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The '2 ton bugswatter' - back for a gentle stroke

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  • The '2 ton bugswatter' - back for a gentle stroke

    I intitially bought the car a couple of years ago fitted Some Bilstein B8's with H&R lowering springs. A can of Barbecue paint and hey presto a nice presentable family car.



    After purchase I discovered I had a spec which wasn't in the brochure, not only did it have full service history incl original hand over documents it also came in a full S6 plus spec.

    Blue Alcantara electric seats with Carbon trim





    But all the chrome was black, bose stereo system with build in sub, 8 x 17" plus wheels etc.... So a nice little find.

    I started a little test project over a year ago to see how different chipsets behaved in the S6 which was then and still is my daily Hack with results of it no longer running properly due to what assumed to be headgasket failure.

    As symptons where split radiator core exhaust gases in water, white coolant smoke etc...

    well...... I was wrong infact we had annihilated the poor little K24 turbo, however more to come on that later.


    So with the assumption of a nuked headgasket I proceeded to drive the car around with copious amount of blockseal to keep her going just long enough to knock together a new engine for her, so long it wasn't mixing oil and water I figured the engine was coming out anyway so what the heck. After all it is my daily hack and therefore my only access to the rest of the world being out in the sticks.

    The plan of attack was to build up another long block using what I had spare and purchasing some other bits in order to do a one/two day swap over a weekend and keep her on the road.

    So having sourced an ABY block with good bores and crank, having a multitude of S2 pistons in stock I decided to buy a set of H Beams from PEC giving me room for maneuver on the power band when the time comes.




    I then made up a jig on the lathe so I could clamp the pistons via the wristpin. So I could add accumulator grooves to the stock pistons to aid the prevention of blow by and aid piston stability under high boost figures.






    Next I checked for sideway play on the small end bearing to make sure the secondhand wristpins whee within tolerance




    Before going ahead and balancing them end over end




    Using plastigauge I checked the current oil clearances with the new bearings




    And polished the journals to bring them to spec




    New timing belt pulley, crank bolt, and cleaned front pulley meant it was all ready to balance.




    I sourced a 7A flywheel as it was easier to find and refaced the clutch mating surface




    Before clocking her up on the lathe




    To give her a small 1.5kg diet, I didn't fancy going too light as it would make my clutch choice not too great for a daily on pull away from lights.




    Made up the necessary bob weights so the crank could be balanced to the correct balance factor, and subsequently set myself the challenge to attempt to internally balance the I5 crank incase I wished to change the flywheel at a later date (In standard form they are externally balanced and flywheels are not interchangeable).




    Next I set about prepping the block, starting with a hone



    and chemical clean




    Moving on to the ring gapping




    Ensuring all ring gap ends where radiused before installation




    Fresh clearanced bearings installed ready for the crank




    Final clean of the crank oil galleries before fitment, note the lovely collection of balancing drill holes, punishment for trying to internally balance the crank. In future I decided to make my live easier by only part internally balancing the crank and then matching it to the front pulley as a zero balanced assembly. Giving the same result of being able to use a zero balanced flywheel with a lot less effort.




    Journals lubed up and crank in




    Bores lubed up



    And finally piston and rods fitted




    That's it for now as I get round to uploading some more pics I'll do a further progress update.
    Last edited by JP; 25 March 2011, 13:34.
    UrS6 Stroker + HTA3586 =

  • #2
    Nice work JP, will keeping an eye on your handywork
    Cheers'en, AndyC
    1994 ABY Coupe - Projekt Alpinweiss

    Comment


    • #3
      Lovely workmanship there - I bet there'll be nothing more satifying than starting an engine that you've completely built up yourself

      On the holes-in-counterweights front; does this now mean that for this engine you won't use a harmonic balancer pulley i.e. because you've already internally balanced the crank? I've just never seen this approach on an I5 and was wondering the reasoning behind it.

      Cheers,

      Matt

      Comment


      • #4
        Thankyou guys

        @knobstar
        No you still use the harmonic dampener,

        Balancing is to get rid of rotational vibration, the harmonic dampener is there to absorb secondary harmonics of the combustion cycle, run the crank without a harmonic dampener and you can get them to split in two over long durations of continuous rpm like motorway cruising. The 4.6 rover engines used in TVR's suffer heavily from that problem between 3000-4000rpm on the motorway.

        By internally balancing the crank it basically means that if I decide to up the power stakes at a later date then I can swap flywheels over without having to unnecessarily pull the bottom end to re-balance it.
        UrS6 Stroker + HTA3586 =

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        • #5
          Wow, nice description. That crank looks like it has a health issue with so many holes.

