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Old 08-13-2017, 04:50 AM
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N99JH
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Default To those who Actually fly Diesels (NOT on a bench)

Hello All
As an avid diesel flier (Davis conversions) I have a question to fellow FLYERS based on my experience and problems encountered in 2 years of flying diesels.
I think that I mastered properly tuning diesel engines using a Tach, optimizing compression ratio Vs. needle position.
That said, a major problem I have to deal with thus far is that in a very short time carbon deposit from the combustion process builds up between the ring and the piston, causing the ring to stick and loss of compression.
The obvious solution is to remove the piston, cook it in antifreeze in a slow cooker and clean the carbon.
Is anyone else who ACTUALLY FLY DIESELS encountering this very same problem?
I am really interested in experience based responses.
Thanks
Joshua
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Old 08-13-2017, 06:38 AM
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Played with Davis conversions and one or two purpose built diesels. Even successfully machined my own conversions. Carbon build up happens its a property of burning kero and lube. My wife hated the smell even when I tried the scented lamp kero. Had to keep them in the shed out back as the garage was attached to house and any hint of smell look out.

Moved to bigger models and sold all my stuff to a die hard diesel nut. It was another interesting facet of modelling I'm glad I tried it but to keep peace in the family I had to give them up.

I used Easy Off oven cleaner on warm parts then scrubbed them clean. You can't leave the oven cleaner on for more than 10/15 min or it starts to etch the aluminium. I would clean the ring grove with an old broken ring.

Converted a few OS FP engines with no ring and had less carbon build up.

All my conversions were older, well used engines I didn't care to much about.

Dennis

Last edited by Propworn; 08-13-2017 at 06:43 AM.
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Old 08-13-2017, 07:09 AM
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Thanks for the quick reply Dennis. How many flights would you estimate could you get on the same engine before needing to pull the piston out for de-carbonizing?
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Old 08-13-2017, 10:35 AM
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Never kept track only took a few apart when they started to run different and setting them became erratic. Was told carbon build up might be a problem and the few I took apart seemed to run better after cleaning. I always felt the conversions were a compromise because you could only use about 2/3 throttle. After that you just waisted any additional fuel.

Most I never gave it any thought just swapped the head and ran it. Remember these were older used motors I was no longer using when I started to convert them. When I got the head for the FP .25 I compared it to the stock head and it measured out the same when the contra piston was level with the rest of the combustion chamber. The FP .40 was the same when it came so I disassembled it measured everything found the viton o-ring was the secret for the seal and proceeded to make my own. I used a fine thread and mine ran as good as the ones from Davis.
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Old 08-13-2017, 04:07 PM
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Quote:
Originally Posted by N99JH View Post
Hello All
As an avid diesel flier (Davis conversions) I have a question to fellow FLYERS based on my experience and problems encountered in 2 years of flying diesels.
I think that I mastered properly tuning diesel engines using a Tach, optimizing compression ratio Vs. needle position.
That said, a major problem I have to deal with thus far is that in a very short time carbon deposit from the combustion process builds up between the ring and the piston, causing the ring to stick and loss of compression.
The obvious solution is to remove the piston, cook it in antifreeze in a slow cooker and clean the carbon.
Is anyone else who ACTUALLY FLY DIESELS encountering this very same problem?
I am really interested in experience based responses.
Thanks
Joshua
Traditionally diesels haven't used ringed pistons probably for the reason you've discovered. The carbon deposits can be controlled to an extent by choosing a low soot kero and a modified castor oil like Klotz Benol. Otherwise people have added a tiny percentage of Lubrizol 52 to their kero. About 0.2% dissolved into the kerosene works. It's really cheap stuff in large quantities and is used in full sized diesels for the same purpose. I have a half Litre can of it in my shed. I got it from the local Lubrizol dealer as a free sample quite a few years ago. I could put some in a small container and mail it to you. I've done that in the past, however posting it internationally these days would most likely get us both arrested.

Last edited by qazimoto; 08-13-2017 at 04:20 PM.
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Old 08-13-2017, 05:29 PM
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Quote:
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Traditionally diesels haven't used ringed pistons probably for the reason you've discovered. The carbon deposits can be controlled to an extent by choosing a low soot kero and a modified castor oil like Klotz Benol. Otherwise people have added a tiny percentage of Lubrizol 52 to their kero. About 0.2% dissolved into the kerosene works. It's really cheap stuff in large quantities and is used in full sized diesels for the same purpose. I have a half Litre can of it in my shed. I got it from the local Lubrizol dealer as a free sample quite a few years ago. I could put some in a small container and mail it to you. I've done that in the past, however posting it internationally these days would most likely get us both arrested.
Thanks for the suggestion. I will see if I can find Lubrizol 52 locally. I am using Davis Diesel fuel so if I find it, how much should I add to a gallon?
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Old 08-14-2017, 03:03 AM
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Thanks for the suggestion. I will see if I can find Lubrizol 52 locally. I am using Davis Diesel fuel so if I find it, how much should I add to a gallon?
Well I calculate 0.2% of a US Gallon as 7.6 milli Litres or 0.26 US Fluid Ounces working the long way 'round :-)

Let's say a quarter of a US Fluid Ounce in a US Gallon of Davis diesel fuel. The stuff is thick like treacle, we usually dissolve it in the kero and then mix that into the fuel, so just make sure it mixes properly.

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