87/16 February ’96
GENTLE WARNING
This series of technical articles has been designed for the “mechanically minded” reader who feels capable of carrying out his own maintenance to this degree. If you have doubts about your ability to cope with the instructions you are earnestly advised to leave the job in the hands of an experienced mechanic. During the combustion of the petrol air mixture of an engine, deposits of carbon are formed. Although the majority of these deposits are ejected through the exhaust system, a certain amount remains and collects on the walls of the combustion chamber, valves and piston. This build up of carbon prevents the engine from breathing and robs it of its performance, in the same way a fire loses its brightness when the chimney becomes blocked with soot.
Very high temperatures are also produced during combustion, which are necessary for the running of the engine. The high temperature and heavy loads exerted on the valves will sometimes cause them to burn after very big mileages. The question now arises as to when a decoke and valve grind are necessary. To give an answer in terms of mileage on this question is virtually impossible, as no two engines are alike. The best guide is in the symptoms; the loss of compression is the key. Loss of compression will cause loss of power, heavy petrol consumption, difficult starting and uneven running, and even misfiring. As the fall in performance is gradual it is often not noticed until the condition gets very bad.
EQUIPMENT REQUIRED
1. A set of ring and open-ended spanners from 3/8″AF to 3/4″AF.
2. Valve grinding stick.
3. Screwdrivers, one large and one small.
4. Grinding paste, coarse and fine.
5. A scraper or rotary wire brush if available
6. Valve spring compressor.
SPARES REQUIRED
1. A set of decoke gaskets.
2. A set of exhaust valves.
3. Spark plugs, points, and hoses etc. as and if required.
Obtain your spares from a Triumph parts supplier and always quote your engine or commission number you are then certain of getting the correct parts.
REMOVAL OF THE CYLINDER HEAD
Whenever working on an engine the first safety precaution to be carried out is to disconnect one of the battery leads.
There are quite a lot of components connected to the cylinder head and other parts of the car, these all have to be removed or disconnected. Drain the Cooling system by the tap on the lower tank of the radiator (if fitted). All the hoses can then be removed including the heater hoses and manifold heating hoses on the Triumph 2000. After unscrewing the clips, give the hoses a twist to break the seal. This will make them easier to remove. Slacken off the dynamo / alternator mountings and remove the fan belt. The water pump can now be removed by unscrewing the three securing bolts, the top right hand bolt also secures the dynamo / alternator stay, the left one the petrol pipe. All three are just above the water pump pulley.
There are only a few electrical points which require disconnecting. These are simply the water temperature gauge, if one is fitted, and the H.T. leads to the sparking plugs. To save damage, remove the distributor top. It is also a good idea to number the leads, thereby preventing them from being connected to the wrong plug.
The carburettors can be removed with the manifold as a complete unit or separate. Disconnect the throttle, and choke controls, remove the air cleaners and disconnect the petrol and vacuum advance pipes. If the manifold and carburettors are being removed as a unit, disconnect the exhaust pipe. A single row of bolts and two nuts, one at each end secures the manifold to the head, these can be removed and the manifold lifted off.
Having removed all the controls and components from the head we can now start removing the head. Unscrew the nuts securing the rocker cover; these have fibre washers and plain washers under them, the fibre washers to prevent oil leaks. Removal of the rocker cover gives us access to the rockers themselves. The rockers are mounted on a shaft and are removed as a complete assembly which is secured by 9/16″AF nuts, one on each pedestal. From each rocker there is a push rod connecting it to the cam follower. When removing the push rods give them a shake, this will free them and prevent dislocation of the cam followers.
With the rocker shaft and manifold assemblies removed we can now have access to the cylinder head nuts, which can now all be removed. The cylinder head nuts are all high tensile nuts and should not be mixed up with other nuts of the same size, so keep them separate. If in doubt about the correct nuts, the high tensile nuts are identified by the letter “R” on the upper face.
The lifting can sometimes be difficult to start with, as sticking sometimes takes place between the faces of the head block and gasket. A slight sideways tap with a piece of wood or soft hammer sometimes helps. The cylinder head removed and on the bench, we can now concentrate on the valves. Removal of the valves from the head is one of the most difficult tasks to be encountered on the decoke.
A special tool is used to compress the spring; this relieves the pressure on the two collets allowing them to be removed. After releasing the spring compressor, the valve cap, springs and valves can be removed. If the compressor is not available the springs can be compressed by placing a block of wood under the valve heads and using a strip of metal pivoted on one of the rocker pedestal stands. When removing the valves from the head, mark them so they can be replaced into the same guide. When new valves are being fitted this is not necessary of course. Clean off the deposits from the valves and combustion chamber, and clean out the ports. A rotary wire brush in an electric hand drill is a useful tool for this job. Wash all loose dirt from the head so it is nice and clean for examination.
Inspect the valve seats for bad pitting. If the seats are too badly marked, they will have to be cleaned up with a special cutting tool; this is best done by a garage. The valve guides are also best removed and replaced by a garage if they are worn at all. Worn valve guides cause heavy oil consumption and reduce valve life considerably. To check a valve guide, place the valve into the guide so it is about 1/8″ off its seat. Then try rocking it from side to side. There should be no more than .020″ movement. A worn guide can also be detected by looking at the stem of the valve; a dull black deposit of carbon on the stem indicates wear on the guide.
Assuming the valve seats and valve guides are in order, we can start grinding in the valves. This is done by smearing the valve seats with grinding paste. Before putting the valve into the guide, lightly oil the stem. Using the valve grinding stick rotate the valve back and forward using the palms; rotate the valve occasionally allowing the paste to return. While grinding in the valves gradually rotate them so they are seated all the way down. Ensure after grinding in, that all the grinding paste is washed off, as an abrasive will produce wear if left in. Inspection of the seats will show if the valve has been ground in correctly. The seat both on the valve and head should have an even mat grey mark all the way round about 1/10″ wide. Too wide a seat will collect foreign bodies.
(Were there any Mk1s factory fitted with non-six cylinder engines? – Uncle Stan Part)