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Model Forum / Radio Controlled / Land Models / January 2007Ofna MBX Ultra, , little drivetrain problem.
My kid has an Ofna MBX Ultra with a soon-to-be-replaced force .26. I removed the failing 2-speed center and replaced it with a center diff. The problem is that the spur on the center diff is so small that even with a 15 or 16 tooth bell, the engine can't be moved far enough for decent gear mesh. I've looked for different spur gears, but could only find a smaller one. Anyone have an idea of how to fix this? Kinda wanted to avoid filing on the chassis, but I'm not finding any other answers. Thanks. Also. I know I asked before but can't find the threads, but where, besides ebay, are people getting the Mach 427 or sportworks engines? I'm thinking about either one of them or an axial motor for this ride. . .Thanks. . Inline..................... > My kid has an Ofna MBX Ultra with a soon-to-be-replaced force .26. I > removed the failing 2-speed center and replaced it with a center diff. [quoted text clipped - 4 lines] > wanted to avoid filing on the chassis, but I'm not finding any other > answers. Thanks. The motor mount slots in the chassis can be lengthened with a dremmel so you can slide the motor over further. If they won't mesh up, it sounds like you might have the wrong spur installed? > Also. I know I asked before but can't find the threads, but where, > besides ebay, are people getting the Mach 427 or sportworks engines? > I'm thinking about either one of them or an axial motor for this ride. > . .Thanks. . You can purchase either of them from www.horizonhobby.com although they can be had much cheaper on e-bay. I grab my 427's on e-bay and Sportwerks .26's from the local hobby shop. If I had to choose between the two right now, I'd say go with the 427. It's just a tad bit hotter than the SWK .26 performance-wise and gets MUCH better fuel economy. HTH, Doc >Inline..................... > [quoted text clipped - 10 lines] >can slide the motor over further. If they won't mesh up, it sounds like you >might have the wrong spur installed? Yea, I did that, ,, but the mounts are getting awful close to the rear driveline. I've not been able to find a BIGGER spur, , just smaller. . BTW, I re-pinched the sleeve on the force .26. . .got back much of the compression, , ,and a bunch of power, , , ,, until, , , , the piston seized and the crank broke at the pin. It was WAY fat on the main needle, but it wasn't a hydraulic lock. I probably got the sleeve out-of-round, , ,but the block held it round when it was cold, , only to let it go back to out-of-round once it warmed up, causing the seize. Siezed the slug in the sleeve, broke the crank, marred the crap out of the conrod, , and knocked a hole in the block. I'd say it's a little past chewing gum and duct tape to get it working again. . good learning experience though. . >> Also. I know I asked before but can't find the threads, but where, >> besides ebay, are people getting the Mach 427 or sportworks engines? [quoted text clipped - 10 lines] > >Doc Thanks, ,, I'm checking them out right now.. . not a bad price on the 427. It's kinda a toss-up between that and the Axial, , , I could save a little by going wit the Axial,, , which I have not read anything abd about, , but, , ,the Axial has a 3-needle carb, , ,a little more complicated in the tune department, but it does come with a pullstart. Thanks for the help. . . >>Inline..................... >> [quoted text clipped - 25 lines] > little past chewing gum and duct tape to get it working again. . good > learning experience though. . <snip> Hey how did you re-pinch the sleeve??!?!?! I'm hell curious! Cheers Dre >>>Inline..................... >>> [quoted text clipped - 31 lines] > >Cheers Dre First, , like all scientific endevors, , start with a few shots of tequilla. Next, find a couple small, narrow wormscrew type hoseclamps that are just big enough to go around the sleeve. Place one around the flange (to portion of the sleeve that seats on the top of the block), and tighten it a bit. You should see a marked difference in how far you can fit the piston up into the sleeve (the clamp is tight enough when the piston, being lightly pushed stops hard about 1/8 of an inch from TDC, which can be seen from the wear lines in the sleeve). Place teh second clapm just below the first, and tighten just enough that you see more piston'liner tightness. Then, you heat the sleeve evenly to 400+ degrees F (remove the piston first). I did this on the stove, but a heat gun will probably work just as well. Once this temp is obtained, quench the sleeve quickly in cold water. This will make the sleeve hold it's collapsed position. Re-assemble the motor and break it in again. Now is where you learn the value of those lessons we learned in school that told you to read all the directions BEFORE you start.. . Keep in mind, , Mine did not work out that well, so I would not suggest this to be done on any motor unless you won't mind (Or maybe even will enjoy) seeing it bite the big one. It is quite possible my method here is the dumbest thing you will read all year, , I am not a rocket scientist, , ,I break things often. . Honestly, Once I got the motor back together and running, I was a little too curious about seeing how much power I re-gained, and the idea of re-breaking it in completely eluded me. I believe that was the major cause of the breakage, I've heard of new engines breaking the rod or crankpin because of hard running when the fit is still real tight. I read somewhere about someone doing the re-pinch, then submerging the engine, with no head, in MMO and turning it for hours with a cordless drill. Sounds weird, , but I guess this 'could' insure that here was not excessive interference once the engine is powered up. I'll probably try that with my next one. L8r >>>>Inline..................... >>>> [quoted text clipped - 65 lines] > up. I'll probably try that with my next one. > L8r Well I'll be buggered! I never even thought of doing anything like that! I can see how it would work too, you can repair car panels with a dent in them like this. Heat the area, then cool it quickly, this shrinks the metal and pops the dent out. I have a few old/stuffed engines lying around so I reckon I'll give it a try when I'm bored one day! Thanks for the info! Cheers Dre |
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