HEAD GASKET FAILURE

Head gasket failure is one of the most common reasons clients seek out our expertise. In times gone past head gasket failure were generally due to the relatively poor quality gaskets available and periodic replacement was inevitable. You may have heard of the expression "blown head gasket" in reference to failure of the gasket in older engines, the name derived from the appearance of the gasket which, when removed, would be missing whole sections of material that had simply been blown out of the gasket by cylinder or coolant pressure like the head gasket in the picture. In modern engines the gaskets have improved dramatically to cope with the extremely high-output engines we have today and many are made with extremely robust material, including the MLS (multi layer steel) gasket found in many newer engines, yet gasket failures still occur.

The reasons for failure are varied, but the important thing to remember during repair is that modern head gaskets almost always fail as a symptom of problems in the vehicle cooling system and are very rarely the cause of the problem, therefore when repairs are carried out it is of the utmost importance that the cause of failure is detected, otherwise you may expect to be repeating the process. For example; a closer inspection of the failed gasket above reveals damage to the"bore binder" or beading around the upper section which appears crimped. The crimping is normally caused by extreme cylinder pressure known as detonation and is primarily related to ignition system malfunctions.

Our expertise is vital once the cylinder head has been removed from the engine, it is most important the cylinder head is thoroughly and professionally tested to determine whether the head is fit to re-use. Depending on the type of head our tests will include:

• Pressure testing to determine the presence of cracks or porosity
• Crack testing to reveal the extent of cracking
• Straightness testing to determine if the head has bowed during overheating
• Hardness testing which will reveal if the head is reusable
• Vacuum testing to determine the serviceability of the valves, seals and valve guides

Once testing has been carried out we will advise our client of any problems and recommend repairs that may be necessary. In almost every case remachining or milling of the cylinder head face will be necessary to remove imperfections in the surface of the head. When Headmaster have completed the necessary machining operations, the cylinder head is ready to go back to the client and a successful head gasket replacement can be guaranteed. 

HEADMASTER has helped tens of thousands of Wellington motorists, over many years, eliminate head gasket problems. All repairs carried out by HEADMASTER carry a 12 months/20,000 kilometres Warranty

EXCESSIVE BLUE EXHAUST SMOKE

From October 27 2006 roadworthiness checks carried out during Warrant of Fitness inspections in New Zealand will include a check for excessive visible exhaust smoke. Dubbed the "Choke the Smoke" campaign by legislators, some motorists fear it will result in remedial engine repairs, or the possibility their cars may be ordered off the road.

If your vehicle is rejected for excessive blue coloured exhaust emissions you may need to speak to an engine specialist before you get back on the road. For some useful information see:  http://www.ltsa.govt.nz/vehicle-ownership/smoky-exhaust-test.html.  Contrary to information provided on the LTSA site page we believe most blue exhaust smoke emitted by 1990 and later petrol engined vehicles is not due primarily to engine wear, since under normal conditions, and thanks to modern materials, fuel systems and lubrication technology, these engines suffer very little from mechanical wear.

Bluecoloured exhaust emission is caused by oil entering the combustion chamber, either bypassing the oil control rings, located on the pistons, or drawn past the valve stem oil seals located in the engine cylinder head. The primary reason for the failure of these components in modern engines is a condition known as glazing.

Glazing is primarily caused by excessive contamination of the engine lubricating oil by the normal by-products of combustion, a heavy coffee-coloured staining develops, sometimes resulting in thick black sludge ( see the picture above ), coating the engine internal parts and literally gluing some vital components together, preventing those components working. All good oils are engineered to prevent glazing occurring, and under normal circumstances, with good maintenance the condition will never become a problem. It usually only becomes a problem when regular maintenance, or ignoring the recommended oil change intervals, occurs. It is especially prevalent on used imported vehicles from Japan.  

The picture on the rights is of a piston removed from a smokey engine, the coffee  colour is due to glazing. On the top part of the piston are the piston rings. The oil control ring is the third ring from the top, and consists of three segments which must be flexible to work. Glazing literally glues the segments together and prevents the ring working. 

A practical firststep to undoing the damage caused by glazing is to add an engine-flush oil additive to the crankcase before having the engine oil changed. The engine flush will help break down the glaze, free up the oil control rings and revitalize the valve stem seals. It needs to be stressed that "flushing" the oil is only a useful method for reducing exhaust blue smoke, and cannot be guaranteed to make a difference. There is a small risk when adding any engine flush product that engine oil pressure may be reduced, since the flush may be so effective that sufficient sludge and varnish is loosened inside the engine for the oil pump inlet pipe screen ( much the same as a sieve ) to become blocked. This is a very small risk, but if a drop in oil pressure is noted it may have to be hastily dealt with by your local repairer. 

Use any engine flush oil additive exactly as directed, and leave the product in the crankcase for no longer than specified. If no noticeable improvement has occurred after using the product, there is probably no point adding further additives, you will need to look at dismantling the engine to replace the effected components, or have us carry out repairs for you.

A typical repair will require replacement of valve stem  seals or piston rings. Repair options will vary from vehicle to vehicle and thus costs will vary too, but repair is usually a good option compared to the sickening costs of depreciation and interest financing incurred when we purchase newer or more expensive vehicles.

HEADMASTER has helped thousands of Wellington motorists, over many years, eliminate excessive exhaust smoke. All repairs carried out by HEADMASTER carry a 12 months/20,000 kilometres Warranty

BROKEN TIMING BELT

The timing belt, or camshaft drive belt, utilised on many engines produced since the early 1980's is a flexible drive system preferred for quietness of operation compared to alternative camshaft drive systems, such as chains or gears. Sometimes belt failures occur, leading to mechanical damage within the engine. Typically the failure may result in damage to the cylinder head, resulting in bent valves and damaged valve guides. Engines which are likely to incur damage when belt failure occurs are referred to in the trade as "interference" engines, and those less likely to incur damage as "non-interference" engines, though there are exceptions in both catagories. In either case it is vital to ensure that no damage has occurred before fitting a replacement belt and attempting to re-start the engine. The photo on the left shows the catastrophic damage which can occur when an engine which has sustained damage has been re-started without addressing the damage which resulted from belt failure. In this particular case two valves in the cylinder head had collided with the pistons at the time of belt failure and the damage was undiagnosed, upon re-starting the valves broke off and dropped into the cylinder.

When damage has resulted Headmaster are able to carry out the precision machining and supply the replacement parts required to repair and restore the damaged head. We have a mountain of experience with all modern engines whether European, Japanese, British, American or Australian.

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