First it is assessed whether doverhaul of the cylinder block is still possible. Sometimes, for example, the cooling ports are damaged to such an extent by corrosion, or the outlet port is burned to such an extent that revision of the block is no longer sensible or even impossible. There may also be frost damage to the block. To be able to determine this properly, it is important that the block is completely free of dirt, paint and rust.
Prior to overhaul all any broken bolts are removed and threads are cleaned or repaired.
Sealing surfaces which are affected by corrosion or which are damaged are reprocessed (surface milling) so that they can again form a good surface seal. This includes the manifold, cooling water inlet, and cooling jacket cover.
The cylinders are machined (boring) to the size of new oversized pistons, or the cylinder block is machined to fit new liners when using standard size pistons. Sometimes the old pistons can be reused, this is assessed after measuring the piston diameter (on the ‘skirt’) and the clearance in the piston ring grooves. If the block is flattened, the top of the pistons is also machined on the lathe in order to end up with the correct compression height. After boring the cylinders, the cylinder walls are honed to obtain an optimum lubrication pattern and running-in behavior. New piston rings are always fitted and the ring gap clearance of the piston rings is adjusted with a specially made grinding machine.
It is often thought that if one replaces the piston rings and hone the ‘old’ cylinders, the job is done. Unfortunately, this is a waste of money and completely meaningless when speaking in terms of proper overhaul. It is not only the piston rings that wear out, but also the cylinder wall; it is all about the correct clearance.
Valves (Albin gasoline engines)
The Albin gasoline engines and also the Volvo Penta MB10a are flathead engines with underlying camshaft. To allow the engine to run on unleaded gasoline without problems, hard steel rings are mounted at location of the exhaust valves. The new valve seats are then machined in the block and the new valve and seat are ground to each other by machine. The valve tappet heads are flattened on the lathe, and the tappets and camshaft are carefully inspected for excessive wear / damage. The valve clearance is set by grinding the valve stems with a specially made grinding machine. The spring pressure of the valve springs is checked and if necessary the valve springs are replaced.
Valves (Albin diesel engines)
The Albin diesel engines are overhead engines (the valves are in the cylinder head) with underlying camshaft. The valves are operated by means of the tappets (cam followers), push rods and the rocker arms on top of the cylinder head. With valve overhaul, the valves and valve guides are replaced, the valve seats are re-machined, and the valve stem seals on the inlet valves are replaced. It may sometimes be necessary to replace the valve springs as well. Often during a valve overhaul the cylinder head is also flattened (then we speak of a complete cylinder head overhaul). After re-assembly of the cylinder head on the engine, the valve clearance need to be re-adjusted according to the manual. The valve clearance must be checked and re-adjusted regularly, where the checking frequency depends on the engine running hours.
Cylinder head and block surfaces
The cylinder head is flattened by grinding or milling, if necessary. The same applies to the cylinder block. When valve overhaul and / or new cylinder bores is included,, the cylinder block is always flattened. In this way, optimum sealing of the cylinder head is guaranteed and unevennesses are eliminated. The cylinder head is mounted again with new studs and nuts and torqued to specification.
The piston pin bearings in the connecting rods are mounted and machined to size. The bores of the connecting rod bearings are also checked for roundness and, if necessary, repaired.
Both the main and the big end journals are measured. If the measured value falls within wear tolerances, it is sufficient to fit new standard size bearings. If that is not the case, then the crankshafts journals are machined (grinding) to its next undersize. New main bearings and big-end bearing shells are mounted.
All components are assembled again with the correct tools and according to specification. New gaskets and seals are always used during assembly.