Final Engine Assembly - Keeping it Clean

The importance of engine cleanliness

During a complete overhaul, parts such as the engine block and crankshaft may have needed machining. Most machine shops will clean those parts if requested. However, if you did not request it to be done, that responsibility falls on you.

Once you get your components back and are ready to assemble, it is crucial that you make sure all oil holes and passages are spotless. Remove any foreign material, dirt, dust or grit from machining or transport. When an engine is assembled clearances are tight. Because of this, you don’t want any debris on any engine part or component. Use solvent or mineral spirits with a brush to clean out any oil holes in the crankshaft and engine block. Then use compressed air blow them dry.

After all of the components are clean

Install the camshaft bearings in the block making sure that all oil holes line up. Some engines only use one front only cam bearing--others use none at all. In rare cases, camshaft bearings need to be line bored to fit the camshaft. Remove any burs that may have scraped off of the outside of the bearing while installing. Metal filings are just as bad as dirt if not worse. Using assembly oil, lube up the journals of the camshaft and install it. Check to make sure it spins freely and there are not interference issues. If there is any tightness, you may need to clearance the cam bearings yourself with a bearing scraper or fine grit sandpaper.

Next you should install the top half of the rear main seal (skip this step for one piece seals) as well as the top halves of all the main bearing shells. Also install the bottom bearings into the main bearing caps. When installing wipe the main bores out with solvent or mineral spirits. Use a lint free rag or paper towel to ensure no foreign material get inside the engine. Check and wipe the backsides of the bearing shells as well. Dirt or debris behind he bearing can hold the bearing up and cause improper bearing clearance and could cause the crank to not turn over during assembly. Lube the inserts in the block with assembly oil and carefully lower the crankshaft into the block.

Once the crankshaft is in place install the main caps and torque them in place. Be sure to torque them to the proper torque value and make sure they are not on backwards. Main caps can only go one way and can only go on in a certain order. The main caps should be numbered so that you know what position they go in. In most cases the bearing notches are aligned on the same side. This does not hold true in all engines so be sure to check during disassembly. All bearing clearances should be checked prior to assembly, but should also be checked at this stage as well. Now that the crankshaft is installed in the block it is a good idea to check the end play.

Install the cam timing components. There may be gears, gear and chain, or belt and sprockets for these components. Be sure to line up any timing marks according to factory specifications. Usually any timing gear will have a dot or line that must be properly lined up.

Prior to installing the piston rings, place a ring in the in the cylinder and using feeler gauges check the piston ring end gap. When installing the piston rings on the piston, install the expander first. Then install the top and bottom scraper rings. These rings are flexible so you can usually install the by hand. Using a ring expander install the remaining compression rings. It is important that you use the expander because the compression rings are brittle and can break easily. The top compression ring should be marked so that you know which way is up. If it is not the ring should be installed with the chamfer up.

Now install the lower connecting rod bearings in the rod caps and the uppers in the rod. Again wipe both the backs of the bearings and connecting rod saddles to make sure there is no dirt or debris. In some cases there is an oil squirt hole in the connecting rod. That hole is used to lubricate the camshaft so when installing the piston and rod assembly that should go towards the cam. However the pistons should be marked with a notch or arrow which will point to the front of the engine. Stagger the piston ring gaps and lubricate the piston skirts with assembly oil. Also lubricate the bearing shell in the connecting rod.  Then compress the piston rings using a piston ring compressor. It is a good idea to use a bolt boot or a piece of rubber tube to put over the connecting rod bolt. This will prevent accidental damage to the crankshaft when installing the piston and rod assembly. Any nick or ding on the crankshaft will damage the bearing and put metal debris into the engine. If bad enough it may prevent you from turning the engine over during assembly.

Lower each piston into each cylinder. Make sure that the cylinder you are working on is at bottom dead center. Use a rubber or dead blow mallet to gently tap the piston into the cylinder. If necessary you may need to re-tighten the ring compressor. Should a piston ring pop out of the compressor, loosen the compressor and start over. Do not force the ring into the cylinder. This can result in a broken ring and an unhappy engine builder. Guide the pistons in from the bottom until the connecting rod seats on the crankshaft. Once this is completed, remove the bolt boots and install the rod cap. Lubricate the bolts and torque it to the proper torque value. Install the oil pump and pickup tube at this stage and torque it to the proper torque value as well.

When installing the cylinder heads, check the gaskets for a “top” and/or “front”. If markings do not exist install the gasket aligning all oil and cooling passages. Make sure that if you are attempting to reuse the head bolts that they are not one time use bolts (torque-to-yield). Also make sure that all of the threads are clean. Check to see if any bolts go into the cooling system and apply sealant to the threads, otherwise use oil. Unless specified never use gasket spray or and type of gasket sealant on the head gaskets. This can prevent the gasket from sealing properly.

Engine contamination is one of the biggest causes in engine failure. So if at any point during the installation you notice that your hands have become dirty, clean them! Washing your hands takes only a couple of minutes but can save you many hours of having to redo the job.

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