Another dead motor

[Steve Macdonald]

The stock Losi air filter box is a pretty bad design. It is extremely easy to get the filter elements caught on the bolts when you're assembling it, and almost impossible to tell when it happens. For the second time the inner element became slightly entangled in one of the bolts, twisting it just enough to allow unfiltered air into the motor.

This is made far worse by the fact that my local bash spot is covered in extremely fine dry soil -- much finer than sand. It's basically dust. My electrics like the X-Maxx can bash at that spot all day long and just need a bit of compressed air afterward. The gas trucks on the other hand seem ultra-sensitive to this sort of fine dust.

I've had maybe an hour of running time with this Losi and have gone through two motors -- the latest one an OBR.

Hopefully it can be rebuilt OK.

So I'm getting rid of the stock Losi airbox and replacing it with the Turtle Racing unit that adapts an HPI style filter, which is far less likely to leak.

As for bashing where there is fine dust everywhere, maybe I'll just have to stick to grass or something from now on.

Any tips regarding protecting these trucks from dirt much appreciated. E.g., I couldn't even *find* outerwears designed for the new square Losi airbox.

 

[Steve Macdonald]

 

[Ghibbert]

Ouch Steve - That's painful to see! +1 for the baja style air filter from me - Plenty of dust at my spots and not a speck past that thing for me yet, plus it's easy to make sure it's on right after installing. How much got in to the motor do you think? I'm quite optimistic it'll be ok, the foam is quite evenly dirty, so air's been coming through the foam for the most part. What did the carb tunnel look like? Wondering if you can flush the engine out with some fuel poured in or if you're ordering gaskets & bearings... You could always make ghetto outerwears from suitable fabric by the way, only has to catch the worst of it.

Edit; This reminds me of running grounds tools with no air filter on and being told, don't get any dust in there... I wouldn't have minded but it was a blower! Thing created a dust storm - lived for a couple of years like that. Then died horribly. Your OBR will be fine though!

 

[Steve Macdonald]

Thanks for the reassurance Ghibbert

Going to look into what I can rig up re outerwears as per your suggestion.

Today I took the Zenoah 290RC from my Baja clone (it had been exposed to seawater on the beach). The motor started when I put some fuel in the sparkplug hole. I put a spare carb on it and tried it out. Fired right up first pull. So I decided to swap out the OBR in the Losi and try that 290RC. Got it all together, again started first pull and sounded great. Each time I only ran it for about 30 seconds. Then I tried to run it longer and in less than a minute it just abruptly died. Can't get a thing out of it now.

It stopped so suddenly, just moving along slowly on pavement... no dirt involved this time. Almost makes me think it's electrical... will try some fuel through the hole again and if that doesn't work I'll put in a brand new carb and a new plug.

Hope this time it's something minor. Sooner or later my luck has to change, right?

Also I did put the Turtle Racing HPI air filter on there and it seems fine.

 

[Steve Macdonald]

OK I think I just made the dumbest n00b mistake in 1/5th scale history...

While I was putting the Losi back together with the 290RC my nephew came by and was asking me all sorts of questions -- sort of distracted me but I'm always willing to chat about my Losi

So I got him to help me put the body back on. Due to being distracted, I forgot to put the GAS TANK back in (I had removed it for cleaning). Yup. I took a car out on the road with no gas tank. There was enough gas in the lines/carb for it to run fine for a minute or so, but then she stopped dead. Anyhow I finally caught on, and man do I feel dumb!!!

 

[Steve Macdonald]

Gas tank back where it belongs. Fired up after a few pulls -- once it got some fuel circulating again.

That Zenoah 290RC is one incredibly reliable motor -- it's been exposed to seawater and after a general cleaning and a new carb it works like new. OBR is still a question mark. I'll strip it down this week, but at least I'm ready to bash again.

I'll find out more tomorrow, but just firing it up in the garage, the stock Zenoah 290RC + Victory pipe feels a lot more responsive and free-revving than the OBR + Victory pipe. I found it really hard to tune the OBR for smooth throttle response. I'm sure someone with more experience could do it, but for now the stock Zenoah is an awesome little engine.

Never using that Losi airbox/filter again. The Turtle Racing HPI filter adapter is great!

 

[Ghibbert]

Ah well, man enough to admit it will do for me - We've all done something stupid sometime
Yep, stock motors should be a bit more forgiving with regard to tuning and 'abuse' - use and enjoy the 290, get some more experience whilst you make sure that obr's ok I reckon. Something I've not seen many people talk about is the relationship between engine airflow and stinger diameter/length - to my knowledge most pipes are designed to add power to a stock motor, with the airflow that has. There are rules and ratios to determine optimal stinger I/D & length based on the exhaust port size. As far as I know smaller stinger = higher backpressure - more mixture packed back into the cylinder each cycle. So put that pipe on a modified engine with greater flow and now that stinger's too small, not enough total flow through the system - Engine cannot work to it's full potential.
Someone with more knowledge feel free to chip in - I had the stock ss/ghost pipe on a cy29 - was ok, but had a tiny powerband way up at the top of the rev range - not good, lost the stinger on a tumble so brazed on a slightly shorter and larger I/D one - also removed the awful pipe joint and replaced with hose + clamps - adding about 12-15mm to the tuned length at the same time to try and bring the powerband down the revs. Performance is far superior imo (not too hard as the pipe is notoriously crap) Much more responsive at low rpm, a lot easier to get the correct speed coming up to a jump or out of a corner, still revs well, runs cooler.
Need to find out more, want to hassle the guys in the shop to measure all the stingers for me!

