Top end knocking | The Z Club of Great Britain
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Top end knocking

Discussion in 'S30 (240Z,260Z,280Z) Engine' started by Peato40, Apr 26, 2018.

  1. Peato40

    Peato40
    Z Club Member

    Hello All,

    My project got to the stage of build, where I started the engine for the first time and it didn't go quite as smoothly as I had hoped. Some timing issues and carb set up still to sort out but I'm concerned about a knocking noise I'm getting from the top end ..... or at least I think its the top end.

    A bit about this engine:
    L26 bored out to 2.8
    Flat top pistons
    Big valve conversion
    Schneider upgraded springs
    Schneider lash pads to suit cam
    Fast road cam
    Triple Dellorto's
    Z story headers and exhaust

    Now I learned a lot from PMac about valve train geometry measurement and lash pad selection and believe it to be correct.

    I've ensured I have clearance between piston and valve.

    Timing is correct.

    I just can't figure out where this knocking is coming from. Although very messy, I ran the engine on idle without valve cover and listened and observed working valve train and nothing appeared amiss, other than this annoying noise. I then used my stethoscope and listened to each cam tower in turn and found that the noise gets louder the nearer I get to the timing gear, but then I have no further place to put stethoscope other than front cover, which doesn't give me much feedback.

    It very much sounds top end and in sync with cam, rather than crank, but I cannot see or feel anything wrong when I crank by hand. It has a exhaust gasket and I'm pretty sure it's not blowing.

    Any other ideas anybody might have would be very gratefully received.

    Phil
     
  2. franky

    franky
    Z Club Member

    does the knocking match cam speed? Did you build the engine yourself? If not, have you approached the company that did? Is there a vibration you can feel also?
     
  3. Turn & Burn

    Turn & Burn Forum User

    If all ur top end appears good, your lash pads are all set correctly and your valves are behaving themselves the knock is maybe big end or little end. I’ve had a Vauxhall red top do this and stripped the full head before I found free play on a big end bearing that had run dry. Fingers crossed for something trivial on the top end stuff.
    Ps Who did ur head work, I’m looking around for good options.
     
  4. jonbills

    jonbills
    ZClub Administrator
    Staff Member Committee Member

    I had my oil pump drive and spindle break which made timing end knock.
    [​IMG]
    But you’d only be able to have that I think if they were already gone when you assembled.
    What was the piston deck height?
     
  5. Farmer42

    Farmer42
    Z Club Member

    It's difficult to know what it could be without listening to it to hear the pitch or depth of the knocking note. Before jumping to expensive conclusions, are you running a mechanical fuel pump? If so, it could be that.
     
    AliK likes this.
  6. Jimbo

    Jimbo 1978 260z in yellow

    are all the lash pads still there? i had one fall out once somehow, never worked out how but popped it back in its been fine since.
     
  7. SacCyclone

    SacCyclone
    Z Club Member

    How are you oiling the top end???
    Oil spray bar or internal cam oiler.
    With the valve cover off you should have oil flying all over.
    Mike
     
  8. Peato40

    Peato40
    Z Club Member

    I'm beginning to wonder now if it a main or big end bearing.

    BTW, it was Automotive services in Northampton that did my head work, machining only, I did the assembly.
     
  9. Peato40

    Peato40
    Z Club Member

    Internal and yes it did get a bit messy but i was mostly just cranking when I had the valve cover removed.
     
  10. Peato40

    Peato40
    Z Club Member

    Hello All,

    Thanks for your comments. So today I tried to get a video of my running engine and have posted a link to it on YouTube, to see what you guys think?
    I'm starting to think it might not be top end after all, what do you think?



    Phil
     
  11. Jimbo

    Jimbo 1978 260z in yellow

    that does not sound good:EXTRAeek:
    first thing i would be inclined to do is to drop the oil and sump and hava a look to see whats going on, there may well be loads of bearing bits in the oil which would be a dead giveaway.
     
  12. franky

    franky
    Z Club Member

    Have you checked your chain tensioner? Sounds 'whippy'.

    Hope you get it sorted easily. You've one of my worse fears there.
     
  13. jonbills

    jonbills
    ZClub Administrator
    Staff Member Committee Member

    I could hear a knock at the start but after that It sounds like carbs out of balance and maybe missing on one or two cylinders.
    I agree with Jimbo, drop the oil and see what it’s like. If it’s ok, put it back in and see if you can get it running on all 6 (if it isn’t!)
     
  14. SacCyclone

    SacCyclone
    Z Club Member

    Oil pressure good????
    Sounds like top end to me.
     
  15. Jimbo

    Jimbo 1978 260z in yellow

  16. Peato40

    Peato40
    Z Club Member

    Hello All, Many thanks for your advice ...... Sounds like a plan to drop the sump and take a look at the weekend.

    Okay so to answers some of those other questions:

    Q. Have you checked your chain tensioner? Sounds 'whippy'
    A. I installed a Kameari L - Type chain tensioner and set it with 2mm of stoke as they recommended.

    Q. Firing on all 6?
    A. I did check to see if I have a spark on all cylinders and can confirm that I do but I'll also pull the plugs and take a look at them at the weekend.

    Q. Oil pressure good?
    A. On initial tickover (Just Warm) the gauge is showing about 40 -45

    I agree that the sound is very much like the piston slap heard in the link that Jimbo sent, but surely I would have noticed warn oval pistons when installing wouldn't I?

    Regards
    Phil
     
  17. jonbills

    jonbills
    ZClub Administrator
    Staff Member Committee Member

    What piston to bore clearance did you set Phil?
    And are you sure the pistons and rods are the right way round?
     
  18. Peato40

    Peato40
    Z Club Member

    Hi Jonbills, I didn't measure the bore/piston clearance on assembly but the pistons and rings fitted snuggly
    Rods were already assembled to pistons and then I installed them with notch facing forward, towards timing gear.
     
  19. Peato40

    Peato40
    Z Club Member

    Okay, So coming back to this subject now that I've had a bit more time to investigate. Now Jonbills was right, the carbs needed setting up and it wasn't really running on all six, which it now is after some painstaking carb cleaning and tweaking. The engine seems to tick over and rev much more comfortably now but it still sounds like a diesel to me with this knock noise ..... surely it can't be normal for a tuned engine is it?

    Anyway I decided to drop the sump and see whats going on. The oil was much dirtier than I was expecting as the engine has only run for some minutes at a time whilst testing setting up etc. I didn't come across chunks of metal in the sump though but who knows how rich the oil could be with tiny particles of metal. Attached here are some photos.

    20180514_174431.jpg 20180514_173019_001.jpg 20180514_173018.jpg 20180514_173009.jpg 20180514_173002.jpg

    Crank by hand with the spark plugs out is not giving we have sense of knocking, it all turns over smoothly.

    So anybody got any ideas about what I can look at next or is already a lost cause with the state of the oil after minimal running?

    Regards
    Phil
     
  20. jonbills

    jonbills
    ZClub Administrator
    Staff Member Committee Member

    If you’re running rich, the oil will discolour quite quickly, so I wouldn’t necessarily worry about that.
    Can you make a new recording of what it sounds like now?
     

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