Cox Rubber Engine Spinners Question

What are you flying? Control line or radio control?

Fortunately, Matt at Ex Model Engines has new Tee Dee crankcases complete with crankshaft and prop hub, $35 US.

http://www.exmodelengines.com/product.php?productid=18207


Ex Model Engines - Cox .049 Tee Dee Crankcase Assembly

May be using a break away engine mount with rubber bands to hold the engine module in place like on the Ace R/C Grasshopper or Goldberg C/L Wizard might help?

I would recommend the small black rubber spinner that Bernie and Matt are selling. This may soften the touch of a running TD with the ground sufficiently.

https://coxengines.ca/cox--049-rubber-spinner-hub-black.html

The larger red spinners add considerable weight and may affect the prop balance..they may also detach from the engine at high rpm and fly away, in my experience.

https://coxengines.ca/cox-049-engine-hub-red-rubber-spinner.html

Found this, may be I'm jumping to conclusions, but gather a way to protect an engine:

pkrankow on Oct 11, 2012 wrote:This is a set of scans of my Lil wizard rubber band mount.  The plane is 30 years old.  I measured and dimensioned the images.  They can be reproduced from 1/8 inch plywood.  I have found this mount allows for 2 things preservation of a trainer in crashes, the engine mount rubber bands "give" instead of things breaking ability to use the same engine on several models with little effort at the field, Enjoy, Phil

Of course, if one wanted to pass the honors of repair to others, Matt at @EXModelEngines has:

http://www.exmodelengines.com/home.php?cat=275

Cox .010 .020 .049 .051 .074 .09 .15 Engine Rebuild Service (Any Additional Parts Extra) - $14.95

Bent crankshafts? Well good for you!

Too many of these adorable engines sit collecting dust when they should be flying.

Which reminds me of ("my") quote:

The best compliment you can make to something (anything) that you bought is that you wore it out!

Thankyou for all those replies ! I am flying control line. I use RC for air cars and air boats, but control line for flying planes. I am fine to build and assemble the new motors myself and have bought plenty of parts from Bernie and Matt over the years. Fortunately I have a number of spare crankcases assembled with crank from Matt and cranks and cases on their own. I will uses a new case and crank with a new cylinder and piston as I stupidly ran one of the engines after, and Im sure it will have tried to make itself all fit together again with everything out of line. Lol.

I will get a couple of cases complete with crank from Matt to put back into my little stock and I will get some of the black rubber spinnsers as Andreas suggested. They are worth a try, even if only to serve as a reminder to keep the thing out of the ground

Gallopingghostler, thanks heaps for the suggested rubber band mount setup. Im actually going to give it a go on one model first and see how it works. On my PT 19 I think it was when I was young I recall the engine being mounted in with rubber bands and it saved it a couple of times. Thanks for providing the templates/sizing. It will fitup very closely to how I mount my engines at the moment but with nuts and bolts. will be interesting to see if the engine maintains allignment at all times during flite when being flown hard. But the rubber band idea was one I had considered in my sleep lastnight and the detail you have provided me has convinced me its worth a go on a model to at least evaluate and understand!!

Certainly wont be the first parts Ive used in engineering over the years that break/give to protect the greater whole. Sacrificial mounts are very good in many applications.

Thanks for all of the helpful and informative and detailed replies! greatly appreciated.

Hope to fly for a couple of hours today and keep my figure eights to eights only and no nines.

Yabby

To get back to the basic question. Yes, I believe those spinners help in a couple of ways, especially in a straight into the dirt crash. First the point itself lessens the shock as it parts the soil, giving almost an extra inch of deceleration. Even a pointy metal spinner will do that. But a rubber spinner adds a tad more cushioning, although the distance from the spinner's point to the face of the solid aluminum spinner nut is only a quarter inch or so.

Bob

Thanks Bob makes sense. and it only has to make just enough difference to stop the shaft bending and if it does that once, then its been worthwhile. I think the black rubber spinner as Andreas suggested and is inline whith your thoughts mixed with the engine mount held on with rubber bands as suggested by GallopingGhostler may well make the difference. When I pulled the engine apart I could see on the crankcase backplate where the crank pin and small end had gone back and hit the metal backplate. Not a circular wear mark, but a localised ding Im sure is from the crank going back, or depending how you want to look at it, the back plate still going foward when the crank was no longer going foward.



Yabby

Ouch Yabby. Two Cox TD .049's!!!!!!

Lawn darting into ground as hard as concrete - I can't agree with the majority, a soft spinner isn't going to help you much. Better as Eric says, careful up. No Saint here, I have mushroomed my share of Cox engines. It happens.

