1QwkSport2.5r

I'd suspect my engine is a later model being it has two rings and I'd also suspect with the time and fuel I've put through it, it's probably "there" but with less than stellar results. Of course this is based only on bench testing. I've read elsewhere on the forum of guys with double ringed pistons using a single Bowman ring in the top groove and having good luck with it that way. The second ring adds drag which will have an effect on power output.

I have a few few other engines that I need to get spare rings for anyway, so maybe I'll put a call in to. Mr. Bowman and get some rings ordered.

1QwkSport2.5r

A little update on my Fox .50 Diesel experiment. First off, it was deceiving looking at the piston through the transfer port. Originally I thought it was a dual ringed piston but it turns out to have only one ring; however there is a groove machined into the piston that looks like a second ring. Anyhow, I believe the ring wasn't sealing very well so I ordered a new ring from Frank Bowman. We ran it up with the Fox ring and Davis head on Davis ABC mix on a MA 12x8 2-blade and were getting 8,900rpm rich and slightly under compressed. Oil color was about the color of maple syrup. Throttle response was a little choppy but it ran okay otherwise. We will see how a new ring does.

Hobbsy

My Feedback: (102)

Tim, have you done any more wringing out of the Fox .50, Thanks, Dave

1QwkSport2.5r

Nah. Between not having a lot of time and being pretty cold, we haven't run the diesel fox yet. I got a carb adapter to use a smaller carb on it so I need to pull it down and get a smaller carb on it. I need to pull the MDS P/L out of it and put in the new Fox P/L I got from you and get her going. Lots of winter left here in Minnesota unfortunately.

1QwkSport2.5r

I'm bumping this up because I'm gonna try to get my Fox .50 set back up as a diesel and get her running. I posted this on another RC forum but I think there's more diesel guys here on RCU than over there.

One of my buddies and I have run some diesels before using either Davis or Aerodyne fuel (I think that's what it's called - I can't recall off-hand the place he got it from) and I have a diesel conversion myself I'm going to get running again one of these days.. So I will need some fuel. I have read tons of info on using John Deere 80% starting fluid to mix my own small batch of fuel. Looking at the MSDS for the JD starting fluid, it appears that it's 80-90% ether and basically the rest is propellant and maybe a marginal amount of lubricant. Do I assume the contents of the can is mostly all ether with the propellants removed? I'll be using regular kerosene from a local fuel station, castor oil, and most likely Amsoil Cetane booster/ignition improver to mix the fuel.


The process to extract the fluid from the aerosol can varies with some folks, which method is the best to prevent as much ether loss as possible? Put it in the freezer and bleed off the propellant afterward seems most logical, but I'm still a little new with diesels. My conversion engine is a Fox .50 with a Davis head and was run several times using Aerodyne fuel mostly. What would be a good formula for a Schnürle ported conversion engine?

gerryndennis

G'day Quick,

Davis has three mixes in the instructions he sends out with his heads,1/2a (.049 to .12), ABC & Racing, (.15 to 1.08) and Formula 'T' (1.0 to 3.6)(Super Tigre?). He recommended ABC for my lapped iron .20 engine? I think what he means is 1/2 A for small engines, T for large ST's, and 'ABC/Racing for the rest even if they are ringed or lapped.

Using that logic his mix would be 32% Ether, 2% Booster, 12% Oil, 56% kero for your engine. The ratio of Ether to Kero in this mix is 37/63.

I needed a mix with 20% oil for some vintage diesels and to make it easy I use the same mix in my modern engines (the .20 and a .40).

My mix is 20% oil, 30% Ether, 50% Kero, 1% Amsoil cetane improver. (I know that's 101% but it's easier to mix that way). The ratio of Ether to Kero is about the same as the Davis mix so I assume it starts and runs about the same just more lube.

I'm sure either mix would work fine in your Fox.

I would treat the John Deere as 100% Ether for the purpose of mixing fuel.

I've never milked a JD can but two methods I've read are to either chill the can, invert and spray off the propellant, then open the bottom with a can opener (the type that makes a triangular hole I'm guessing). The disadvantage is there's always some pressure left so maybe a little dangerous and you have to either store or mix the entire cans worth of Ether.

