User Tools

Site Tools


head_gasket

Changing the Head Gasket

You will need:

  • New head gasket
  • New oil stem seals
  • New head bolts
  • Valve spring compressor
  • New exhaust manifold gaskets
  • Fresh engine oil
  • Rocker cover oil seal

Fistly drain the engine oil. See Oil change and filter renewal and drain the engine coolant.

Remove the upper cam belt cover and ensure that the flywheel and camshaft sprocket are locked.

Disconnect the HT leads from the spark plugs and any other electrical connections that would prevent removal of the cylinder head.

Remove the rubber coolant hose from the thermostat housing and disconnect the fuel lines ensuring that relevant precautions are taken to minimise fuel loss.

Next remove the rocker / cam cover by undoing the two bolts at either end, remove the two washers and and use a screw driver to lever the cover off

Remove the cambelt, See timing belt

Remove the exhaust manifold, it is not necessary to remove the inlet manifold.

Now undo the 10 head bolts in the correct removal sequence a few turns at a time once they are removed you can also remove the the rocker assembly.

Now remove the cylinder head by rocking it gently backwards and forwards, take care when carrying out this procedure on alloy block engines as too much movement could displace the cylinder liners.

With the head removed secure the liners in place using suitable clamps (alloy block engines only).

Inspecting the Cylinder Head

Inspect the cylinder head visually and with the use of a feeler guage for any cracks or pitting, if the surface is uneven the head will need to be machined or “skimmed” by a professional. If the head is cracked or severly pitted this may not be repairable and a replacement part should be obtained.

Valves and Valves Stem Seals

Place the head on a suitable work bench and use the valve spring compressor on each valve in turn to depress the spring, undo the retaining nut and remove the spring and collet. Using a suitable set of pliers extract the stem seal from the base of the valve a replace with a new one (remember to add a smear of fresh oil to the seal), replace the spring and collet and tighten the nut.

It may also be a good idea to re-lap the valves whilst they are accessible.

Preparing to Refit The Head

Prepare the mating surface on the bottom end by using a plastic or wooden scraper to remove any traces of gasket or other debris and clean the surface of the piston crowns with a solvent soaked rag (ensure you block the oil ways with some rag or tape to prevent debris entering the oil system as this could cause the pump to fail).

Position the new gasket on the bottom end using the markings provided.

Place the head carefully in position on top of the bottom end ensuring it is lined up correctly and replace the rocker assembly.

Insert the new head bolts into each hole and tighten each one by a hand until finger tight and then tighten each one a full turn at a time in the following sequence until each one is torqued to 20nm/15lbft:

i35.photobucket.com_albums_d163_mark_fern_bolts.jpg

Now working in the same order turn each one by the following angles:

  • Alloy block = 240'
  • Iron block = 120' and then a further 120' working in sequence

Refit the rocker cover using a new Rocker Gasket with a smear of fresh oil.

Refit the manifold using new gaskets.

Refit the HT leads and electrical connections.

Refit the upper coolant hose.

Re-fill the engine oil to the required level and re-fill the coolant.

It will now be necessary to bleed the coolant system. See Bleeding the coolant system

NB: Ensure you remove any timing tools before attempting to start the engine. The engine may smoke for a short period after replacing the head gasket, due to oil or grease in the head or piston chambers being left in during work carried out. If this continues for a long period of time then there may be a problem with the cylinder head and should be looked at by a specialist or replaced all together.

head_gasket.txt · Last modified: 2016/08/18 20:27 (external edit)