I hope this works out for you.  However, I am a little skeptical that it will go the way you intend.  Those spinners were really designed for Bee type engines.  Since the TD spins up so much faster, I think you will find yourself throwing those spinner in-flight.  Also, just a minor bump on landing and they go flying. They are not the most securely attached item. If it were me, I'd go for the plastic Cox spinners.  They'd break on crashing, but they'd still absorb much of the crash energy due to their design. They click in place on the hub and will stay attached in-flight and with minor bounces.  I have plastic spinners with plenty of scuff marks showing their resilience.

The "Been There" Mark

Engine sacrificed itself to saved the plane. Sacrificial lamb engines, that is what Estes Sure Starts and Fox .15s are for. (Comments, Ken? )

Thanks Mark! All of the input and views are greatly appreciated. so much "done it" experience is really helpful, The spinners bother me slightly from the prop balance point of view. Maybe that wont be the case. and I do think if they make a difference it will be very marginal. I also much prefer the look of the aluminium spinners I use. I will definately make up and try out a rubber band mounted engine mount. That has possible help save the engine on impact quality and definately be soo much easier to swap and engine from model to model. I carry a big bag of good strong rubber bands I use on my RC air cars so thats not an issue to me. My first plabe was Cox PT19 I reckon christmas day 1972/3. I had one go at flying it in the morning and Dad said thats not how you do it!, Ill show you how to take off and fly it!! Yep, after that it was straight to the shed to start string to put it back together with fibreglass and plastibond and stuff. Boy was my mum angry with mu old Man but I flew it for ages in various states of almost broken, and I seem to recall the wings and engine were held on with rubber bands and worked really well.

GallopingGhostler you are correct! The planes did pretty much survive both times! And I guess the TD were the sacrificial component, Ive flown a good twenty or so really good flights (for me) since and not looked like crashing. Yay. Be it flying models or other motor sports, for some reason I have always tended to c`rash in clusters. Maybe it the moon affecting my brain or something, but I really have always tended to crash in clusters.

Thanks Bob:Thumbs UP: Im glad to hear Im not the only one to have crashed at times.



Yabby

I understand the sacrificial engine part. Even broke the rear mounting lug on a pre-Testors Wen-Mac .049 Rotomatic engine with hard ground impact handling.

We have different methods on how we repair or disassemble our engines. I managed to straighten a bent prop shaft on a bargain E-Bay buy Enya .19-VI TV. Did such a good job (with a lot of careful hammering) that it ran perfectly without a hitch, salvaged it into a good runner since it had like new compression.


Enya .19-VI TV with Tatone .29-.40 Peacepipe Muffler. It is too small for anything larger than a .25 engine. (Many a modeler ruined his engine I imagine, by trying to muffle pre 1970 engines not designed for muffling, with these aftermarket "too small of expansion chamber" mufflers that caused chronic overheating.) Found a "prop" nut that fits from my motorcycle junk hardware box. "Prop" washer is a standard fender washer with hole reamed to size. Who says you need to go OEM on a salvage engine?

Here is me removing the back off my Cox .049 Medallion engine.


After you've broken enough things, then you are less afraid to give it the old college try.

Goodaye GallopingGhostler. I like yout attitude and aopproach Yep, I had allready had a chat to a fella who has been a good friend since way back when we were young and racing yamaha TZ GP bikes. I was racing solos and he was campaigning a Yamaha TZ 750 in a road race outfight. He also builds and flies CL models now We might get too old to race but we still love playing with two stroke.! He is a genuine mechanic and an ACE race engineer as he also raced a Kawasaki 1200cc Yoshimura engine in a speedway outfit for many years. He has some suitable V blocks and we can dial the crank and the crank pin.

The compression on both of the engines was raised enormously after the crashes and I had to put a standard glow head on them and heaps of gaskets to get them to run. The increased compression makes me suspect the crank pin/ small end pin is bent, and the engines both backfire really badly when trying to start them which could be also caused by the bend in the crank pin or by an actual slight twist in the crank shaft. We will know for sure once we set them up on the V blocks with dial gauges. I think there is a good chance we can make runners out of them again, but their parts will never be used on anything else or any new parts put onto them, as given I very stupidly got them to run again like I did they will have tried to wear themselves into a fit, which will have put other parts out of round etc. But we will see what we can do, never know might turn thgem both into handgrenade engines for a while.

thankfully my firend is awesome at straightening bent things and building/setting up/balancing TZ crankshafts and such. I was always able to do all of my own engine rebuilds, and could change pistons and rings myself between races. (chrome bores. Warm up lap runs them in. :-) ) But I could not do crankshaft rebuilds (every 500 km) and I couldnt straighten the frame, forks, swingarm, tripleclamps etc. Fortunately a fella with a race engineering shop sponsered me for all of that stuff, and I was very lucky as I could bend a frame in qualifying on Saturday and he would work all sat night to straighten the frame/forks etc. for me ready race on sunday!

so when I get back to the city we will see how we go with get the TDs sorted and running again! Cant make them anymore broken than they are. so we can only gain from trying,

I like the way you have/are using the tools at hand to do the job. Thats something my Dad who was an amazing Race engineer was soo good at. I needed the right tools, but he would make tools from other tools and make jigs and stuff using G and F clamps just as in your pictures. Brings back great memories for me.

