In search for the COX engine with the longest runtime on its clock

Thanks, David, then your engine must have 100 hours or so runtime. It is not clearly visible if this is a COX and what size? How about its wear on the cylinder and crank by the 100 hours of use?

The engine was a dieselised rc .049 the red one rc back then was 50$ in 2009 tink i used wit os glow plug it was its crankcase that has wear faster du To The rc choke carb as the engine idle it suck the crank chaft inside the crankcase last run the engine has lost the thrust wascher which was surely too thin du To friction This engine already has a disadvantage with the hd crankshaft which is looser from factory Result the connecting rod has become loose the pin of the crankchaft is irremediably damaged by the misalignment the crank chaft was deeper in the engine the connecting rod was at an angle during the operation of the engine the engine was stil runing but was hard To start that morning and i have had To change seting of the neadle valve I didn't really pay attention this morning, that should have given me a clue that something was wrong. After: 20 min the engine started To sound strange at idle the piston and cylinder Was still like new on the very high compression side If it weren't for the thrust washer which had been due for a replacement for a very long time this engine would still be good even after another 300 flights those thrust washer on sur start rc choke tube carb engine Now I always lubricate before use also check the play

Hi Andras, I can’t add anything significant to this thread other than it sparks a memory of what not to do…. Flew them out of dusty cotton fields as a teenager…. When they landed (or crashed) just hose it down with fuel and go again…. Wore out a few prematurely this way…. If I suspect one has a spec of dust in it now it doesn’t get turned over until careful disassembly and cleaning….

So, now that I regard them a little better, It’s good to know a very long service life can be had…. So if you would please share some more detail on your long run engine, Congratulations by the way …. Maintenance, Fuel, Type of plane and flying? What have you learned from this long run jewel?

Thank you indeed!

First off this engine had a tapered bore cylinder with very good fit from the beginning. I did not particularly run it in, just chucked it in the nose of my Toucan RC plane and let it do what it does best: run dependably hours after hours.

I reset the balljoint only once in its early hours..then it got work hardened, and the fit is still as good as it can get...

Never had less than 20% castor nor more than 30% nitro in my home blended fuel. Never had a drop of synth oil, always used castor.

Kept it clean and as you said, if some dust got into it on a harsh landing, removed the prop immediately to prevent inadvertant cranking of the piston that would sweep dirt into the cylinder and kill compression, then disassembled the engine and washed it clean.

Always added after run oil into the cylinder by removing the glow head, after the daily flight session.

Did not use the devarnisher brush that not only removes varnish, but unavoidably eats away cylinder tolerance too. Put some kitchen cold grease remover fluid on a cotton swab, and rubbed the cylinder bore until the brown varnish disappeared and the next fresh swab remained clean.

Made sure the prop was always well balanced. With front rotary valve engines good crank fit in the case is important, because the port on the shaft is near the nose end with only a short shaft nose to seal the crankcase. I had badly used TeeDee-s from a previous owner who ran unbalanced props on it until the fit and seal were gone such the engine was very hard to start.

I think this is it basically that kept my 051 alive and kicking so long...without becoming an obsessed engine maniac, just giving the engine the care it deserves.

Living far from where COX engines and parts are/were abundant i.e in the US, one needs to take this care, relying on original stock parts with limited replacements available around. Like Cuban taxi drivers still running the pre-Castro revolution American classic cars of the 50-s..many of them still with the original engines in them..

If you check the last item on Instruction sheets at the bottom, an interview with Larry Renger talks about a longevity test by COX that ended after 400 hours with the COX engine still alive, though needing a starter to restart..

Great explanation, Thanks !!….Taking notes

One interesting thing I have noticed about castor oil;…. When rebuilding  an engine I pre lube it with castor oil…. With the ball/socket clean and dry you can feel that tiny bit of play in the joint (close to tolerance)… Dribble a little oil into it and seems to go away… Or at least damp it really well…. Interesting how it performs

Another way to may be estimate amount of wear and tear on an engine is the accumulative linear feet or meter a piston travels along its bore. Since our Coxes normally operate at higher RPM's to produce optimal power may explain why one ends up replacing cylinder and piston sets more than in the larger engines. At least that has been in my limited experiences.

After a long season of flights, I replaced the R/C Bee's piston cylinder set, which restored compression to new. Engine still had compression, but it was noticeable the amount of leakage, that bubbling one gets when compressing the cylinder with a fresh shot of fuel or light oil. One season back in 1983, I estimated about 200 flights on my Minnie Mambo.

Flights were roughly 4 minutes each, about 15 hours accumulative. Based on its predecessor, the QZ, optimal BHP was at 15,000 RPM. I used throttle, so may be it spent 2/3rds to 3/4ths of its time at full RPM with the optimal 6x3 prop. But for the sake of academic discussion, lets just assume for now that it was run at full power those 15 hours.

