Type 4 2.0l Deck Height and Compression Ratio

Discussion in 'Mech Tech' started by Deefer66, Feb 29, 2016.

  1. MorkC68

    MorkC68 Administrator

    Isnt the minimum height set at 1.0mm (I cant find the Wislon book at the mo, the cleaner must be reading it :D ) to avoid piston and valve kissing?
     
    Deefer66 likes this.
  2. Sorry that's barrels straight onto case .. ordered and will be adding a 40 thou (1mm shim) to lift them..
     
    Last edited: Mar 8, 2016
  3. MorkC68

    MorkC68 Administrator

    Ahh that's more like it!! :D

    it'll be a cracker with good compression ratio when its done!

    We have to drop our Hydrocarbon level down a bit, its up at 1384ppm, should be a quarter of that. We're thinking the main jets are too big and the mixture needs toning down slightly!
     
    Deefer66 likes this.
  4. Zed

    Zed Gradually getting grumpier

    You won't notice, all vw a/c engines will similar to that.
     
    77 Westy and Deefer66 like this.
  5. 77 Westy

    77 Westy Supporter

    Yes, but not to avoid piston and valve intimacy; it’s to avoid the piston hitting the head.
     
    Deefer66 and Zed like this.
  6. MorkC68

    MorkC68 Administrator

    Yes indeed it is - the cleaner returned my book :) I reckon she is modding the hoover & borrowed the book for some background information :thumbsup:
     
    Deefer66 likes this.
  7. Ive resurrect this topic I hope that's OK
    Ive started to take some preliminary measurements of my deck height Type 4 2.0.

    1) I've assumed the assembly is done without piston rings?
    2) Should the barrels be torqued up or just tight as per photos?
    3) Measurement method.
    a) Directly above the gudgeon pin where there is minimum "rock" on either side?
    b) 90degs to the pin either side, add measurements and half the figure?
    4)How accurate do the measurement shave to be

    I've done both and they work out within o.o4" for each barrel.

    Just want to know I'm doing it correctly.

    Note: I was trying the pin in the small end bush and dropped it inside the sealed-up crankcase. Fortunately it didn't go to the bottom and I managed to get it out:eek::eek::eek:
     

    Attached Files:

  8. I didnt explain that on my thread very well did I.. I'll go back and edit....

    Rings , yes, I put on just the bottom oil ones as the hold the piston right but load and move easily.
    Torque up ideally but tight will be very close ( I couldn't tell) watch out if pushing on fins and nort on a spreader bat across top of cylinder..
    Difference from straight edge across the cylinder and top of piston ot a feeler gauge between straight edge and piston top...I see you have a deck height measuring tool!
    I did all 4 quarters but above the gudgeon pin is best.. both sides and average it.
    I went to 0.01mm but 0.1mm would prob be good enough.

    0.04" is 1mm so a good tight deck if your CR is ok.. it made mine a bit high.
     
    Last edited: Jan 26, 2020
    Gnasha likes this.
  9. 77 Westy

    77 Westy Supporter

    1) I don’t fit the rings; they won’t stop the piston rocking but they’ll make it more difficult to feel the rock.

    2) Barrels snugged tight but not torqued up.

    3) Measure along the axis of the gudgeon pin. I use a parallel and feeler gauges but a depth mic is perfect.

    4) Obviously the more accurate the measurement is the more accurate the CR will be. And you should be able to get repeatability within a couple of thou.

    ‘I've done both and they work out within o.o4" for each barrel.’ Is that the deck height? Hopefully it isn’t the difference between each barrel.

    What CR and deck height are you aiming for?
     
  10. Initial deck height attached.

    Im still looking for two heads that arent cracked, so no measurements yet for CR

    Ill may sell this engine, would it be better to sell with a CR for a bus or my Khamann Ghia. If I was to keep it as a spare (hopefull wont need it) I'd go for a static CR of about 8.5.
     

    Attached Files:

  11. That's going to need a 0.03" (0.75mm) shim to get No 3 in the safe zone..
     
  12. Thanks, I'm going to run another set of measurements today as a recheck. I think the gudgeon pin results look like they all "lean" low in one direction, as if the crank tilts in one direction.
     
  13. 77 Westy

    77 Westy Supporter

    0.006” difference from one end of the pin to the other on #4 is huge, something isn’t right.
    Are the cylinders the same length and mating surfaces parallel?
    Are the crankcase cylinder registers flat?
    Are the conrods straight?

    Build the engine with a CR to suit the cam; the cam will determine whether it’s a bus or a car engine.
     
    Last edited: Mar 11, 2023
  14. I think I'm miss reading the top bottom left and right.. I assumed it was piston rock in the cylinder and gudgeon pins were similar but I see what you're saying now..
     
  15. 77 Westy

    77 Westy Supporter

    Comparing 1&2 with 3&4 the numbers suggest the crankshaft C/L is slightly offset to the crankcase C/L. That’s common and is corrected by selecting barrel shims to equalise the deck across all cylinders.

    However, the dimension difference from one end of the pin to the other and the difference between across the pin to along the pin suggest the barrel faces aren’t parallel, or they aren’t bolted down evenly, or the crankcase registers aren’t true, or the rods are bent.
     
    Last edited: Jan 28, 2020
  16. Mine were quite scattered on first round but settled down a bit closer when cleaned up better for checking spacer inclusion.
    Put some (most) down to user error as I'm a bit rough and ready really .

    Sent from my SM-G930F using Tapatalk
     
  17. I took many readings yesterday, they were all near enough the same. Gudgeon pin readings are a concern @ 0.006/7/8. I held the piston over to one side firmly while I took the side to side readings.


    So today I’ll start with the process of elimination. I’m going to put a different barrel and piston in the No4 position and retake take the measurements. However. my money is on the case deck being machined at a taper.

    I hope it’s not. Ill be truly disappointed.
     
  18. 77 Westy

    77 Westy Supporter

    0.006” over the length of the pin is a lot and you’ll easily see if the case is distorted by removing the cylinders and putting a straight edge across it.
     
  19. 77 Westy

    77 Westy Supporter

    The case won’t be machined on a taper; it’ll have sagged in the middle. If you’ve written the dimensions as I think you have from flywheel to pulley end #4 is 0.019” to 0.013”, low in the middle and #3 is 0.012” to 0.015”, also low in the middle. # 1&2 show the sag too but not so bad.
     
    Gnasha likes this.
  20. Good point ill have to look closer.
     

Share This Page