The other method is to get a jar with a metal lid, punch two small holes in it, put a straw in the JD nozzle and spray out as much Ether as you need then tip it in to you fuel mix straight away. The rest of the Ether is safely stored in the can.

I guess whatever works best for you.

Good luck with your Fox, be good to hear how you get on.

Dave H

1QwkSport2.5r

Thanks for the tips. For glow use, it was recommended to use 20% oil so that's what I'd like to stick to. I would likely back off the kerosene and add oil. So I'll probably start with something like your mix of 20/oil 30/ether/ 50/kerosene and a shot of ignition improver. It ran okay as a diesel before, however the liner was worn out and had little compression. I now have a MUCH nicer piston/liner/rod for the engine so it should run much easier. We couldn't get it to run without a starter before. I should be able to hand start it now.

gerryndennis

Kerosene is quite a good lubricant itself, while Methanol isn't, which is probably why Davis recommends the lower oil content. I'm sure it would be fine in the larger engines (he recommends 6% oil ! for the large Super Tigre's)

Having said that I'm using 20% for the moment and there's no problem with it, I might experiment with lower percentages sometime.

I've never run a ringed engine as a Diesel (I'm hoping to soon). Diesels are totally reliant on the heat generated by compression to start so you might find your engine is still a little bit reluctant if the ring seal isn't perfect. Worst case you might have to run the engine on glow to seat the new ring and liner before changing back to Diesel (This is what Davis recommends). There's plenty of guys running ringed Diesels with no problem so it obviousely works fine.

Dave H

1QwkSport2.5r

The piston & ring/liner/Rod came from a running engine - it appears to have sufficient runtime to have the ring seated reasonably well. I planned to run it on glow for a tank or two to ensure the engine runs reliably on glow before trying to run it with the diesel head... The piston/liner that came in this engine was in poor shape and I didn't know any better to know I should have gone a different route in buying it... Oh well. Lesson learned. A fella here from RCU hooked me up with the really nice P/L/R so it should run really good. I have a Bowman ring that has 3 tanks of fuel on it from the old piston I could swap in and just re-break it in. Might be the best route so I know it's going to have the best ring seal possible.

Diesels turn big props and given I'm fairly new to diesels, I'd rather err on the side of caution at first and have extra oil until I'm more comfortable with the adjustments. I left the compression screw at the setting it had last time it ran. Basically I up the compression until it runs off a prime and get it to run on its own then up the compression until it falters and back off a tiny bit then lean the needle until it runs smooth? It's been a year since I saw a diesel run and I didn't make the adjustments myself so I'm a bit rusty. Thanks for bearing with me.

gerryndennis

Sounds like you've got the ring well and truly sorted out then which is good.

I agree 20% oil might be best.

If I'm reading your method of getting the running settings right there might be a better way to go about it. When you say you 'increase compression till it falters' do you mean the engine starts to slow down? It sounds like you may be well over compressed at this point. When you back it off then lean you are probably ending up with a pretty good setting, but you are over compressing to get there.

Over compressing a Diesel is just about the only way you can break them so best to avoid that. If you over lean a Diesel they just stop, no damage or over heating, they just stop. That's totally different to a glow engine. With a glow if it starts to die the natural reaction is to richen the needle, with a Diesel if it starts to die over compressed that same reaction of richening will result in higher compression and more damage. The correct thing to do is to reduce compression or throttle back instead.

Here's how I go about getting the setting, take it for what it's worth, just my method.

Firstly I'll use the terms 'advance' and 'retard' to avoid confusion. Most people talk about over or under compressed but then tell you to adjust the needle, they are right but it's not obvious why sometimes.

When you adjust the settings on your engine you are essentially setting where ignition occurs. You can advance or retard the ignition to match the load (prop), RPM, and temperature of the engine.

There's four factors that affect ignition timing:

1. Temperature, as the engine warms it advances.

2. Mixture, lean to retard and richen to advance.

3. Compression, increase to advance and decrease to retard.

4. RPM, high RPM (small prop or fast model) requires more advanced ignition and vice versa.

One thing to note is that you can balance mixture against compression to get a 'correct' setting ie if you are quite rich (advanced) and have a low compression setting (retarded) then the ignition point will be good. You won't be developing full power but it's a useful setting for running in for example.