Stroke is 0.386 inches. 1 RPM is double that or 0.772 inches. 15,000 rev/min x 60 min/hr = 900,000 rev/hr x 15 hrs x 0.772 in/rev x 1/12 ft/in = 868,500 ft x 1/5,280 mi/ft = 164.5 miles that piston traveled.

Theoretically given my assumptions, the piston traveled quite a bit of distance. This may explain why, although perhaps by babying the engine, one got more longevity out of it with significant compression left, that others of us including mío got a couple seasons before replacing the set. This is because half-A's must run at their peak for most of our half-A planes to fly decently. There is less loafing around as one would do with a larger engine. When I use a .09 or .10 engine, I can usually throttle back halfway after takeoff and plane flies very .049 like.

Anyway, my for what it is worth.

rdw777 wrote:Great explanation, Thanks !!….Taking notes

One interesting thing I have noticed about castor oil;…. When rebuilding  an engine I pre lube it with castor oil…. With the ball/socket clean and dry you can feel that tiny bit of play in the joint (close to tolerance)… Dribble a little oil into it and seems to go away… Or at least damp it really well…. Interesting how it performs

Yes, it is the surface tension of thick, viscous  castor that keeps it in the gap between the balljoint and the cup..another important feature of castor is that it polymerizes at high temperature, (instead of burning like synth oil) i.e. forms the varnish inside the balljoint cap, that keeps the metal parts away from rubbing on each other. The reason non-castor fuels will kill the COX engine is related to this varnish in the balljoint cup, that would not form with synth oil..

GallopingGhostler wrote:......

Stroke is 0.386 inches. 1 RPM is double that or 0.772 inches. 15,000 rev/min x 60 min/hr = 900,000 rev/hr x 15 hrs x 0.772 in/rev x 1/12 ft/in = 868,500 ft x 1/5,280 mi/ft = 164.5 miles that piston traveled.

Theoretically given my assumptions, the piston traveled quite a bit of distance. This may explain why, although perhaps by babying the engine, one got more longevity out of it with significant compression left, that others of us including mío got a couple seasons before replacing the set. This is because half-A's must run at their peak for most of our half-A planes to fly decently. There is less loafing around as one would do with a larger engine. When I use a .09 or .10 engine, I can usually throttle back halfway after takeoff and plane flies very .049 like.

Anyway, my for what it is worth.

This was my estimate after my  TeeDee 051 completed 250 hours runtime in the nose of the Toucan:

balogh wrote:This was my estimate after my  TeeDee 051 completed 250 hours runtime in the nose of the Toucan:

András, at 21,000 RPM (max recommended by http://sceptreflight.com/Model%20Engine%20Tests/Cox%20Tee%20Dee%2009%20RC%20and%20051%20RC.html that means your .051 Tee Dee R/C piston traveled 3,838 miles (6,292 km). It is possible with the more efficient fuel-air supply by front venturi that overall it may run cooler than a reed valve engine (although I say this through casual observation by gut level feeling).

George, it may very well be that with the less obstructed air-fuel mixture flow the front rotary engine has stronger suction and is therefore less susceptible to lean runs than reedies?

I forgot to mention that my 051 never experienced a lean run that I saw on other engines wear cylinders rather  fast..but this is just my guess. The test engine Larry Renger said ran for 400 hours must have been a reedie no matter the slightly more obstructed respiration.

András, Larry Renger's test was under laboratory conditions, not field. How many field tests, did the customer not simply wash the dirt from a crash with a shot of fresh fuel, refuel, fly again? I did. It's a thing all "children" do when they are young, "eat dirt".

And, how many field sites are free from dust in the air? I didn't overtly mistreat my engines, but then I did not pamper my engines, either. And, I'd peak out my engines, then open the needle 1/8 - 1/4 richer, just a tad RPM drop, so engines ran at their peak in flight. There could be a lean run or two.

Most of my cylinder/piston changes were because I damaged them in removing them to clean them (devarnish, etc.) However because Cox parts were relatively cheap back in the day and readily available at department stores and hobby shops, I just buy and fix. (Cylinders back then didn't have convenient flats, had to wrench from the exhaust ports.)

And, no telling what the alternative and cheaper Testors fuel had in oil content back then.

Yes George, no doubts the lab conditions Larry Renger refered to must have helped reach the 400 hours on the clock of the test engine...I just reiterated this citation to corroborate that longevity of COX engines, under normal care conditions with no abuse, are measured rather in 100 hours than in 10 hours...

Piston travel is a neat way to measure what the engine has done George, Never thought of it that way…… If the 300 hr engine traveled at say a conservative guess of 40 mph it would have covered 12,000 miles… Impressive! (I know it wasn’t all air time, just speculating)….

Glad someone else admits to the rough treatment we gave them in younger days …. They were inexpensive and common…. We could get fuel at the department store in town…They’ve taken on a different meaning now…

Andras, How easy is the engine to start and how do you start it?

Robert it still starts easy when cold, but a bit finicky when hot, when compression is a bit tired. Then an electric starter helps start it..

