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Pulling heads off for a visual? or a costly waste of time

Discussion in 'Engine & Transmission' started by Ian and Shelley, Apr 28, 2020.

  1. cbus

    cbus Well-Known Member

    Messages:
    12,814
    Location:
    sunshine coast
    Top end only rebuilds often have a short life due to wear in the bottom end .
    Will pay to check what you can given there appeared a significant amount of wear in items already checked in top end.
    Rick or similar would be better to advise such checks on non disassembled case than me so I'll leave it to the suitably experienced.
     
    Barry likes this.
  2. rstucke

    rstucke Well-Known Member

    Messages:
    1,415
    Location:
    Wamberal NSW AUS
    I wouldn't trust the bottom end
    You've gone this far, a little more and you'll have something you can trust
    Send the bottom end to a trusted air cooled engine builder

    If you're intent on using yours in its existing state, with the barrels and pistons removed, pull number 3 rod
    This big end bearing is the furthest from the pump and the last to be lubricated and theoretically has the most wear.
    Use plastigauge to check clearance to the journal
    Also check tension on case bolts and nuts
    But this is ignoring cam lobe and cam bearing wear, loose mains (specially center main), case fretting, cam gear wear,
     
    cbus, Grantus and Barry like this.
  3. Barry

    Barry Well-Known Member

    Messages:
    4,852
    Location:
    Abbotsford NSW
    Hmmmm...... all started with a little shudder in the clutch
     
  4. Ian and Shelley

    Ian and Shelley Active Member

    Messages:
    299
    Location:
    Umina Beach
    Indeeed.......all started with a little shudder in the clutch...


    Where do i stop.....where do we say that's enough for now
     
  5. Barry

    Barry Well-Known Member

    Messages:
    4,852
    Location:
    Abbotsford NSW
    Whenever you want.
    Your motor.

    if it’s getting a life of it’s own and getting out of control - just do the top end. has to be better than mis matched heads.

    Just be aware you may have to re-visit in the future sometime.
     
  6. Ian and Shelley

    Ian and Shelley Active Member

    Messages:
    299
    Location:
    Umina Beach

    I greatly appreciate the advice....

    No need to stop yet...!!!
    I will keep on digging..


    I will take a read through the manuals and study a few videos and see what next...and come back with more questions...

    Thanks again
     
    Barry likes this.
  7. Ian and Shelley

    Ian and Shelley Active Member

    Messages:
    299
    Location:
    Umina Beach
    Thanks again
    As in earlier message I will study up and see what's involved and come back with more questions..

    Appreciate the advice.
     
    Aspudis and Barry like this.
  8. David H

    David H Well-Known Member

    Messages:
    6,084
    Location:
    newcastle
    Hi Ian and Shelley,
    The worst case of your exploration is you get the case, cam & barrels, heads real good & know where your bus is up to.
    It's nice knowing that your engine will do another 150,k before any work:).
    Cheers
     
  9. Ian and Shelley

    Ian and Shelley Active Member

    Messages:
    299
    Location:
    Umina Beach
    Hi Barry

    Thanks for the info

    I have new heads, new pistons and new cylinders and will plan to measure deck height / head CC and calualte CR this weekend..

    Will probably come back with more questions this weekend

    Thanks again
     
    Barry likes this.
  10. Ian and Shelley

    Ian and Shelley Active Member

    Messages:
    299
    Location:
    Umina Beach
    Hello....

    Could you please review my calculations and advise if they are correct or if any foolish errors have been made..

    I have 1800cc types 4 motor and Haynes manual states the following

    Bore..93mm
    Stroke..66mm
    Required compression ratio 7.3:1


    I have measured and calculated following

    New head CC chamber 56cc

    Deck height currently all pistons rise ABOVE cylinder by average of 0.105mm

    From following website..
    http://www.cbperformance.com/v/enginecalc.html

    If I enter info I have a required deck height of 2.23mm.

