HPI Crawler King - 1979 Ford F-150 - # 120099 (Radio Controlled Model Review)

Buying a Used HPI Rock Crawler (and What to look for)

   There are essentially three reasons you might want to buy a used HPI Rock Crawler; you may be a collector, looking to restore and display it; restore and sell for a profit; or simply restore and race an iconic vintage model. Personally, I used to get a buzz out of restoring an old clapped-out model, installing modern day electrics and maybe a few hop-ups, then showing the gang at our local club, just how competitive those old models could still be.

   Cheap, pre-loved bargain models, parts and spares are always coming up for sale, but once you have made your purchase, the one thing you will always need, is an instruction manual. If not supplied with your purchase, they can often be downloaded from the HPI website, or purchased separately on eBay. With an instruction manual, any problems with your model Rock Crawler you may discover, can easily be fixed.

Make a General Visual Inspection

   When you receive your used HPI model, make a general visual inspection of the chassis, front and rear wishbones, suspension shock towers etc, for any broken parts that may need to be replaced. Then, take a screwdriver and box spanner and check each self tapping screw and nut for security, taking care not to over tighten.

   Next, for those HPI models with oil filled shock absorbers, remove them from the chassis and dismantle the coil springs. The damper shafts should push in and pull out with a smooth action. If you feel a jolt as you change direction, this means the oil has leaked out and must be topped up. At the same time, change the O-Ring seals to prevent more leakage. Also check the damper shafts for damage. If they are scratched, change them as soon as possible.

Check the Body-Shell

   If the body shell of your Rock Crawler is broken, ripped or damaged in any way, this can be easily repaired with rubber solution glue. Also, for added protection and if available for your model, fit an under guard to stop dirt and gravel entering the chassis.

Drive Shafts and Turnbuckles

   Examine the drive shafts for wear and replace as required. If possible, change them for titanium. The steel shafts wear and bend too easily.

Examine the Drive System

   The gearbox of your used Rock Crawler should be opened up to check for damaged gears and wear. If there is excessive backlash in the gearing, these should be replaced. A thin coat of grease on the gears is enough to allow smooth operation and reduce further wear.

Pinions and Spur Gears

   Gears are a weakness on all RC models. Head on collisions can easily damage the gear teeth on nylon and plastic spur gears. Heavy impacts can also loosen the nuts or self tapping screws that hold the motor in Position, allowing the pinion gear to pull out of mesh slightly and rip the tops off the teeth on your spur gear. To minimise this possibility, fit bolts with locking nuts to the motor mount and remember to check them for security after every two or three runs.

Steering Servo and Servo-Saver

   The steering servo is also prone to damage, the fragile gear teeth of the servo can be broken off, rendering your expensive servo useless, so be sure to obtain a good quality "Servo Saver". Check out my Servo Information article.

Don't Forget those Bearings

   If your used HPI Rock Crawler comes with plastic and sintered brass bushings (ring type bearings), check the shafts that run in them for wear. Dust and grit can get into these bearings and abrade the shafts. Therefore, you should replace them all with shielded ball bearings. If the model has been run with ring type bearings, you may have to change all the axles and driveshafts. For more information, take a look at my article, How to get the best from your Bearings.