Cylinder Head Repairs

Cylinder Head Pressure Testing

In an engine the cylinder head sits above the cylinders on top of the engine block.  If your engine has overheated or had a cooling system failure it could crack or distort the cylinder head.

If your cylinder head is removed we would always recommend a pressure test  as a cracked head can be the cause or a symptom of overheating.

When we pressure test a cylinder head we are looking for any leaks external or internal.  We do this by blanking the water outlets on the cylinder head and then pressurising the cylinder head with compressed air at 40psi.  We would then confirm if the cylinder head is leaking. 

The head is heated up to temperature of 40 degrees as we test it.

Due to the constant thermal expansion and contraction of the cylinder head any flaws in the casting can be exposed causing cracks in the cylinder head, a pressure test can check if these cracks are leaking. 

A cylinder head can crack internally, so even if no cracks are visible on the cylinder head it is always worth pressure testing to confirm the cylinder head is ok to re-fit.

We are able to pressure test cylinder heads of most vehicles, from the smallest car to the largest commercials.

Cylinder Head Resurfacing

If an engine has overheated or blown a head gasket the cylinder head can become distorted, if this is the case we are able to resurface or skim the cylinder head to bring it back into tolerance and create the perfect sealing finish. 
In modern engines the cylinder head finish should be within 10 microns, this is because most modern engines use a steel laminate head gasket, called a M.L.S gasket i.e. “multi layered shim”.  These gaskets provide a stronger body plate and helps conduction between block and cylinder head, this helps stabilise thermal expansion and contraction, thus reducing stress.  Since the M.L.S gasket material is unforgiving any flaws in the surface finish of the cylinder head can lead to premature gasket failure.  In our well equipped workshop we are able to obtain the correct surface finish using our precision equipment and years of experience.

As well as a head becoming distorted it can also become corroded over time which may necessitate a skim.  If a gasket has blown it may leave a mark on the surface of the head which may require skimming. 

We are able to resurface most petrol cylinder heads with the valves in place, however on the majority of diesel cylinder heads the valve protrude above the surface of the head and would need to be removed prior to resurfacing the head.  Once the head has been resurfaced we may need to resurface the valves and valve seats to set them back to the correct depth/height.

When resurfacing the cylinder head we always try to remove the minimum amount of materials as possible to remove any distortion without drastically altering compressions. 

We are able to resurface cylinder heads of most vehicles form the smallest cars to the largest commercials.  As well as cylinder heads we can also resurface cylinder blocks and manifolds if they are damaged or distorted.

Valve & valve seat resurfacing

Inlet and exhaust valves are precision engine components used for sealing the combustion chamber that controls the gas exchange process in internal combustion engines.  This seal is created between the valve and the valve seat.
Due to the constant opening and closing of the valves, the valve seats and the valves themselves can become worn on the sealing surface.  This will reduce the effectiveness of this seal which would cause combustion gasses to leak, which may lead to a loss of compression. 

If this were to happen instead of replacing the valve and valve seat we are able to resurface or cut them to recreate the perfect sealing surface.  After resurfacing valves and valve seats we then vacuum test them to confirm they are sealing correctly.

Using our modern valve and seat cutting equipment we are able to resurface valves and seats for a wide range of vehicle on the road.

Valve guide replacement/re-sleeving

For every inlet and exhaust valve there will be a valve guide fitted into the cylinder head.  This valve guide serves to positively locate the valve to the valve seat so it makes proper contact.  Guides also serve to conduct heat away from the exhaust valve to the cylinder head.

If an engine suffers a catastrophic failure i.e. cam belt failure, the valve guides can crack due to the valves bending.  If this is the case we are able to remove the damaged valve guides and replace them with new guides.  If for any reason new valve guides are not available we are able to manufacture guides to suit.

Over time a valve guide can become worn, which can lead to smoking and oil consumption problems.  Rather than replacing valve guides we are able to re-sleeve them.  What this entails is for us to fit a phosphor bronze guide liner directly into the valve guide.  The benefits for re-sleeving valve guides rather than replacing are numerous, but they include durability, as the phosphor bronze guide liner is a harder wearing material the guides have been shown to outperform cast iron guides in durability, heat conductivity and friction reduction.

As well as the benefits listed above, re-sleeving valve guides is a less traumatic experience for the cylinder head.  As the guide liners are fitted directly into the valve guide it removes even the small risk attributed to removing and fitting valve guides.

We have a wide range of guide liners available to us, therefore we are able to offer this repair to the majority of vehicles on the road.

Valve seat replacement

The valve seat is the surface that the intake and exhaust valves sit on when the valves are closed.  The valve seat is a critical component in the combustion process, if the valve is not seating correctly it can cause combustion gasses to leak reducing compression.  As well as this important operation the valve seat also serves to transfer heat away from the valves into the cylinder head.

Over time a valve seat can become worn which can reduce its effectiveness and lead to a loss of compression.  If we are unable to resurface the seat due to the extent of the wear we can remove it and fit a new valve seat insert.
If a valve seat is not available for your vehicle we are able to manufacture valve seat inserts to suit using blanks.  If the valve seat is cast into the cylinder head we are able to machine it out using an I.D.L and then manufacture seats to fit.

Valve seat replacement is also an important part of converting engines to run unleaded fuel.  When doing a conversion you have to replace the exhaust seats with a harder wearing material due to the increase of temperature during the combustion process.

We are able to get valve seats in a range of sizes which we can machine to fit almost any vehicle on the road.

Aluminum welding

If an engine is run without the correct coolant/antifreeze mix the cylinder head can become corroded around the water jackets.  This corrosion can interfere with the sealing of the cylinder head gasket.  If this is the case we are able to weld the corrosion and then resurface the cylinder head recreating the correct sealing surface.

If your head has received any external damage we may be able to offer a weld repair.  This is dependent on where the damage is and how extensive it is.

Injector sleeve replacement

Some diesel engines are fitted with copper injector sleeves.  These sleeves are fitted directly into the cylinder head.  If an injector sleeve is found to be leaking we may be able to remove and depending on what type of sleeve it is fit a new one.  On some injector sleeves we may only have to remove the sleeve, fit new seals to it and then refit.  However on certain vehicles the sleeves need to be fitted with an installation tool, we do have some of these installation tools, but there are certain vehicles we may not be able to do, please enquire with us to see if we can offer this repair for your vehicle.

On certain vehicles we are able to do this repair with the cylinder head in-situ.

Unleaded conversion

If you have a classic car and are still running it with leaded petrol we can offer an unleaded conversion for your cylinder head.  For an unleaded conversion we need to replace the exhaust valve seats with new harder seats.  We would also recommend fitting new exhaust valves. 

Rescribe commercial cylinder heads

Some commercial cylinder heads are manufactured with a scribe mark around each cylinder on the cylinder head.  If a cylinder head is distorted and needs to be resurfaced it can alter these scribe marks, however we have the tools and the experience to reintroduce these scribe marks.