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          • #6
            Thanks for the explanation

            I'm therefore guessing that drilling holes is preferable to knife-edging wrt reducing rotational mass and eliminating rotational vibration?

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            • #7
              Knife edging has to be done to every counterweight and is the preferred method for lightening a crank and reducing powerloss by giving less surface adhesion for oil.

              By drilling holes as per standard manufacturing methods you can minimise the total weight removed from the crank which came to approx 65gramms in the case of this crank.

              As I'm going for a streetable engine reducing masses of weight of the rotational assembly through knife edging is not a preferred route for two reasons.

              1) the lower the rotational mass the less torque the engine will produce in the midrange

              2) takes longer to come back on boost in between gear changes as the revs will drop quicker from the lower rotational inertia.

              hth
              UrS6 Stroker + HTA3586 =

              Comment


              • #8
                Can you explain how do the lower rotational masses make the engine produce less torque in the midrange?

                Comment


                • #9
                  I am loving this thread.
                  Looking forward to the next installment.
                  sigpic
                  Other cars:VW Transporter T5 4motion, 'S3 sportback

                  Comment


                  • #10
                    Originally posted by JariP View Post
                    Can you explain how do the lower rotational masses make the engine produce less torque in the midrange?
                    Slight misinformation on my front, realistically it's throughout the rev range but the midrange is where it is most noticed due to the nature of power delivery on a roadgoing FI car.

                    So in an extremely oversimplified visualization,
                    torque is a measurement of a twisting/turning force aka a moment. The longer the lever applying that moment or the more pressure applied on it the more torque that is produced at the centre point of the turn.

                    If you compare this to a crankshaft once it has rotational motion introduced by a starter motor it has something called rotational inertia.
                    If you where to leave the head of an engine of crank it over by the starter and then stop cranking once at full speed the rotating assembly will carry on spinning for say 'x' seconds.
                    The heavier the rotating assembly is the longer it takes to get to full speed but also the longer it carries on spinning. The lighter the assembly the quicker it gets to speed but the shorter it will continue spinning once the force from the starter is removed.

                    So you now add the head back into the equation and add the combustion cycle. Now you keep on adding to the rotational inertia on each combustion stroke. If you make the rotating assembly lighter then it will require greater combustion force to keep it moving at the same speed as it slows down more in between combustion cycles.

                    So working on an oversimplified assumption that at a given rpm the combustion force is always going to be the same then automatically you make less torque. (Basically no other factors are changed other than a heavy and light crank)

                    This can now be applied in various other ways, increase the force of the combustion cycle by increasing boost pressure and you can create more torque, stroke the engine by increasing the length of your lever that you are acting on and you get more torque.
                    In the same token if you are running a silly size turbo or a set of cams with huge overlap then maximum force from the combustion cycle won't happen until much higher up in the rev range. So you make a compromise and lighten the rotating assembly so less effort is required to get you up to the required rpm band at the sacrifice of midrange torque delivery.

                    Long and short of it once you know what you want an engine to do as an end result you can then carefully match everything for an optimized results.

                    My target is a mid powered daily hack that can be pokey when needed but is civilized enough to use as a daily in it's power delivery. Hence my choice not to knife edge the crank.
                    In an easy world for the size of turbo I'm opting for I should stroke the engine to improve midrange torque. However I've decided to go the route of optimizing the engine's efficiency therefore increasing the force of the combustion cycle to increase torque instead, but I'll cover that later on in the build thread.

                    hth JP
                    UrS6 Stroker + HTA3586 =

                    Comment


                    • #11
                      Originally posted by RWD19T
                      My target is a mid powered daily hack that can be pokey when needed
                      Cheers'en, AndyC
                      1994 ABY Coupe - Projekt Alpinweiss

                      Comment


                      • #12
                        .

                        And you did all this in your garage?

                        Ummmmm...nice...
                        Carlos.

                        On the look out for less bits for my s2 saloon project. Now supporting myself by shooting for my food. www.airgunforum.co.uk

                        Comment


                        • #13
                          Nice build. But what the hell does HTH meen? Seen it loads of times and am just curious.
                          Audi 80 Competition -94 Daily driver

                          www.garaget.org/fish for more picĀ“s of my cars

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                          • #14
                            Hope That Helps...

                            Hth...
                            Carlos.

                            On the look out for less bits for my s2 saloon project. Now supporting myself by shooting for my food. www.airgunforum.co.uk

                            Comment


                            • #15
                              nice work there

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