It is essential that block and head faces are meticulously clean and free from all traces of old gaskets. Waterways in the head should be flushed out, preferably using a high pressure washer with detergent. This will prevent scale from falling onto the new gasket resulting in dirty assembly. Re-usable head studs/bolts/nuts and block threaded holes must be clean and finger free to assemble. (Threaded parts which are tight will give false torque readings).
If the cylinder head has been removed to renew a failed head gasket then it is probable that the head face will be distorted. It is most important to have the head resurfaced. Engines which have badly overheated may require the block face resurfacing also. Bolts and studs should be closely examined for thread distortion/ stretching and corrosion pitting. A weak thread will allow torque settings to relax and promote failure of gasket. Most modern engines employ cylinder head stretch bolts. These must NOT be re-used. As a golden rule any bolt that is subjected to angular tightening, (rather than torque stages), must be renewed.
Multi-Shim steel head gaskets are becoming standard fitment on many modern engines. Fitting conditions for replacing this type of gasket must be as good as original factory fitment. (1) Block and head machine faces must be flat within 0.08mm/0.003" & free from any scoring, scratches, corrosion pitting or any surface damage whatsoever. (2) Surface finish is to be within 10 microns/32 C.L.A-N6. (3) Block threads must be tapped out & hole core depth cleaned of any debris. (4) Cleanliness during assembly is of the utmost importance. (5) New cylinder head bolts must be employed & torque down procedure strictly adhered to.
If the head gasket is being replaced because of failure through overheating, then the cooling system must be thoroughly checked. Flush radiators with clean running water. Check the tubes inside the filler neck If any choking is visible or the radiator appears to "Slow Fill", then have the unit "Flow Tested" by a local radiator specialist. Closely examine radiator and heater hoses for cracks and "spongy" perished areas. Suspect hoses must be renewed. If a thermostat is of an unknown quality then renew as required. Water pump - Check that impeller is tight and that impeller vanes are not corroded and wasted. Check that the pump seal has not been leaking - normally visible by a rusty stain on the pump housing. Cooling fans with clutch units or electronic sensors must be checked in use. An inactive fan will promote immediate overheating!
We strongly discourage general use of any gasket compounds/sealers on cylinder head gaskets. A very light application of non hardening compound, such as Ultra-Parts "ULT705" may be applied around oil way eyelets, but otherwise fit the gasket as supplied. Gasket compounds may be applied in moderation to water pump/thermostat/waterway gaskets particularly where parent parts axe corroded. Exhaust, head to manifold gaskets should be fitted as supplied. Cork and rubber gaskets should be held in position with spot adhesives. Sealers, oil or grease should not be used as these will encourage the gasket to slide during assembly. Crankshaft & Camshaft oil seals should be fitted into their housings dry. A little smear of grease may be applied to the inner sealing lip to prevent drag and possible tearing on initial start up.
Instructions given by the vehicle manufacturer for torquing down cylinder head must be strictly adhered to. Engines with torque bolts will require re-tightening after initial run to normal working temperature & after 500 miles. Please note that cast iron cylinder heads should be re-torqued whilst the engine is still hot, aluminium heads to be torqued when cold. Generally each bolt must be slackened by one quarter turn and immediately retorqued to the highest stage of the torque down procedure. Most engines employing cylinder head stretch bolts do not require re-tightening, however please consult workshop manual or see data on Ultra Parts Head bolt box.
Fan belts should be examined for splits/cracks or fraying and renewed if necessary, ensuring the correct type is fitted i.e. alternator or dynamo - do not overtighten belt. Re-check the tension at 50 miles and 500 miles and adjust accordingly.
The majority of diesel engines require a choice of different thickness head gasket. These are normally selected by measuring piston protrusion above the block face at top dead centre.