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

2 ltr type 4 engine re-build journey

Discussion in 'Engine & Transmission' started by rstucke, Jan 13, 2018.

  1. rstucke

    rstucke Well-Known Member

    Messages:
    642
    Location:
    Wamberal NSW AUS
    Ok This might be a long answer.
    For starters the std comp ratio is 7.3:1 for a 2ltr
    You don't have to machine anything out off the AMC heads if your happy with standard comp ratio.

    Compression ratio is a calculation between the volume that the piston displaces between top and bottom dead centre (swept volume, and if you multiply that by the number of cylinders it's also the size of the engine)and the volume above the piston at top dead centre (clearance volume).The calc for piston volume is PI RADIUS SQUARED x Stroke (don't know how to show symbols) A better way to do this is 3.142 x bore diameter x bore diameter divided by 4 x stroke. If you do the calc in mm you will end up with a very large number in square mm. If you divide your answer by 1000 your answer will be in cc. 1cc is the same as 1ml, important for later.

    The clearance volume is a combination if deck height and combustion chamber volume. The deck height is the bit above the piston at top dead centre and the flat section of the head (squish area, important for turbulence, 1mm gap good for a vw, much smaller for inline and v8 engines). it can be measured the same way as swept volume.
    The combustion chamber is a different kettle of fish. It must be physically measured (see the photos in my post). Usually in millilitres, which is the same as cc's (cubic centimetres).

    Now after all that the actual calculation is swept volume + clearance volume divided by clearance volume.
    The best way to adjust all this is by shims under the barrels.

    As a mater of interest Andrew (1500king) machined his AMC heads to achieve 7:8:1 compression ratio with dished pistons

    If you pm me with your email address I can send you an exel spread sheet that does the calcs for you (assuming you have exel.)

    The reason I opted to up my comp ratio is complex (combo of camshaft, power, heat dissipation bla bla bla)

    I hope my explanation is not too confusing.
    Rick
     
    Last edited: Jan 15, 2018
    David H, cbus and oldman like this.
  2. saabman

    saabman Well-Known Member

    Messages:
    4,740
    Location:
    Goulburn
    Beautiful work - wil be watching with interest
     
  3. Barry

    Barry Well-Known Member

    Messages:
    2,697
    Location:
    Abbotsford NSW
    You can use this as well
    http://cbperformance.com/v/enginecalc.html
     
  4. Alpal

    Alpal Moderator Staff Member

    Messages:
    8,323
    Location:
    Melbourne Bend of Islands
    Thanks Rick. Probably leave with standard compression as I have not renewed bottom end. Would like a copy of spread sheet for further ref. Have PM'd
     
  5. 1500king

    1500king Well-Known Member

    Messages:
    1,532
    Location:
    Adelaide, SA
    Nice work.. . Be careful with valve collets, the valve still needs to spin, agree that they are too loose. I lap mine too.

    I take the step off the heads to bring the volume down and also decrease the width of the head to get valve geometry right.. you will find the valve adjusters go in too far with stock pushrods... unless you are going to aftermarket with lash caps/ 911 elephant foot adjusters and 1700 rockers.. with a bigger cam, they are a must.

    The magic number for dynamic compression is 6.6:1.

    Which cam did you head For? Web73 torque cam? Or a bit hotter?


    Will go well!
     
    cbus likes this.
  6. 1500king

    1500king Well-Known Member

    Messages:
    1,532
    Location:
    Adelaide, SA
    Alpal, also have a spreadsheet if you need it.
     
  7. saabman

    saabman Well-Known Member

    Messages:
    4,740
    Location:
    Goulburn
    What is the reasoning behind 6.6:1 ?
     
  8. rstucke

    rstucke Well-Known Member

    Messages:
    642
    Location:
    Wamberal NSW AUS
    dynamic compression is always less than the calculation. Caused by volumetric efficiency (what gets into the cylinder compared to the amount that would fill it) governed by when the valves open and close, how far they open, valve overlap (so basically the cam design), and also changes with engine speed.
    This can't be reliably calculated but has been measured and evaluated (and published) by reputable cam designers and engine builders.
     
  9. 1500king

    1500king Well-Known Member

    Messages:
    1,532
    Location:
    Adelaide, SA
    VW engineered dynamic compression for the type 4 at 6.6: 1.. yes indeed the complex formula relies on rod angle, stroke, acceleration of the piston... and deceleration, bore, the position of the piston the moment the exhaust valve closes from overlap on the compression stroke, then how effectivily the cavity can fill.. inlet/exhaust port design, size, valve sizes, restrictions etc.. at WOT on acceleration then vacuum in the inlet ports... if efi, you aim for zero. ... ... but for a reliable result, 6.6:1 Is it.. so if you have a bigger cam with more overlap, the exhaust valve closes later while the piston is going up on the compression stroke. To keep the dynamic comp, you need to increase the static comp accordingly.
     
  10. 1500king

    1500king Well-Known Member

    Messages:
    1,532
    Location:
    Adelaide, SA
    This is why if you have a worn standard cam, dynamic comp falls below 6.0:1, the lower limit, although static comp might be standard perfect.. the motor will be hard to start, idle like crap or not at all.. and have no torque.
     
