T-maxx - first run and some Q's

gs39t

I've just been breaking in the engine on my T-maxx, by the book (and DVD) but have some issues that arent covered by either.

Firstly, the truck seems to stutter under accelleration from low-mid throttle. It will fly away if i give it half throttle or above, but from a low rpm start will take 5-6 feet to stop stuttering and begin to move properly. Any ideas? The DVD only shows that if its too lean the model will stutter at high speeds.

The other problem is, that after 10-15 minutes of running im having a wierd shifting problem. Sometimes the truck will just not shift the other way (forward to reverse, say). I will put the switch to reverse, the idle speed will increase to a high rpm, but will remain in trying to move forward, and no amount of hitting the switch back and forward will change it, and i cant get it out of high RPM and either need to shut off the truck or it will die anyway.

I suppose the third question is, is there no way to shut it off without pinching the fuel line?


Other than that, ive destroyed many, many things in my back garden, including having accidentally mowed into a fountain, which fell over backwards soaking the truck in water. Scared the crap outta me but luckily the truck suffered no ill effects

tallus

gs39t wrote:

I've just been breaking in the engine on my T-maxx, by the book (and DVD) but have some issues that arent covered by either.

Firstly, the truck seems to stutter under accelleration from low-mid throttle. It will fly away if i give it half throttle or above, but from a low rpm start will take 5-6 feet to stop stuttering and begin to move properly. Any ideas? The DVD only shows that if its too lean the model will stutter at high speeds.

The other problem is, that after 10-15 minutes of running im having a wierd shifting problem. Sometimes the truck will just not shift the other way (forward to reverse, say). I will put the switch to reverse, the idle speed will increase to a high rpm, but will remain in trying to move forward, and no amount of hitting the switch back and forward will change it, and i cant get it out of high RPM and either need to shut off the truck or it will die anyway.

I suppose the third question is, is there no way to shut it off without pinching the fuel line?


Other than that, ive destroyed many, many things in my back garden, including having accidentally mowed into a fountain, which fell over backwards soaking the truck in water. Scared the crap outta me but luckily the truck suffered no ill effects

Sounds like you might be running it a bit rich at low-mid throttle?, or is it that the engine is a bit cold. I'm Not an expert by any stretch of the imagination and I know some of the guys here are very knowledgable, .. that's my 2c anyways :P
On the shifting/reverse problem I'm lost, dont have any experience in that field at all.
If I can't get at the fuel tubing,I usually cover the exhaust outlet with a rag or with my foot, that always works :-)

gs39t

I guess im running too rich and thats why its taking off wierd. The shifting issue is a wierd one, maybe im not stopping the truck fully before shifting and thats why its causing the problem, not engaging right? Will have to test out that theory tommorrow!

T-Maxx

By the sound of things I'd say your low speed mixture is too rich which means you should turn the Low Speed Needle (LSN) in (clockwise) in 1/16 to 1/8 turn increments. It's very sensitive so don't turn it more than that at a time. Have you done the pinch test as per the DVD/Manual? Remember to do a few high speed runs before adjusting again. Also you'll have to turn the idle adjustment screw out (anti-clockwise) because leaning the LSN will increase the idle.

If the truck doesn't want to shift between forward/reverse the idle is too high.

To turn the truck off simply pinch the fuel line - works easy enough I'd say.

The TRX2.5 is a tricky engine to tune, but very powerful. Have fun with your truck!

gs39t

I got the truck out in the open today for some high-speed runs (very, very high speed :eek: ) and a problem that has cropped up is that when i brake from high speed the engine cuts out. Normal speed operation is grand but high speed to stop, engine dies.

Any ideas?

T-Maxx

It could be that the idle is simply too low, or it's the LSN that's too rich.

coolwings

Your tuning is off and you are giving your piston liners a workout :eek:

Because you have it too leaned for top, (not necessarily needle adjustment, could be fuel tube length, tank air seal, carb air seal, too much nitro for running-in, or other cause), it is going a tad into soft seize at full throttle, and when you throttle down that's it, it is too tight to run and it cuts out.

Betcha there is no problem when you go back to start it after it's had time too cool down.

Be careful. Piston and liners are using their lifetime up kinda fast with this treatment (maybe 5%-10% done already) . Also your glowplug will be a bit knackered too.

