Noob Mistake - Pretty sure I seized engine!

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A

aelliott70

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Messages
18
Location
Los Angeles, CA
I'm a total noob to 5th scale (and gas engines). I haven't had an RC car in 30 years. I Wanted to get back into it, and why not go with something I've always wanted, a large scale gas RC, so I went with a DBXL 2.0. I stumbled on a good deal on a preowned rig at my local hobby shop, and pulled the trigger. I've been driving it for about 3 months without issue. I never even tuned it. The mechanic at the hobby shop tuned it for me, but that was in August, and using the VP premixed fuel. I've since switched to pump fuel, and its gotten COLD. The engine started running like crap, and a lot of smoke. Figured I have to learn sooner or later to tune my car.

I started by starting the car the way it was on a stand, and letting it sit there and idle for 10 minutes to get warmed up. Shut it down, then reset everything to factory. Turned the Idle screw all the way out until it barely touched the throttle. Reset H/L back to factory, and pulled the starter.

So glad it was on a stand. The wheels immediately took off spinning! When I hit the breaks, the car stalled and shut down. I turned the Idle screw in a turn, then repeated. This repeated until I got the idle in far enough it didn't turn the engine off when I hit the breaks (but wheels still spun at start). Then I started increasing the LOW (richer) until I got the idle where I wanted. Wheels not spinning at startup, and rich enough it would idle about 20-30sec then shut off, unless I gave it some gas.

Then I started on the HIGH needle. I hit full throttle and the car shut off. I increased H (Richer), and restarted. Hit throttle, it shut down again. I increased H. This repeated until it stopped shutting down, and the RPM's were climbing with each increase in H. I finally got it to where I think I had maxed out the RPM's, and just to be sure I pulled the throttle all the way back and held it for roughly 30-40 sec maybe... then it just stopped! When I went to pull the starter, this time it wouldn't budge! I waited a couple hours to let it cool all the way down, and still it wouldn't budge.

Is this engine toast as in throw it in the trash and buy another? Is there something I should check? Can this thing even be rebuilt?
 
Nope, the ignition coil didn't drop (see attached photo). The wheel won't even turn by hand. I have a kill switch, and the light is on saying "ok to start".

Like I mentioned above, this was my first time tuning. I was under the impression from what I've read, and from the DBXL manual itself, that engine damage can occur from going to "lean". I thought I was safe going "rich".

I really would like to learn from this experience. Can someone share with me (and other noobs, so their engines don't share the same fate)) what I did wrong so I don't make the same mistake next time? Don't go to lean and and don't go so rich as to make your car go as fast as possible is all I learned from this experience.... so far...

igcoil.jpg
 
Cold weather means leaner engine because of more oxygen in the air. You would want to richen it. That why engines run better in cool/colder weather. Hotter air with less oxygen you go leaner. Same as going to different altitudes will effect it also. Higher up less oxygen. Lower in elevation means more oxygen.
 
can you give us a bit more info on what ya did fella?
like what engine is it,
what carb is it,
what were the factory settings you used for the needles,
have you mixed up leaner and richer in the way you were turning the needles,
how far were you turning the needles with each adjustment
just seems a bit odd how it revved so high to engage the clutch going back to factory settings and backing off the idle screw so much,plus revving for 30 to 40 seconds with no load on the engine is a bit long,
 
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I suggest you loosen up that coil and double check it to be sure. The pic you provided appears it’s flush against your flywheel possibly. Probably wouldn’t hurt just to make sure.
 
Not sure why you would ever want to pin the engine full throttle for 40 seconds with no load. Chances are good you blew it up, especially if you're not 100% sure how to set the carb. Good luck it's not blown.
 
This engine is a 100% stock g320 out of a 100% stock preowned DBXL 2.0. It has as a wt-1107 carburetor. I run 91 pump gas with Caster 927 oil at 30:1. Factory Settings I used L- 1 7/8 out and H 1 3/8 out. Turned counter clockwise 1/16 at a time.

