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Author Topic: cox engine siezing  (Read 1313 times)

Offline philip metzner

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cox engine siezing
« on: February 05, 2010, 09:20:52 AM »
This has never happened to me, but i have heard, and read some about it. I would like to know just what causes this, and what is happening inside the engine. I'm not talking about when one sticks from storage, but rather when they tighten up wile running.
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Offline Robert McHam

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Re: cox engine siezing
« Reply #1 on: February 05, 2010, 09:52:19 AM »
I would have to say not enough castor oil for lube or run very lean.

Robert
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Re: cox engine siezing
« Reply #2 on: February 05, 2010, 10:12:13 AM »
Or too much old castor.

If you look in the cylinder and see a brown "luster", you may need to remove the varnish from the cylinder and piston. Fine steel wool has and some type of solvent (acetone, lacquer thinner) has been recommended.

You aren't trying to "hone" the cylinder or piston here, just a light scrub.
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Offline Wayne Collier

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Re: cox engine siezing
« Reply #3 on: February 05, 2010, 10:23:54 AM »
Could also be a manufacturing defect on a particular engine.

  I personally have never had a cox engine seize while running.  The closest I've seen was on a cox car that didn't have the benefit of a prop blowing fresh air across the cylinder.  Even it did not seize, but it did tighten up as it got really hot.  I have used a variety of fuels, but lately I've been using powermaster fuel in my cox engines.  15% nitro and 18% oil (castor/synthetic blend) 
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Offline Larry Renger

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Re: cox engine siezing
« Reply #4 on: February 05, 2010, 12:21:27 PM »
Cox engines need a good bit of Castor oil in the fuel, but I find that a 50/50 mix of castor and synthetic gives good runs, but never varnishes up.  Best of both worlds.  Minimum 18% oil, 20% to 22% is better.
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Offline Mark Misegadis

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Re: cox engine siezing
« Reply #5 on: February 05, 2010, 03:06:58 PM »
I had an engine seize up last year for the first time. Now this wasnt the catastrophic type of seize like I have seen occur with a racecar engine where you end up with holes in the block. I have however picked up some Cox parts recently that had a hole in the block and another that had a hole in the piston. So it can occur.

I was testing engines on a test stand and had one of these just Stop. You could still turn it over by hand but you could feel that the rod socket in the bottom of the piston had loosened up. I suspect tht the piston and rod bound up at the top of the bore. (Engine heat was also a contributing factor I am sure) This stopped the engine instantly. I reset the piston and it later happened again. (First time for me and I think I left it too loose being cautious) The engine overall didnt have more than 8-10 tanks through it so it was still new. I have replaced the piston and it should be fine. I havent found anything else that is sloppy or where there could be friction.

Fuel: I was running WildCat 35% Nitro, The lube is 20% and is a Caster/Syn mix. I like Sig fuel in these engines but am going to try Magnum brewed to the same ratios as the Sig.

Mark
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Offline George

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Re: cox engine siezing
« Reply #6 on: February 05, 2010, 09:25:55 PM »
Quote from: philip metzner on February 05, 2010, 09:20:52 AM
...I would like to know just what causes this, and what is happening inside the engine...

Causes: HEAT! This can be a result of insufficient/wrong lube or running too lean.
Fuel should be 18%-22% lube. All castor will protect the engine but will gum up with castor varnish from running too lean. All synthetic runs clean but will flash off at high temperature. A combination seems to run best.

Effects: Fuel carries off heat as well as lubricates. Running too lean allows heat and friction to increase. As the top of the piston gets hotter, the bottom of the piston housing the ball socket has increased wear. I understand the ball socket can freeze up and break the conrod in extreme cases. The piston to cylinder fit can also have excessive wear.

Other stuff happens but there are the basics. Bottom line is use good fuel and learn to needle well.

George
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Offline kenneth cook

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Re: cox engine siezing
« Reply #7 on: February 06, 2010, 06:41:38 AM »
         Recently I had purchased what appeared to be a Black Widow. The case and tank were mill finish though. The engine was in new condition looking as though it had never been run. It had the copper reed in it which also appeared to be brand new. I was quite astounded by the condition of this engine inside and out. I figured I'd just take it easy on it at first. This engine did have the slit exhausts and I'm quite sure this was stock on this engine so I'm guessing early eighties. I got it running and things were sounding good in a rich run when all of a sudden it started sagging real bad then it just locked up. I thought this was odd as it was quite rich and without forcing the engine over , the prop wouldn't turn. I took it home and disassembled the crank when I discovered a small aluminum shaving from where the oil groove is located had jammed between the crank and the case. A little polishing of the crank and case took care of this and all was good. I'm sure this is probably not what your asking,  but this was the first time I had a Cox engine seize on me. I did have engines that sat for years have problems with varnished castor on the crank though. A thorough cleaning will fix this. I discovered that running the engines will not rid it from this gooey mess. Ken
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Offline philip metzner

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Re: cox engine siezing
« Reply #8 on: February 06, 2010, 07:16:15 AM »
Like i stated in the beginning, i have never had this happen to me, but i think it has something to do with something i did as a kid. I was too young to know any better and didnt understand what was happening but it worked. I would get my hands on wen-mac engines more so than cox, and sometimes they would have very poor compression and hard to start, probably due to no break in by the previous owner. Now, here is what i would do with them, and remember is was maybe 12. I would remove the offending cylinder-piston assembly and install it on a car engine i had mounted on a board. It had no prop for cooling, just a flywheel and gear. I would get it started, even if i had to wrap a string around it and pull start it. I would needle it so it broke between  four and two stroke and let it run. It would get hot as blazes! Oil would boil on the head. After a run or so the compression would come back and they ran fine afterwards. I still have many of those engines and they still run fine. I think what happened is that the castor cooked on the cylinder and filled up the slop in the fit. Obviously i dont condone this but i wonder. Most of the people i have had first hand contact with that had compression problems with engines like a 35 redhead were using fuel with some level of synthetic oil in it.
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