1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

exhaust valve opens during intake

Discussion in 'Norton Commando Motorcycles (Classic)' started by dlou0338, Feb 8, 2019.

  1. dlou0338

    dlou0338

    Joined:
    Aug 25, 2016
    I'm in the midst of a complete overhaul of my 72 750 just got my new head bolts in last week put the head on and located the pushrods on the rockers lightly bolted the head down and spun the engine over by hand everything seemed fine until the left cylinder was on intake about half way through the exhaust valve opened slightly and then snapped shut im new to nortons but this did not seem normal wondering id it might not be properly located on the tappet any help would be appreciated
    thanks dave​
     
  2. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    Could be that your cam is not located centrally on the folllwers and the ‘other’ lobe caught on, and partially lifted, the follower.

    It definitely needs looking at cos if it is this, and it happens at speed, you could tangle your valves.
     
  3. dlou0338

    dlou0338

    Joined:
    Aug 25, 2016
    thank you, i'm definitely going to look at it tomorrow but if that were the case wouldn't it happen to both exhaust valves? it only happens to the left cylinder
     
  4. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    Maybe, maybe not.

    If the cam is pushed over too far one way, then one lobe is just pushed out more into thin air, but the other lobe is pushed towards the ‘wrong’ follower and could foul it, resulting in a partial lift.

    The only other thing that I can think of that could cause this is an incorrectly fitted pushrod. That’s easier to check.
     
  5. dlou0338

    dlou0338

    Joined:
    Aug 25, 2016
    Ok Thanks a lot
     
  6. swooshdave

    swooshdave

    Joined:
    Apr 15, 2009
    Tale the head off and spin the crank and watch the lifters?

    If the cam was pushed over too far I think you’d see it somewhere. Maybe check to see if the cam chain is ok?

    Is th engine in the bike?
     
  7. dlou0338

    dlou0338

    Joined:
    Aug 25, 2016
    its just set in the frame with only the front bolt through it thats where ill start and if i can't see anything i'll have to tear it down
     
  8. Peavey Jeltz

    Peavey Jeltz

    Joined:
    Jan 12, 2019
    That snap you heard when you rotated the engine sounded to me like you didn't have a rocker ball end perfectly seated in the top of a pushrod. The ball end was probably riding on the edge of the cup and slipped off the outside. That could cause an intake pushrod to start rubbing against the exhaust or maybe the slipped pushrod is also engaging both rocker ends. I'd pull the head bolts and repeat the pushrod / rocker seating procedure again. I find it takes a little time and patience to get the pushrods located and that's after you've blasphemed your way through getting the head on in the first place.
     
  9. texasSlick

    texasSlick VIP MEMBER

    Joined:
    Jan 2, 2013
    I agree with Peavey Jeltz (reply #8) but I do not think it necessary to pull the head to get the rocker balls in proper place. Try backing off the adjusters, then while rotating the engine, guide the pushrods into place with a hooked wire.

    Slick
     
  10. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    FWIW, I fill the pushrod and cam follower cups with grease. Then when fitting the head I gently push rockers down into the pushrods and you can quite easily feel and hear the ‘suidge’ as the ball goes into the grease filled cup. You can also feel the resistance due to the grease holding it in when gently trying to lift the rocker back up too as a confirmation that things are seated correctly.

    Not saying it makes this fiddly job totally error proof, but I find it helps.
     
    Last edited: Feb 10, 2019
    Nater_Potater and 998cc like this.
  11. dynodave

    dynodave

    Joined:
    May 28, 2003
    Do you have the original 2S cam?
    My original combat cam was bent from the factory. It would result in a shift of the base circle circle.
    Cams are bad enough with wobbly base circles which makes it a bit inaccurate when setting valve clearance.

    However the extreme 2S lobe ramp and accompanying big clearance would make it more likely that a cam bush/thrust washer problem is failing to properly locate the cam. Symptoms as described above are quite probable, including push rod not being properly positioned.

    You didn't put in a briggs and straton EZ start cam that slightly lifts the exhaust valve while starting???? LOL
     
    dlou0338 likes this.
  12. dlou0338

    dlou0338

    Joined:
    Aug 25, 2016
    I believe it is the original cam. I just pulled the head off and watched the lifters both are definitely engaged at the same time my issue is that I inspected the thrust washers and I believe I have put them in correctly so I am unsure how to rectify this issue
     
    Last edited by a moderator: Feb 9, 2019
  13. Deets55

    Deets55 VIP MEMBER

    Joined:
    Oct 3, 2013
    Just a thought, but is there suppose to be a hardened steel washer between the cam and the Rt. hand case? I almost left my out on reassembly.
     
    cash likes this.
  14. acadian

    acadian VIP MEMBER

    Joined:
    Mar 5, 2010
    Assuming the cam thrust washer is in place, I would put some engineers blue on the lifter surfaces then rotate the engine to see exactly where the cam is making contact with them
     
  15. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    The first thing I thought of was - is the thrust washer in the correct place ? I am about to replace the cam in my 850 and I remembered there is a thrust washer, but I cannot remember which side of the crankcase it goes. I know it is either behind the cam sprocket or it is on the inside keeping the cam to the left. If you have got it wrong, you might have to split the cases again.
     
  16. dlou0338

    dlou0338

    Joined:
    Aug 25, 2016
    From everything I've been reading In The manual the tab washer goes inside on timing case with a steel bushing beveled edge facing in also on ts unless I'm reading something wrong I'm gonna have to split the case and redo and hopefully get it straightened out
     
  17. acadian

    acadian VIP MEMBER

    Joined:
    Mar 5, 2010
    Inside TS case, bevel toward tach worm gear... at least on the 750 I'm currently building.

    Thinking more on this, if the problem is indeed with the cam position in relation to the followers, I'd think it would be present on both pistons... no?
     
    dlou0338 likes this.
  18. dlou0338

    dlou0338

    Joined:
    Aug 25, 2016
    I thought that too but I'm not really sure fast Eddie was saying it's possible that one lobe is pushed into open air while the other is being pushed slightly onto the wrong follower I can't think of any other cause I went through the engine this am all push rods were located properly and when I removed the head it was evident that the left cylinder follower were being lifted together
     
  19. acadian

    acadian VIP MEMBER

    Joined:
    Mar 5, 2010
    The right cylinder would evidence the opposite effect I would think, since the exhaust lobes are outboard on the cam.

    Regardless, I think you'll have to be splitting the cases to ascertain cam/follower relationship, and ensure the thrust washer is in place. If your cases have a big sump plug, you can see the cam/follower positioning with the cases bolted together and the barrels in place by shining a small flashlight up through the bottom plug hole (sans crankshaft of course)
     
  20. Dances with Shrapnel

    Dances with Shrapnel VIP MEMBER

    Joined:
    Jul 8, 2011
    Any chance you left the cam follower locating/locking plate and the lifters twist in their bores - its a stretch.
     

Share This Page