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-   -   letmo 0.06 diesel (http://www.rcuniverse.com/forum/everything-diesel-87/7137717-letmo-0-06-diesel.html)

AMB 02-25-2008 10:19 PM

letmo 0.06 diesel
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Finally pony express ( US mail) made the trek from Arizona to Florida my letmo 0.06 #269
of a series of 500 arrived, nice high quality Czech made by MP jet
the box was so light thought it was empty, when opened there was all 1.5 oz of it

Interesting way of mounting prop the prop driver surface is smooth but has a 2mm pin
you position the prop at your flipping position then drill a hole in the hub that matchs the pin
being left handed I position the left blade about 8 oclock on my engines and down flip you then put on the prop, front washer and nut. the venturi assembly carries the little attached tank and
needle valve is a push fit. Looks like a tube could be made up with a small RC carb without too much of a hassel martin

j.hiner@comcast.net 02-26-2008 12:05 AM

RE: letmo 0.06 diesel
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Here is the little motors big brother. 2.5 cc diesel. Jack

AMB 02-26-2008 12:29 AM

RE: letmo 0.06 diesel
Jack looks just like mine only on steroids. I just drilled my 8x4 zinger put a drop or two of fuel
in the exhaust got a good grip it off it went for a second or two will make up a mount plate tomorrow morning for the bench run martin

misfitsailor 02-26-2008 07:54 PM

RE: letmo 0.06 diesel
I had the MP Jet little Letmo but resold it before trying it out. It looked like a pain to mount to anything. I ended up buying a couple of MP Jet Classics instead.

MP J sure makes nice engines, don't they? :D

johnvb-RCU 02-26-2008 08:06 PM

RE: letmo 0.06 diesel
What size prop do you run on your 2.5 Letmo Jack?

I have been using a 12*6 on mine. I didn't tach it but it seemed to do around 4000 rpm. Nice engine, shame about the mount

AMB 02-26-2008 08:07 PM

RE: letmo 0.06 diesel
I looked long and hard at this a U shaped slot to clear the rear bypass and tank on the ply mount and some little stand offs behind the mount screws will do it no big deal martin
I am going to make up a couple of fire wall out of 1/6 ply with mounts to fit a couple o engines and will also use bolts on for the gear mount so it can be switched should make a a pretty
quick switch possible with my 06 PAWand one maybe for the OS 10 LA Have cut 3 today

j.hiner@comcast.net 02-26-2008 08:55 PM

RE: letmo 0.06 diesel
John, Yes MP Jet does make some nice engines, I break in these old time side port 2.5 cc diesels with a 10/4 prop. Later using larger props such as 11/7 as suggested in the instructions. I did not record the RPM with the Letmo 2.5 cc diesel. But since my Oliver Jaguar 2.5 cc got beter fuel economy and I was looking for an engine for A Texaco I went with the Oliver Jaguar. Oiled up the Letmo 2.5 cc diesel and put it away. This was in March 2003. The Letmo turned up faster on the smaller props than the Oliver Jaguar. Folks use stand offs to mount the motor with the 3 screw radial mount. Beam lugs would be much easier. Jack

gcb 02-27-2008 11:16 AM

RE: letmo 0.06 diesel

Yes, drilling the prop is a PITA, and from observing the mounting holes on mine, I came to the conclusion that it was meant to be mounted BEHIND a notched firewall. Does anyone have info on how they were mounted in "the old days"? Of course, as previously mentioned, standoffs are a viable solution.

Although it has these limitations, it is an easy starting/handling, smooth running engine.

Enjoy yours!


lildiesel 02-27-2008 04:33 PM

RE: letmo 0.06 diesel
I once saw an add for a repro of an ancient Swiss made diesel that had the mounting lugs on the FRONT of the crankcase. Clearly that one was meant to be mounted behind a firewall or at least to a couple of crossbeams.

fiery 05-04-2012 12:23 AM

RE: letmo 0.06 diesel
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For me the word "cute" springs to mind

johnvb-RCU 05-04-2012 12:41 AM

RE: letmo 0.06 diesel
Do you get to the Muswellbrook veterans meet Fiery? David Owen is usually there selling MP Jets, Schlossers and sundry others

earlwb 05-04-2012 03:22 AM

RE: letmo 0.06 diesel
That little MPJet letmo .06 engine looks great too.

It isn't too difficult making a firewall mount setup for the engines. Yes you have to have to sort of make a cut out and a tapered thin section to clear the fuel tank. But when these engines were first made there was no standard for how to mount the engines, so many engines in that era were tricky to mount up to something so you could use them.

MP Jet Atom 1.8cc engine test run


comparing a MP-jet Atom 1.8cc to the MP Jet Letmo 2.5cc engine

MP Jet Letmo 2.5cc

MP jet .040-PB engine

j.hiner@comcast.net 05-04-2012 10:55 AM

RE: letmo 0.06 diesel
When running these old time side port long stroke diesels is Davis Plane fuel OK or should I ad some castor oil? Jack

earlwb 05-04-2012 12:15 PM

RE: letmo 0.06 diesel
I don't know what Davis has put in his fuel as to oil percentage, so I added a little extra Castor oil into the fuel container, just to be a bit on the safe side.
I think his 1/2a fuel should be fine, as he says it is for the little engines and vintage engines too.

fiery 05-04-2012 12:18 PM

RE: letmo 0.06 diesel
Earl has it - If you use DDD fuel for these, the 1/2A blend is preferable due to it's higher castor oil content.

