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Fixed Compression Diesel Head?

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Fixed Compression Diesel Head?

Post  NEW222 on Thu Mar 26, 2015 9:48 pm

Hi there again.  So, while going back in time a bit, I had started a topic titled 'Pop Can Glowhead Gasket' (https://www.coxengineforum.com/t793-pop-can-glowhead-gasket)  .  While going back over it again tonight, I came across something I must not have noticed before.  This was posted by nitroairplane 'Well i have never tried that but by using a can you can make a fixed compression diesel head and that i have done.  Indra' (post#3 in topic).  Anyways, this does have me wondering.  Is this something that I may be able to do or re-create?  I think it would be a fun little project, but have no clue where or how to start the project, let alone starting a diesel engine.  I have done some searching with no luck on such topic.  If anyone here may know more about what was mentioned, or pics, it would again be greatly appreciated.  Thank you all again.
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Re: Fixed Compression Diesel Head?

Post  pkrankow on Thu Mar 26, 2015 10:08 pm

I ended up using .003 shim brass when I ran out of Teflon discs. It ran better on the brass than the Teflon! Yes, the compression still adjusted.

I gave up on diesel and went back to glow.

Phil
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Re: Fixed Compression Diesel Head?

Post  NEW222 on Thu Mar 26, 2015 10:22 pm

So, what is it? Do i just cut out a circle the diameter of the head gasket and install? As I have zero knowledge of model diesel engines, it sounds just that easy to me. Sorry for all the questions, but is interesting.
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Re: Fixed Compression Diesel Head?

Post  Surfer_kris on Fri Mar 27, 2015 9:54 am

Yes, it is that simple...
But you do want to have an adjustable compression ratio, there is no way you will get it just right without one.

The Davis Diesel Development ones are just that, a flat disk (a metal one is better than Teflon) that gives you a higher compression ratio that the domed glow head does. But they also have an adjustable support behind the disk that gives a little bit of a tuning ability.

The RJL heads are much better, they give you a full adjustment and there is no silly teflon stuff that leaks...
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Re: Fixed Compression Diesel Head?

Post  gcb on Fri Mar 27, 2015 10:30 am

Adjustable compression allows you to adjust ignition timing for a specific fuel, prop, and atmospheric conditions so it should be conceivable to adjust to a fixed compression with fuel and prop...like they did with the original Drone diesel back in the forties. :-)

I have not tries he RJL head but I have run the Davis one. The Teflon is used to protect the engine. Good for a beginner to diesels but a PITA to a seasoned diesel user.

George
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Re: Fixed Compression Diesel Head?

Post  NEW222 on Fri Mar 27, 2015 3:40 pm

This is great.  Thank you all for the great help and advice.  It is greatly appreciated.   Now to look into buying something(i know they're not that much ), or converting an old head when I find a burnt out one.  Thanks again.
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Re: Fixed Compression Diesel Head?

Post  getback on Fri Mar 27, 2015 4:24 pm

Well thanks for bringing this out New222 I did not know some of this good info the one time I tried to run a 049 medallion with a diesel setup I could only get it to pop now and then and it was like 50 degrees outside so I had to give .. after taking it apart and not knowing what I was looking for I said heck with it and put a reg head on it , It still had like very little compression so I think the pis/cyl. is worn out . But I have another dedicated diesel that I want to try , maybe things will work better for me . I will keep in mind the .003 brass plate for better compression . Thanks Guys .
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Re: Fixed Compression Diesel Head?

Post  chevyiron420 on Fri Mar 27, 2015 5:11 pm

My first try into the diesel world was with my tee dee. I got a RJL head, and made up some fuel. I got it to sputter a couple of times, then nothing. I bent the rod on the best piston set I had. I still didnt give up and installed the second best set on it. Yep, I ruined it to. I still have the head, but i wont use it. I got a DC Merlin engine and some fuel from davis. Its tricky to start but runs pretty good if I feel the need to ruin my cloths, I use it. I have it on a baby ringmaster and has to be hand launched. When my son see's I broght it with me to the field he cusses me! DAMMIT!
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Re: Fixed Compression Diesel Head?

Post  RknRusty on Fri Mar 27, 2015 6:50 pm

Haha, must be one of those flavors that has to grow on you. Or it might grow on you whether you like it or not Lol. I've never experienced it.
Rusty

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Re: Fixed Compression Diesel Head?

Post  Surfer_kris on Sat Mar 28, 2015 3:48 am

The fuel is very important plus you need to use a much larger prop on diesel engines compared to glow. For beginners I strongly recommend commercial fuel, as there are too many things that can go wrong otherwise.

A high level of pure ether (33-35%) plus a bit of ignition improver is needed in order for the compression ration to not be so high that it will damage the engine. The larger prop also helps to keep the load down. Contrary to glow engines a larger prop gives a lower load on the engine by requiring a lower compression setting. Here are some typical prop sizes;

Cox PeeWee: 6x3
Cox .049: 7x4
Cox Queen Bee: 8x4

The reed engines perform very well when converted to diesel. One should prop these for top revs of around 10krpm to ensure a low load. At these revs you don't need any of the large fancy porting that the TD has, instead it is all about a good fuel draw and reliable running.

