vsv123

The latest versions of MK17 engines (released during 80s) have comp screws with sloped tips, instead of earlier versions with flat round (like described here http://www.rcuniverse.com/forum/ever...ml#post6037296).
The fact is that this sloped tip feature is really prevents comp screw from loosing on MK17 engine. The comp screw itself rotates freely (actually it's loose) in thread, however while engine runs, comp screw stays still.
As the point of contact with counter piston (btw it has flat top) is off the center, while running the engine, I believe counter piston skews a bit and seize in cylinder liner. Or may be it is because of comp screw off-center point of contact
The question to experienced dieselists is, will such method damage cylinder liner and counter piston while engine's life cycle?

Mr Cox

This is a very common trick design is used to stop the screw for unwinding when the engine is running. It will not be off center enough to cause any harm to the counter piston.

Recycled Flyer

Probably does as much harm as Conrod angularity driving through a piston.

The side walls on both should counter any skewing.

If there was narrow side contact you may have a problem.

qazimoto

My Feedback: (1)

Seems to me that the contra piston skewing theory is only going to work if the engine's clapped out or has very bad fits anyway.

Perhaps it only seems to work because the contra fit is good enough as it is.

Besides the MK-17 already has an adjustment feature on the Comp screw fit in the head.


:-(

fiery

My Feedback: (2)

Continuing the Russian theme, my favourite 'cheapie' diesel is the the MARZ 2.5. They feature a well executed compression screw.

The photographs tell the story. A deeply recessed facing end shows a nice chamfered 'doughnut' contact point.

There are a number of nice engineering touches under the journeymanlike exterior of the MARZ engines. Another distinction. Unlike the MK-17, every MARZ 2.5 I have opened has been commendably clean inside (apart from preservative). Manufactured at a military helicopter servicing facility. Perhaps that explains it?

vsv123

Can you describe how muffler is sealed with the MARZ crank case?
I've tried to make a 3D printed muffler for MK17, it works well. Exhaust temperature of diesel is so cold that printed ABS plastic does not melt (it has ~210..230 deg.C melting temperature). However engine with ABS muffler is heating more (I assume engine with metal muffler will be less heated than with plastic one)



Here is completed muffler on my RC plane with MK17

ffkiwi

Good effort vsv123-that approach might well prove useful for others. My only concern would be the effect of sitting in contact with so much hot metal-the exhaust is simply passing through-at some velocity-so there is little time for heat transfer to occur-but as the engine runs (an even after it has stopped) there is a lot of residual heat in the head and cylinder. Some diesels run very hot indeed-AMs being a case in point. My concerns would be mainly around the mufffler casing warping over time from the heat-it may be I'm over analysing the situation. There is quite a market for someone who can develop silencers/mufflers for the many existing diesels that never had them-but now need them either to satisfy club rules or to allow flight at noise conscious sites. [my old club-Dunedin MAC had a rule that all motors .15 and above had to have mufflers-and I've seen many similar rules over the years. As written there were no exemptions for diesels-though I don't recall it ever coming up as an issue. PAW and the MARZ have shown that diesel mufflers do not have to be large and bulky. But the tooling costs to retrospectively produce metal ones for the 50s, 60s and 70s diesels that a lot of us here still use is prohibitive-and 3D printing would appear to offer a very good solution-especially if a generic muffler could be developed [which of course has been done in the past with conventional metal mufflers such as the Semco and Kavan range-which were essentially one or two 'standard' designs with a large range of 'brand specific' adapters to mate them to a specific brand and model of engine.

This is a good forum to post your 3D printing engine experiments to-(it's not called 'Everything diesel' without good reason.............)

ChrisM
'ffkiwi'

PS Tempting though it might be, I cannot see the same approach working for glow-they run significantly hotter-I found out the hard way in two quite distinct uses-one was F1C models with rear exhaust engines where the exhaust would char even fibreglassed wood with time-and on another occasion-running the little G-Mark Humming Bird 0.5cc glow without the muffler fitted-the exhaust started to melt the top of the integral plastic fuel tank (which brings to mind the modern non OEM Coxes-many of which now have plastic-as opposed to metal-tank bells. I wonder how they get on......

fiery

My Feedback: (2)

vsv123, the Marz 2.5 exhaust collector is seated on top of the case and seals on the bottom fin of the colling jacket.


Further details from Adrian Duncan's article on the MARZ in Model Engine News (MEN):

"[the engine is] fitted with a simple ring collector around the exhaust belt to serve as a muffler. This was not produced in Russia but was an accessory produced in Australia by Macheast to enhance the engine's appeal as a sports engine. It is quite effective, but robs the engine of a significant amount of power at the top end, although performance on larger props is relatively unaffected."

There is also an article in MEN on the MK-17 which you may enjoy.

Nice work on the printed MK-17 collector ring. You may wish to download the specs for others to copy if it is a success. There is a link to a shop that will produce printed components on the "Club ED" thread.

vsv123

The first version which is on previous picture of RC model was with an exhaust hole situated at one-side

The engine running with this version of muffler chokes on max RPM while model flying, it works unstable on max throttle, RPM was reduced to ~9000..10000 from initial 11500 with stock propeller


The latest version of MK17 muffler I came up on practice is a "twin" version of muffler with increased output barrels diameter and increased intermediate exhaust holes:


There is no noticable RPM and flying performance reduction with such version of muffler. Furthermore, RC mod of MK17 with silencer has a very good throttle response and it has stable performance in idle, middle and hi RPM (without muffler middle RPM is unstable). And as exhaust ports are enclosed with muffler, it is possible to make richer mixture in idle, thus lower idle RPM. Without silencer I get ~5500 idle RPM, with silencer ~4000..4300 idle.
Full throttle is ~11500 RPM in both versions (with and without muffler) on my MK17 with stock propeller, and it is the same with stock MK17 venturi inlet

I flew at about 40..60 minutes with this ABS muffler (about 6 flights each ten minutes), the only thing I've noticed is that printed ABS parts become fragile under constant vibrations. 3D Print temperature must be increased for better welding of printed layers, thinner layer is way more better (printed with layer 0.2 mm). Parts are glued together with CA glue, crank case-muffler gaps are sealed with glue for EPP foam (it's resistive to ether and kero)
I'll test more this ABS type of muffler. Also the question is how ABS resists to ether and kerosine. Probably it's better to print with nylon filament

Here is STL files of the latest muffler version for those who might be interested in [ATTACH]2041928[/IMG]. Parts are in positions they were designed and are not aligned for 3D printing (rotate parts before printing)

gcb

When I broke-in my first MARZ 2.5 (aluminum muff) it had the exhaust collector ring. I turned the ring upside down to get exposed exhaust ports during break-in time. After it was run-in I returned the collector to its original position.

BTW, I have three MK-17's and all three were clean inside...I always flush the crankcase in a new engine.

George