BTW Just how much nitro is in your running-in fuel? Is it castor oil (should be) or is it synthetic oil ? (shouldn't be while running-in)

gs39t

It happened 3 times in a run, but not every time i stopped. It's running rich, maybe too rich, as theres a lot of smoke. I didnt have a screwdriver with me to tune it. I'm running 16% nitro. I'm not sure on the specifics as i dont have the can infront of me. If its relevant, the truck ran well otherwise, didnt hesitate or anything. Was just those few times high speed braking that shut it off. I thought the most obvious thing would be the idle too low, as i have to give it some revs to start it too, otherwise it wont start in idle, or sometimes dies straight away if i dont rev it. I cant hear any audible difference changing the idle speed.

tallus

I have the same thing with my Savage while running in teh engine, I found that the normal Idle just doesn't seem to be enough to get the engine to start, it seems to need the throttle to be open a fair bit and when it does eventually start, it runs higher than i'd like it to for idle speed.

coolwings

gs39t wrote:

It's running rich, maybe too rich, as theres a lot of smoke..

It will always smoke some .... do you know how muck smoke is a lot?
Have you used model engines before?

gs39t wrote:

I'm running 16% nitro. ..

Wrong fuel for running-in. The engine is getting a roasting no matter how you do the settings...my estimate 10% of engine life gone in first 2 hours of use.

gs39t wrote:

I'm not sure on the specifics as i dont have the can infront of me. If its relevant,......

It is relevant. Synthetic is a better lubricant,at working temperature, but it can't tolerate abnormal high temperature, and that is what running in and especially high nitro running in delivers.
The synthetic oil evaporates and goes out as smoke, leaving the engine running unlubricated on neat fuel. Need I say any more?
castor is an inferior lubricant, but it just thickens at high temperature, it doesnt dry up. So you should have castor for running in, and synthetic after, for best engine quality and performance.

gs39t wrote:

I thought the most obvious thing would be the idle too low.....

Once you are over 30% throttle, the idle jet has no effect that can be measured, it is not that, unless the idle is too lean, and your problem comes after you throttle down into the low end, but the high temp partial seize problem was caused by what was happening before, while the fast jet was (not) doing it's job.
There is a technical explanation of running-in model engines on my website...
http://uk.geocities.com/norm_flyer/index.htm
It might be useful to you at this stage.

vectra

coolwings wrote:

It will always smoke some .... do you know how muck smoke is a lot?
Have you used model engines before?
Wrong fuel for running-in. The engine is getting a roasting no matter how you do the settings...my estimate 10% of engine life gone in first 2 hours of use.

It is relevant. Synthetic is a better lubricant,at working temperature, but it can't tolerate abnormal high temperature, and that is what running in and especially high nitro running in delivers.
The synthetic oil evaporates and goes out as smoke, leaving the engine running unlubricated on neat fuel. Need I say any more?
castor is an inferior lubricant, but it just thickens at high temperature, it doesnt dry up. So you should have castor for running in, and synthetic after, for best engine quality and performance.

Once you are over 30% throttle, the idle jet has no effect that can be measured, it is not that, unless the idle is too lean, and your problem comes after you throttle down into the low end, but the high temp partial seize problem was caused by what was happening before, while the fast jet was (not) doing it's job.
There is a technical explanation of running-in model engines on my website...
http://uk.geocities.com/norm_flyer/index.htm
It might be useful to you at this stage.

I used 16% Model Technics in my sons T-Maxx to run it in .... would that be ok ?
I have now bought a Revo for a guy that races T-Maxx's and he says it is no problem to run them in with 20%.. { which he gave me 3 litres of when I bought the revo from him} Tornado 20% I think it was, Not too sure as I havent even started it yet

coolwings

The main reason for giving someone 10% nitro or over with a car, is to be sure it will start for them. What happens afterwards can be blamed on them. After all it started when they bought it. Didn't it?

BTW Tornado 20% = Model Technics 16% AFAIK.

The Model Technics could be castor or synthetic oil, and could be dynaglo, duraglo goglo, formula irvine or goglo plus. You could look at model technics website, check the blend and make sure it has 18-20% oil - that would be ok.

Purely for the engineering point of view.... Why don't you read the info on my own webpages, and then let us know what you think, based on your own experiences?

vectra

coolwings wrote:

The main reason for giving someone 10% nitro or over with a car, is to be sure it will start for them. What happens afterwards can be blamed on them. After all it started when they bought it. Didn't it?

BTW Tornado 20% = Model Technics 16% AFAIK.

The Model Technics could be castor or synthetic oil, and could be dynaglo, duraglo goglo, formula irvine or goglo plus. I think most shops sell the cheaper blends to achieve a low retail price, and maximise margin. You could look at model technics website, check the blend and make sure it has 18-20% oil - that would be ok.