 

[Steve Macdonald]

Ah well, man enough to admit it will do for me - We've all done something stupid sometime
Yep, stock motors should be a bit more forgiving with regard to tuning and 'abuse' - use and enjoy the 290, get some more experience whilst you make sure that obr's ok I reckon. Something I've not seen many people talk about is the relationship between engine airflow and stinger diameter/length - to my knowledge most pipes are designed to add power to a stock motor, with the airflow that has. There are rules and ratios to determine optimal stinger I/D & length based on the exhaust port size. As far as I know smaller stinger = higher backpressure - more mixture packed back into the cylinder each cycle. So put that pipe on a modified engine with greater flow and now that stinger's too small, not enough total flow through the system - Engine cannot work to it's full potential.
Someone with more knowledge feel free to chip in - I had the stock ss/ghost pipe on a cy29 - was ok, but had a tiny powerband way up at the top of the rev range - not good, lost the stinger on a tumble so brazed on a slightly shorter and larger I/D one - also removed the awful pipe joint and replaced with hose + clamps - adding about 12-15mm to the tuned length at the same time to try and bring the powerband down the revs. Performance is far superior imo (not too hard as the pipe is notoriously crap) Much more responsive at low rpm, a lot easier to get the correct speed coming up to a jump or out of a corner, still revs well, runs cooler.
Need to find out more, want to hassle the guys in the shop to measure all the stingers for me!

Ghibbert: The Victory pipe in question was recommended by Sean at OBR -- I bought it together with the engine.

I only had the OBR in there for a short time, but I have to say I'm having trouble noticing much difference between the OBR and this stock 290RC (both hooked to same Victory pipe). Now of course I may have not tuned the OBT properly, but still the 290RC just rips. For my purposes (just bashing for now until I gain a few years experience) the stock motor is more than powerful enough.

Can't believe the abuse that thing can withstand. It was literally in the ocean a few weeks ago (in my Baja clone), but doesn't seem any worse for wear.

BTW, Sean at OBR gave me some tips on what to look for in the OBR motor that had the air filter come loose. Fingers crossed it's not badly damaged. I didn't see any dirt in the intake port, so maybe I got lucky...

 

[Steve Macdonald]

OK back in action now, at least with the Losi (Baja clone still disassembled).



I put the Turtle Racing HPI filter adapter on -- seems much safer to me than the Losi airbox. The Zenoah certainly seems happy with the setup. I'm waiting for a set of filter outerwears which should be here tomorrow. No running on dirt until then -- only parking lots. Also arriving this week is the Futaba, and another new Zenoah motor from DDM: a 320RC.

Anyone have any opinions on the 290 versus 320 Zenoah for the Losi?

Of course I'm hoping to resuscitate my OBR motor as well -- eventually it will find its way back into the Losi.

My goal for now is to get this rig stable and protected enough that I can do regular bashing without destroying another motor. Learning as I go, with some expensive lessons along the way

 

[Phill2]

OK back in action now, at least with the Losi (Baja clone still disassembled).

View attachment 44461

I put the Turtle Racing HPI filter adapter on -- seems much safer to me than the Losi airbox. The Zenoah certainly seems happy with the setup. I'm waiting for a set of filter outerwears which should be here tomorrow. No running on dirt until then -- only parking lots. Also arriving this week is the Futaba, and another new Zenoah motor from DDM: a 320RC.

Anyone have any opinions on the 290 versus 320 Zenoah for the Losi?

Of course I'm hoping to resuscitate my OBR motor as well -- eventually it will find its way back into the Losi.

My goal for now is to get this rig stable and protected enough that I can do regular bashing without destroying another motor. Learning as I go, with some expensive lessons along the way

The 320 is a longer stroke so will have more torque but less revs.
The 290 being a shorter strokes has less torque but more revs.
I've never tried the 320 but am very happy with my 290.

 

[Steve Macdonald]

The 320 is a longer stroke so will have more torque but less revs.
The 290 being a shorter strokes has less torque but more revs.
I've never tried the 320 but am very happy with my 290.

Phill2 -- makes sense. Thanks. I'm sticking with the 290 for the time being. 320 is on the shelf as a spare.

 

[Madspeed]

Ah well, man enough to admit it will do for me - We've all done something stupid sometime
Yep, stock motors should be a bit more forgiving with regard to tuning and 'abuse' - use and enjoy the 290, get some more experience whilst you make sure that obr's ok I reckon. Something I've not seen many people talk about is the relationship between engine airflow and stinger diameter/length - to my knowledge most pipes are designed to add power to a stock motor, with the airflow that has. There are rules and ratios to determine optimal stinger I/D & length based on the exhaust port size. As far as I know smaller stinger = higher backpressure - more mixture packed back into the cylinder each cycle. So put that pipe on a modified engine with greater flow and now that stinger's too small, not enough total flow through the system - Engine cannot work to it's full potential.

Its been many years since Ive modded 2 strokes. It has nothing to do with port size. there is SOOOOOO much involved in a proper tuned pipe its rediculas. 1 is length from center of cylinder to fattest part of pipe. is rpm band it will hit at. shorter makes the pressure wave push the pulled fuel air charge bank in before the port closes ( its actually a supercharger in a sense) the wave comes out expands until it hits the part tapering back down and bounces back in the cylinder. the taper on both side plays into all of this as well as the actual outlet size and length. @ 13 I read a book on how to mod 2 strokes and I made a .040 model air plane engine pull a small oak work bench by the time i was done. It was not able to do that before. @ 17 I raced model boats and had an OPS .090 in a fayva fast cat .75 to .11 cc boat doing 119 mph . UMM looky looky http://www.amrca.com/tech/tuners.pdf