Rebuilding a Marine Engine

13 Easy Steps to Rebuilding a 2-Stroke Cycle Marine Engine

Whether you are a 2-stroke cycle engine owner or a marine engineer, there comes a time when you need to rebuild your 2-stroke marine engine either in your maintenance schedule or due to an unplanned engine failure. While two-stroke engines are relatively simple mechanical devices, rebuilding them requires knowledge of how they work, attention to detail, and a systematic approach.

Here are 13 easy steps to rebuilding, repairing or overhauling a 2-stroke cycle engine on board a marine vessel:

1 | Washing the parts

Washing the parts is a process that includes decarbonizing of engine block, piston, top cylinder head, blower, skirting, sump, and every other accessories in preparation to rebuilding an engine.

2 | Bedding of the crank shaft

Bedding of the crank shaft has to do with loosening of the main bearing – extracting the old shell bearing, inspecting and installing a new one according to its part number.

After installation, ensure to retighten the main bearing bolt according to its specification.

3 | Refurbishing of cylinder head

Refurbishing of cylinder head is a very vital step with the following procedure:

1. Dismantling of rocker arm bracket
2. Dismantling of cam-follower
3. Extraction of rocker arm
4. Extraction of poppet valve
5. Extraction of poppet valve oil seal
6. Decarbonizing of top cylinder head and its accessories
7. Pressure testing of cylinder head
8. Inspection of poppet valve, valve guide and poppet valve seat insert.

4 | Bursting of rings

After decarbonizing the piston, the next step is to inspect the piston groove before installation of new rings by:

1. Picking up ring pack
2. Opening and checking it out for the rings.
3. Separate the rings and check out for the mark.

5 | Installation of piston to sleeve

When done with rings installation, turn the sleeve upside down (the installation of piston has to start from BTC and not TDC). Place the piston installer on the sleeve, lubricate the rings with required lubricants; hold it from the connecting rod end and gently insert it into the installer. Apply a little force for the rings to compress from the installer to the sleeve.

6 | Installation of power pack

Power pack is the combination of rings, piston, connecting rod and sleeve; installed together. To install the power pack, first loosen out the nut on the connecting rod, remove the connecting rod cap and install a bearing shell with its correct part number. Apply lubricant on the bearing and the power pack body for easy installation. Insert it into an engine block; directing the connecting rod to connecting rod journal of the crankshaft. Install the connecting rod cap and tighten its nut to a required specification.

7 | Installation of oil pump, regulator valve and relief valve

Once the main bearings are completely changed, and power pack has been installed and torqued correctly, oil is applied to the gear connected to crankshaft gear at the front of the engine. After installation, tighten the oil pump nut to a required tightening value at the right side of the engine, while oil relief is at the left side.

8 | Installation of skirting and sump

Following the completion of oil pump, regulator and relief valve installation, skirting and sump are ready for installation with a gasket to prevent oil leakage during engine operation and the bolts tightened to required specification.

9 | Installation of the refurbished cylinder head

With cylinder head completely refurbished and engine block completely decarbonized, carefully install water ferrous, compression gasket and compression seal according to its part number. With pilot bolt on the engine block, carefully pick the top cylinder head and install it correctly together with the cylinder head bolt. Tighten its bolt according to the sequences and specifications. Then, fill and bleed the cooling system to remove air. Failure to do so will cause the top cylinder head to crack.

10 | Installation of refurbished blower

With your gasket placed on the engine block, pick up your blower and carefully install it; tighten your bolt to its specification. Then, install blower shaft; and connect air emergency shut off.

11 | Installation of injectors

Check for part number; install as required with injector clamp, tightening it to its specification. Connect fuel line; and bleed the line to remove air.

12 | Connection of valve bridge and rocker arm

With injectors completely installed, carefully install valve bridge, rocker arm shaft and rocker arm bracket; then, tighten it to its required value.

13 | Valve and injector clearance

Valve lash or valve clearance is the gap between the rocker arms and the valve tappet.

Please, note that this clearance must be tightly controlled. If it is too little, the valves may not seat properly. However, if it is too much, you create valve train noise, and excess load on the valves and valve components.

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