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Post  Yabby Sun Jun 06, 2021 5:43 am

Hi,

with a standard Cox 049 surestart engine with 25% nitro and 20% castor what is it that tends to wear the fastest. Assuming proper (reasonable many different views) run-in (break-in) of the engine and then sport flying on weekends. As the engine wears does the cylinder or the piston tend to wear the most. Again assuming the piston has been reset properly and the prop is balanced, and the engine needled back a fraction from Max, etc. I suspect it might be the cylinder liner itself that wears out faster than the piston, causing compression loss and reduced engine performance.

I have read that the cylinder liners are softer than the pistons which may be hardened? I cant think of any reasonable cost effective method to repair cylinder wear other than buying a new cylinder. Putting in a new piston might tighten it up a bit if there is also some piston wear.

I am basically wondering what is the typical wear characteristics of the cylinder and piston on a Cox 049 surestart used for sport flying on weekends and well maintained (not deliberately abused).

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Post  KariFS Sun Jun 06, 2021 5:50 am

My experience is very limited when it comes to running the engines myself, but I have run across many old reed engines with ”popping” compression but a worn crankcase. This allows the crankshaft to wobble a little which has an effect on how the engine runs.

This is probably caused by running the engine with an unbalanced propeller.

Usually both the piston and the cylinder have a long service life.

I have also come across a few ”new” late-model engines with poor compression, so for a strong reliable runner you may want to do some mixing and matching of parts.
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Post  Yabby Sun Jun 06, 2021 6:08 am

Thanks for the reply KariFS,

I hadn't considered the relationship between crank wear and piston / Cylinder wear. Good point made. Thank you. I will ensure I watch crank wear and keep my props balanced and use props that are not damaged. I tend to use the Killer Bee cranks instead of the standard crank in the hope the crank is better balanced etc. itself. Its good to hear the cylinder and piston tend to have good service life.

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Post  Ken Cook Sun Jun 06, 2021 8:07 am

Regardless of crank type, you can't balance a single cylinder engine and you will always have wear. When the materials used are inexpensive such as what is used on the Sure Start, your going to further accelerate this wear. Use the recommended oil content, make certain your fuel is clean and you don't stuff it in the dirt too often and you will have the engine for many hours of enjoyment.
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Post  Paulgibeault Sun Jun 06, 2021 3:01 pm

This is a most excellent question to ask!

I don't know the exact answer but my experience wearing out many engines seems to suggest the following:

I believe they BOTH wear, but I'm suspecting the piston wears faster than the cylinder. On my all conquering mouse race engine run with only Nitro, Prop. Oxide & Oil, I would wear out (or break) pistons after a season of racing & most every time I fitted another piston to the cylinder, the power was restored.
That one amazing cylinder went through quite a few pistons.

I did try running a Venom on 70% nitro / 10% prop. Oxide / 20% K&B X2C synthetic oil. This engine set a new British Vintage Class 1 record.... BUT the piston was
worn after 3 flights! This is what tells me some castor oil (5% minimum) is still required for engine longevity.

This being said, I have a few good cylinders that no piston (of my 30 collection) will fit anymore. They all push right through the top. This of course indicates the cylinder bore is worn oversize. Although I have a piston micrometer that reads to 50 millionths, I cannot make any sense as to exactly what is wearing, because I cannot duplicate readings on a given piston. The amount of wear is much easier to feel by hand than to measure!

The ONLY real fix I've ever seen that worked in competition was to chrome plate the piston. With the right equipment & knowledge & skill, I've seen this done at home, but sadly it wasn't my home! Such a process is beyond 99.9% of us, me included.

It should be possible to chrome plate the cylinder, but I have not come across anybody yet who has successfully done that yet. The cost is absolutely not worth it, unless you use the chrome plate & honing equipment for other purposes.

Although running Cox engines on such abusive fuels, and resulting high RPM's (22,000+) wears them out, for research purposes I've simply accelerated the normal wearing characteristics. As mentioned, running dirt through the engine also greatly accelerates the wear on both piston & cylinder.

ONE factory flaw on the Sure-Start engines is that due to cost cutting & just not caring anymore, the factory matching of the pistons to the cylinders was hit and miss.
If you had a "tight" fitted piston, your engine was strong and would have a very good service life. If however, the piston was fitted on the "loose" side, then although it needed almost no break-in, it's service life was much shorter than normal. It was thought that perhaps by going to the non tapered cylinder, then break-in was not really needed as most customers may not know the difference between rich & lean settings. This was thought to perhaps reduce returns of the product, but keeping the cost down was the overriding factor of course...

My experience for what it's worth...

