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Your Head Bolts & Cylinder Head Bolt Kit worn out? » Read more about common malfunctions • Repair • Replacement manual
Keeping the engine together: Cylinder head bolt
Cylinder head bolts are connecting elements subject to high strain. They fix the cylinder head on the engine block. They keep the cylinder head tightly shut and fixed in its place despite the high pressure from the combustion chamber. These bolts can only be used once and must be replaced once they are removed.
Cylinder head bolts: function and location
The cylinder head bolts are located under the valve cover. Removing the cover makes the bolts visible and accessible. Usually the camshaft does not have to be removed in order to remove the cylinder head. Nevertheless, the valve control must be taken apart which makes the removal of the cylinder head a complicated task.
Replacing cylinder head bolts
Cylinder head bolts are removed on occasion of the following repairs:
- replacement of the cylinder head
- valve replacement
- invasive repairs such as replacement of the cylinder liners, drilling out cylinders, etc.
For the replacement of a cylinder head bolt, three things must always be observed: 1. These are expansion bolts. Tightening them with their specified torque changes their structure permanently. They cannot be used again and must always be renewed. 2. These bolts must be tightened with the specified torque. If the tightening torque is too weak, full tightness is not guaranteed. If it is too tight, the bolts can break off. 3. These bolts must be tightened in the correct order and step by step. Indiscriminately screwing them tight will warp the cylinder head, risking extensive engine damage.
Necessary and useful additional repairs
Cylinder head bolts do not break off just like that. A bolt breaking off during normal operation is extremely rare. Once a tightened bolt is removed, it must be replaced by a new one. This implies necessary additional repairs. As a rule, cylinder head and bolt replacement go hand in hand. It makes sense to simultaneously perform the following repairs:
- replacing all oil seals
- renewal of valve control (timing belt, belt tensioner pulley, water pump or timing chain with tensioner)
- replacement of valve stem gaskets
These works require certain special tools which should be purchased by any well-assorted DIY garage. These repairs are very expensive in a garage and the investment pays itself back very quickly. Required are:
- Valve spring compressor
- Straight-edge for the cylinder head
- Feeler gauge
- torque spanner.
Furthermore, an oil change and a thorough check of the camshaft accompany these repairs. Ultimately, the cylinder head should be thoroughly cleaned prior to installation and the bearing cups of the camshaft as well as the hydraulic tappets must be replaced. These spare parts do not cost much and bring the car in an excellent maintenance condition.
Costs for spare parts and tools
The price for a handy valve replacement tool set starts at ca 70 EUR (± £62). A straightedge costs ca. 50 EUR (± £45). It must be handled with care to ensure its longevity. Once it falls from the tool cart, it can no longer be used. High-quality torque spanners are available at 80 EUR (± £71). As a lot depends on the correct use of the measurements, refrain from using cheap tools. Feeler gauges in excellent quality can be obtained for 20 EUR (± £18). Cylinder head bolts are available at 20 EUR (± £18) per set. These low prices make replacement on occasion of repair very cheap. Therefore there is no excuse for re-using the old ones. Costs for a set of hydraulic tappets start at ca. 25 EUR (± £22). Valve stem gaskets are available at 3 EUR (± £2,50) apiece. A new cylinder head costs ca. 60 EUR (± £53). A complete set including all O-seals, oil seals, manifold seals and further smaller components starts at ca. 100 EUR (± £90). Depending on car type it can set you back as much as 250 EUR (± £223). Cylinder head bolts are usually not included and must be ordered separately. Replacement of a cylinder head gasket is a task for experienced DIY'ers with extensive skills. Having this expertise opens wonderful opportunities. Cars with defective cylinder head gaskets are often being offered at surprisingly low prices. A real expert can get a real bargain and later sell on a car in perfect condition.