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MP Jet Letmo 0.6 Replica

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Help! MP Jet Letmo 0.6 Replica

Post  Grosvince Sun Feb 13, 2022 5:20 pm

Hi Guys,

Another one I've found : a limited edition of the tiny MP Jet letmo 0.6. This one is the #211 (out of 500 ?)

MP Jet Letmo 0.6 Replica 20220213_223759

Unfortunately, the last owner tryed to remove the tank, and unfortunately (bis), the mounting is silly : tank seems to be screwed from the inside on the carburettor and then the bottom of the tank is pressed in place. So, I don't know how I can fix that without sacrifying the tank... Any ideas ?

Vincent
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Help! Re: MP Jet Letmo 0.6 Replica

Post  ffkiwi Sun Feb 13, 2022 5:58 pm

These are a bit tricky-a pity since they're very well made. The tank is simply made of three parts-the top, the cylindrical wall and the hemispherical base-and they're just pressed together. You should-with care and the use of a SOFT jawed pliers or some form of clamp-be able to pull the body of the tank off the top by means of a downwards and back and forth rotation motion-the top -as you surmised being attached to the venturi by the screwed in jet tube. this should then allow you to see how badly bent things are.

On a (probably) positive note-this replica formed the basis of the later-and far more common MP Jet Classic 040-the beam mount one-far more practical than that awkward radial mount of the Letmo....and I'd suggest that the NVAs are almost certainly identical. MP Jet's website lists a reasonable range of spare parts for their 040 and 061 models-so you should b able to find a suitable replacement NVA jet assembly-even though you may have to purchase the entire NVA to get it.

See: https://mpjet.com/shop/gb/899-spare-parts-for-040-classic



I have two of these MP Jet Letmos-they run quite well-but that pegged prop driver is a pain , as is the radial mounting-and the tank setup equally problematic. the Classic has a simple spun metal tank bowl that screws onto the tank top-a far better arrangement.

ChrisM
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Help! Re: MP Jet Letmo 0.6 Replica

Post  Grosvince Mon Feb 14, 2022 7:01 am

Hello

Actually the tank is not bended, but just loose. And there's no trivial solution to thighten it back because the nozzle turns in the tank hole ! I think nothing is broken !

The NVA from the Classic MPJet cannot fit on this engine, because on the Letmo it's press fitted and screwed on the Classic (like a mills)

Vincent
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Help! Re: MP Jet Letmo 0.6 Replica

Post  ffkiwi Mon Feb 14, 2022 1:49 pm

Grosvince wrote:Hello

Actually the tank is not bended, but just loose. And there's no trivial solution to thighten it back because the nozzle turns in the tank hole ! I think nothing is broken !

The NVA from the Classic MPJet cannot fit on this engine, because on the Letmo it's press fitted and screwed on the Classic (like a mills)

Vincent

Well it would seem your only practical option would be to get a complete tank assembly for a Classic 040 from MP Jet, press out the jet from the top side of the Letmo venturi, fit the Classic tank top, and press the jet back in-using some kind of thread locker to ensure it stays put, as pressing it out will have loosened the fit slightly. As mentioned earlier-the Classic tank bowl screws onto the tank top, so there is no problem is reassembling the tank.

It won't be quite authentic for the Letmo-but it WILL allow the engine to be used.  If you had access to a lathe you could machine up a new tank top for the Letmo-thread part of the upper  OD of the jet piece closest to the hex or locating flange and screw the tank top in place on the jet-and then use the sidewall and base  portion of the original tank to complete the assembly-but you would have to destroy-or at the very least damage -the original tank top-in the process of disassembly. From the photo you posted I initially assumed that the jet portion had been bent, but in light of your second post I'd now guess that the original owner has enlarged the hole on the tank top by mishandling, and the entire assembly is now loose on the jet piece.

If you are exceptionally lucky and manage to get the tank apart without significant damage to the tank top-other than the enlarged central hole-I suppose it should be possible to fit a custom made rivet in this hole (which might have to be enlarged further to take it) and then drill this rivet to the original correct diameter to be a close fit on the jet, and press things back together as before.

A lot would depend on how thick the tank top material is-and how soft, as to whether this approach would work. From memory-and I haven't looked at my small Letmos for over a decade-the material thickness is fairly thin. If it was thicker i'd consider fitting a screwed bush rather than a rivet-but I doubt there is sufficient thickness to get an adequate thread.

ChrisM
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Help! Re: MP Jet Letmo 0.6 Replica

Post  Grosvince Mon Feb 14, 2022 2:45 pm

Hello,

Thank you for your advice, but the 2 engines are very different in many points, especially when it come to tank mounting/construction.

There's simply no easy way to put a Classic tank on the Letmo (as I own the 2 engines, I will take some pictures to clarify this).

Vincent
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Help! Re: MP Jet Letmo 0.6 Replica

Post  ffkiwi Mon Feb 14, 2022 2:57 pm

So do I -I own nearly two dozen MP Jets of all varieties-other wise I wouldn't have offered the advice in the first place. You asked for suggestions-you got them-I've provided you with a variety of possible options. You are of course entirely at liberty to reject the suggestions. I wait with interest to see what you will do in that case.

