Logo
Builders' Plan Gallery  |  Hip Pocket Web Site  |  Contact Forum Admin  |  Contact Global Moderator
August 09, 2020, 09:58:07 AM *
Welcome, Guest. Please login or register.
Did you miss your activation email?

Login with email, password and session length
 
Home Help Search Login Register
Pages: [1]   Go Down
Print
Author Topic: Getting to know your diesel engine  (Read 1599 times)
0 Members and 1 Guest are viewing this topic.
TheDope
Silver Member
****

Kudos: 7
Offline Offline

United Kingdom United Kingdom

Posts: 118

Topic starter


Ignore
« on: June 13, 2012, 09:16:35 AM »

Hi all,

I now have 2 diesels that have been purchased second hand. A couple of Mills 75s were my first though I sold one and kept my favorite, and my latest is an Allen Engineering 0.5cc. The instructions, if you receive them with the engine, often assume you are the first owner of the engine and that the compression screw is still in the correct factory setting for running in and starting. As a result the instructions are often next to useless when the engine your holding has had every conceivable control fiddled with over many years of dust collecting. This is how I approached the problem with my engines and I'm hoping that you'll come forward with suggestions of how to improve this procedure to help other newbies like me.

First I install a suitable propeller such that it is in a comfortable position for starting. It should be horizontal just as the compression part of the turn starts to come on. Props generally turn clockwise from the pilot's perspective and anti clockwise from the modeller's perspective. I check that the engine turns over and that I can feel some compression while doing so. If it does I mount it ready for initial testing. If the engine doesn't turn over or has no compression then I go into maintenance mode until it is fixed. I've found it's a good idea to check an engine over thoroughly even if it seems in working order. I had a Mills P.75 just prior to purchasing my present S.75 and that Mills had a load of metal swarf in the venturi and had obviously had a lot of DIY work done on it. It ran nicely but I chose to keep the Mills S.75 with the built in engine cutout just because it's a nice feature in my opinion.

If all seems well I move on to locating a good range for the compression screw. This is a major trial and error process for me at the moment. To do this I put a bit of fuel in a syringe. I do not put fuel in the fuel tank because if the engine doesn't want to play ball in this initial session I'll have a load of unused fuel sloshing around in the tank. I close the needle valve completely as I won't be needing it and closed is a good starting position for the next step. On a small engine I rotate the prop so that the piston closes the exhaust ports and put a couple of drops of fuel against an exhaust port, then let the piston drop back down pulling a bit of the fuel in with it. My Mills is less sensitive and doesn't seem to mind being primed with the exhaust open. This primes the engine just as would be done when starting it for an actual engine run but of course, this time it will stop running once the prime runs out. Once primed I give the prop a good fast flick. If I am lucky the engine will fire. If not then I need to use the opportunity to find the range of compression settings where the engine starts relatively easily. I keep an eye on the prime while doing this and replenish it every now and then when necessary being careful not to flood the cylinder.

Once I get the engine running briefly but reliably from a prime the next stage is to find the needle settings. I put a little fuel in the fuel tank. Open the needle valve a little, close the air intake of the engine and turn the prop over so that fuel is sucked up to the needle valve assembly. If the fuel does not get sucked toward the needle valve I might need to open the needle valve a little more until it does. I prime the engine as above and if the engine is a front rotary type I might also put a drop of fuel into the venturi too. I found that the AE 0.5cc positively required two drops of fuel in the venturi for starting. The Mills .75 doesn't seem to need this. I flick the prop over to try and start the engine. If the engine runs but does not continue past the prime I will open the needle valve a little more. I keep doing this until finally the engine starts taking fuel. This is the right range for the needle valve. If the engine is spitting fuel out of the exhaust I have the needle valve open far too much!

Now that I have the engine starting and pulling fuel from the tank I can start to fine tune it. I usually just do this by trying to make it as loud and obnoxious as possible though a tachometer would probably be useful.

This is a newbies perspective and I would really appreciate it if you'd chime in with further advice and modifications to this procedure if you can think of any.

