| Lawnmower Engine Repair -- Engine Completion and Installation |
From "Weekend Mechanic"
episode WKM-104 |
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With the new oversized piston and new rod installed in the refurbished block, the new components need to be checked for spec, and the external engine parts and accessories re-installed before the engine can be put back in the mower. Following are the major steps in the in the engine-completion and reinstallation as shown in the episode. - For this engine, the piston is set (for top-dead-center compression-stroke) 1/4-inch down in the block. This is the proper setting for this engine as prescribed in this mower's service manual. With the piston set in this location, the valve-clearance adjustment needs to be checked.
- Locate the valve tappet and valve stem inside the engine (figure A). The gap between these two is the valve clearance. Use the appropriate thickness on a feeler gauge to check the clearance (figure B). You should feel a slight drag as you pull the feeler gauge through the gap.
- Next, the exhaust valve needs to be installed and checked. Apply lapping compound to the valve (figure C) and seat it in the block (figure D).
- Use a valve-lapping tool to rotate the valve in the block.
- Check the exhaust valve for any wear. If it is good condition, clean the lapping compound from the block and replace the valve.
- As before, check the valve clearance using a feeler gauge. If the valve needed adjustment, it could be achieved by grinding down the end of the valve stem (figure E) using a bench grinder until the proper gap adjustment is achieved.
- With both valves adjusted, the next step is to install the valve springs. Install the springs using a specialized valve-spring tool (figure F).
- Install a breather valve along with a new gasket (figure G).
- Re-install the carburetor, again with a new gasket.
- Bolt the muffler in place (figure H).
- Attach the flywheel (figure I) and the fan assembly (figure J).
- When re-attaching the fan assembly, be certain to tighten the bolts to proper specs (according to your service manual) using a torque wrench (figure K).
- Re-install the breather screen.
- Re-install the coil (figure L).
- Re-install the starter (figure M).
- When re-installing the head, be sure to install a new replacement head gasket (figure N).
- Torque-tighten the head bolts to the proper specs (figure O), according to those listed in your service manual.
- Install a new air filter, and re-install the upper engine housing (figure P).
- With the engine fully re-assembled, it is ready to be mounted back on the mower (figure Q).
- Re-connect the fuel line and electrical wiring.
- Re-attach the battery cables and ground wire.
- Re-install the grill and hood assembly.
- As part of this engine refurbishment, routine maintenance was done as well, including installing a new fuel filter and new sparkplugs.
With the repair complete, start the engine and give the mower a trial run. For the initial run, operate the engine for only about three to five hours. After the trial run, change the engine oil. The mower engine should now be good for several more years of service.
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
Small Gas Engine Repair
Model: 0830641424
Author: Paul "How to Troubleshoot" Dempsey
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