These are the symptoms of Retarded and Advanced ignition:

Retarded; The engine 'lopes' or 'burps', it goes 'brrrrm brrrrrm brrrrrm' if you like. It can be quite a quick variation or quite slow. This is a safe setting and is often used as a low power setting in vintage Diesels without throttles.

Advanced; The engine will run hard and will start to slow down (note not because it's lean), it will start to heat up which will advance it further, which will make it slow further until it eventually stops. The oil out of the exhaust will be dark or black. Running the engine like this will damage it.

What you are after is a setting just slightly more advanced than burping. If your model burps in the air then you will have to advance slightly from here (normally by adding compression) but remember the symptoms of over advanced.

So if I was you, after you've got the engine running reduce the compression until it just starts burping then increase till it just smoothes out. Let the engine warm up (you may notice the burping reduce as the engine advances with the temperature increase). You can't get the final setting until the engine is up to temp. Next lean (retard) the engine till it burps. Then increase compression (advance) till it smooths out again. Keep leaning then bringing up the compression until you are at the mixture setting that you want. What setting is that you say?

Well obviousely if it just stops then you are too lean (if it runs hard then slowly loses RPM you aren't lean remember, you are over compressed. Don't richen. Decompress or throttle back instead)

Maximum power will occur at the leanest possible setting, you might notice a slight crackle to the exhaust at this setting. The engine will also be running quite hot so if you go over advanced things will go down hill pretty quickly from here.

For these reasons most people don't run quite this lean unless they are competition flying. To richen first decompress (retard) till it burps then richen (advance) as required then bring your compression back up to just stop the burp.

Once you are happy with your settings throttle back and set your idle needle for a good transition. You might have to play around a bit with this, at idle the engine will cool down (retard) if you idle for a while then accelerate the full throttle setting might be a bit retarded for a few seconds till it warms up again. A rich idle might help with the acceleration in this case. If it sounds metallic and clanky on throttle up then it's too advanced during the transition try leaning the idle a bit.

You may have better throttle response with a richer (and lower compression) full throttle setting.

The other throttling issue you can have with Diesels is due to the glow carb actually being too big for Diesel operation, especially if you are using the bigger propellers (lower RPM) that the engine is now capable of using. If you do have problems try restricting the throttle opening to around 80% then re tune the high end from there. Some guys fit a smaller carb to their engines, you might have good luck with a .35 to .40 size carb (ASP are cheap), but I guess you would need an adaptor for your Fox.

Sorry for such a long post, you probably know most of this, but maybe something will be helpful.

Dave H

1QwkSport2.5r

That's pretty helpful. Thank you. My buddy adjusted his PAW a bit differently but got to a good running setting still. Your method sounds good and I'll keep it handy for reference when I get the engine mounted up to run.

I do have a carburetor adapter to use a smaller choke carburetor on the Fox B-case engines. The Fox Carburetors I have that fit the .46/.50 Foxes all have a .330" choke which is on the edge of too big for glow fuel. I think a .270" choke is better. I think I have a Perry on the .50 right now which is around .270" I think. I'll have to see if I have a 2-needle carb that fits.

gerryndennis

Sounds like you are well sorted out.

Tuning always sounds way more complicated than it really is when you write it down. Any one with a bit of a feel for engines, which I'm sure you have, won't have any problem.

As long as you remember if it goes harsh, metallic sounding, slows down hot, etc back off the compression straight away. Other than that you won't hurt it so experiment till your hearts content.

Cheers,

Dave H

1QwkSport2.5r

I'll do exactly that Dave. Thanks for your help, I very much appreciate it.

gerryndennis

No problem, I'm looking forward to hearing how you get on.
​
Dave H

Hobbsy

My Feedback: (102)

All that Dave said will quickly become automatic to you, I use a 12x7 on the .45 to .50 sized engines. A 12x7 is a hair small for the Irvine .53, I don't let my Diesels run over 10,000. The Webra .50 with Dykes ring turned the Graupner 12x7 at 9,999 and the Irvine .53 turned it at 10,120. Your Fox .50 should turn a 12x7 at 9,700 give or take a hundred. Depending on which brand.