I

Never thought much about piston travel. I guess 3/4 of an inch piston travel gives the propeller maybe 4" of forward motion with, say, a 5-4 prop. I found the reedie's crankcase never lasted long, while the TD case outlived the piston/cyl. I have one TD that really has no compression at all but will start with an electric finger after a long time. No history on that motor as it was just a swap meet find.

Thank you aspeed..I guess the longer nose of TeeDee crankcase results in smaller radial forces to counter the piston thrust on the crankpin, so the wear of the crankcase in TeeDee-s is less...added advantage is the better lubrication because of the port of rotaey valve.  The blow-bye, interestingly, is limited even on fairly used engines by the rule of gas dynamics, i.e. over a certain pressure differential between the cylinder and atmosphere, the loss of gases through blow-by cannot increase unless the gas passes in a cross section like a Laval nozzle...and the radial gap between the cylinder and piston does not act as a Laval nozzle...this may explain that even worn engines, once started, will reach the rpm near that of a brand new one...

balogh wrote:Thank you aspeed..I guess the longer nose of TeeDee crankcase results in smaller radial forces to counter the piston thrust on the crankpin, so the wear of the crankcase in TeeDee-s is less...added advantage is the better lubrication because of the port of rotaey valve.  The blow-bye, interestingly, is limited even on fairly used engines by the rule of gas dynamics, i.e. over a certain pressure differential between the cylinder and atmosphere, the loss of gases through blow-by cannot increase unless the gas passes in a cross section like a Laval nozzle...and the radial gap between the cylinder and piston does not act as a Laval nozzle...this may explain that even worn engines, once started, will reach the rpm near that of a brand new one...

Back in the day, 1970s, we used to lap the piston/cylinder to be quite loose for the speed motors with the steel/iron lapped motors. Some of the big D Speed planes would go 200 mph and run out of fuel, and would take a few laps for the motor to wind down, because there was so little compression. The leakage did not seem to affect the performance too much, mostly less friction. Often, they were very hard to start. The crank does have to seal well or there will be an erratic run. Nowadays with ABC it is a different story for a loose fit, and the motors can take the odd lean run without burning up.

balogh wrote:Robert it still starts easy when cold, but a bit finicky when hot, when compression is a bit tired. Then an electric starter helps start it.

András, I think I now understand the perspective where longevity is being measured. I always wanted my Cox engines to operate at their peak potential. When I saw signs of it through extra bubbling during compression not seen when new, I figured it time for a new piston and cylinder. I was probably changing them out prematurely. But, given half-A flight especially where throttle wasn't used, the sport reed valve engines needed to run at their peak to provide decent sport flight. I saw that numerous times pulling a 1 or 2 channel half-A sport plane, where the RPM sagged a little or I didn't use an optimal prop, barely lumbered along with poor wind penetration and altitude gain.

Here in US, being closer to the factory source, it was easier to purchase since parts were readily available and cheap. Even back in the 1970's, I could run down to Ala Moana Center, Pete's Model Hobbycraft or Hobbietat off Kaimuki Boulevard and get what Cox parts I needed. Even for a short time after, could pick them up at Hickham AFB or Pearl Harbor Sub Base Hobby Shops, Sears & Roebuck or Montgomery Ward department stores. (Those sources disappeared around the mid 1970's.)

I am amazed at the quantities in which half-A engines were produced back in the 1950's and early 1960's, a run of 1,000 engines of one size per day wasn't unusual, according to a Wen-Mac historical information video on their glow products.

I have a well worn out Enya .15-III TV engine that has noticeable compression loss. However, I was surprised that once it started, it seemed to have the same amount of power turning an 8 inch prop, compression loss had minimal effect. The same holds true for a used OK Cub .049B that I purchased on the net. Once started, seems to run OK. Optimal? I don't know, at the time I didn't have a tachometer, but run it did and seemed to wind up fine for a relatively high torque lower RPM engine. (I gather that rather than propping like a Cox, go slightly larger diameter or wider pitch to take advantage of its 12,500 or so max BHP RPM.)

So, in essence, I can see how that one could continue a Cox engine. I just never had the interest to prove a point. But, this thread has renewed interest in me that even though an engine may appear to be slightly tired, has not lost its spunk yet to provide decent flights. Then the hundreds of hours run make sense.

George I am the same way as you are particular about the compression of my COX engines even though I know that at high rpm the.loss of compression in an engine does not have such a detrimental effect as one would think when seeing the bubbles in the exhaust port when cranked by hand.

It may have something to do with the scarcity of parts in my environment..an old reflex, seeing something of a scarcity getting worn is bugging me.. ...I try to suppress it   and not retire the worn engine before it is really finicky to start ..in fact for the 12 years of my renewed tinkering with COX engines and many RC planes built and flown for long hours, I have not really worn out one single COX engine, even that 051TeeDee with near 300 hours on its clock is still capable of hauling my Toucan..