thrilsekr

I was driving around the gravel pit yesterday. Did a nice no-damage cartwheel. Landed upside down. And died. Tried to restart it, and it sounded real funny, backfired and died. Noticed the air filter came off, so I put it back on. Restarted it, drove a couple of feet still sounded funny, backfired and died.
Any ideas? Maybe the LSN is too rich? I know it is a little rich because I am still beaking it in a bit. But it never did this before... Only six or so tanks through a new motor. It has been running around 215.

Thrilsekr

Oh yeah. Sometime that day I stripped the hex inside the rear left wheel and the other part the wheel secures to. Too much tourque I guess... Running 300,000 diff oil!

Nitro Goose

300,000 wt. diff oil?? That'd be like filling that thing with frozen peanut butter! I'm assuming you meant 30,000 wt. (Or maybe it really is 300,000) LOL

Anywho... have you checked to see if your engine sucked any crud into it while the airfilter was off? I'd be tempted to pull the engine apart and give it a good cleaning and inspection before starting it again.

thrilsekr

No. It is Associated 300,000 weight oil. Steering under heavy throttle is nearly impossible, but if a tire gets loose the oil helps keep some power between the two. It helps quite a bit for crawling... Also if you manage it get a nice tight turn and a wheel picks up, it keeps power to both wheels. Steering definately lacks. You just have to adjust your driving style. It is definately not thick enough to lock the diff though. Slow speeds I don't notice a steering difference at all.

You need to use a screwdriver to scoop out the oil to put it into the diff case. It is really sticky stuff.

Yeah. I think it would be wise to clean the whole thing out. I just don't want to because it is still a new engine. I suppose I will though.

This is a quote from another forum. But this is in regards to rc18t. Uses a set screw to tighten/loosen the diff, but it is essentially the same thing as changing oil weights....

"Front diff:
looser:
More steering into corners (off power), too loose and steering may become inconsistant, and the truck may lose all steering coming out of the corner (understeer/push).

Tighter:
More stability when braking into corners, and more steering at the exit of the corner getting back on the power.

Rear Diff:
Looser:
More cornering traction, and steering into corner (off power), truck steers quicker into the corner. May oversteer getting back on the power at corner exit.

Tighter:
Truck will push (understeer) on power, and will have less overall traction while cornering.

The truck will be more forgiving to drive (and faster around a track) if the front diff. is a bit tighter than the rear. "


Just depends on how you want to drive. Since I don't really race, high speed turning is not that important to me.

Thrilsekr

Nitro Goose

I can see where you'd give up control in some areas but gain in others... You're right. It is all about what you're using the truck for.

MEANDMYRC

Sounds like you have an air leak, thats why your air filter came off reattach your air filter with a good tight zipp tie. Won't be sucking all that air. Or reajust carb. Fuel mixture might be off. What head temp you running at?

thrilsekr

I am running at about 215 on speed runs and 190 bashing. Also the temp changes quite a bit (+30) from day to day without me even changening the settings. But the amount of change from day to day has settled down now that the engine is more broken in.
But the LSN is rich. It will only idle for a couple secs, and is bogged when accellerating from a stop. It also spits fuel when first starting.
The airleak may be the problem. But isn't a backfire usually too much fuel, not air??? I don't really know for sure.

Any recommendations on exactly what to look for when I have the engine apart. Besides loose debris. Maybe scratches on the sleeve or piston...

Thrilsekr

MEANDMYRC

These are the key things I have noticed your temp is low, spitting of fuel which can be a good thing at this point your problem might be hydraulic lock, this happens when unburned fuel lays on top of the piston and the piston is on its way up blocking the ports, the unburned fuel has no where to go thus when you try to start the piston comes up and the fuel has no where to go and this is where engine damage can occur such as bent connecting rod, wrist pin or crankshaft which could explain the back firing because it would be out of time, always make sure before you try to restart your engine that your piston is at the bottom of the stroke. I would take my engine apart and check the connecting rod the bearings then wrist pin and crank also check for debris. If it is what I have seen the connecting rod will go first and your looking at about $33. If your engine is new and tight your going to have problems getting the rod off the crank so be patient it may take a while and remember if you scratch the rod bearing it is toast. While your at it its a good time to check your bearings, you may consider putting in one way bearings. Good luck and Happy RC ing. If I can be of any help.


