Lotus Excel – Cylinder head gasket replacement

Symptoms – traces of oil in coolant header tank and coolant loss via pressure relief valve of header tank. Also slight leak from lower O/S of radiator.

Diagnosis – cylinder head gasket leak between main oilway and coolant line. Oil pressure is over-pressurising the coolant system.

Rectification – replace cylinder head gasket and check cylinder head.

Preparation

Parts required – Cylinder head gasket set, including camshaft housing O rings; new gasket for exhaust manifold to downpipe; exhaust and inlet manifold gaskets; new copperised nuts for exhaust manifold; 3-5 litres of ethylene glycol antifreeze, 3-5 litres of de-ionised water; 5-6 litres of new engine oil (e.g. 15w50, 10w60), new oil filter, replacement shims as required to adjust valve clearances.

Special tools

Torque wrench / angle gauge;

12 mm hex Allen key;

Star socket - size E10, 3/8 drive

Permabond A136 zero-clearance gasket (and surface activator spray);

Procedures

1. Jack up car, support on stands, remove front wheels (4 x 21mm dome-headed nuts). Remove bonnet (2 x 13mm nuts, the threaded Allen bolts usually undo with the nuts, 13mm nuts for bonnet strut and 10mm nut for earth strap; disconnect windscreen washer jets). Place old sheets / soft cloths over wing tops and nose cone to avoid scratches etcetera.

2. Disconnect battery negative terminal.

3. Remove caps from the header tank, remove lower radiator duct (2 x 10mm nuts, 2 x 17mm bolts with captive nuts inside headlamp pod recess), loosen bottom hose jubilee clip, remove bottom hose and drain coolant into large bowl or similar receptacle.

4. Remove the air box (3 spring clips), air filter and air intake trunking (undo strap / cable tie securing end to wire support).

5. Working under a securely supported car (i.e. on ramps or axle stands), unfasten 3 x 17mm nuts holding exhaust downpipe to manifold. Lever the joint apart using a strong, flat-bladed screwdriver (and hammer if necessary). Remove the metal gasket.

6. Unfasten the nearside engine mounting by undoing the nuts and bolts (2 x 17mm) securing the base of the mounting to the chassis.

7. Remove the toothed belt guard (cam belt cover) by turning the 3 turnbuckle clips and lifting off the cover.

8. Disconnect the water hoses from their connections to the cylinder head and to the inlet manifold.

9. Undo all 13mm nuts holding the inlet manifold; recover nuts and washers; disconnect the breather pipe from the flame trap at rear; disconnect throttle cable support bracket on the inlet cam cover (2 x 4mm Allen bolts) and place the carburettors on a suitable soft support.

10. Remove the spark plug leads and tuck them carefully out of the way on the inlet side of the engine; label with cylinder numbers if needed.

11. Remove the camshaft covers by undoing 3 slotted screws for each. Check valve clearances, carefully rotating engine clockwise and reading clearance at the heel of the cam. Measure in imperial as the replacement shims are marked in thousandths of an inch.
INLET : 0.005 to 0.007 inch ( = 0.13 to 0.18mm )

EXHAUST : 0.010 to 0.012 inch ( = 0.25 to 0.31mm )

12. Note the clearances as below. Any out of specification should be followed up by measuring the corresponding shim and calculating the new shim thickness. You will usually find that the clearance reduces over time, so change shims to re-set to the maximum clearance.

13. Tabulate readings and calculate any changes – all readings in 0.001 inch, example in italics.

14. Leave the engine positioned at TDC for the firing stroke of cylinder #1. Mark the cams, auxiliary pulley and belt with white paint spots. The inlet and exhaust cams should have timing marks that align with each other in a horizontal line drawn between the pulley centres. The auxiliary pulley should have a reference mark that aligns with the edge of the bracket above. Place a flat screwdriver into the starter ring gear through the crankcase slot (lower driver side of engine for RHD) to lock the bottom end in place.

