Diesel guru needed

[extra slim]

Hi guys, I am having a bit of a diesel period and have picked up a couple of PAW's. The 2.49 is great and runs well. My recently acquired 1.49 early one, appears very new, and taking off the back plate, reveals a nice tidy inside, with no play on the conrod etc.. no scratches on mounting holes etc.

When it came, it had a silencer fitted, and was tricky to get running, but when it did, got hot and stopped. On taking the silencer off, I noticed the liner was put in wrong, and so the venting to the silencer was blocked off a few degrees. I removed the silencer altogether, and got it running, but it was a real pig, and had to resort (cover you ears) to a starter (carefully). Once running it is really quite nice, but starting hot and cold, is incredibly hit and miss, and frustrating.

I have taken the spray bar out and ensured the single hole is facing down, the needle on it appears to have a pretty short taper, and when running, it is only really 1/4 to half a turn open. and adjustment is very sensitive.. and it is prone to flooding quite easily.. which I guess it would with a stubby needle.

I'm thinking I need a new needle for sure, but that wouldnt really explain the unusual behaviour. I have hand started it a few times since, but then struggled and resorted to starter again.

It is running hot, and hot starts with compression backed off just dont work.

I cant imagine it is worn out as it looks to have done next to no running. Is what I am describing, a "new engine" kind of behaviour?, is the piston now lapping in to a new position, now I have turned the liner to the right position?.

Also, running an 8x4, but perhaps a larger diameter prop may help me..

Any ideas, suggestions welcome.

[sticky fingers]

Dont claim to be an expert but diesels can take a good bit of running in from new, running richer to aid cooling. Did you get a set of instruction with the engines ,if so follow the 'running in' procedures, ifyou dont have any I could probably fix you up with a set.

Dave

[Keith Evans 3]

HI,Doing the same thing myself with a P.A.W .35 .

There are a couple of points to note in their starting and running instructions .

Quote " Fuel level in tank during starting procedure "MUST NOT BE HIGHER THAN IN THE SAME HORIZONTAL PLANE AS JET . A LITTLE LOWER (UP TO 1 cm.) IS ALRIGHT . "

"------- If it misfires at the begining of the flight, and continues running in that manner to the point where the engine slows down and stops,it means that the needle setting is too lean ,and the needle requires to be opened further .This will also be confirmed by the engine being hot ,and difficult to re-start ,This is most important in control- line flying , but also applies to long free flight runs ,such as in radio controlled flight "

Sounds as if it is being run too lean is my best guess .

Keith

[Engine Doctor]

Hi does it feel smooth and bouncy with good compression? If yes then it might just need more running in. If there is any stiffness it may be that you have put the cylinder in a slightly different position. Try turning cylinder slightly until its free an bouncy . Once set and run in don't remove cylinder unless absolutely necessary .Is crankcase compression good? Any leaks there will cause hard starting and hot running. Is the silencer a genuine PAW ? If yes then it should run without serious overheating problems. What fuel are you using ? Standard sport mix or Model technics D 1000 is ideal for running in and general use on engines up to 1.5cc. Anything bigger use D2000 or high performance engines useD3000.A s already said in earlier post, diesels take a lot more running in than modern glow engines and will only hold full power without overheating once fully run in. Let us know how it goes. 

Edited By Engine Doctor on 06/09/2016 12:55:09

[Ultymate]

plenty of info on their website **LINK**

[Keith Evans 3]

Hi again .

Recommended prop for 09 sizes , max.--8x6 , run in 7x6 , min.6x3 .

"Too lean a setting ,over compression ,or too"hot " a fuel will also cause hard running particularly on hot days ."

Keith

[Keith Evans 3]

On the same subject --why do the instructions state----"stop by cutting the fuel supply ,NEVER by throttle or choking ,"

What harm does this do to the engine ?

How does one go about stopping the engine if the fuel lines are hidden in the body or cowl of the model ?

I don't think it would be good practise nowadays to throw a rag into the prop like the old days ! ! !

Keith

[Jon H]

This article http://www3.bc.sympatico.ca/dieselcombat/about_diesels.htm is the best i have ever seen for describing diesel run in. i would recommend you read it through and go from there.

My PAW 149 is a little peach and i use an 8x4 prop. I estimate its doing about 10k at full power but im not really sure. I will check next time i run it.

