| Jet-Boat Engine Repair -- New Engine Prep |
From "Weekend Mechanic"
episode WKM-113 |
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New Engine Prep With the engine disassembled, and the damage assessed, it was determined that this engine was severely damaged. The engine can be rebuilt, but will require significant parts replacement -- including cylinder head, block, piston and rod. Still, rebuilding the engine, rather than purchasing an entire new one, will result in savings of several hundred dollars. Though this project was originally given a difficulty rating of 3 out of a possible 5 on the intermediate difficulty-rating scale, the severity of the engine damage has raised that assessment to the most difficult level. It now rates 5 out of 5. 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 engine's negative battery cable before you begin work on any electrical or mechanical components. Steps: - New engine parts are purchased, but first the old engine was assessed for salvageable parts. A number of parts such as the impeller coupler (figure A), the flywheel, the starter and other components were saved from the original engine.
- First, flip the new engine block over and remove the bolts from the block (figure B).
- Remove the bottom portion of the block and inspect the block interior and bearing surfaces and seal grooves (figure C). In the block portion, identify the holes where pins are installed to hold the bearings in place.
Safety Alert: Note that these new-block halves usually have very sharp edges. Use caution when handling them. - Inspect the new crankshaft (figure D). On this crankshaft, the connecting rods come already connected to the shaft -- unlike an automotive crankshaft in which the rods are installed separately. Also note the roller bearings on this crankshaft (figure E).
Note: Return the crankshaft to its packaging to protect it and keep it clean until you're ready to install it. - Before installing the crankshaft into the block, the seals need to be installed onto the crankshaft. This particular seal has raised ridges on the surface (figure F) indicating which side is oriented to the outside. Carefully lower the seal onto the end of the crankshaft, making sure not to damage the seal or the crank.
- The opposite end of this crankshaft utilizes a double-seal (figure G). One of the pair has raised portions on one side -- again, indicating the side that should be oriented toward the outside. Carefully install the inner ring and the outer one, making certain that they are oriented correctly.
- With the seals installed, carefully lower the crankshaft into position in the block (figure H).
- Apply sealant to the mating surface of the lower half of the block (figure I), making sure to get complete coverage.
- Place the lower half onto the other half of the block (figure J), lowering it carefully into position.
- Using a pounds-per-inch torque wrench, tighten the crank-case bolts to the proper specifications (figure K), following the torque specs provided with the new engine block. Be certain to follow instructions for tightening the bolts in the proper sequence. Improper tightening of these bolts could warp the block.
- The last step before turning the block over to reassemble the internal components is to reattach the motor mounts (figure L).
- The next step is to install the pistons onto the connecting rods. First, use a lint-free shop-towel to cover the opening to the crank case to ensure that no debris falls in during the procedure.
- Install the roller bearing into the connecting rod (figure M).
- The piston is then installed onto the connecting rod using two shims (figure N). One shim is used at the front opening of the piston, the other at the rear.
- Hold the shims in place as you position the piston on the rod and slide the piston-pin in place in the piston assembly (figure O). Once the pin is installed, a retaining clip holds the pin in place. When installing the pistons, consult the manufacturer's instructions and make sure that they are installed in the proper orientation; not backwards.
- With all the pistons installed, put on a new base gasket (figure P). Always replace gaskets in an engine repair of this type. Do not reinstall old gaskets, even if they appear to be in good shape. Gaskets are relatively inexpensive -- much less expensive than a possible subsequent engine repair if a worn gasket should fail.
- With the gasket installed, lay the cylinder portion of the block in place (figure Q).
- Install a new cylinder head gasket (figure R).
- Torque the cylinder down to proper specification, and install the cylinder head (figure S).
- With the head in place, reinstall the starter (figure T).
- Install a new exhaust manifold gasket (figure U).
- Reinstall the exhaust manifold (figure V).
- On the other side of the block, install the intake manifold (figure W).
- Next, install the starter drive (figure X).
Important: Be sure to apply a small amount of lubricant to the drive-shaft before inserting it into the starter. - A key is inserted into the flywheel shaft to help ensure that the flywheel is positioned correctly. With the key in position, install the flywheel (figure Y ) and bolt it into place.
- Install a new gasket for the ignition-cover assembly (figure Z).
- Position the ignition-cover assembly and bolt it into place.
- Install the spark-plug wire harness.
- Finally, reinstall the impeller coupling.
In the segment that follows, the engine is reinstalled in the jet-boat, along with associated parts. Weekend Mechanic Factoid : In jet-boat and watercraft engines, the cylinder closest to the impeller is the one most likely to fail, since there is more heat generated in this portion of the engine.
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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