Yabby

Yabby you may want to check if the "increased compression" you feel is in fact a mechanical contact between the piston crown and the glow head on TDC. A very little bend of the crankpin may result in that, so the compession change, if any, is only a secondary effect.

The impact when hitting the ground may have forced the crankshaft to hit the backplate, and when it happened, the crankpin - or the entire flywheel web with the pin on it - may have been bent. As a result, the pin tip is running now on a larger circle, and is forcing the piston higher up on TDC, hitting the head.

This forced impact pushing the crank into the backplate would have left deep dent marks on the softer aluminum TeeDee backplate too, that you can easily check visually.

If you have a conversion head for a normal or turbo glow plug application, remove the plug from the head, remove all shims from cylinder, mount the head and try cranking the engine by hand. The contact between piston crown and glow head at TDC will be instantly recognizable. If it is such, adding shims may be a solution, but I would avoid running an engine with a bent pin, because that will wear out/ruin the big end of the piston conrod,too.

Sorry if my comment is a no brainer.

Thanks Andreas! Its not a matter of being a no brainer! Its excellent analysis that contributes spot on to what I am seeing and believe happened and the damage that has been done. I am highly appreciative of such expertise being offered!!! It is very helpful to have my thinking and what Ive looked at and worked through, confirmed by someone else with a serious mechanical engineering background.

I think you are spot on. there is a very clear dent in the rear crankcase plate. Not a round wear mark. a clear hard dent. I could see that the fron prop plate was no longer straight and not running parrallel to the front of the crankcase and was rubbing a fraction on the case. I guess as the plates are` pressed on, and what we do to take them off is effectively what I did by driving the engine straight into the ground. But the rear crankcase cover stopped the crank going back further and bent it. V blocks and a really good dial gauge will tell the story. I did get it to run again by putting a new crank/prop plate on the front and lots of head gaskets. But then the head kept coming loose, which is no doubt because of all the vibration from the bent crank. I was pretty stupid doing what I did to run it again, because deep down I knew what had happened but wondered if I could get away with it. If the head didnt keep coming off no matter how tight, new gaskets, different heads I would have kept using it. to me, that means all the parts in the engine now live together for ever as they will have tried to fit thermselves together again and worn things out of round and off centre. I should have and do know better, but............ Lol.

Im going to have a look out of interest to see if the standard TD screw in backplate and the Kamtechnic one protrude as far into the crancase. I was using a Kamtechnik rear plate/radial mount and they run very close to the crank pin. to be clear though. That is NOT the cause of the problem. but Im just interested now. :-) I know on Yamaha TZ GP two stroke engines we used to do things to reduce the crankcase volume as that helped push the next fuel charge up the transfer ports as the piston came back down and definately improved performance. I use the Kamtechnik rear crankcase cover/radial mount and the Kamtechnik head on my TD 049s and they go really hard, start easy and hold their revs from launch right through flight. So Im interested to see whilst mucking with the bent crank if their is a difference in the rear crankcase covers that would alter the volume.

ive ordered and they are on their way, two new complete crankcases from Matt, and I have some spare crankshafts ayway. so even if I cant straighten up the bend and or twist a new crank will likely see it running hard again! Though its life might nbe a bit shorter than others!

thanks for offering your experienc Andreas ! And thanks to all the others that have also offered thoughts and ideas

when I eventually, assuming I do, get the crank into the V blocks and dial it, I will let you all know what was found. I will post a picture also later of the dent in the crankcase backplate. I dont like breaking engines, but when I do, I like to truly understand and learn what broke/bent........At least I get something out of it that way.

Yabby

Thanks , Yabby, it is really easy to imagine what may go wrong with those 2 or 3 parts if they are hit hard, and I am happy to help you prove the root cause.

The bent crankshaft may also quickly wear out the crankcase, and because only a short nose section of the case between the prop drive plate and venturi opening seals the crankcase, if it is worn out, the engine will not start because the crankcase pressure will be lost when the piston goes down. A bent shaft will grind the crankcase like an unbalanced prop.

So replace the crankshaft as early as you can with a straight one.

If you have  Kamtechnik head, you could as well test if the piston hits it from below, by just removing the plug and allowing the piston to move up freely without compression. I trust you will be able to quickly rebuild your gemstone TeeDee-s!