  11. 1500king

    1500king Well-Known Member

    Messages:
    1,532
    Location:
    Adelaide, SA
    Fuels also play a part... you can go higher, but then need to add more octane and also keep heat away. The ideal deck is no less than 0.8mm
     
  12. 1500king

    1500king Well-Known Member

    Messages:
    1,532
    Location:
    Adelaide, SA
    The 2.o 914 chamer shape is far superior for chamber swirl, flow into the chamber at the valve heads and also less hot spot creation from less sharp edges which bring on detonation.
     
  13. 1500king

    1500king Well-Known Member

    Messages:
    1,532
    Location:
    Adelaide, SA
    In terms of basic porting for a mild motor, inlet ports don't need much, just blend and get rid of / shape the lump around the guide. Same for the exhaust port. With a mild cam, standard carbs are fine but increase the venturi size and jet up on the main jets.
     
  14. 1500king

    1500king Well-Known Member

    Messages:
    1,532
    Location:
    Adelaide, SA
    50cc on the chambers (no step) with 0.8mm deck and standard dished pistons for 7.8:1 static. Or 52cc for stock comp. You will find heads out of the box anywhere from 54cc-59cc with step... and take the dags off from the edge of the rocker boxes so the covers fit properly.
     
    Last edited: Jan 16, 2018
  15. 1500king

    1500king Well-Known Member

    Messages:
    1,532
    Location:
    Adelaide, SA
    Rick.. if you have a 009 on your new lump... get rid of it.. wasted energy. Tune 123+ distributor with ported vacuum from one of the Webers. Set it up with a bus curve and vacuum point shift between load/ no load with the carbs.. + vacuum map. You will love it! They have WiFi programmability from their mobile app and pin code security so no stealing arsehole can ever start the car. Yeh.. it' $600.. but perfect in every way.
     
    David H likes this.
  16. Alpal

    Alpal Moderator Staff Member

    Messages:
    8,323
    Location:
    Melbourne Bend of Islands
    Thanks Andrew. Will revisit later. The engine I am taking out of the kombi is a 2L that is tired. Probably a full rebuild. Hopefully will have the time to play with it a bit more than the current project.
     
    David H likes this.
  17. rstucke

    rstucke Well-Known Member

    Messages:
    642
    Location:
    Wamberal NSW AUS
    Already done

    P1160036.jpg
     
  18. rstucke

    rstucke Well-Known Member

    Messages:
    642
    Location:
    Wamberal NSW AUS
    Ok enough of this, on with the show

    It’s pretty important to use an anti-scuff past on the base of the lifters and on the cam lobes. Also when starting the engine it should be run at around 2000rpm for about 20 minutes. This is because the new surfaces need to work harden (they are a bit soft) and idling tends to scuff up the surfaces which can lead to wearing off the tops of the lobes. More on this latter.
    upload_2018-1-17_9-36-37.png

    Next hurdle to overcome is the rocker geometry. This has got to be right to avoid premature valve guide wear. This should be checked on any engine rebuild especially if new and aftermarket components have been used (AMC heads, barrels or machining of surfaces) or deck heights changed.

    I used the bubble method to get it right (some do it by eye)

    So first thing is to find exactly ½ lift. Dial gauge and push rod to find full lift, go back to half that amount, mark front fan in line with split on crankcase.

    upload_2018-1-17_9-37-41.png
    upload_2018-1-17_9-38-13.png

    I used a bubble balance on the end of the valve stem and rotated the whole engine in my stand until it was level

    upload_2018-1-17_9-39-3.png

    Then I used an adjustable pushrod and put on the rocker gear (1 section). Rechecked the whole thing again.

    upload_2018-1-17_9-40-1.png
     
    grantw likes this.
  19. rstucke

    rstucke Well-Known Member

    Messages:
    642
    Location:
    Wamberal NSW AUS
    I took out one of the adjusters and tipped the end (with the screw slot) on my valve facer exactly square to the thread. Screwed it in to the rocker gear till it touched the valve, set the correct clearance and locked it. Rotated the crank until the line on the fan was lined up with the split on the crankcase (half lift). Put the bubble on the adjuster (nice and square now, no burs) and adjusted the adjustable push rod till the bubble was level. The length of that push rod is now the correct length for that side of the engine. I actually did this to each valve and averaged the length (they were pretty close to each other but 1mm longer than the standard pushrod). I bought unfinished pushrods from Rod Penrose and parted them off to the correct length on my lathe.

    Unfortunately all the photos from the above process have gone missing (Bugga). When I find them I’ll edit this part of the post. I think what I have written is understandable though.
     
    Last edited: Jan 17, 2018
    saabman and cbus like this.
  20. rstucke

    rstucke Well-Known Member

    Messages:
    642
    Location:
    Wamberal NSW AUS
    I do have 3 photos of at rest, mid stroke and full stroke of the finished setup. This shows the angles of the adjuster on the valve end. As you can see it pushes the valve one way for half the stroke then the other way to full stroke. You can also see the machined ends of the adjusters (nice and flat)
    upload_2018-1-17_9-44-0.png
    upload_2018-1-17_9-44-20.png
    upload_2018-1-17_9-44-44.png
    Ok I’m done for now, I’ll post some more later.
     
    1500king, grantw and oldman like this.

Share This Page