let me start off by saying that, i have had my 4.6 savage x for a year, love the wheelies and the power. i have changed the suspension uprights forward and rear, so with the original roto start on the car, the motor is driven directly via the roto start shaft and starter motor or your drill gun on forward rotation. that being said. i twisted off or broke the tip off the stater shaft, cause of the extreme angle the upright put the shaft at while starting. i ordered the replacement shaft and soon found out the replacement was changed to a dog-bone style and NOT the original rounded hex head drive that came with the car!! very frustrating to say the least. some hours later after i couldn't find the part on any of the major hobbie shops i deal with didn't call me back after i called and left a trouble call with them. i was pissed and thinking of selling the car. I finally called HPI. the tech told me i had one of many cars that were sold, and hpi didn't tell anyone they changed the back-plate configuration back to a previous style of set up inside. well i took the parts list he gave me and looked up the picture parts list and compared the parts with the originals as well as compared them to the parts of the 5.9 motor, i have the 4.6. and guess what the parts he told me to replace were the same ones that came originally on the car. THE ONE WAY BEARING IS THE ONLY THING I HAD TO REPLACE. AND THE 5.9 ONE WAY BEARING IS THE SAME AS 4.6 AND WAY CHEAPER. BUY THE 5.9 ONE WAY BEARING. don't forget the direction of installing the one way bearing. ALSO i had bought the ofna roto- start back-plate. it was cheaper and at a corrected angle for the new dog-bone starter shaft. i also have had to reverse the drill motor to accommodate the new starter set up. i have had the new setup for 2 days and so far so good.
For sure, this is one of the worst investments when your one-way bearing fails. Not only is it extremely overpriced, it fails repeatedly. With all the one-way bearing failures, the price really adds up. I have two HPI nitro engines; an F3.5 with a pull-start, and an F4.6 with a roto-start. I'm on my second one-way bearing in the F4.6, but the second one has held up pretty well. As for the F3.5, I'm on my third so far, as well as my third pull-start, because they break all the time. If you want to save yourself money, there's a solution that's actually quite simple; buy a lock nut that has a 12mm outer hex, with about a 5.5mm inner diameter, so that the threads can be sanded down to a smooth surface with a Dremel, resulting in a 6mm inner diameter. After that, it must be test fitted on the start shaft on your engine. If it's snug, the next thing you have to do is find an M4 grub screw and drill M4 threads into the new nut. Once that's done and the grub screw fits, the next thing is to use a Dremel to create a flat surface on the start shaft, so the grub screw can keep the nut in one place. This is similar to a pinion gear on an electric motor. Once you've created the flat surface, place the nut on the start shaft, put some thread lock on the grub screw, insert the grub screw, and bam! You now have a "one-way bearing" that'll never fail. After you've secured it on the shaft and all, re-install the pull-start or roto-start system, and celebrate by running your nitro car until you run out of all the fuel you brought with you!