Will definitely loosen coil just to be sure

UPDATE: I found this gash in the case (see photo) next to the fly wheel. It was on the side of the car next to a brace. I've only had the rig a few months, and never removed the engine until now, so never noticed it. There's no metal fragments inside the car, so maybe it was there when I purchased.

Also, I called OBR and talked with them, since they do engine repair (and their shop is about 5 miles from my house).

I explained what happened as I did above, and he politely explained how it was my own fault. (Ignorance will get you every time LOL) What he (Dan) explained was that I did everything correct EXCEPT rev my engine for so long when it was on a stand. By being on a stand it wasn't under load. "free revving will cause "over revving" and will blow up your engine every time" was his exact words. Under load it will pull in fuel/oil and get what it needs. Under no-load it was only a matter of time with prolonged revving. He told me that when tuning on a stand the engine shouldn't be revved more than a second or two at a time. Me standing there, throttle wide open for about 30 seconds was bad news waiting to happen. If the rig was on the ground, under load, it wouldn't have been an issue.

Decisions Decisions: How much to fix

Without inspecting it, OBR told me worst case scenario would be $240 for a modded g320 top end
for an additional $80 they would convert it to 34cc full mod (they don't repair back to stock)

DDM options:
$169 Engine core (sku:BB127) - Top end and case, just move everthing over from old engine
$89 New Stock top end (sku:CA290)
$49 Top end taken off new engine (sku:CA290-T-OFF)

My plan was to learn what I could before investing in higher priced engines. AS of now I haven't even tuned an engine, and driven it afterwards. I'm leaning torwards first taking the engine apart, and seeing if it's just the top end, and trying to fix it myself. As this is my first gas rig, I've never taken apart one of these engines. I'm an engineer by trade and do well with figuring things out. Is this something that a noob to the hobby should try, or just leave it to the professionals? I have tons of tools, just none of the specific ones used for working on these cars except allen wrenches. Thoughts? I looked around youtube and couldn't find a lot in the way of step-by-step repairing a seized motor.

Also, I had a kill switch installed. This is the first time removing the engine and having it wired to the car is a pain. Do most people cut the wire and insert a quick disconnect to make engine removal easier?

P.S.- Hope my learning experience helps others :)

I appreciate any help or guidance that can be or has been given. Thank you

gash.jpg
 
To add to what I said, that gouge at the bottom looks like it came from the outside and not from the inside. I'm pretty sure someone took a Dremel to that as that isn't a case of fins breaking off the flywheel. Also If the flywheel is good save that and the woodruff key.

Do yourself a favor and remove the head and see what happend. Take good pics of the bearings and connecting rod, chances are you just need a top end. The right thing to do is buy the 32cc long block and start over with a fresh engine that you know where its been.
 
You have a great attitude about the situation, many can learn from you.

Thank you for sharing your story with no pointing fingers at other’s.

I suspect that once you have it up and running that your next experience will be awesome.
 
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If you're going to do something, might as well give it your all LOL

Took a break from this during the holidays, now back to it. In deciding what to do next I was looking around the internet as one does, and found someone on youtube talking about rebuilding engines. He said the piston rod should have no movement other than going around on the crank. If it moves at all in the other direction, it's non-serviceable, and should be discarded. Mine has about 2mm of movement at the end where the piston connects. So my question is this guy correct, and this should be discarded or not?

BTW-The reason I did what I did was because I'm a big dude (6'8" 340lbs), and I always use a stand just because it's easier. I start my car on a stand, then put it on the ground. When I was looking around for information on how to tune, I kept coming across directions that involved lifting the rear wheels off the ground, and revving the engine while listening for highest pitch which would indicate highest RPM. These directions are obviously for a baja type rig, and not a 4 wheel drive. So I put my rig on a stand and went for it.

At least others can learn from my mistake
 
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