1QwkSport2.5r

Anyone have a base needle setting for the Fox .50 diesel for either the EZ-adjust or MkX carbs? Also, is the contra setting a trial and error thing where maybe I back it all the way off and increase it until it runs or is there a reasonable base setting? The last time it ran, we ended up with the contra flush with the squish band probably in part due to a large head spacing... What would be an ideal head spacing? I have the case milled .020" lower and have shims installed to put the Fox liner at the factory location however it has a .030-.045" head spacing depending on which glow head button I use. The piston at TDC is approximately .206" below the top of the liner and the Fox glow head and even the Davis diesel head are about .170" deep. My custom head button is about .185" deep.

Also, I'll be mixing up my own fuel and I wanted to find out if I should measure by volume like I do glow fuel or should I be measuring by weight? I was going to be shooting for 20% castor, 30% John Deere ether, and maybe 2-3% Amsoil Cetane booster with balance Kerosene.

1QwkSport2.5r

I was originally going to try getting my Fox .50 running on diesel this weekend maybe, but the rear bearing is making noise and the conrod that I got with the replacement .50 Piston/liner set has too much play in the big end. I think I have a good rod I can use and I might have a good 6902 rear bearing I took out of another engine that might fit. I'll have to dig through my parts bin and see if I still have those bits.

gerryndennis

G'day Quick,

I added some comments in light of your answers and some rethinking.

Good is to hear you are getting close to running your engine again.

I mix my fuel by volume, my mix is very similar to yours at 20% oil, 30% ether, and 50% kero. I then add 1% Amsoil (I know that adds up to 101% but it's common to do it that way just for the ease of mixing). I don't know too much about cetane boosters in diesel fuel but 1 or 2% is normally the maximum, any more than this makes no further improvement. Obviousely there's no reason that you couldn't adjust the numbers and mix by weight if that suits you better.

Initial settings can vary a bit from engine to engine but a good start is to set the contra so that the compression feels similar to a glow engine or slightly highe. Davis says to wind the compression right down then back of (from memory) one turn? as a starting position. Make sure that the piston does not touch the contra though. The length of the Davis compression screw screw should prevent this from happening.

A good technique to get the initial setting is to remove the muffler and prime the side of the piston ie rotate the engine to close the exhaust port and squirt a couple of drops of fuel on to the side of the piston (diesels are quite easy to flood, slightly too much fuel and they just won't fire, even more fuel and you risk a hydraulic lock and potential damage). Once you have primed start flicking, if you don't get a burst after three or four flicks increase compression by an 1/8 of a turn or so. If it backfires and whacks your finger back off the compression. Keep flicking and increasing compression until you get a burst (you may have to reprime after a dozen or so flicks). Once you can reliably run out a prime you've found the starting compression setting (this may or may not be close to the running setting).

You need to develop a good, quick, flick from the wrist, 'diesel' flick not a lazy glow flick. Use the dreaded electric finger (electric starter) if you need to, but only in a short burst, then increase compression and check for hydraulic lock by hand, then another short burst.

Refit the muffler.

Next step is to try priming through the carb. Open the needle a couple of turns and with your finger blocking the carb (full throttle) rotate the prop to bring fuel to the carb then one more turn. Close the needle then check for hydraulic lock and start flicking. If it doesn't start try two priming turns, you shouldn't need more than three but you might. Remember if you flood the engine it won't start. You'll have to get the fuel out of the crankcase before continuing. Once you get it to run out the prime you have established the correct priming technique.

Now open the needle one turn, prime and start. You are aiming for a deliberately lean needle to avoid flooding. Open a further 1/2 a turn each start until the engine runs continuously. You'll probably need to richen it further once it's running.

Once again it's not as hard as it sounds, you'll be setting the comp, priming, and getting one flick starts at idle, quicker than starting a glow before you know it.

Let the engine warm up before establishing the running settings.

For subsequent starts you may have to adjust the comp to the starting setting if it is significantly different to the running setting. The engine will be retarded until it warms up. It may need to have the needle set richer to keep it running or it may just burp on the running needle setting until it warms up.