Earl, that Atom 1.8 ccm Replica is a smooth looking piece. I heard it out performs the Letmo 2.5 ccm Replica. Is that your experience?

ffkiwi 05-04-2012 05:05 PM

RE: letmo 0.06 diesel
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OK gents here's a comparison of both of them side by side-the 2.5 is wearing an 11x4, and the 0.6 an 8x4. The mount for the 0.6 is entirely my own effort-but the only logical way to do it-once you start cutting clearance holes in the front of models and THROUGH firewalls, you're setting yourself up for grief down the track.........far better to use a 'standard' firewall radial mount setup-especially and these engines vibrate a bit-the 2.5 especially!
The mount details (I made it a decade ago, when I had fewer machining skills than now, so its a bit rough!) are: standoffs 3/16" dia aly, 30mm long [you could make them shorter-but then you can't get a finger in to choke the engine!], tapped 2mm at each end. The flange is 1-3/8" dia Delrin, ~5mm thick, with the rear screwheads (skt hd) countersunk flush. There is an angled scallop filed in the top flange to allow easier finger access for choking.

A couple of words of warning to users-as I indicated a bit further up-both engines vibrate a bit. [due to totally inadequate counterbalancing, exacerbated by a heavy piston]. I haven't experimented with unbalanced props, which is sometimes a cure in this situation. What is a minor nuisance though, is that both have screw-in front housings, which can loosen up under vibration. You need either a custom made pin spanner [which AFAIK MP Jet don't offer as an accessory-though they'd have had to use one for assembly]-or a pair of special soft jaw pliers [which you can get from Micromark!.....see item #85161] to tighten it up. I've had the 2.5 come undone during bench running, but not the 0.6-though it remains a potential fault with the latter. Secondly, the venturi assembly is a PUSH FIT in the casting, it is not screwed in-so use caution if you need to re-position it in the event of side or inverted mounting-if you loosen the fit, you'll have no option but to glue the assembly in place-which is less than ideal! Thirdly-in the case of the 0.6, the tank is in three pieces-simply pressed together-again, don't loosen the fit!

Now I will revisit the 2.5 mount one day-with a view to milling one from solid Delrin bar-with a big U-shaped channel for tank clearance. I think this is a situation where going for a minimalist approach on the mount is not going to work. I did make one from aly rod similar to the 0.6 one shown in the photos, but can't find it at present to photograph it.

For Johnvb-I think a 12x6 is probably a bit much load-I use an 11x4 for FF and I'd use a 10x6 for RC as a starting point-I'd expect these engines to peak around 7000 or 8,000-so at 4,000 rpm on a 12x6 you're probably getting less than half the power the engine is capable of-unless of course you're flying Texaco or similar and going for low fuel consumption. My Letmos will be going on a full size 'Simplex' and the KK 1/2A Texaco Playboy respectively-in due course.........which at my current rate of building could be several years away..........

Otherwise I reiterate what the others have said-MP Jet produce great engines, to a very high standard, and from good materials-so they last. It's great that they have resumed diesel production again after nearly a decade of producing electrics.


AMB 05-04-2012 05:12 PM

RE: letmo 0.06 diesel
Chris thats a great mount simple disc, standoff spacers and bolts and you have an intact firewall martin

fiery 05-04-2012 05:31 PM

RE: letmo 0.06 diesel

Thanks so much for sharing details of your mount design.

I query why MP Jet does not offer something along those lines as an accessory. I'd buy it. That said I can make one up 'with a little help from a friend'.
Thanks also for clarifying manufacture of the tank. I could not see any way to get it apart. I am glad I did not try to.

I just received a book from the UK published in 1946 about (then novel) model diesel engines. Several photographs of the 'Atom" and 'Super Atom' are shown in it. It was advanced design at the time.

ffkiwi 05-04-2012 05:43 PM

RE: letmo 0.06 diesel
Martin-that was my intent-I suppose the idea was already there in my mind from previously using a Cox Thermal Hopper on a 1/2A Spacer, and being aware of-but unable to get hold of -the Cox machined aluminium mount for one, I had to make something equivalent-which I did using a couple of washer style discs separated by aluminium spacers-which is also where I discovered the need for adequate 'finger access clearance' The Letmo 0.6 mount is very much in similar vein-as was the 2.5 mount. I had also mentally assigned the small Letmo to the as yet unbuilt KK Playboy Snr-which being a 1/2A Texaco design, already had a firewall mounting setup, so I was thinking radial mount from the word go. [ My intent was building a FF version from the RC plan for vintage duration use-the Letmo, being a vintage motor under NZ rules would qualify for a 20 sec engine run, and on a light model..........the intent is still there....but the execution leaves a lot to be desired...........]
The last thing you need is a firewall only supported on-at best-3 sides, and the area behind open to fuel soakage and exhaust residue.........

