{
  "reviewed_date": "2026-10-17",
  "engine_identity": "Assumed ABL for user-confirmed 2001 T4 1.9 TD; verify engine stamping before treating this as vehicle-specific",
  "sources": [
    {
      "id": "abl_rotation",
      "title": "ABL injection-timing procedure, original illustrated T4-Wiki guide, checked 2026-10-17",
      "url": "https://t4-wiki.de/wiki/F%C3%B6rderbeginn_(ABL)",
      "kind": "original_illustrated_workshop_procedure",
      "supports": ["ABL/1X normal crank rotation is clockwise at the crank pulley / central bolt", "Counterclockwise crank travel is described as against normal engine rotation"],
      "limits": "Community-authored illustrated procedure, not a VW engineering drawing. Viewpoint is the timing/pulley end (+X in this model), not the flywheel end. Does not verify the estimated accessory ratios or reversing idlers in the user-supplied timing route."
    },
    {
      "id": "diesel_cycle",
      "title": "Cummins, How do diesel engines work?, updated July 2026",
      "url": "https://www.cummins.com/en-na/news/how-do-diesel-engines-work",
      "kind": "engine_manufacturer",
      "supports": ["Air intake, air compression, late fuel injection and compression ignition, followed by exhaust"],
      "limits": "Generic diesel cycle, not ABL timing, fuel spray, flow, temperature or acoustic data. Viewer colors, injection/burn windows and sound waveforms are original schematic demonstrations."
    },
    {
      "id": "user_timing_diagram",
      "title": "User-provided service-style timing illustration AD18505, 2026-10-17",
      "url": null,
      "kind": "user_supplied_reference",
      "file": "codex-clipboard-5ef4c324-ee5c-490d-a1b4-3210f526d1bf.png",
      "sha256": "D50EB71C757BEEAF520CCA1258FABFFCDA99B690E74E9038D9B2240BA9858306",
      "supports": ["Cam / injection / intermediate-drive / crank / tensioner route", "reverse bends at intermediate drive and tensioner", "relative pulley sizes and center positions"],
      "limits": "No metric pulley diameters or stated scale. 25 Nm and 45 Nm are torques. Identity/application is not factory-verified for this ABL. Pixel centers rectified onto the model's cam/crank axis; existing estimated cam height anchors scale. Crank 60, cam/injection 120, intermediate 75, tensioner 60 mm remain editable contact-envelope estimates, not pitch diameters. Source artwork is not redistributed."
    },
    {
      "id": "user_vehicle",
      "title": "User vehicle configuration, this chat, 2026-10-17",
      "url": null,
      "kind": "user_confirmed",
      "supports": ["2001 model year", "no A/C", "power steering fitted", "2026-10-17 correction: swap timing/accessory and flywheel ends viewed from injector side", "alternator low, steering pump behind and slightly below crank pulley"],
      "limits": "User describes relative positions only; numerical accessory offsets remain estimates. Behind interpreted as negative Y, away from injector side."
    },
    {
      "id": "vw_owner_manual",
      "title": "Volkswagen Transporter owner's manual, August 1992, technical data p.141, archived scan",
      "url": "https://westfaliat4.info/Aug_1992_VW_T4_Oweners_ManualWestfaliaWM.pdf",
      "kind": "manufacturer_manual_archived",
      "access": "Technical-data table available in search index; direct PDF fetch failed",
      "supports": ["4 cylinders", "1896 cc nominal", "79.5 mm bore", "95.5 mm stroke", "22.5:1 compression ratio", "50 kW at 3700 rpm", "140 Nm at 2000-3000 rpm"],
      "limits": "Earlier manual, not a 2001 VIN-specific parts listing"
    },
    {
      "id": "russek_manual",
      "title": "Peter Russek / Brooklands Books, Transporter T4 Diesel Models 2000-2004, introductory pages 10-11",
      "url": "https://vandimensions.com/media/pages/database/volkswagen/transporter-t4-california/34fd3cce14-1626780416/l-g-0003586520-0006912755.pdf",
      "kind": "workshop_manual_publisher_scan",
      "supports": ["1.9 diesel engine code ABL", "bore/stroke/compression/output", "belt-driven overhead cam and injection pump", "direct-acting hydraulic bucket tappets"],
      "limits": "Only 17 introductory pages accessed; not a factory casting drawing"
    },
    {
      "id": "bosch_ve",
      "title": "Bosch diesel system components, distributor-type injection pumps",
      "url": "https://www.boschaftermarket.com/xrm/media/images/services/downloads/parts_14/diesel_system_components/diesel_system_components_brochure_en_reworked_92903.pdf",
      "kind": "manufacturer",
      "supports": ["VE axial-piston distributor pump architecture for indirect injection"],
      "limits": "Generic VE architecture, not exact ABL pump dimensions or calibration"
    },
    {
      "id": "motorservice_catalogue",
      "title": "Kolbenschmidt passenger-car catalogue, ABL applications",
      "url": "https://www.ms-motorservice.com/MediaAssets/1809297_ks_50003929_web.pdf",
      "kind": "manufacturer",
      "supports": ["ABL 1.9 TD 50 kW application identification"],
      "limits": "No head/block surface CAD recovered"
    },
    {
      "id": "nvh_paper",
      "title": "Mohite and Bhatia, Mahindra, Vibro-Acoustic Analysis of Motorcycle Engine Under Combustion Load",
      "url": "https://www.comsol.com/paper/vibro-acoustic-analysis-of-motorcycle-engine-under-combustion-load-19447",
      "kind": "original_research",
      "supports": ["Excitation/multibody dynamics -> structural vibration -> acoustic radiation workflow"],
      "limits": "Different single-cylinder engine; no ABL acoustic validation"
    },
    {
      "id": "order_tracking",
      "title": "Dewesoft Order Analysis manual, diesel/gasoline engine section",
      "url": "https://downloads.dewesoft.com/manuals/dewesoft-order-tracking-manual-en.pdf",
      "kind": "instrumentation_manufacturer",
      "supports": ["Four-cylinder four-stroke firing has two events per crank revolution", "Orders are frequency references, not unique source identification"]
    }
  ],
  "geometry_policy": "All external shapes, attachment coordinates, internal dimensions other than bore/stroke and non-manual ratios are estimates. No vendor CAD, photographs or scanned manual artwork is redistributed.",
  "firing_order_policy": "1-3-4-2 is an editable conventional inline-four assumption in this baseline, not a factory-verified valve/injection timing map.",
  "unverified": ["exact engine and pump codes", "as-installed tilt", "all flange bolt patterns", "accessory variants and belt routing", "firing order and cam timing against the vehicle workshop data", "turbo type and speed", "water/oil gallery shapes", "casting wall thicknesses", "mass/inertia/material damping", "every OEM washer, seal, clip and fastener"]
}