How to Rebuild a Blown Engineby Richard Rowe
A blown engine can either be a nightmare of epic proportions or a fairly simple weekend project--the difference comes down to knowledge and preparation. Think of your engine disassembly as an autopsy and don't take anything at face value. Stay vigilant for cascading, cause-and-effect failures and expect to spend twice what you think you will. A "blown" engine can be the result of anything, from a simple head gasket failure to a crankshaft snapped in two, so don't buy any new parts until you know what's going on with the engine.
Diagnose the engine during teardown, taking it slowly and staying organized. Remove the valve covers and intake manifold, checking for debris in the oil and broken valve springs/valve train components. Remove the cylinder heads and examine the piston tops and combustion chamber roofs for signs of oil leakage, water leakage and melted components.
Check for cracks in the heads, the combustion chamber and deck surface, the piston tops and cylinder bores and the engine block deck surface. This is just a preliminary check. If you don't see anything wrong, don't assume that the engine is fine; be prepared to take it to a machine shop to have the block and heads magnafluxed to check for cracks invisible to the naked eye. This is especially crucial if the engine blew from overheating.
Remove the crankshaft, rods and pistons. Pay close attention to the bearing surfaces, checking for signs of gouging.
Send the block to the machine shop to have the crankshaft, bearing bores, cylinders, engine block and cylinder head deck surfaces machined to factory specs. Order whatever new parts you need, including over-sized pistons, rings and bearings.
Install the new piston rings onto the pistons. Install the crankshaft bearings into the block, followed by the crankshaft itself, rod bearings then the pistons and connecting rods. Pack the oil pump with petroleum jelly, then install it and the oil pan.
Insert the new head gaskets and bolt the heads onto the block. Slide the new camshaft lifter in place. Install the camshaft either into the block or onto the cylinder heads and then install the valve train onto the heads. Install the intake manifold gaskets, intake manifold, exhaust manifold gasket, exhaust manifold, valve cover gaskets and valve cover(s).
Fill the engine with oil then use a drill and priming shaft to prime the oil pump. For many engines, the oil pump drive shaft is accessible through the distributor hole. Have an assistant manually turn the crankshaft with a large wrench while you prime. Once you see oil pushing through the valve train, the engine is ready to install and fire up.
- Always use specialized engine assembly lube on friction surfaces, such as main/rod bearings, camshaft bearings, lifter bores and throughout the valve train. If your engine uses a flat-tappet cam (one that doesn't use roller-tipped lifters), use a chrome molybdenum-based break-in lube on the camshaft lobes.
Items you will need
- Full set of basic hand tools
- Full set of metric and standard sockets
- Tools for cutting, grinding and welding metal
- Fabrication and metal-forming equipment
- Torque wrench
- Clearance and measuring tools
- Auto Engine image by Andrew Breeden from Fotolia.com