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Determine engine wear?

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Determine engine wear?

Post  av8tor1977 on Sat Oct 01, 2016 10:31 pm

I have never seen this addressed in any of the Cox publications, and I imagine the info is here in the forum, but I am sorry I couldn't find it. It is the question of determining the engine wear of the Cox .049 engines. I want to introduce my 10 year old daughter to the joys of 1/2a flying, and I bought a bunch of used engines to resurrect. I am quite capable of tearing them apart, cleaning, etc., etc. But how do you determine if the piston/cylinder wear is excessive?

AV8TOR
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Re: Determine engine wear?

Post  TDbandit on Sat Oct 01, 2016 10:48 pm

First of all, welcome to the forum av8tor! Very Happy
Determining piston/cylinder wear in a cox 1/2A is done pretty much by feel or its starting/running manners a worn or loosely fitted cylinder/piston set will feel spongy and lack pop when flipped slowly through compression (make sure the head is tight first with a shim under it) it should rebound when put through top dead center. When running it will be hard to needle and in excessively worn cases will quit after it warms up, it will also be hard to start by hand to a point to where an electric finger (Starter) is needed or the spring starter to get it going. Hope this helps man and again welcome to the forum!! Very Happy (Bandit)


Last edited by TDbandit on Sat Oct 01, 2016 10:50 pm; edited 1 time in total (Reason for editing : fixed typos)
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Re: Determine engine wear?

Post  Mudhen on Sat Oct 01, 2016 10:59 pm

Another quick way to determine piston wear/fit:
Wash both the piston and cylinder in rubbing alcohol. Use a cylinder brush to clean the cylinder walls and then flush again with rubbing alcohol.
Use a cotton ball rolled into a cylinder shape and “screw” it into the cylinder to dry and remove any foreign material. Make sure it is dry.
Also make sure the piston is clean and dry. Try not to touch, or add any oils to the cylinder and piston.
After all this, gently run the piston up through the cylinder. A good fit is had when the piston stops just below TDC.
This doesn’t guarantee that the piston is not out-of-round. But it is a good start.
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Re: Determine engine wear?

Post  balogh on Sun Oct 02, 2016 12:53 am

Mudhen's diagnosis is reliable,and particularly valid for older TeeDee049 and 51 engines with tapered cylinder bore. Later engines did not have tapered  bore and the piston of even a new cylinder/piston set may be easy to push over the TDC.

My diagnosis is very simple and the same as written by others above. Check compression by looking at/listening to the hissing blow-by at the exhaust ports when the piston wet in fuel moves upwards.

I have a COX TD 051 engine with near 300 hrs runtime on it that I retired because of its impaired compression. The engine starts with electric starter but drops speed under heavier loads e.g. when the plane climbs steeply.

BTW welcome to CEF.
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Engine wear

Post  706jim on Sun Oct 02, 2016 10:17 am

I've had three engines that deserve comment on their wear.

1. OK Cub 0.049A. Worn out in a single afternoon of flying. Castor oil fuel, snow on the ground so no overheating or dust. Just a soft cylinder or piston.

2. Pee Wee 0.020. Had poor compression and would only run with added oil in the fuel. This engine had a silver tank and I suspect was pulled from a Cox rtf plane.

3. Fox Rocket 0.099. Just gradually lost compression after many hours of running under a combination of summer and winter conditions.

When there is no compression......it's worn out!
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Re: Determine engine wear?

Post  av8tor1977 on Sun Oct 02, 2016 1:26 pm

Ok guys. Thanks for the nice welcome and the info. I've got her an .049 profile trainer for she and I to throw together, and I've got the engines soaking in glow fuel. Yesterday I bought some 25% 1/2a glow fuel. Man, this is bringing back some fond old memories!

Thanks again,
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Re: Determine engine wear?

Post  RknRusty on Sun Oct 02, 2016 3:01 pm

I'd just like to add that engines which use separate tanks are a lot more cooperative. The ones with built-on tanks have so many more opportunities to leak air and drive you mildly mad while your young protege stands by getting fidgety.
Good luck, thanks for joining CEF.
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Re: Determine engine wear?

Post  Ken Cook on Sun Oct 02, 2016 4:42 pm

I would also like to add if there's no compression, it's not always a worn out piston cylinder. That being said, a loose head, a damaged head gasket, a head not properly flattened which is leaking, a loose backplate, all will reveal signs of low compression which cause hard starting and problematic engine runs. A ball socket not properly set can punch a hole in the center of the piston as well. It doesn't mean the fits are worn out, just that a hole in the piston doesn't hold compression.  Bottom line is evaluate the simple things first before heaving the piston cylinder. some of my best running engines were the engines with the lightest compression.
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