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Will new engine create excess crank pressure?

Discussion in 'Norton Commando Motorcycles (Classic)' started by joshtjeerdsma, May 22, 2018.

  1. joshtjeerdsma


    Oct 11, 2015
    I have started breaking in my new combat engine rebuild and am having a similar problem that I had before I tore the engine down. I am getting excessive crank pressure and the engine is leaking oil out of the points housing and a tiny grub screw on the lower crank housing. The engine leaked out of the points housing before the rebuild also. The engine was rebuilt by a well known builder. I am using a Colorado Norton Works breather setup and the oil tank breathers seem to be working. Is it possible that the engine will create excess crankcase pressure until the rings seat completely? Sorry for starting two threads at once, but I hadnt had time till now to post. Thanks
  2. ashman


    Jul 11, 2010
    If you are leaking oil from the points housing then the oil seal has been damaged when fitted thats if the seal was replaced in the first place, very easy to damage the seal when installing it if you don't have a tool to put it in, just replace the seal as for the grub screw take it out and put some sealant on the thread should fix that, you say you have a breather set up and you have no other oil leaks so it must be working, if your breather weren't working you have a lot more gaskets leaking from to much pressure.

  3. pierodn


    Nov 10, 2012
    Replace a new CRANKSHAFT OIL SEAL using his tool.
    Easy and quick to do.
    But, first, pay attention that the thread on the timing cover where in the points house you screw the pillar bolts are not bored up to into; in this case the oil will spray into the points house.
  4. Fast Eddie

    Fast Eddie VIP MEMBER

    Oct 4, 2013
    If you have a reed valve breather installed and working, I cannot see how the engine could create any meaningful pressure.

    I can’t remember, is it possible to instal one incorrectly? Reeds the wrong way around, etc?

    You have two leaks: the points seal, which as Ash says, could be damaged. And a ‘tiny grub screw’.

    Which grub screw is it? It sounds to me like a oil gallery blanking grub screw. IF it is, then this is not effected by crank case pressure (its handling oil pressure).

    My worry with this grub screw would be why is it leaking? IF it is an oil gallery blanking screw and IF it is loose, you’re in danger of it coming out, along with your oil, and you’ll be looking at another engine rebuild !
    Last edited: May 23, 2018
  5. Brooking 850

    Brooking 850 VIP MEMBER

    Oct 3, 2011
    Someone may have put the cam end seal in the timing cover in the wrong way?
    Use a proper installation tool or a socket of the same size and bolt to the end of cam prior to installation.
    Regards Mike
  6. RoadScholar

    RoadScholar VIP MEMBER

    Dec 28, 2008
    Some good responses; for me they distill to replace the points/cam seal (spend the money on the correct tool, it won't break you. And do have a hard look at the seal seating surface, be mentally prepared to remove the timing cover if they seating surface is gouged.

    And, it is rather unusual to remove the oil gallery grub screw, but not unheard of. As stated earlier, remove it clean it and the hole it lives in, use a good sealer/locker (Loctite MS 222 works for me). The factory staked the grub screw with, I'd guess, a dull cold chisel; a couple of whacks on a prick punch works as well.
  7. joshtjeerdsma


    Oct 11, 2015
    I did replace the points oil seal to no avail. I have the tool and have replaced a couple through the years. I also checked that the seal was oriented the right way. As for the galley screw, i was planning to seal it when I do my first oil change. It will leak all the expensive break in oil out if I pull it before the oil is drained.
  8. comnoz

    comnoz VIP MEMBER

    Dec 10, 2008
    When you installed the CNW breather did you block the holes between the timing chest and the crankcase. If you did then you need to drill the new oil return hole or too much oil will build up in the timing chest.
    Check your oil pump conical seal. If it is leaking that can also build up extra oil in the timing chest.
    A head gasket that is leaking between the cylinder and pushrod tunnel can cause too much crankcase pressure as can poor ring seal.
    More break -in time is not going to make a significant difference in blowby.
  9. joshtjeerdsma


    Oct 11, 2015
    I did not do anything but bolt it on. My engine builder was Leo Goff and he knew I was using th CNW breather. I think he did some crankcase flow mods and I assume he would have the knowledge to know what needs to be done when using that breather. Maybe I will give him a call and ask him what work he did. I did check the conical seal when I had the timing cover off. There is only about 40 miles on the complete rebuild. The main pain is that the oil leaks directly onto my new exhaust.
  10. comnoz

    comnoz VIP MEMBER

    Dec 10, 2008
    Crankcase pressure is not going to be related to the leak at the grub screw. It just needs to be removed and sealed.

    A leak at the camshaft points seal could be related to crankcase pressure or too much oil in the timing chest or simply installation problems. [it's awfully easy to fold that seal on installation.]
    You would also want to make sure that there is nothing up with the timing cover gasket surface that would allow oil to leak into the hole for the points wire.

    Have you retorqued the head gasket? It would need to be retorqued after the first heat cycle. Head gasket leakage can sure cause excess crankcase pressure.

    I would have expected Leo to modify the scavenge oil pickup [move it to the back] but I doubt he would have changed the holes between the chest and crankcase so that is not likely a problem.

    Possible blockage of the scavenge pump inlet passage could sure cause excess oil in the crankcase -and leaks. I have removed more than a few broken off camshaft washer tabs from that passage.
    Last edited: May 23, 2018

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