Purely for the engineering point of view.... Why don't you read the info on my own webpages, and then tell me what you think, based on your own experiences?

Strange you should say about different blends... I bought some 16% from a fellow member here.. T-Maxx runs fine... I friend of my sons bought a gallon from a retail source and my sons maxx refused to run properly on it..:rolleyes:

I would read your webpage but to be honest.... there is a difference in reading it and understanding it

gs39t

All the documents with the T-maxx say "10-20%" nitro, either is OK, and to use the same mixture as you run it in with all the time. Nothing about moving up through the range

I think you've pronounced my engine DOA a little early; i ran the engine in by the book. The truck cut out, after slamming on the brakes and coming to a stop. Same for not starting, needed revs. I havent owned a nitro model before, but from tuning cars to me that means the idle is too low

coolwings

He he he
Yes, there is a lot there. But at least it's accurate. Whatever problem you get, the answer is in there somewhere.....

coolwings

gs39t wrote:

All the documents with the T-maxx say "10-20%" nitro, either is OK

I know they say that. I also explained why they say it.
Please understand that there is not the slightest bit of criticism of you intended in my post.

gs39t wrote:

I think you've pronounced my engine DOA a little early; i ran the engine in by the book.

Nope, didn't say DOA. Just used very hard.
I know a fair bit about engines, and my engines don't have to work that hard for me.
Some people are happy that it goes, others expect it to still be going 5 years + later. I would be in the second category. :cool:

gs39t

coolwings wrote:

Some people are happy that it goes, others expect it to still be going 5 years + later. I would be in the second category. :cool:

If the worst comes to the worst, ill buy a new engine. They are only about £70.

Dont worry; im just trying to convey the correct symptoms to get an accurate diagnosis I did exactly as the the strange man with the wig on the DVD said. There was no mention of special run in fuel, infact i think they specifically mentioned that you dont need special run in fuel.

It will be another week until i can test it out again, but thanks for the tips.

coolwings

Models is one of those things where the more you know the less gear you have to have, to get it to go right.

An example, we had a quiet time in the shop a couple of months ago, so we decided to test out the "TMaxx needs at least 16% nitro or it won't go right" advice.
So we serviced a TMaxx, and ran it on 16%. Perfect. Service completed, job done.
Then we put 5% nitro fuel in. Tried to start it. Very lumpy, not nice. So we shortened the long fuel tube, remopved the filter, (which should be in the filler tube, not the car) and replaced the glowplug with a same size but hotter glowplug. Started and retuned for the new settings.
Hey presto -- it ran just fine.
This was on fuel that costs half as much, or to put it bluntly, on fuel that is €14 per gallon cheaper.
So much for the book and the commonly held advice!

Enjoy your Monster Truck !

Coolwings
(Who when he was a kid, his bike has three wheels, then later it had 2 wheels and it went better, and who looks forward to a unicycle next ! )

tallus

Coolwings
(Who when he was a kid, his bike has three wheels, then later it had 2 wheels and it went better, and who looks forward to a unicycle next ! )[/QUOTE]
LOL :-)

T-Maxx

Does the truck shift into second gear?
How's your temp?

Remember also that all adjustments should only be made once the engine is completely warmed up. Also, you'll have to re-tune every time the weather changes or you change altitude.

BTW I've read of a guy who's had 25 gallons through his mill - still runs but not great.

gs39t

T-Maxx wrote:

Does the truck shift into second gear?
How's your temp?

Remember also that all adjustments should only be made once the engine is completely warmed up. Also, you'll have to re-tune every time the weather changes or you change altitude.

BTW I've read of a guy who's had 25 gallons through his mill - still runs but not great.

Seems to shift ok. I havent checked actual temp of the engine, other than find out not to touch it after a run...

.B.R.

Coolwings, what fuel do you use in your t-maxx?
gs39t- That shuddering is the transmission it will go away the more you run the truck happens with all the maxes when there new... Where you from aswell? We should organise a meet out in marley park with the trucks the BMX track out there is great..
Brian

coolwings

.B.R. wrote:

Coolwings, what fuel do you use in your t-maxx?

Unfortunately I am "truckless" right now.
I've gotten into a jets-and-very-fast-things binge lately.
Only exception has been the tank powered by the clockwork engine which was a "doss" project, and the 3-wheeled aero-car-sandyacht.
Reminds me - I meant to post pics of that, I will dig them out & post into the pics-of your-model thread just for the craic.

