Convert a pull-start to bump-start

Radio Control Car Action, Aug 2001 by Hastings, Bob

HOW TO

Reduce weight and improve acceleration by Bob Hastings

YOU'LL NEED

After-run oil

Non-pull-start backplate

Nitro Wash or denatured alcohol

High-temp sealant

Rotary tool with cutoff wheel or a replacement crankshaft for a non-- pull-start engine

Safety glasses

WARNING!

Before you touch anything, keep in mind that if you cut

the crankshaft as described here, you won't be able to go back to your recoil starter unless you replace the pull-start crankshaft. If you aren't sure about your future plans or if you're uncomfortable about taking a rotary tool to your crankshaft, buy a non-pull-start crankshaft now. Some vehicles also require the use of a different flywheel and engine mount, so be sure to consult your vehicle's manual before you start.

There's no denying the appeal of a pull-start engine; grab your fuel bottle and a glow igniter and go have some fun. Considering the low cost, portability and overall convenience of a pull-start engine, enjoying the hobby couldn't be simpler. However, some vehicles can't accept a pull-start engine because of the extra room required for the starter mechanism. In addition, the weight and increased frictional load of a pull-starter reduces overall engine performance. Converting to bump-start is the solution-one that you'll find is not all that difficult as long as you're comfortable with the basics of nitro-engine tear-- down. To demonstrate, I'll explain the conversion for the .15 I run in my RC1OGT RTR, but the process is virtually the same for any pull-start engine.

Step 1. Clean the engine

After removing your engine from the chassis, plug the carburetor intake and exhaust port with wadded up pieces of paper towel to prevent debris from entering the engine.

Wash the outside of the engine with a cleaner designed for nitro engines, such as denatured alcohol. Carefully work exterior grime off the case and away from the front crank bearing. Even a little dirt or debris washed into the bearings can cause them to fall. When the engine is clean, remove the clutch bell and shoes from the engine and set them aside.

Step 2. Remove the clutch nut

Use a large pair of channel-lock pliers to grasp the outside of the flywheel. While maintaining pressure with the pliers, remove the clutch nut and flywheel. If the flywheel turns when you try to remove the clutch nut, install a piston-locking tool; this will hold pressure against the piston and allow you to loosen the clutch nut.

If the thought of grabbing your flywheel with pliers makes you shudder, try this strap wrench from Bruckner Hobbies, a dynamite piston-locking tool, or use an OFNA flywheel wrench.

Step 3. Remove the head

Remove the cooling-head retaining screws and carefully take the head off the engine. There are usually head-clearance shims between the head and the piston sleeve. Don't lose them! You will have to reinstall them later.

Step 4. Extract the sleeve

If the piston sleeve isn't indexed to the engine's case with a pin or machined-in marks, draw a line across the sleeve and case with a permanent marker so you'll be able to reassemble the parts properly later. Gently pull the recoil starter; the sleeve should rise out of the engine case with the piston's up-travel (if the sleeve doesn't come up, the piston and sleeve might be worn). Grab the sleeve and pull it straight out of the case.

Step 5. Remove the starter assembly

Remove the pull-starter from the back of the engine. A credit card pushed between the engine case and pull-starter will prevent the recoil spring from unraveling as you remove It. Once it's off, wrap a rubber band or some tape around it to prevent it from uncoiling In your spare-parts box. Next, remove the engine backplate. Be careful to avoid damaging the engine seals when you separate the cover from the engine.

Step 6. Remove the piston

Spin the crankshaft so that the piston is at the top of the engine case, and then

slide the connecting rod off the crankpin.

Step 7. Push the crankshaft out

Give the threaded end of the crankshaft a gentle tap to pop it out of Its bearings. As you do this, hold the engine with one hand over the backplate opening to catch the crank.

Step 8. Cut the crankpin

Pad the jaws of a vise with a rag to avoid damaging the threads or the crankshaft, and clamp the crankshaft into the vise. Strap on your safety glasses because now it's time to cut the crankshaft. The best tool for the job is a rotary tool equipped with a cutoff wheel. Be sure to keep the cutoff wheel square to the crankshaft, and work slowly to minimize friction and heat.

Remove only the portion of the crankshaft that interfaces with the pull-starter. When you've finished cutting, use a piece of fine sandpaper or a metal file to remove anv burrs. and then spray the crankshaft with nitro cleaner to remove any fine metal dust that collected while you cut.

Step 9. Test-fit the backplate

Coat the crankshaft with after-run oil and fit it into the engine case, making sure that it's fully seated in the bearings. Hold the non-pullstart backplate in place, and turn the crankshaft gently to be sure that It doesn't rub the crankpin. If the crankshaft rubs the backplate, remove It and shave a little more material off the crank.