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Old 07-11-2010, 06:11 PM   #1
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Questions?? Help! Repair or replace, DBX engine 2.5-gal

I need help from experienced people. My question is, if I replace only the rod and bearings, will this thing likely run another couple gallons, or is it going to die again right away? Maybe I can replace only the bearings? In particular, is the crank pin too bad? Currently the rod is rubbing the crank case, and it is eating glow plugs every like 2 minutes. Despite the scored piston, the compression is fantastic. I don't know if the scores on the piston are from overheating at some point, or from the rear bearing retainer going through the motor when it came apart (notice missing parts of the bearing ball retainer). My options are put $50 into this motor, if it will run a few more gallons, or just replace it with an OS CV-R .18. I don't care if it runs top performance, I DO care that it runs reliably. Opinions wanted!

For the record, this is the stock Kyosho DBX engine and it has almost 2.5 gal of Traxxas 20% through it. There was zero dirt inside the motor.

Rear bearing, broken ball retainer:


Crank pin:


Crank pin:




Notice score marks (bottom of picture) where the rod was rubbing the crank case:








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Old 07-11-2010, 07:01 PM   #2
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What time do the RC stores open? Whatever time that may be, start engine shopping. There isn't anything worth fixing.

crankcase - shot
crankshaft - shot
bearings - shot
rod - shot
piston - TOAST

It's been run too lean..............the top of the piston shows extended detonation.
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Old 07-12-2010, 04:54 AM   #3
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That bad huh? Darn...
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Old 07-12-2010, 06:30 AM   #4
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Ya that thing is toast. Eating plugs and won't run are signs that it's time to try something new. The rear bearing lost some of it's ball bearings. If they came loose while the engine was running then many parts can be damaged. But by just looking atthe pictures the p/s are shot and the crank pin looks like it has lots of wear on it so I would say just start new. Those engines a are a p in the a anyway.
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Old 07-12-2010, 10:53 AM   #5
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If you look closely at the bearing, all the balls are there but the metal spacer that keeps them all spaced out is missing pieces, so the balls have collected together. I wonder why it died so early, 2.5 gal seems early for a bearing to fail.... Hopefully the OS engine will last longer!
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Old 07-12-2010, 01:01 PM   #6
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After the looking at those pictures its a paper weight .
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Old 07-12-2010, 02:35 PM   #7
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Just a heads up............ those oem kyosho motors have a funky 3-foot motor mount that is part of the engine making is dam near impossible to bolt a stanard .12-.18 into those cars........ BUT kyosho sells an optional adaptor motor mount just for those cars so you can put a standard motor in it..... highly reccomended, i would do a os.18 and that motor mount, those stock motors blow and are expensive, btdt last year on one of these cars............ just trying to help.
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Old 07-12-2010, 03:45 PM   #8
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Quote:
Originally Posted by casterdriver View Post
Just a heads up............ those oem kyosho motors have a funky 3-foot motor mount that is part of the engine making is dam near impossible to bolt a stanard .12-.18 into those cars........ BUT kyosho sells an optional adaptor motor mount just for those cars so you can put a standard motor in it..... highly reccomended, i would do a os.18 and that motor mount, those stock motors blow and are expensive, btdt last year on one of these cars............ just trying to help.
You described exactly what I am going to do. My understanding is the stock DBX exhaust will even fit the OS CV-R. The thing that bugs me is I think that rear bearing failing was the root of all the problems. I am tempted to find the cheapest engine bearings I can find, plus a new rod and just see how long it will run for. Anyone know where to get super cheap bearings ($10 range)?
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Old 07-12-2010, 06:20 PM   #9
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http://www.avidrc.com/

Motor looks toast tho.
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Old 07-16-2010, 06:49 AM   #10
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After some thinking, I believe I could have saved this motor if I had known the bearings were going bad, I just didn't suspect bearings to be failing after only 2.5 gal, especially to the point that metal parts were coming off. I started having tuning issues and after looking closely at the parts, I think the front bearing had an air leak and that was the cause of my tuning issues. The tuning issues should have been a hint that the bearings were going bad! I can see light in between the inner race and the bearing seal on the front bearing and I'll bet there was some air coming in there, which is probably why I had such a hard time with a lean idle. Oh well, with the next motor I'll watch the bearings more closely!
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