.B.R. wrote:

We should organise a meet out in marley park with the trucks the BMX track out there is great.. Brian

I have used it in the past - it's excellent for buggies & trucks. Go early to avoid problems with other users and things are sweet.

vectra

I used 16% model technics in my sons T-Maxx and it ran fine.
Now I use 20% Blue Thunder in my revo and it rips up the maxx

tallus

I'm using 16% in my Savage

.B.R.

I use 16% myself but wondering which blend of modeltechnics you guys are using? Im using the dynaglo...
Brian

coolwings

GX-Straight (20%castor oil, zero nitro) high compression MVVS engines in summer

GX-5 (20% castor oil + 5% nitro) for running-in everything

GoGlo Plus-5 (18% synthetic oil + 5% nitro) for high compression MVVSengines in winter, and OS/Irvine/SC engines summer

GX-10 (20% castor oil, 10% nitro) for hotter sport use in cars

GoGlo Plus-16 (18% synthetic oil, 16% nitro) where I'm tuning an engine for someone who will be using 16% . (Not in my engines actually.

Special high revving-high cooling mixes I use....
Wildcat 20,
Wildcat 25,
(nothing at all to do with the fuels sold under that brand name) it is Model Technics special blend made up as follows: 20% EDL synthetic, 2%castor, 20-35% nitro)
I use these blends for
YS 4-stroke turbo engines 20-25%,
high revving water cooled inboard marine engines (30%), and
racing aircooled marine outboards (35-65%)

All above are nitro by volume (not by weight)

On rare occasions when confronted by a model with too much nitro in the fuel which is causing detonation and piston damage, and richening made it lumpy without curing, I have even added water to fuel to adjust the flashpoint !

BTW
BR Dynaglo is just 10% oil, that sort of low lube low cooling is most suitable for very large aero engines 1.20 + and old four strokes - all of them low revving cool running engines. (When I use over 10% nitro I always have at least 18% oil in my fuel) Do you find this mix good? Or does it shorten glowplug life in your cars?

T-Maxx

GoGlo Plus is 15% synthetic and 3% castor, isn't it?

coolwings

That's right.

.B.R.

Coolwings- To be honest I find it to be ok, glow plug has already had a gallon of dynaglo thru it and its still good.. To be honest I feel 8% to 12% is a good range for cars.. I've tried higher oil contents like you've montioned but I feel that the engines don't run or tune very well with it and don't really give a longer life.. The high oil tends to give them a groggy and poor throttle response/performance as if it was too rich and to rid of this can cause you to be overleaning the engines without knowing... Maybe this is ok in planes or helis as there constantly at high rpm where as the cars go from low to high and are only at high rpm for a couple of seconds at a time!:)
Brian

coolwings

Thanks for the info.

You are dead on in that the throttle response with low oil fuels is more snappy than it would be with a high oil fuel at the same tuning, if the high oil fuel were used at the same tuning, but it isn't.

You see ... if you use the higher oil fuel, you would be able to lean it out even more with no overheating due to better lub/cooling, this allows higher rpms to be achieved and that is when the 2-stroke gives its best....on the edge of its limits at high rpm.

Its true a guy with lower oil content can compete against the guy with higher oil content.
But his odds of engine failure and non-finish are greater.
Remember that in Grand Prix racing it is common to blow up an engine and lose all points, and the model engine is exactly the same. They don't win with a broken conrod.

Now if the conrod lasts the important race, and you win, then you can replace it before the next meeting. And that is good. It only costs €16 or so. Less than a gallon of fuel. And you won the race. (By using an engine part as a consumable item).
We have noticed that some engines break their conrods and stop (eg CEN) but others wear the boss in the conrod into an oval eg Carson and keep going, but need it replacing later.

An inexperienced driver will often lean out his engine too much, (not you now, but we all do while learning), and on Dynaglo he has less time to fix the tuning error than on Formula Irvine, GoGlo, GoGlo Plus, or GX before mechanical failure strikes.

The "old hand" knows how lean is ok, and how lean is too lean.

When you mention the glowplug has lasted a gallon, that tells me that you know how to lean it out, but not too far. You have got used to using Dynaglo and tuning to suit it. So you need no other fuel

BTW I agree about the few seconds at top speed bit - the less time at full rpm the more a low oil fuel is favoured, ane longer the high rpm (or the longer the race) the more another blend will be favoured.
So the shape of the race track and number of laps also matters in choosing the most suitable fuel.

These are subjects that are not talked about enough. Most of the guys are looking too hard at the latest gadget to go fast, and not at fuel and tuning and suspensions.