XU9J4 (D6C) Engine

The majority of the BX 16v engines were the non cat version fitted with Motronic 4.1 engine management (2 row ecu) which is explained in detail in the Technical sub-pages. The later engines were fitted with the Motronic 1.3 management (3 row ecu)  utilising a knock sensor mounted on the front of the engine block, this allows the ecu to adjust ignition timing if pinking occcurs.
The cam pulleys are numbered and there seem to be several factory combinations - The most common variations seem to be the early engines using a #2 exhaust cam pulley and a #4 inlet cam pulley this later changed to a #2 cam pulley on both the inlet and exhaust cam. The combination of #2 and #4 seems to give the more harsh power delivery often noticed with the mi16 engine.
The engine is of all alloy construction utilising removeable cast iron cylinder liners.

.XU9J4/Z (DFW) With Catalytic Converter

This is the cat equipped engine using the Motronic1.3 engine management (3 row ecu) along with a lambda (oxygen) sensor and is essentially the same as the D6C apart from the details below.These differences are acheived using lower height pistons and the common cam pulley arrangement is a #3 inlet cam pulley with a #2 exhaust cam pulley. It appears that the #3 pulley was used to improve power delivery and help make up for the loss of power due to the cat and lower compression ratio.

Compression Ratio......................................................9.7:1
Max Power....................................................................148BHP
Cam Pulleys...................................................................#2 - 114 deg     #3 - 111 deg

Engine
Model application:.... . . . . . . . . . . . . . . . . . . . . . . . .  . . . . D6C (XU9J4)
Compression ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.4:1
Maximum power DIN (BHP) . . . . . . . . . . . . . . . . . . . . .  . 160 at 6500 rpm
Maximum torque DIN (lbf ft) . . . . . . . . . . . . . . . . . . . . . . . 133 at 5000 rpm
Valves
Cam Pulleys.........................................................................#2 - 114 deg    #3 - 111 deg  #4 - 108 deg
Head diameter:
Inlet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34.7 mm
Exhaust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29.7 mm
Cam followers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . Hydraulic (no adjustment)
Valve timing
Valve lift 9.2 mm
Inlet opens* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1º 35’ BTDC
Inlet closes* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45º 50’ ABDC
Exhaust opens* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47º 0’ BBDC
Exhaust closes* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0º 30’ ATDC
*With valve clearance of 1.0 mm
Crankshaft
Endfloat thrustwasher thicknesses . . . . . . . . . . . . . . . . . . . 2.33 to 2.53 mm (in increments of 0.05 mm)
Crank journal diameter . . . . . . . . . . . . . . . . . . .  . . . . . . . . . 59.7 to 60.0 mm
Crankpin diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49.7 to 50.0 mm
Lubrication system
Oil pressure:
At 850 rpm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0 bar
At 3000 rpm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8 bar
At 6500 rpm.............................................................................5.5 bar
Oil pressure warning lamp threshold.....................................0.8 bar
Oil filter bypass threshold.......................................................1.2 bar
Maximum running oil temperatures........................................140 - 150 degrees C
Oil filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  ..Champion F104
Oil type (recommended).........................................................SAE 10W40 or 15W40 (to API SG/CD standard)
Oil capacity (with filter change) . . . . . . . . . . . . .. . . . . . . .. . ..5.3 litres (9.3 pints)
Dipstick minimum to maximum . . . . . . . . . . . . . . . . . . . .. ... 1.5 litres (2.6 pints)
Torque wrench settings Nm lbf ft
Camshaft bearing cap Allen screws . . . . . . . . . . . .  . . . . . . 10 7
Main bearing cap bolts and nuts . . . . . . . . . . . . . . . . . . . . . . 50 37
Centre main bearing cap side bolts . . . . . . . . . . . . . . . . . . . 25 18
Sump pan bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 15
Big-end bearing cap nuts:
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 30
Stage 2: slacken, then tighten to . . . . . . . . . . . . .. . . . . . . . . . 20 15
Stage 3: then immediately . . . . . . . . . . . . . . . . . . . . . . .  . . . . Tighten a further 70º
Oil pump bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . 20 15
Flywheel bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 37
Clutch cover bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 18
Crankshaft sprocket bolt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 82
Coolant pump bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15 11
Camshaft sprocket bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45 33
Timing belt tensioner locking screw . . . . . . . . . . . . . . . . . . . . 20 15
Engine mounting bracket at timing cover end:
Larger bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . .72 53
Smaller bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..45 33
Crankshaft damper bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 18
Camshaft rear pulley bolt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 33
Inlet manifold bolts . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . 20 15
Exhaust manifold bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 18
Cylinder head bolts:
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 43
Stage 2: slacken, and then tighten each bolt in turn to . .  . . . 20 15
Stage 3: then immediately . . . . . . . . . . . . . . . . . . . . . . . . .  . . . Tighten a further 300º

General information
The D6C engine is fitted to the majority of UK BX 16 valve models and is a development of the 8v engine.
Introduced in July 1987, the essential difference is the 16 valve double overhead
camshaft cylinder head, this head is based upon the legendary T16 cylinder head and spent 6 years in development alone.
The camshafts are driven by a toothed belt tensioned by two idler rollers.
The need for valve clearance adjustment is eliminated by the incorporation of hydraulic tappets (cam followers).
The pistons have been re-designed, with valve head recesses machined in the piston crown and the gudgeon pins are now of the “floating” type, secured by circlips in the piston.
The undersides of the pistons are cooled by oil jets located in lubrication pipes within the crankcase.
The crankshaft has lighter balancing counterweights with a damper fitted to the
sprocket end.
Pressurised oil is supplied by an oil pump located within the sump pan, the pump being driven by chain from the crankshaft.
An oil to water heat exchanger is also fitted to which the disposable canaster type oil filter is fitted.


Cylinder Head
Detailed data on the cylinder head is available in the downloads section which features the Citroen Manual pages