I may have a crack at making the 'solid' Delrin mount for the 2.5 in the near future-but its quite a big milling job to do on an Emco 5. I'll post it here if/when I get it done. Personally I'm a bit surprised that MP Jet haven't taken the initiative and produced suitable mounts-the Letmos are such a pain to mount that just about anyone who has one would buy the mounts to save themselves the aggravation!


fiery 05-04-2012 07:57 PM

RE: letmo 0.06 diesel
As the small Letmo 0.6 ccm reproduction was a limited run of 500 engines, aimed at enthusiasts and collectors, I'd say no thought was given by the factory to the issue of a dedicated mount for it.

I note your advice on tank attachment. Thankfully mine seems snug. Even so, I won't be playing with it unnecessarily.

Chris, has your tank ever come loose in operation? If it becomes a problem, I could always tap and thread it.

ffkiwi 05-04-2012 08:24 PM

RE: letmo 0.06 diesel
fiery-I've only ever bench run the 0.6 and 2.5-my comments on vibration were largely aimed at the 2.5, my comment on the tank purely at the 0.6 [the 2.5 tank bowl screws on] and the comment on venturi and front housings applies to both engines. When I was making my mounts I of course had to move the tank and venturi out of the way for access and measuring. Naturally I assumed that the venturis threaded into the crankcase and proceed accordingly. I rapidly discovered this wasn't the case, fortunately before doing any harm to either engine. Not a very clever setup-and requiring just as much precision-if not more, than a threaded setup-so I don't know why MP Jet did it this way except for authenticity! The only other bit of stupidity which comes close in my experience was the Fox 36RX muffler (a vertical 'Pitts' style) attachment-a hidden grub screw that you don't know is there until the muffler comes off-and which no mention is made in the instructions..... Tapping and threading the venturi and intake boss is of course an option for the Letmo if the fits ever loosen-but might then require some thin shim washers to get the orientation right-much like an Oliver Tiger venturi.
As for the 0.6 tank itself, I never noticed any problems-but it remains a tight push fit, so potentially could loosen. Actually, with my new found tank making skills it would not be difficult to make a translucent replacement tank, which might be a lot more practical than the existing metal one...................


earlwb 05-05-2012 03:47 AM

RE: letmo 0.06 diesel

Earl, that Atom 1.8 ccm Replica is a smooth looking piece. I heard it out performs the Letmo 2.5 ccm Replica. Is that your experience?
Hard to say,my Letmo 2.5cc replica engine turned a 11x6 prop at about 5,300 RPMs. It doesn't rev up high, but it can turn some really large size props well though. I found some more pics of my MP-Jet 1.8cc Atom engine being run. I was using a 11x5 wood prop on it at the time. It tended to turn the 11x5 prop at a little under 5,000 RPMs though. So the Letmo has a slight edge in power over it then.

My pics and videos for the 1.8cc Atom and 2.5cc Letmo came out bad as a oil drop got on the camera lense and it got more worse as time went on. I hadn't noticed it or I would have cleaned the lense off. I want to rerun and get better pics later for both engines.

Now both engines vibrated a lot, but the 1.8cc Atom seems to vibrate more as I remember having a lot of trouble trying to get a grip on the compression lever in order to adjust the engine. You want to get a strong grip on it but you have that spinning prop right close in front there too. I think one would want a short bar that they could notch or something so they could get a handle on it better.

Running a MP-Jet Letmo 2.5cc engine.

Here is the MP-Jet Atom 1.8cc engine.


I was having trouble getting the tachometer to work that day as it was quite windy and the sunlight coming through the leaves was playing havoc with the tach. The peak reading is false in this case.

AMB 05-05-2012 04:04 AM

RE: letmo 0.06 diesel
THATS a bunch of torque Davis says 9x7 as a starter prop for a 15 martin

Of course a long stroke not square like glow conversions

earlwb 05-05-2012 04:16 AM

RE: letmo 0.06 diesel


THATS a bunch of torque Davis says 9x7 as a starter prop for a 15 martin

Of course a long stroke not square like glow conversions
The Instructions for the engines suggest large props. For example with the Atom 1.8cc engine they suggest a 12x5 to 13x7 size prop. For the Letmo 2.5cc they were suggesting a 11x7 prop and using a 11x6 for break in.


Recycled Flyer 05-06-2012 03:38 PM

RE: letmo 0.06 diesel
Ihave an MPJet classic with beam mount lugs on it but Ido know how the radial mounts work and I am under the impression that they do not mount on any real firewall at all.

Just to clarify here, the first former of F1 in most designs remains unchanged (or at least simply pushed back a bit) and to accomodate the radial lugs here you extend the nacelle of the model forward to incoporate (for want of a better term) a false 'F0.5.'

A 'U' shaped former supported on three sides should have plenty of strength as theses are not large capacity engines regardless of how much they do or don't shake.

And I don't see why its any more of a bother adding a false former? (I bet Icould cut the ply for it an modify the design far faster and easier than making custom stand offs and mounting disks.)

Iapplaude the alternative engineering though!


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