind down so the chain wouldn't hit it. I also used red or blue locktite on the studs into the crank. It also makes for easier assembly. You can get the proper studs at the auto store. I think they were 1" 1/4-20 UNF on one side and 1/4-20 UNC on the other. I had one bolt that was stripped out when I got the bike, I just went up another size with that one. This was a hint from hobot a long time ago. I also use a smear of RTV on the primary to crank gasket. My leak is in the crank flange. I didn't do a good job with the Hylomar but I'd have to split the whole engine down to fix it. I wish there were a fix for that. The proper breather would help, bit it leaks just sitting, not too bad, a flower base takes care of it. I also don't let it wet sump with a dreaded manual oil ball valve.

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