Valve Guide Repairs
Some cylinder heads are very common for the valve guides to wear during every day use. It is not known why this is more common on certain makes of cylinder head than others. Also when a head goes through timing failure it is most likely to cause two problems, first is the valve guides will crack, second is that the valve guide will distort from its original shape due to the valve being bent.
Motorcast Components offer a variety of repairs to valve guide problems. Valve guides fitted to some makes of head are made of cast iron, when cast iron valve guides are damaged due to wear or timing failure the only way to fix this is the replacement of the valve guide with new guides. This procedure is carried out by pressing the damaged valve guides out of the cylinder head, and measuring, firstly the outer diameter of the old valve guide, secondly the diameter of the bore in the head where the guide has been removed. The new guides are then measured for correct tolerance before being pressed into the cylinder head, at this stage the new guides are set to the correct depth to avoid problems with the valve springs.
Other material used in the manufacture of valve guides is phosphor bronze, there are two types of repair for this type of guide. Firstly, if the guide is cracked it will need to be replaced using the same procedure as with cast iron guides, if the valve guides are worn, then a more cost effective repair can be carried out, this is done by special guide repair kits where the centre of the guide is bored out slightly larger than its standard size then a bronze insert is pressed into the guide, then trimmed to the correct length followed by various sized steel brooches which are pressed through the guide, this will gradually expand the bronze insert until the correct tolerance has been achieved in order for the valve to fit with the correct amount of tolerance. If the valve guide is too tight the valve might seize within the guide or if the valve is too slack it will cause the engine to burn oil that has run down the guide due to a slack fit. So the correct fit is very important.