| Jet-Boat Engine Repair -- Engine Disassembly |
From "Weekend Mechanic"
episode WKM-113 |
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Engine Disassembly With the engine removed from the boat, disassembly can begin to determine the extent and nature of the engine damage. Important: Included below are the steps in this engine-repair procedure as shown in the episode. These steps are general guidelines that are applicable to most similar engines. With any particular engine, there may be procedures, specifications, settings, tolerances, components, etc. that are specific to that boat or engine. There are also variations according to the type and brand of repair components you select. Always consult your service manual when undertaking significant engine repairs, and read and follow the manufacturer's directions and precautions that come with your kit or replacement parts. Safety Alert: Always wear eye protection, and follow proper safety precautions, when working with power tools. Safety Alert: As a standard safety precaution, always disconnect the vehicle's negative battery cable before you begin work on any electrical or mechanical components.
Steps:
- Begin the disassembly by unbolting and removing the exhaust manifold (figure A). With the manifold removed, residual sealer -- without the presence of a manifold gasket -- is a first sign of what might have caused this engine failure.
- The next step is to unbolt and remove the engine cover (figure B).
- Next, remove the top plate of the cylinder head. Close inspection of the internal side of the cylinder head (figure C) reveals copious amounts of loose metal particles (figure D) -- presumably fragments of a destroyed piston.
- In fact, inspection of the pistons themselves confirms the severity of the problem. While the #1 and #2 pistons are in the down position, the #3 piston is raised and virtually shattered into metal fragments (figure E).
- Thus far, the damage indicates that the block and at least one piston will need to be replaced.
- Next, remove the bolts on the cylinder head (figure F), carefully pry the cylinder head loose and lift it off the bottom portion of the engine (figure G).
- Inspecting the inside of the cylinder head (figure H) confirms that the #3 piston is destroyed.
- The wall of the #3 cylinder has a large hole (figure I). By deduction, it would appear that, in an earlier engine repair, the engine was disassembled and then later reassembled without replacing the gaskets -- with only a sealer used on the mating surfaces. Or the gasket was faulty. On a 2-cycle engine like this one, the reliable sealing with the proper gaskets is critical to the life of the engine. The resulting air-leak caused the engine to run way too lean (i.e., receiving to much air in the fuel/air ratio), which in turn caused the engine to run way too hot and sustain this serious damage.
- The replacement-parts list continues to grow for this repair. It now includes cylinder head, block, piston and rod. The next decision is whether to replace or rebuild the engine. That decision is made in the segment that follows.
In the segment that follows, the new engine is assembled and prepared for installation.
RESOURCES :
The Haynes Small Engine Repair Manual
ISBN: 1850106665
Author: Curt Choate, John H. Haynes
Haynes Publishing Group
Chilton's Small Engine Repair Up to 20 Hp
Model: 0801983258
Author: Kerry A. Freeman
Nichols Publishing
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