15. To access the cambelt tensioner, slacken the alternator drive belt by undoing the friction clamp nut (13mm) and the mounting bolts for the supporting bracket.

16. Place a block of wood under the front nearside corner of the sump and gently jack this up to ease the engine up from the nearside mounting. Continue jacking until the stud on the exhaust flange just clears the chassis. This is to give clearance for the exhaust manifold to be removed with the cylinder head.

17. Slacken the locking bolt (17mm) and loosen the cam belt tensioner by turning clockwise using a 19mm spanner. Slip the belt off the camshaft pulleys and position carefully to one side. Place newspapers or other absorbent material under the car, as the next steps will result in oil and coolant spillage………..

18. Remove the camshaft housings complete with cams. Each housing is retained by two 13mm nuts (with washers) and eight star-headed bolts, for which a special socket is required. The nearside bolts are covered by inspection caps that require a 12mm hexagonal key for removal. Access to the rearmost caps and star-headed bolts is limited by proximity to the bulkhead, necessitating a short 3/8 drive or ¼ drive ratchet. When removing the camshaft housings, tilt the camshaft housing so that the followers are horizontal in their tunnels or are angled towards the camshaft and should not fall out. Be careful not to lose/drop followers. The shims will be stuck inside the followers by a film of oil. Place the camshaft housings on a clean, level surface covered in paper towel or newspaper to absorb the oil. Remove the followers and shims and place in logical order or on a marked sheet of paper. Inspect the followers carefully for cracks and measure/read the shim thicknesses, tabulating as above.

19. Remove the screwdriver from the starter ring gear. Carefully rotate the engine backwards through 90 degrees to bring all pistons to half stroke. Replace the screwdriver. The engine must not be rotated with the cylinder head off, otherwise the liners may lift, requiring a full engine re-build.

20. Remove the cylinder head nuts (10 x 19mm) evenly and progressively, starting from the outside in reverse tightening order and working diagonally. Retrieve the nuts and washers.

21. Remove the cylinder head, gently adjusting the jack to raise/lower the engine from the n/s mounting to give clearance for the exhaust manifold. Pry the inlet side of the head gently with a piece of wood to ease the joint faces apart. Lift the head clear and place on a clean, level surface lined with absorbent material.

22. Unbolt the exhaust manifold from the cylinder head (12 x 13mm nuts). Clean up the cylinder head mating face with fine wire wool or wet and dry (600 grade). Corrosion is common around the main coolant jacket. Take care not to dirty or scratch the mating face. Retain the old gasket if required for inspection and reference.

23. Inspection. Check the head gasket for signs of leaks or failure. Check the head for trueness using an engineering straight edge. Tolerance is +/- 0.003 inch, but consider having the head re-faced by skimming off 1-2 thou (for which the head must be stripped of valves and springs). Check the condition of combustion chambers and valves, cleaning carefully if required. Check the Nikasil cylinder bores for marking or pitting and inspect the piston tops for marking. If required, remove valves using a valve spring compressor and check for play between valve and guide. Inspect the valve seat and rear (seating) edge of the valve. If the seating area is reduced by pitting, consider grinding the valve into its seat. This will require re-checking the valve clearance subsequently. If the shim is already very thin (<90 thou), a new valve seat may be required.

Head removed with face cleaned up but not skimmed. Note dark pitted areas between water and oil ways believed to be due to corrosion that resulted in leak.

24. Remove the old studs from the block by tightly locking two 19mm nuts on the upper thread and applying a spanner to the bottom nut – it needs a fair bit of leverage to remove them. Absorb spilt coolant and oil from the pistons using clean paper towel. Clean the mating face carefully (easier when the old studs are removed), using 400-600 grade wet and dry and wiping away any grit. Be careful when cleaning up the tops of the piston liners to avoid disturbing them with subsequent lifting. Place a small amount of oil on the lower thread of the new studs and fasten them in, torquing down as specified. Wipe away debris and clean the face with alcohol/brake cleaner and compressed air to give a grease-free finish. Place the new gasket in position, which is an all-in-one fitment. The gasket is fitted dry and does not require sealant.

