Sad day for a neat old Fox 45 - Page 2 - RCCanada - Canada Radio Controlled Hobby Forum
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Old 04-16-2019, 07:22 AM   #11
Cougar429
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Re: Sad day for a neat old Fox 45


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Some castor helps, but is not exclusively required here. Duke used to recommend it since early tests on synth tended to see them flash and not protect the engines very well.

Mike, what nitro content? Can you post a pic of the head button, specifically the combustion chamber?

The reason is older Fox engines were built for low to no nitro, (FAI) fuel and tended to detonate if over 10% was used. There were mods you could do to open up the head button to allow for it and I have done that with a button head end mill, (no pun intended). The first pic is a before and after on a 50BB which, depending on the version should be close to your 45.

I also fabbed several different head buttons for a pair of Eagle IV 60's. Tested them and the best of the lot looked almost identical to the new version they sent me with the repaired 60 when the piston burned out during break in. Those are seen in the next 2 pics.

Although the stock muffler did not work very well, the basic engines were nearly bulletproof. Worth making the effort to make them behave. The last pic is of the same 50 bolted to my Seamaster. Resurrected that plane a decade ago and fabbed adapters for OS carb and exhaust. Carb was just an experiment since the original tended to rich mid range, (mods for that, as well) but the OS muffler worked fine, quieting the exhaust with no power loss.

Over the years have had to replace rings on some 3 times, while the sleeves survived with almost no wear. That hardened sleeve required longer break in and I used to find a lot of low time Fox engines at swap meets since most did not put in the effort to get there.

Unfortunately a quick search shows the Fayetteville site that had the mods listed down and out.
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Old 04-16-2019, 08:42 AM   #12
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Re: Sad day for a neat old Fox 45

If it was designed for FAI fuel then maybe I should repair it. I'm heading that way anyhow because the local Hobby Shop has closed and Nitromethane seems to be big trouble to get hold of.

The fuel was Cool Power 10% with full synthetic oil. Floyd says it's probably only 17%.
I should have asked you guys before flying it.

Pics of combustion chamber attached.
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Old 04-16-2019, 09:04 AM   #13
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Re: Sad day for a neat old Fox 45

If memory is correct I believe Mecoa now has Fox replacement parts:

http://www.mecoa.com/parts.htm

Rings can be had from the gentleman that took over Frank Bowmans business.

RJM Machine works contact info here:

[email protected]
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Old 04-16-2019, 09:24 AM   #14
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Re: Sad day for a neat old Fox 45

Great statment Jim , and that's only part of the story , oil is not just a lubricant it also . cools ,cleans, cushions ,seals . so while a lubricant may be far superior in one area that does not mean it's what the engine needs . I would guess you are correct and the older engine with larger clearances needed thicker oil . the oil viscosity sets the ring to land gap and if that gap is too large you will have excessive combustion pressure forcing the ring to seal against the cylinder wall , this excessive ring pressure is what most often causes over heating and piston land failure .. Picture attached showing the principal for ring seal






Quote:
Originally Posted by controlliner View Post
A piston ring needs good oil, Especially in a Fox .40 as it is a floating unpinned ring. It cannot catch in a port due to the port designs. What probably happened is the ring at the gap probably got hot and expanded in one the exhaust port windows. If your oil is not good enough or high enough percentage, a Fox ring will bang the hell out of the upper ring land and cause failure similar to yours. As stated, a freely rotating piston ring needs a cushion of high viscosity oil to go between the ring and the ring land.
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Old 04-16-2019, 09:48 AM   #15
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Re: Sad day for a neat old Fox 45

A lot of time our nitro engines suffer from inadequate cooling or lean run conditions if not set up correctly. Lean running raised the temps to the point synth oil broke down, while castor had a higher flash point so would still provide lubrication. True, synths were cleaner and tend not to varnish the exterior, but I opt for fuel with a mix of synth/castor to try and get the benefits of both.

Although damaging to both 2 and 4-strokes, the former at least had the advantage of internal fuel/air charge flow to help cool the engine. 4-strokes do not and require better air flow management.

Still, to get back to the original topic, higher compression and nitro provides more opportunity for the ignition to occur before it should and for the flame front to violently propagate. The higher pressures and temps were the cause of internal mechanical damage, including breaking rings and burning pistons. With Fox you would hear a "Crackling" sound like wood on a fire. Sometimes the louder exhaust with the original muffler would hide that.
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Old 04-16-2019, 10:44 AM   #16
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Re: Sad day for a neat old Fox 45

I would recommend that you do what the manufacturer tells you to do , they consider more factors then most of us would ever understand .
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Old 04-16-2019, 11:03 AM   #17
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Re: Sad day for a neat old Fox 45

True, but technology has also evolved since some of that testing was done. Dukes posting on synth oils is quite long in the tooth now.
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Old 04-16-2019, 11:06 AM   #18
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Re: Sad day for a neat old Fox 45

Mike I suggest you move on to a newer engine. The new OS engines run fine on FAI fuel and require no Nitro. You can find a Video on YouTube where a OS 95V is tested with nitro fuel and without. The engine ran the same and impressed the person doing the test. Most of Europe run FAI fuel only, North America uses Nitro. Other than Saito's not many other engines need any Nitro.

If you do fix the engine you'll need to bump the oil content way up. To have a 25% oil content you need 250ml oil and 750ml methanol to make a liter. I mix 160ml to 840ml to make a liter, of 16% oil. Your Cool Power fuel would need almost 12 ounces of Castor oil to a jug. Most engines nowadays are supposed to run 20% oil content, but other than PowerMaster fuel which have a 20/20 oil blend no one else does, to my knowledge. Nitro and methanol are still for sale in Ontario. Cheers Floyd
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Old 04-16-2019, 12:50 PM   #19
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Re: Sad day for a neat old Fox 45

Floyd, your suggestion makes sense but may not be the most fun.
I will check out that video, I've been watching David McIntire who has some videos on FAI.

I have seen your posts on NitroMethane from VP fuels but have never got to the point where I could order it or go pick it up.
I'm probably moving towards FAI anyway.
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Old 04-16-2019, 01:55 PM   #20
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Re: Sad day for a neat old Fox 45

David McIntire is the guy that did the comparison test on the FAI and Nitro fuel. I use isopropyl alcohol from Canadian Tire to mix down some high Nitro fuel I have now. Because I have gallons of oil its cheap for me to mix. I remember calculating the cost to mix the fuel if I had too buy the oil and it came to $17.00 for a 4 liter jug. Hardly worth mixing when I can buy jugs for not much more. I've yet to find a oil supply place in Ontario to suite my needs.
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