The ideal setting (running, not starting) for the Davis head (is this what you've got?), is with the contra flush with the squish band (you can adjust the shims to achieve this if you want to). It won't make much difference if it's recessed slightly from this though. I adjust the head shims to get close to this. The danger with too many head shims is that the contra ends up proud of the squish band, too far and it can hit the piston. You won't have this problem, I couldn't get enough compression (the screw was too short) with my head so I replaced the compression screw with a longer one. The engine ran with the contra proud of the squish band and very close to the piston. I have since found that the head seals fine with no shims, and by using the Amsoil I can back off the compression setting so that it is now close to flush.

Looking forward to hearing how you go.

Dave H

1QwkSport2.5r

Thanks much for your feedback and help!

I do indeed have a Davis head, and the contra was pretty much flush with the squish band last time we ran it but the gentleman I got the head from had a thin shim on the head that we did use, but based on the head spacing, I'm not sure it will be required. I'll try it without first and if need be, I'll add it back in. I'll stop at the hobby shop and pick up a petrol fuel bulb for priming/filling the tank too.

I pulled my good Fox conrod and got a good rear bearing, so I'll replace those today and get it buttoned back up. The compression is pretty good, but I'll run a couple more tanks of glow fuel in it after reassembling before I put the diesel head back on it just to make sure everything is kosher. The engine should be in good shape, it'll just be the learning curve of tuning that may take me a bit to get used to. Looking forward to learning something new though, not to mention the smell... That's not something that's easy to forget.

The cetane booster I have is the same as what everyone else uses, they just call it by a different name on the bottle now I think. Amsoil calls it Diesel Cetane Boost, but it's the same ignition improver everyone else uses. The MSDS lists it at 60-100% 2-EHN. It's been said to be about 98% in reality. I'll probably do 2% Amsoil to start with and after I get the tuning mastered, I'll try 1% and see if the starting difficulty increases any. I have all of the chemicals to mix the fuel up now, just need to make up a capture jar and lid for decanting the Ether. Should be an easy job.

Thanks again for the help and guidance.
Tim

Hobbsy

My Feedback: (102)

My experience with the .50's is as Dave H. suggested, the contra needs to be almost all the way in.

1QwkSport2.5r

Thanks for the info Dave. I'll probably start with the contra slightly recessed and go from there.

I replaced the parts in the engine that needed to be replaced and have it buttoned back up. It feels nice and the bearings are smooth as butter. If all goes well, I should be burning some kerosene over the weekend. I'll post about my experience and findings.

gerryndennis

G'day Quick,

I added a couple of thoughts to my last post.

I'm glad you have good compression seal. The better the compression the easier they start.

You are right about the smell... heavenly. If you do it right the smell can last for days in your clothes and workshop.

I'm out of town for a few days after the weekend but I'll look in when I can so that I can read about your success.

Dave H

1QwkSport2.5r

Greetings and Salutations. Thanks for the extra info in your last post. Most of it confirmed my suspicions, so I should be in great shape to have some sort of success. Many thanks for your time to share all of that. It seems there are only a couple of conversion diesel guys willing to help, so what help I get is very much appreciated.

The smell of a model diesel engine exhaust reminds me of the days when I was growing up when my dad would take my sister and I to the big international airport and watch planes take off and land on Saturday or Sunday mornings. It's a nice throwback in a way.

As as for the Fox - I'll run a couple tanks of fuel on glow to reseat the ring again (it killed me to have to take it apart and need to do this again) and get some baseline rpm figures to compare the diesel operation to. I'm going to attempt to mix my diesel fuel Saturday morning as I have some plans after work the next couple days. I'm visiting the local flying club tomorrow (Thursday) to attend a club meeting and meet the fellows there and see if it's a good fit for me. I've been low on funding and time to get into a club, but my boy is getting old enough to be able to take with to the flying field so I'm eager to have that ability. He loves anything with wings, wheels, or floats. It's too bad this diesel Fox isn't gonna be enough snort for my Mig target drone, I don't have a plane I could fly it on if I wanted to.

Anyway, when I get there, I'll update how it goes with maybe a video or something.
Thanks again Dave H!!

-Tim

gerryndennis

No problem at all Quick,

I'm looking forward to the vid.

Dave H

1QwkSport2.5r

One more question - use muffler pressure or not? Carb is .330 or .270"", .50ci/8cc displacement, inlet channel in crank is .405" in diameter.