The 2.5 cc Alag X-3 is probably the best known of this family.
As it happens, I have an X-4 (1.5 cc) and an X-5 (1 cc) that have lived, fairly anonymously, in my box of bits, for lots of years....
Back then, in the late 50's, these engines were "cheapos", not sold by the "serious" hobby dealers. You could purchase them, mail order, from importers that didn't know a thing about the aeromodelling hobby.
Among "serious" aeromodellers, these engines were rated very low, and I figure most of them were bought by pure beginners, that either ruined them immediately, or, after failing to start them, threw them away. All in all, you didn't see many of these Alags actually running (I didn't, anyway...)

My 2 examples are "brand new", i.e. unrun, and recently I dismantled them to remove the "factory-gunk" and tidy them up.

A pleasant surprise
After dismantling, cleaning and adding some fresh oil, I fiddle around with the parts, and I get the obvious feel of GOOD engines...!
Nicely built crankcases, drillings centered. All threaded parts have a good & non-sloppy fit, indicating good manufacturing standards, and providing a pleasant feel when fiddling & fitting....
Cylinder/piston lapping seems just perfect....and, when I press the contra-pistons out, I feel just the "right" resistance, and they DON'T just fall down the sleeve, but I can "feel" a tapered bore, just a tad, all the way down...and the CP's are steel, NOT of alu, as sometimes seen on cheaply produced engines.
The prop driver taper is a perfect fit, on both....
The X-4 backplate is plastic though, but even "respectable" makers (like e.g. ED) have practised this, with no trouble.. The X-5 backplate is metal, the traditional way...


Junk engines...?...I'm no longer sure of that...!...so far these engines seem just great...! (I am not able to comment the metallurgic standards, though...)

Both engines are very compactly designed (small really, for their displacements)...and lightweight:
The X-4 weighs in at 68 grams...not bad for a .09..!
The X-5 weighs just 52 grams...about 2 grams (!) more than a British Mills P75...

It seems the Hungarian guys knew exactly what they were doing.......I get no "junk engine feel" at all, really....

Eventually I will run them in, carefully, to give them a fair chance to refute their bad old reputation....

BTW I think they look good too...

The following article by O.F.W. (Peter) Fisher appeared in the Jan-Feb 1972 issue of "The Engine Collectors Journal", which even then was Edited and Published by Tim Dannels ! Tim is still with us today, so please take a look at his website at - http://www.modelenginecollecting.com/
The 2 photo's of the Rawlings courtesy of Ron Chernich's website at -
http://modelenginenews.org/prod/r30.html

Here is another east block engine a Vlatavan twin made in Russia shown here with the single on which it was based, there was also an ignition and a glow version, the engines still do need some cleaning

Originally Posted by Twin-Stack

The following article by O.F.W. (Peter) Fisher appeared in the Jan-Feb 1972 issue of "The Engine Collectors Journal", which even then was Edited and Published by Tim Dannels ! Tim is still with us today, so please take a look at his website at - http://www.modelenginecollecting.com/
The 2 photo's of the Rawlings courtesy of Ron Chernich's website at -
http://modelenginenews.org/prod/r30.html

Funny how that original Dyno shape went on beeing used by others

Originally Posted by Reginald

Funny how that original Dyno shape went on beeing used by others

"When your on a good thing, stick to it" - Old Aussie saying.

As I've got a soft spot for small displacement diesels, I took a chance on this OTM Kolibri from 1976...
A cute little engine indeed, but as I'm aware of a few "dark spots", I started with a dismantle, to see what I really purchased....

First, the compression T-bar ends were rough in an unpleasant way...sharp really, like they've been trimmed by my local electrician....
This was an easy fix, with some wet emery paper. The T-bar feels much nicer now...

The engine was moderately oiled from factory, with a slightly rough feel. I guess a VERY careful run-in is essential.
Cyl/piston fit is good, with a noticeable taper.
The contra piston (steel, luckily...) fit is slightly on the tight side "upstairs", but probably functioning.
(is there a safe & simple fix for this...?...advices are gratefully received...)

All threaded fits are good.

As I've heard of a "short gudgeon pin" issue with this engine, I was a bit worried, but it doesn't seem to be the case with this example.
The pin ends, roughly, 0.12 and 0.20 mm from the cylinder wall, so there's no chance it could slip out of the hole one side, like I've heard of. I just hope that the pin is a tight enough press fit, to prevent it from moving around and chewing the cylinder wall....
I did a slight "cold" press test, and so far it seems fairly tight...

I didn't manage (dared) to press the propdriver off, even when applying heat, so I left the crankshaft in place.

One point of critisism is the turning of the crankcase, which is NOT quite centred (see pics) in any direction....we'll see how this might affect things....
Hopefully the "two holes" are 90° to each other. (,,,am I an optimist?...)

An intresting note, is this engine's similarity to the Webra Piccolo...trying to be a gentleman, I say it is "inspired by" the same....
(I tried the Piccolo cylinder liner on the Kolibri....same thread...!)