CJM
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Help! Re: MP Jet Letmo 0.6 Replica

Post  sosam117 Mon Feb 14, 2022 5:13 pm

Vincent,
I know of your problem of the MP Jet Letmo MD - .06.
I have three of them. S/N-113, S/N-251 and S/N-260.


MP Jet Letmo 0.6 Replica Mp_jet10


And there is a complete difference in the MP Jet .040 PB Classic Diesel.

MP Jet Letmo 0.6 Replica Mp-jet10

I know that you cannot use the parts from one (Letmo .06) to the other (.040 PB)

As for your loose fuel tank (as I did the same mistake of loosening it like yours)
1st I tried to pull down on the tank then tried to screw the nut inside by using the tank to maybe tighten it back up.

Maybe the curvature of the top of the tank would catch the nut to tighten it back up? NOPE!

Maybe do the opposite by pulling down on the tank and unscrewing the tank.
Hopefully have the nut catch on the curvature of the top of the tank to catch and not turn? NOPE!

Well, the last resort I did was to enlarge one of the fuel holes to 2.5mm.

MP Jet Letmo 0.6 Replica 2_5mm_10
MP Jet Letmo 0.6 Replica Over_f10
MP Jet Letmo 0.6 Replica Both_h10

Drilled a hole just slightly smaller than the outside diameter of the fuel tank in a 50mm block of wood.
Heated up the outside of the tank, then used an ice cube to cool down the bottom of the tank,
then tapped out the bottom of the tank using a 2mm rod in the 2.5mm fuel fill hole (that you enlarged)
while using the wooden block (with the hole for support) and tapped out the bottom of the tank.

The quick cooling with the ice cube at the bottom of the tank shrinks the aluminum while the bigger dia. of the tank os bigger because it is hotter (expanded from the heat).

One thing you will have to do is replace the vinyl fuel tubing inside because of the heating of the tank.


The MP Jet .040 is a nice runner.
The Letmo MD - .06 not so much.
The .06 has an aluminum contra piston in a steel liner.
You can adjust it at the start, but after it warms up that aluminum contra piston does not want to move.
I made steel contra pistons for mine and they are now great running engines.


Here is the drawing of the contra piston with the original "aluminum" contra piston on the drawing.

MP Jet Letmo 0.6 Replica Contra10

The next photos are of the head off the engine with the "new" steel contra piston.

MP Jet Letmo 0.6 Replica Head_o10
MP Jet Letmo 0.6 Replica New_st10

Last is the photos of my three Letmo .06 diesels.

MP Jet Letmo 0.6 Replica My_3_l10




Best of luck!
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Help! Re: MP Jet Letmo 0.6 Replica

Post  Grosvince Mon Feb 14, 2022 5:32 pm

ffkiwi wrote:So do I -I own nearly two dozen MP Jets of all varieties-other wise I wouldn't have offered the advice in the first place. You asked for suggestions-you got them-I've provided you with a variety of possible options. You are of course entirely at liberty to reject the suggestions. I wait with interest to see what you will do in that case.

CJM

My apologies. You have right, the Classic tank fits on the Letmo carburettor. I must double check before to write.

MP Jet Letmo 0.6 Replica 20220215_001312

Vincent

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Help! Re: MP Jet Letmo 0.6 Replica

Post  ffkiwi Tue Feb 15, 2022 12:22 am

Now that you have established that-you have the option-should you want it-of fitting one of the enlarged Classic 040 tanks and getting a longer run out of the Letmo for R/C use should you desire that option. Obviously MP Jet realised some of the shortcomings of the Letmo and improved on them when they designed the Classic.....the Letmo tank set up is a right abortion of an idea-and the mounting not a whole lot better-nor the pressfit venturi-which is also on the big 2.5cc Letmo MP Jet replica.    I machined up a Cox Thermal Hopper type 'cage' mount to fit mine-both the 0.6 and the 2.5- for model use.

ChrisM
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Help! MP Jet Letmo MD - 0,6 c.c.

Post  fiery Mon Dec 18, 2023 8:29 pm

Video showing homemade engine mount.

https://www.youtube.com/watch?v=icMDsIldse0&t=66s
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Help! Re: MP Jet Letmo 0.6 Replica

Post  Grosvince Tue Dec 19, 2023 3:21 am

Nice mount !

Does this engine runs well despite the shortcomings related by ffkiwi ?

Here in France rules are getting harder and harder for RC modellers, thus I will focus on small planes (below 800g) and this engine is a perfect fit for small oldtimers.

Regards,
Vincent
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Help! Re: MP Jet Letmo 0.6 Replica

Post  sosam117 Tue Dec 19, 2023 11:08 am

Grosvince wrote:Nice mount !

Does this engine runs well despite the shortcomings related by ffkiwi ?

Here in France rules are getting harder and harder for RC modellers, thus I will focus on small planes (below 800g) and this engine is a perfect fit for small oldtimers.

Regards,
Vincent

The mount is nothing special.
I went to the local hardware store and got the "standoff" nuts that are used for electronic boards for mounting.

Here are two Cox engines with the standoff nuts.

MP Jet Letmo 0.6 Replica Space_22
MP Jet Letmo 0.6 Replica Space_23



You should be able to do the same for the Letmo?
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Help! Re: MP Jet Letmo 0.6 Replica

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