How to: Replace a piston and sleeve

Radio Control Car Action, Dec 2001 by Vogel, Greg

TO

Make your engine run like new

Is it difficult to work on an engine? Could I do it? Should I try it myself? Do you sell Pokemon cards? Back in my behind-thecounter days at the hobby shop, these were the most commonly asked questions. My answer to all of those questions was "Maybe," because the real answers lay within the abilities of the person doing the asking (for the record, we did sell Pokemon cards, but I just liked to mess with the kids' minds). In my experience, with a little instruction, anyone can work on a nitro engine. That's where this "how-to" comes in; the following will help even nitro novices complete the most common (and most beneficial) engine-maintenance tasks-piston and sleeve replacement. After you've completed this job, you'll know your engine inside and out, and it will run like new!

Step 1. Remove the engine from the car

An engine is usually held in with four screws on the bottom and Is connected to the throttle linkage and exhaust. Remove the retaining hardware and yank the engine out of the vehicle.

Step 2. Remove the heat-sink head

Most heads are held on with four screws, and some have as many as six. Access the screws from the top; remove each one and then gently pull the head straight up and off the engine case.

Step 3. Remove the pull-starter

If your engine doesn't have a pull-starter, move on to step 4. Starter assemblies are held on with three or four screws on the back. Remove the screws and pull the assembly off the back of the engine. While removing the starter, I like to slip a flat screwdriver between the starter and the backplate and apply pressure to the inner spool. By doing this, prevent the spring and spool from uncoiling (a huge

headache!). Having removed the starter, stretch a rubber band around it to prevent It from uncoiling.

Step 4. Remove the backplate

The backplate Is held on with four screws that you unscrew to remove It. If your engine has a pull-starter, when you remove the backplate, watch for the one-way bearing falling out. If It falls out, note how it comes out because you'll want to reinstall It In in its original position. Also note the flat part on the inside of the backplate; it always faces upward to allow the piston to clear the backplate when the piston cycles.

Step 5. Slip the sleeve out

Depending on your engines age and how much you've run it, this part can be tricky. In this step, we'll remove the sleeve. If you look down at the top of the engine, youll see a brasscolored ring-the sleeve-with an aluminum circle-the piston-in Its center. Push the piston down with one finger. Now apply pressure to the sleeve's Inner wall and pull the sleeve out. It should slide right out; If It doesn't, you may have to pull It out of the engine case by grabbing its top with a large pair of pliers and gently rocking It free.

Step 6. Remove the piston and rod

This step is also a little tricky, so take your time. Hold the engine upside-down so the piston Is at the bottom. Grab the rod with a pair of long-nose pliers, and gently rock it off the crankpin. You may need to rotate the crank slightly to remove the piston and rod assembly (this will depend on your engine). When the rod is clear of the pin, the assembly should slide right out of the top of the engine. Note how the piston comes out; many are notched and can be Installed only In a certain way, and you'll want to reinstall the new piston correctly.

Step 7. Assemble the new piston and rod

If you're replacing the piston and sleeve, consider also replacing the connecting rod and wristpin. You could use the old one if it isn't damaged, but this is a highly stressed part and could break when you run it with a new-tight-piston and sleeve. If you use it and It does

break, not only will you have to replace the rod, but you'll need a new piston and sleeve as well because they are usually damaged when the rod falls.

Assembling these parts is fairly easy. Put the connecting rod Into the piston and slide the wristpin through the larger hole in the piston and then through the rod to the other side. Now use a needle-nose pliers to clip the wristpin Into the retaining clip. This can be tricky; the clip can be very stubborn and might pop out. I complete this step holding the parts in a large clear bat, if the clip pops out, I have a better chance of finding it.

Step 8. Install the new piston assembly

Some piston/sleeve assemblies are notched so they clear the crankshaft when they rotate. When you reinstall the assembly, make certain that the notch is In the correct position. Just slip the assembly into the engine, and use needle-nose pliers to put the connecting rod on the crankpin.

Step 9. Slip the sleeve in

Most sleeves are aligned In the engine by a pin; note where the pin is in the crankcase, and align it with the notch in the sleeve and slide the sleeve in. You may have to rock the piston to get the sleeve to slide all the way in. Use the eraser side of a pencil to rock the piston into place.

Step 10. Button it up

The major surgery has been completed.