Many thanks.
Logged
Bingo Fuel
Gold Member
*****

Kudos: 8
Offline Offline

United States United States

Posts: 274



Ignore
« Reply #1 on: June 28, 2012, 09:27:38 PM »

Thanks so much for the lesson.  The only diesel I ever owned and ran was a India made Mills .75 also.  I got it used so had no  instructions and had no idea how to get a diesel running.  I did fill the tank with fuel  and put the compression screw about mid range of its full travel and like you started with a closed needle valve and tried to start on prime into the exhaust port.  It did fire after not much monkeying around but I accidentaly over primed which is quite easy to do and flipped the prop and got a liquid compression lock and bent the con rod.  I took the engine apart and straigtened the con rod in a vice and was surprised at how crude and soft it was.  I put her back together and it fired right up and ran perfectly.  I played with the needle valve and the compression screw which needed a bit of increase to bring up the rpm.   I was very surprised at how easy it was to start after it had been run and was a little warm as it needed no prime at all.  I must say I only ran it in the upright mode and I would think it might be a bit tricky to start inverted and not get a compression lock and again bend the con rod.  Any comments out there on starting diesels inverted?  I now own other diesels but have yet to try them out.  I am dying to get my hand back into diesel free flight.  Bingo
Logged
BlueBaron
Silver Member
****

Kudos: 1
Offline Offline

United States United States

Posts: 220



Ignore
« Reply #2 on: June 30, 2012, 11:25:06 AM »

How about starting it rightside up and when running flip the model over after it starts.  Smiley
Logged
ffkiwi
Gold Member
*****

Kudos: 23
Offline Offline

New Zealand New Zealand

Posts: 565



Ignore
« Reply #3 on: September 26, 2012, 07:25:52 PM »

I have been playing with diesels for 40+ years of active modelling, and have hundreds of them, so here are a few suggestions for the tyro-and applicable to the typical second hand purchase. Its not all bad-by the way-sometimes a good second hand purchase can be better than a NIB option-for a start they're often run-in, and brand new diesels can often be pigs to start the first time, [the much maligned Chinese Silver Swallow 1.47s and 2.47s being a case in point] and normally improve over the first 20 minutes running (they may not necessarily be run-in after only 20 minutes, but will certainly be bedded in and have a better piston cylinder fit!)

OK, you've bought a second hand diesel, of indeterminate parentage and history (I was going to say dubious.....but I'd better not!). You haven't a clue of where the comp and needle should be. Here's some advice:

(1) Fuel-unless you're able to make your own, buy a commercial blend with plenty of oil-'run-in' mix or similar [in the US this probably means Davis 1/2A blend rather than ABC, and in the UK Model Technics D1000]  What you want is plenty of oil-to improve piston seal (your 'bargain' second hand engine may be well worn after all!) and plenty of ether to ensure good ignition. Power is not going to be a concern at this point, so lower kerosene content is not an issue. If you do have the facilities and knowledge to mix your own, then make up some good old fashioned 1/3-1/3-1/3 mix [yes I know its got more oil than you need-but its never harmed an engine yet, and its got good sealing characteristics] By analogy Fox Superfuel has/had 28% castor-to help out the piston seal in tired glow engines-and worked well.

(2) Props-use a big prop-and by big prop I mean large diameter and fine pitch-for plenty of flywheel effect, and appropriate to the engine size. Here's a list of suggested sizes:
     0.1cc.........Cox 4x2.5
     0.2-0.25cc  thin blade 5-1/2x3 or 6x3
     0.3-0.4cc    6x3 6x4
     0.5cc         7x3, 7x4
     0.75-0.8cc  8x4
     1-1.5cc      9x4
     2-2.5cc      10x3-1/2, 10x4
     3.5cc         11x4
     .29-.35       12x4-12x6

 Note that these sizes are purely to assist you starting, and finding the settings, and may well be larger than the manufacturer's suggested props. There's a few buts-sideports will happily turn larger diameters at lower revs than FI or reed valve engines-so a Mills 75 will turn an 8x4 very comfortably and a 9x4 if it has to, the 1.3 a 10x3-1/2 and the ED 2cc and Letmo 2.5 sideports will hang on to an 11x4 and relish it.

(3) Mount on a stand or block, not in a model. If you're a newbie, keep things stable, accessible and at a comfortable height-and you can't easily do that in a model. Set the prop at the time honoured 'twenty to two' [or 'ten past eight'] clock position as the engine reaches compression [for right handed people] (this should be with the piston roughly halfway up past the exhaust-and you should feel the resistance against compression.

(4) Tanks should be no higher than the spraybar-and may need shimming up or down relative to the engine to maintain this relationship (you may need ply or balsa shims to raise, or some clever attachments if the tank you're using needs to be lowered......