Mating faces cleaned with #400 wet and dry; de-greased with brake cleaner and debris removed with compressed air line. New studs (dimple on top) fitted.

25. Replace the exhaust manifold on the head, using new copperised nuts. Position the head on the block and very lightly oil the top threads. Ensure that oil does not run down onto the gasket or sealing surface. Fasten on the nuts and then tighten in sequence, following the sequence provided with the new gasket and working diagonally from the inside to out. Use the torque and angle settings indicated.

26. If needed, replace the oil seal in each camshaft housing, but I would only do this if there is a leak as it is a time-consuming job. Place the appropriate shim (calculated as above) in the top of each valve retainer, using a dab of grease to help retain it, and the corresponding bucket in the correct tunnel of the camshaft housing. Ensure that the camshaft housing and cylinder head faces are clean and spray with surface activation agent.

Apply a continuous bead of Permabond A136 all around the outer edge of the mating face of the camshaft housing to provide a zero clearance seal. Install a new O ring on the knock pin and re-fit the exhaust camshaft housing. This is easier if the engine is still lifted off the nearside mounting as there is better clearance. Carefully slide the housing down the studs and bolt down, starting at the central bolts and working diagonally outwards. Rotate the camshaft pulley to the TDC#1 setting. The pistons should be well down the bores so that cam rotation cannot damage valves.

Repeat the above for the inlet camshaft, preferably aligning the pulley before installation to avoid any risk of valve-to-valve contact. Check that all bolts are secure (a bead of A136 sealant should now extend all around the exterior of the housing at the joint) and align the cams correctly with their marks. Remember that the valves can touch each other if the timing is a long way out, so roughly aligning the cams is advised before fitting the inlet cam.

27. Remove the screwdriver and carefully rotate the crank 90 degrees clockwise to bring the pistons to TDC with #1 at compression. Check all pulley alignments and re-fit the timing belt. Re-position the tensioner and fasten it, checking the belt tension. Re-check all timing positions against their marks and, if OK, carefully rotate the engine. If unexpected resistance is felt, immediately stop, reverse and re-check. After two full revolutions, re-check belt tension and adjust if needed.

28. If all is OK, re-check the valve clearances and note the final clearances. If these are not correct, the camshaft housings must be removed again and shims replaced. One of my shims managed to drop out, so make sure you check! When the clearances are checked and OK, replace the 12mm hex Allen caps. Using new gaskets and a thin smear of gasket cement to retain them, replace the cam covers and fasten down the three slotted screw fasteners. Replace the throttle cable support bracket and filler cap wire on the inlet cam cover, and the earth strap on the exhaust cam cover. Lower the engine back into the mounting and re-fasten the bolts. Using a new gasket, re-fasten the exhaust manifold to the downpipe. Clean the mating faces, fit a new gasket and replace the carburettors on the inlet manifold, tightening the nuts.

29. Re-fasten all coolant hoses and check that the clips are secure. Remove the sump plug (18mm hex socket) and drain the engine oil. Remove and replace the oil filter. Re-fill with fresh oil.

30. Replace the radiator lower duct, replacing the headlights if these were removed to access the ‘captive’ nuts for the radiator duct. Fill the coolant system via the header tank, using a 40% (minimum) mix of antifreeze in pure water.

31. Replace the air intake trunking, air filter and airbox. Make sure the trunking is clipped/tied in place. Replace the timing belt cover and re-connect the battery. Check over to ensure no left-over pieces! If all is OK, start the engine and listen carefully, especially to the timing belt. A whine indicates tension is too tight, flutter (especially on overrun) indicates the belt is too loose. Check for leaks and loose items. If all is OK, replace the bonnet and tidy away tools.