Fix It

When rebuilding an engine, the clearance between the main bearings and the crankshafts main bearing journals are critical. Too much clearance results in engine knocks, while not enough clearance results in burned bearings because they cannot get proper lubrication. These clearances are especially important to measure and adjust after machining the crankshaft to remove imperfections. Although it sounds complicated, measuring the clearances and adjusting them to specifications is really quite simple.

Instructions

1

Dip a set of standard size main bearings in engine oil and slip them into the block and main bearing caps.

2

Set the crankshaft in the block, ensuring that the main bearing journals of the crankshaft sit on the main bearings in the block.

3

Smear a light coating of grease across the center of the bearing journals on the crankshaft. Put a string of Plastigauge in the grease on each main bearing journal. The grease will keep the Plastigauge in place.

4

Install each bearing cap in its original position, thread the bearing cap bolts into the block through the bearing caps. Tighten the bearing caps with any tools necessary from a toolkit. Torque the main bearing cap bolts with a torque wrench.

5

Remove the main bearing caps, one bearing cap at a time. Measure the Plastigauge with the built in scale on the Plastigauge packaging. Subtract the recommended factory main bearing clearance from the Plastigauge reading. The result will be the size of the oversize bearing needed for that particular main bearing journal. Repeat for all main bearing caps.

6

Remove the crankshaft. Slip the appropriate over-sized bearing in the block required for each crankshaft journal, depending on their individual Plastigauge readings, after dipping them in motor oil. Slide the other half of the bearing into the main bearing cap after dipping it in motor oil. Plastigauge each bearing again to ensure all bearing clearances are correct before proceeding any further. Adjust the bearing sizes as needed.

Rebuilding a small engine can be more cost-effective than replacing it. To determine if the small engine is suitable for rebuilding, consider how serious the damage is, the amount of wear on the engine and what parts need to be replaced. Youll also need to make sure you have the right tools on hand to do the job.

Basic Tools

The basic tools and equipment needed to rebuild an engine include a set of hand tools, such as screwdrivers and wrenches; a torque wrench; feeler gauges; a ring compressor and a ring expander. You can also simplify the task of rebuilding a small engine by purchasing the parts you will need in an engine kit. A kit comes with bearings, pistons, rings, gear set, timing chain, gaskets, valve seals, camshaft, oil pump, lifters, and other necessary parts.

Crankshaft Bearings

Rebuilding a small engine will most likely require you to install new crankshaft bearings. As you detach the old bearings, determine if they are excessively damaged. If they have scoring, debris, dirt embedded on them, flaking or pitting, then you may need a new set.

Piston Rings

Oil burning and low compression are indications of worn rings. To restore the compression in the engine, this means you must replace the piston rings. Replacement rings are available in different sizes and materials. Most rings are made of cast iron, although there are engines that have steel rings. Rings can come plain-faced, with a molybdenum inlay, chrome-plated, or nitrated. When purchasing new rings, you should try to get them as close to the original rings as you can. Take the original rings with you when you buy new ones to make this task easier.

Camshaft

When replacing the camshaft, you can install either a performance camshaft or a stock replacement. Performance camshafts provide increased duration and lift for additional power. You should follow the recommendations of the camshaft supplier for the proper duration and lift.