Holly

sk8ingsailor

[link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXFTY0&P=7]Wow 300K dif fluid is TRUE[/link]

thrilsekr

Thanks for the engine info, Holly. I will definately tear it apart now, since I have a broken wheel as well, and it will be a bit before I get the new one.

sk8ingsailor -- I would never lie about diff oil, or anything elso for that matter...

Thrilsekr

MEANDMYRC

Your very welcome Hun, anytime

sk8ingsailor

thrilsekr

I was not saying your were lying. ...I just never heard of anything over 100k. So i looked it up on Tower. Just like Nitro Goose said, that has to be like Peanut butter.... just crazy thick like dried maple syrup.

thrilsekr

No. It is thicker than maple syrup. It is more like, well. It is hard to describe. I guess you could say it actually is like maple syrup, but way more dense. You have to scoop it out, and it very sticky. When trying to fill the diff you either have to put a bit in, and wait and wait for it to sink down, or what I do is scoop some in and then turn the gears so the gears help pull the oil down into the diff. 300K is almost more like grease than oil.

Try it sometime, it is fun!


I know you were not accusing me of being a fibber, I was just making a funny.


Thrilsekr

Nitro Goose

Thrilsekr - does it help to heat up the diff fluid before transferring it to the differential? Just wondering if the silicon fluid would act as oil does and change viscosity when heated (making it thinner and more accessible to pouring).

Curious...

thrilsekr

That is a good question. I have not tried it. There are a lot of variables to consider when heating tho'.
Is it flammable?
Will it seperate/breakdown?
Would it harden/bake?
Microwave or oven?
It comes in a plastic container so will that melt?
Could the vapors be toxic?
Do I really want to burn my fingers?

Hmmm. So many questions. I will have to try it next time I do a diff service. I just think you would have to get it pretty durned hot to get it a pourable state.

How hot do you think a diff gets when driving? Do you think that after some driving the diff oil loosens up for all viscosities of oil? Such as 30k, 50k, 300k. And to what amount would they loosen?

Interesting question...


Thrilsekr

Nitro Goose

Good call. What if you submersed it (assuming the container is watertight) in hot water for a period of time? It could be held down with a weight of some sort. Probably not the quickest way to heat it, but may be safer for the user. How much heat the container can withstand would certainly be a variable.

Interesting point about the friction created in the differential possibly causing a physical change in the fluid. There must be some heat caused by friction in the diffs. Never thought to check the temp of my diffs after a run. If anything, diff fluid should create a lubricating/cooling effect in the differentials. But whether the by-product would cause a physical change of the fluid...I just don't know enough about silicates to say with much accuracy.

This article may shed some light on the subject:

[link=http://www.silicone.jp/e/products/oil/about/feature.html]About Silicone Fluids[/link]

If the compositional makeup of diff fluid being sold for R/C applications is like what is described here, it would seem that heat would have little effect on its physical state.

thrilsekr

I think this paragraph says it all. In regards to oil and temp.

"Silicone fluid shows little change in viscosity due to changes in temperature. It is thus ideal for use as instrument oil in instruments used in airplanes, automobiles, and trains, and for other applications that make use of silicone fluid’s viscous properties. Low-viscosity (10 mm2/s and below) products aside, DM-FLUID offers the advantage of less temperature-dependent viscosity change than common mineral and synthetic oils or other silicone fluids."

I will check my diff temp after next run. The only problem is that where the diff oil is, you cannot really check that temp. The diff oil is in the inner case, so checking the temp from the outside would only show the temp of the spur and pinion gears. The 300K is on the spider gears. I don't think you could check that temp with any degree of accuracy. Maybe you could check the temp of the outdrives, which are connected to the spider gears....


Thrilsekr

Nitronutt

My Feedback: (2)

It is possible that your glow plug is damaged and/or too hot. Backfiring is from ignition at the wrong time. I would swap out the plug for a McCoy MC9 when you tear down your engine for a cleaning. Remember to seal that engine back up!

http://www.wildhobbies.com/news/defa...articleid=1233

thrilsekr

That could be possible. The plug has maybe a half gallon through it.
I leaned out the LSN last night. Got it to run without backfiring. Maybe it was too rich... Well it ran until the rear left wheel fell off anyway. I guess glue just isn't strong enough.


Thrilsekr