(5) With no fuel in the tank, and the needle valve fully closed,try a couple of drops of fresh fuel applied directly to the exhaust port[and for initial running and familiarisation, if the engine has a muffler-remove it for this phase. You'll likely have enough difficulties without the additional complication of trying to start with a muffler on.] Turn the engine over a couple of times by hand to distribute the prime, then try a good hard flick-if the engine fires, you're probably in the ballpark as far as compressiom is concerned. If nothing happens then repeat the prime. If the engine hardens up, and becomes hard to flick over, then the compression is likely to be too high or you've flooded the cylinder. In this case,reduce compression by half a turn and try flicking again-hopefully you should hear a 'click' or 'snap' as the contra piston moves back to the lower setting. [the 'click' is the upper surface of the contra coming into contact with the end of the compression screw-you turned the screw back, so then there was a small space between those two surfaces)
    If nothing happens from your exhaust primes, it is likely that the compression setting is too low. An excellent method of getting close to the correct setting is to apply the following method: turn the compression screw clockwise to increase compression-half a turn at a time, and checking each time by turning the engine slowly over compression. As you proceed you will feel the resistance increase. Eventually there will come a point where you can't turn the engine over-and you can 'feel' metal to metal contact. At this point the piston and the contrapiston are touching. Reduce (turn the comp screw anticlockwise) one full turn, and carefully flick the engine over-hopefully the contra will snap back to the new lower setting. [if it doesn't you may need a drop of fuel to raise the cylinder compression higher still] This new setting (one full turn backed off from contact) should be close to a starting compression setting for virtually all conventional diesels.

(6) Repeating the exhaust priming process until you can get the engine to first fire, and then run out the prime-which might only be 1 or 2 seconds. When you are comfortable that you have found the right setting, and prime amount, THEN fill the tank, and open the needle. Most diesels will run between 2 and 3 turns open. Block the venturi with your finger, turn the engine over slowly with the prop to suck the fuel through the line from the tank to the needle valve assembly. That's usually enough-over choking will easily flood the crankcase, and then you're in for grief.

(7) Repeat your exhaust priming process and see if the engine continues to run. For some you need to 'catch' the prime and increase compression to keep the engine running. If it dies out, ensure the fuel line is full to the jet and give it one choked (with your finger over the air intake) flick. Repeat the prime process-if it still dies, try 2-3 choked flicks-and repeat. If it still dies out after the prime, then open the needle half a turn more and go through the complete process again, until you can produce sustained running.

Several other relevant points:

Some engines prefer exhaust priming, some intake priming, and some require both. The optimum comp setting will depend on your prop size: small props, higher revs=higher compression setting required (and also leaner needle valve setting) Normally the optimum running setting for the compression screw will be about 1/2-3/4 of a turn more than the best starting setting. Learn the difference between uncompressed (intermittent misfiring) and overcompressed-engine sounds 'hard' and laboured running. Compression is your key adjustment and has a greater effect (within limits) than needle valve adjustment. Most engines will require the compression to be adjusted slightly once they have warmed up-this is usually after about 30 seconds to one minutes running, and requires the compression to be backed off slightly-usually no more than 1/8-1/4 of a turn.
   Check your exhaust residue-grey or silvery powder in the exhaust means something is wearing badly inside-could be conrod bearings, or backplate contact wear.

The small engines-0.8cc and below seem to have individual personalities-and starting procedures may vary between examples of the same make and model. This is especially
pronounced in the very small ones 0.5cc and below.

  ChrisM
  'ffkiwi'
 
Logged
OZPAF
Palladium Member
********

Kudos: 186
Offline Offline

Australia Australia

Posts: 5,714



Ignore
« Reply #4 on: September 26, 2012, 08:40:41 PM »

Good one Chris - lots of good info. i'm an old diesel man as well and agree with all of Chris's info. I would only reinforce that you use Castor oil or Castrol R - if it still exists - what a great smell! This is particularly the case with old motors and novices.
I haven't had any experience with starting inverted diesels but using an exhaust prime - only wetting the piston side(closed port) without an intake prime(choke) should give an easy start. All team racers use inverted motors so it it is only a matter of technique.
Diesels also prefer a much stronger flick of teh propelelr than a similar size glow and the actual position of the prop depends on the person. i actually prefer the prop to be at the 2 0'clock position near max compression. Flick through the arc of the props rotation and do not follow the prop around the arc with your finger. Also with motors over 1.5cc a bit of protection your finger is a good idea  -especially for fast firing motors. I have used a finger stall over a bad aid on my finger when necessary.
So TD I think you had most of it right.
John
Logged
ffkiwi
Gold Member
*****

Kudos: 23
Offline Offline

New Zealand New Zealand

Posts: 565



Ignore
« Reply #5 on: September 26, 2012, 09:33:52 PM »

John I was trying to write a guide for diesel newbies and slant it from the perspective of someone new to diesels and/or someone with a second hand diesel with the settings lost and not much diesel experience. Equally it could have been done as a multipath flowchart-but that would have required ppt or something to draw and probably not uploadable.
    Like you I'd also endorse the use of castor as a preferred lube..........despite the mess. Being a chemist/biochemist by training, of course I mix my own fuels....

 ChrisM
 'ffkiwi'
Logged
Pages: [1]   Go Up
Print
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.21 | SMF © 2015, Simple Machines Valid XHTML 1.0! Valid CSS!