So far, my feelings are mixed.....basically I love this little engine for its "cuteness" and small size...on the other hand I am slightly dissapointed with the manufacturing standards at a few points....
I was somehow prepared for this though....

We may, however, have runner here...future will tell....

Is the centering that bad or is that the way it looks due to the thread?

Greg

Originally Posted by gkamysz

Is the centering that bad or is that the way it looks due to the thread?

Greg, your are right...the "true" run-out is less than what the photo indicates...nevertheless, we've got an issue....
The liner fitting is about 0.32-0.33 mm off center.
Backplate fitting is about 0.22-0.23 mm off center

I haven't checked the angular relation between the two bores though...if this is "ok", we may have a runner anyway. If it's too bad, we've got a self-destroying machine...

Gluehand..
Maybe offset for a reason?? Look on Ron's web site for a 'splanation, it's a french word for "offset" and it's done to reduce side loads. CRS Attack..

The latest Mk 17 from CZ showed up for your carby.. This one is different from any of the others.. No replaceable venturi inserts on this one.. I wonder if it's an older or newer model? Anybody on the list know?
The other I got from Ed Carlson last week has the inserts so it goes under the knife..

Al

Found it.. http://modelenginenews.org/

desaxe'
Means unbalanced ... in this case.. from the offset.

The offset Gluehand describes is due to the way they hold the casting for machining. Either the machinist was not careful about placing the casting in the fixture, or the fixture was not designed to take casting tolerances into account to center the bore in the casting. As long as the machining was done correctly, it's just an aesthetic issue. A very bad case might have structural problems, but this is OK. I think I have an OTM 0.8, I should check mine.

Greg

A delayed reply to the CNC thoughts.

What sort of CNC machine would work for finishing cylinders? I would guess a cylindrical grinder, but I suspect few toy engine cylinders are built on 1/2 million dollar (new cost) CNC grinders. I would guess most are still finished on manual (automated) grinders. Some discussion a while back suggested OS burnishes their sleeves. At OS the production volume is ~2 orders of magnitude larger than diesel engines. Sometimes the finishing method is evident to the eye, other times it's not. Using a CNC grinder for cylinder sleeves is certainly possible. Some equipment can resolve .0001° angles in the grinding head. This is more than adequate for a ringless engine. I doubt that many model engines are made on equipment this advanced, except maybe the high volume or high quality mfrs, OS, Saito, YS.

The piston to cylinder "feel" could be quantified with a specific taper angle (on the bore and piston) and materials, etc., but piston and sleeve pairs must still be hand selected for the proper mating fit. The entire idea behind successful high volume manufacture is to get the operators feelings out of the design equation. This is done by putting tolerances on the parts. This isn't to say a modern CNC machinist doesn't need "feel". In the case of CNC, operator feel is knowing how much the dimensions change as the machine warms and how much tooling wears and being able to account for that with tool offsets to keep parts within spec to avoid making scrap.

I understand CNC and the tolerances they work in. There is a difference between a diamond turning machine with air bearing spindles and ways with 0.01 nanometer resolution and machines which make engine parts. But CNC is just as much program, tooling, operator, as a manual machine. My father programs, sets up, and runs old clapped out CNC lathes at his place of work and can obtain ±.0002" when called for. This, while programming the taper due to worn ways out of the part. When running ±.0002" parts he can't let the machine stand idle more than a few minutes before dimensions begin to change. The machine cuts air for an hour or two in the morning if possible as well, otherwise the changes are hard to keep up with as the machine warms from cold overnight. Making scrap on a CNC is all too easy.

For those who haven't seen, Peter Burford goes into great detail explaining how his little engine is made. http://www.peterburford.com.au/manufacture.php There is also this bit on Tom Ridley. http://modelenginenews.org/cornell/oliver_reprod.html

For reproduction engines I don't have much to say. To me, anyone who makes a repro is taking advantage of the heritage of the name. The vintage competition rules make it a necessity. The rules do limit engine designs to technology (materials, porting) of the era, why also limit the external appearance? I don't compete and I'm certainly not nostalgic for these types of engines, but it seems such competition rules created a market. And, like everything else there is good and bad.

Greg

Thanks Greg, good information.
John

Has anyone been in contact with the Russian diesel builder Kalmykov? I got the message below from PAL Model Products who is having him produce the Imp Diesel for R/C and FF.


Tom:
I'm looking to find Aleks Kalmykov, of Ruse Engines, Russia!
I've not been able to get a response from him (despite e-mails and phone calls) for over a month and a half!
I'm interested in communicating with anyone who knows if he is well or knows where he is??
Would you please do that?
"Bobbylang"
bobbylang@earthlink.net

Greg,
That was a pleasant & educational tour into the world of CNC...thanks..!

I figure the temperature issue mentioned, (kind of) equals an old-school hand lapper who stayed too long at the pub the night before.......er...no, that's probably even worse...

.