    If I add HIGH pistons average of 0.105mm to 2.23mm I get a total 2.335mm

    So I THINK I need a shim of 2.335mm ..approx 0.09 inch as below

    http://rodpenroseracing.com.au/barr...90-905-92mm.html?search_query=Shim&results=56

    Is this all correct...

    Appreciate your help
     
  11. Kai

    Kai Well-Known Member

    Messages:
    4,770
    Location:
    Sydney, NSW
    did you add the cc in the dish of the piston. usually 1800 are approx 10cc? someone may be able to verify. remember new AMC heads have a step built which equals ~6cc if I recall.

    If you are targeting the ~7.3:1 compression I would have:

    bore: 93mm
    stroke: 66mm
    deck height: 1.5mm
    cc: 60cc (heads with step removed (~50cc), inc cc from the piston dish (10cc))
    compression: 7.4:1

    Someone more experienced than me might be able to verify my calculations
     
    Last edited: May 26, 2020
  12. Ian and Shelley

    Ian and Shelley Active Member

    Messages:
    299
    Location:
    Umina Beach
    Hi ..thanks.

    I have not added the volume of the dishes piston.
    Wasn't certain if this volume was meant to be I cluded in the calculations..
     
  13. Barry

    Barry Well-Known Member

    Messages:
    4,852
    Location:
    Abbotsford NSW
    Any reason for 7.3 compression?
    Just seems low?
    I have run 8.5 to 9.0 in my type 1 motors with out problems

    getting out of my comfort zone as all motors I built were flat top pistons - but I would have thought 2.335 mm deck is too much

    reading on squish here

    https://www.thesamba.com/vw/forum/viewtopic.php?p=8862803
     
  14. Ian and Shelley

    Ian and Shelley Active Member

    Messages:
    299
    Location:
    Umina Beach
    Hi Barry.

    The compression ratio of 7.3:1 is what I found in the Haynes manual, and so took this value to be the recommended ratio.


    Happy to adjust if better options are advised

    Thanks
     
  15. Barry

    Barry Well-Known Member

    Messages:
    4,852
    Location:
    Abbotsford NSW
    That was in the days of low octane fuels.

    I had the benefit of an engine building mate / drinking partner that walked me through the many hours of discussion and drinking.

    no simple answer.
    As you will see if you read the Samba link

    gets even more complicated when Jake Raby gets involved
     
  16. Ian and Shelley

    Ian and Shelley Active Member

    Messages:
    299
    Location:
    Umina Beach
    Now I understand..

    Would an increase in the compression ratio have potential to blow the bottom half the motor apart?

    My Thinking is...if it's always been at 7.3:1 and now 40 plus yrs old would I be best to keep at same and not stir things up down there?
     
  17. tintop

    tintop Well-Known Member

    Messages:
    730
    Location:
    Canberra
    Hi Ian, yep, if you aren't rebuilding the whole motor then go easy on the compression ratio. Patrick
     
    grumble and cbus like this.
  18. Barry

    Barry Well-Known Member

    Messages:
    4,852
    Location:
    Abbotsford NSW
    Sorry - thought you were doing the bottom end
     
  19. Ian and Shelley

    Ian and Shelley Active Member

    Messages:
    299
    Location:
    Umina Beach
    Hi again..

    Rechecked and remeasured everything again AND added 10cc volume of Piston dish into combustion chamber volume...

    Total combustion volume of 67 cc
    Bore 93mm
    Stroke 66mm
    Reqd compression ratio 7.3:1

    Gives a deck height of 0.61mm
    Pistons heads in motor are 0.105mm above cylinder at TDC..

    I need a shim of 0.61 plus 0.105 = 0.715mm

    0.715 mm shim or 0.028''

    Does this shim size seem correct?

    Thanks all
     
  20. tintop

    tintop Well-Known Member

    Messages:
    730
    Location:
    Canberra
    Hi Ian,

    Sounds like the right ballpark.

    I grew up with setting deck height at 40 thou (1mm) and didn't (need to?) do all these calculations....might now be necessary with aftermarket bits.

    Patrick
     

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