Here is a little video of the Queen Bee that I have posted on this forum before, It is perhaps not very interesting (I'm just fiddling with the throttle stop on the radio) but I'm very pleased with the way it runs on diesel fuel with the RJL head, and an APC 8x4 prop:

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Re: Fixed Compression Diesel Head?

Post  roddie on Sat Mar 28, 2015 7:09 am

Surfer_kris wrote:The fuel is very important plus you need to use a much larger prop on diesel engines compared to glow. For beginners I strongly recommend commercial fuel, as there are too many things that can go wrong otherwise.

A high level of pure ether (33-35%) plus a bit of ignition improver is needed in order for the compression ration to not be so high that it will damage the engine. The larger prop also helps to keep the load down. Contrary to glow engines a larger prop gives a lower load on the engine by requiring a lower compression setting. Here are some typical prop sizes;

Cox PeeWee: 6x3
Cox .049: 7x4
Cox Queen Bee: 8x4

The reed engines perform very well when converted to diesel. One should prop these for top revs of around 10krpm to ensure a low load. At these revs you don't need any of the large fancy porting that the TD has, instead it is all about a good fuel draw and reliable running.

Here is a little video of the Queen Bee that I have posted on this forum before, It is perhaps not very interesting (I'm just fiddling with the throttle stop on the radio) but I'm very pleased with the way it runs on diesel fuel with the RJL head, and an APC 8x4 prop:


Thanks Kris, I had seen this video before.. and it's very inspirational. Nice throttle response on a great running engine! Were you running commercial fuel.. or a blend that you mixed from separate components?
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Re: Fixed Compression Diesel Head?

Post  Surfer_kris on Sat Mar 28, 2015 8:07 am

This was on semi-commercial fuel, the only source I know of in our country (3F-Hobbyservice for those interested). They can blend small orders to specification, and my standard order from them is the following;
Ether: 33%
Castor: 25%
IPN: 1.5%
(the rest is Kerosene)

For those tempted to convert glow engines to diesel, the more "timid" engines tend to do very well as diesels. You simply do not need large crank bores and transfer channels, due to the low rpm's that they will turn anyway. From Cox I think the reedys do particularly well. Medallions should do well too but I haven't tried that, yet...
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Re: Fixed Compression Diesel Head?

Post  gcb on Sat Mar 28, 2015 9:09 am

A few comments and observations:

When learning to operate small diesels, never, ever, ever use an electric starter. You may break your engine if you do.

Approach a new diesel from low compression and adjust it up to where it fires. Initial settings should be with the tank empty and just running off a prime. When you are running off the tank, final adjustments should be made after the engine is up to full operating temperature. Don't run it over compressed.

Old Cox reedies had crankshaft problems when using diesel conversions. DDD made a special crankshaft to use with diesel conversions. Cox had one made for the "Killer Bee" that worked well. The new ones must be stronger.

The TD crankshaft is strong enough as-is.

Diesels are not hard to operate, just a different process from what you use for glow.

If you can, and it varies with different engines, try to establish a starting procedure that does not involve fiddling with compression. Plan "B" is to remember where the normal running compression setting is.

George
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Re: Fixed Compression Diesel Head?

Post  NEW222 on Sun May 10, 2015 7:08 pm

Ok. So while looking things up and playing around on Google, this video had popped up. And what a surprise to see who had made and uploaded the video. Same person with the comments in my topic as well. I was very glad to see this. Looks funny though, as I am used to seeing videos and pictures with an authentic 'diesel' glow head.
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Re: Fixed Compression Diesel Head?

Post  NEW222 on Sun May 10, 2015 7:09 pm

Oops. Video link here:

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Re: Fixed Compression Diesel Head?

Post  RknRusty on Sun May 10, 2015 7:58 pm

NEW222 wrote:Ok.  So while looking things up and playing around on Google, this video had popped up.  And what a surprise to see who had made and uploaded the video.  Same person with the comments in my topic as well.  I was very glad to see this.  Looks funny though, as I am used to seeing videos and pictures with an authentic 'diesel' glow head.
Nitro airplane, he was a prolific poster, but I guess he got burned out... in more ways than one. On forum posting, he was a moderator, and actually had a shop fire if I recall correctly. Not 100% sure about that. He was a brilliant and industrious teenager with his age listed as older in his profile because he worried he wouldn't be taken seriously. A massive collector too I think. One of our English friends, I kind of miss him. He lured me here from RCGroups.com. I hope he still looks in on us.
Rusty

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Re: Fixed Compression Diesel Head?

Post  NEW222 on Sun May 10, 2015 8:21 pm

Yes, I do remember him. As thing happen, and I got away for a bit too. But upon my return, I do see and remember a lot of the names from times past, but his was one I did not see recently. And I was wondering if he was still around and alright. Agreed too that I hope he is still watching.
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