Cheers,

Paul

Cheers,

Paul
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Post  rsv1cox Sun Jun 06, 2021 3:26 pm

That is an excellent question and one I have pondered for a long time.

Assuming that all the stars were aligned and conditions perfect for both piston and cylinder which one would wear first? With inherent production variations in both metallurgy and machining would that ever happen. But on average....................... i'm thinking cylinder.
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Post  aspeed Sun Jun 06, 2021 5:53 pm

OK, I'll bite.  Since you mention a Surestart (reedy)  I will say the motor will not run well enough to be useful after the crankcase wears out and leaks air first.  The piston cylinder will still run fine, maybe even somewhat faster till a point.  It will just be very hard to start when the PC is worn out.  I have an .051 like that.  I looked very closely at an unusable worn case and it had a wear spot on the bottom of the bore in the back, not the front like one might expect with an unbalanced prop. I am sure that many of my props were not balanced and revved quite high too. I have made bushings for the worn reedies but don't really use them so have not tested them. They are not marked either so they have to be taken apart to know.  I think a TD is different for the leaking and the P/C would wear first.  I never had a problem with leaking of the crank.  I also believe the cylinder on the older motors wears faster than the piston. A piston could be replaced twice but really that did not make much difference after so I believe the cylinder wore the most.Then there is the ball socket. Can't say for the newer stuff, never played much with those.  YMMV
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Post  Yabby Sun Jun 06, 2021 8:05 pm

Thanks very much everyone for your thoughtful and detailed replies of your experiences, ideas, and knowledge! Hand Shake It is greatly appreciated! All of the comments make sense and cover the question from sensible use and maintenance ( clean fuel, use castor as recommended, keep the motor clean, crash less :-) dont run over lean) and then answers from a technical mechanical aspect as to different people experiences.

This has provided me with very good guidance on how to fly with my much loved surestart engines and keep them running and flying for me on the weekends for pure fun/sport for as long as possible. All of the replies make sense and are well within my capability to perform, do, and monitor, and try replacing a piston if needed (I have new pistons) to get a bit of compression back, and also watching the crank and case for just in case. I have already found papering the back of the crankcase over glass before assembly as recommended in many threads has helped hugely with keeping a good seal and stopping air leaks, and the same for using fuel tubing over the needle.

I have used Chrome and Nikasil in an earlier life in not for control line engines and it works amazingly! But the pistons always used a ring, and I suspect it would be insanely expensive to get someone to chrome or Nikasil an 049 barrell. Laughing But it certainly lasts, you just replace pistons and rings regularly. maybe 3 sets of rings, then pistons and rings. I think the 049 design is just right for what I need. :-)

Great replies, very appreciated. Beer Cheers

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Post  davidll1984 Sun Jun 06, 2021 9:45 pm

My experiments with plating the cylinder Its yes it is possible to plate the cylinder but the piston must be changed To aluminium because using the same type of material results in an exchange of material with a very fast over heat the one y have use for test stil working Good wit the rc ring piston is aluminium in m'y tether cars after couple of test it survive has Good compression its posible To plate the piston out side skirt it work
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Post  balogh Mon Jun 07, 2021 1:28 am

I am flying RC planes with COX engines, where the typical flight times are not just short runs but sometimes last for 10 minutes each. They are in a kind of touring service...

I have very good experience with old-stock COX engines with taper bore and the legendary COX tolerances,  that can run up to many hundred hours. Some here on CEF may already be bored reading that I have a tapered bore old stock COX Tee Dee 051 with 300 hours runtime on it. Perfect crank and case fit. The compression is a bit impaired by now, but it still runs very strong.


On the top of page 2 of this link below you may read about the factory experiment by COX themselves, where an engine was constantly run up to 400 hours and it was still OK, though already needed an electric starter to start up...probably because of the  compression impaired after 400 hours.

https://web.archive.org/web/20170410030959/http://www.mccookfieldfac.com/helpful-info/cox-engines.pdf

I am always using fuels in my COX engines with at least 20% castor in it, and leave synthetic oils for the big brothers with gudgeon pins and compression rings. The good thing about  castor is that unless it is excessive, the varnish that it leaves behind on the cylinder wall will heal the micro scratches - by sticking/caking in the unwanted micro-grooves - and this will keep the compression very strong for long times.

In order to avoid even the minimum damage inside the cylinder,  I will not even touch the crankcase if dirt comes in contact with the engine so that the piston should not plough dirt against the soft cylinder wall,   before I blow the dirt off first by high pressure water then disassemble and clean it thoroughly. Other then keeping them clear, I use after run oil in the cylinder, and that is all it takes to keep a COX engine in good condition for many-many seasons.
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