Edited By Jon Harper - Laser Engines on 06/09/2016 13:37:38

[Jon H]

I just thought, if you can, take a video of the engine running and upload it so we can see/hear the engine. Might give some more clues as to the cause of the trouble

[Peter Christy]

Keith: Diesels run a MUCH higher compression ratio than glow engines, and choking them can easily cause a hydraulic lock. If this is done at running speed, a bent con-rod is almost inevitable! An oily rag chucked into the prop probably is the best way to stop one!

ES: I've had a number of PAW 1.49s, and they run beautifully. An 8x4 is the ideal prop for a sports RC model, and contrary to popular belief, PAWs throttle beautifully.

However, fuel is critical! Diesel goes off a lot quicker than glow, due to the ether evaporating - unless it is correctly stored (in a well-sealed can and in a dark, cool place!).

My own experience is that "Easy-Start" (like D-1000) fuels are anything but! I found mine started easiest and ran best on D-3000, but I gather this is not recommended for plain bearing engines, so I now compromise on D-2000.

I have a little PAW80 (0.8cc) that flatly refuses to start or run on D-1000, but goes like a dingbat on D-3000! On D-2000 it can be tricky to start, but is fine once its running.

--

Pete

[extra slim]

Thanks guys, I've read the article before as it is really good. Tank and fuel are ok as I ran the 2.49 straight after without issue. Interestingly I am going to try the needle out of the 2.49, as it is longer and appears to give a wider range when I blow through it. It might be that the stubby needle when opened up a bit when running just isn't fine enough and makes it too rich to continue running...its behaviour is very much on or off. I'll try and get some vids. Thanks again

[extra slim]

Hi Engine doc, it is nice and bouncy, started from cold just now by hand, fuel not connected, few drops in the venturi and about 10 flips later got a nice bang, connected fuel and wound needle out 1 turn and off she went nicely...ran it for a minute, then stopped it by pulling line off, she was hot even with compression turned right the way out and needle open another half turn (the max it would run on minimum compression)...tried hot start but no joy, seemed very easy compression wise once it is hot... Noticed a puddle of blackened burnt fuel around the back of its mount low down where the backplate is, so you might be right that the backplate isn't quite tight enough showing up more when she's warm...need to make a tool to do that as the Mrs won't appreciate me using the end of a dessert spoon again..(handle end).. Hope to get there with it as I do like engine messing..

Edited By extra slim on 06/09/2016 17:55:21

Edited By extra slim on 06/09/2016 17:56:00

[Jon H]

If you like engine messing slim you need one of these

[extra slim]

Oh I like that, nice bit of black on ya knuckles!... bet it smelt nice in the workshop for a while... diesel is proper aftershave!. Was this just a bit of an experiment?

[Jon H]

nope, we have sold them and they have been very popular within the diesel scene. They are not easy to operate, but once you get the right fuel mix and get the engine set up as i have in this video, you can just fire it up and go (after it warms up!).

They are not really suited to applications where they are throttled a lot and are best tuned for a specific throttle setting on a specific prop when fitted to a specific model. You then take off, set the engine to the tuned rpm and it will then gladly purr along all day long. Vintage models or even something like a 30's biplane where throttle use is always between 40% and 70% are ideal. If the engine runs too slowly for too long it cools off and wont open up again. Also if ti runs flat out for too long it overheats and knocks as you can hear in the video as i was a bit over compressed.

if you accept their limitations they are great fun and super reliable as there is nothing to go wrong once its up and running.

Let me know if you want one

[David Mordecai]

It sounds like it's pre deternating. Very hard running. Maybe the compression could be backed off and the timing altered slightly

[Keith Evans 3]

Hi again.

Would fitting a two needle carb. , as most glows engines at the present have ,solve the problem of a possible hydraulic lock in a diesel when operating the TX throttle cut to close both the fuel and air intake to the engine ?

[Denis Watkins]

No Keith. An hydraulic lock is caused by too much neat fuel in the cylinder. Air will compress, but this excess liquid, fuel, will not compress and causes a solid response against the piston, an hydraulic lock, that can bend and break bits. Just avoid excess drawing in of fuel or syphoning

[Martin Harris - Moderator]

Posted by Keith Evans 3 on 06/09/2016 13:04:29:

I don't think it would be good practise nowadays to throw a rag into the prop like the old days ! ! !

Keith

I'm wondering why not? It was accepted practise "back in the day" and I don't recall any problems then...

[Peter Christy]

+1 for chucking an oily rag in! Never fails!

It might be worth turning the spray-bar slightly so that the hole is not facing straight down the venturi. Having it offset slightly can dramatically increase the fuel draw.

--

Pete

[Peter Android]

**LINK**

Some of you may enjoy this ?

A Modelling buddy ( Sam) test - flying His late Father's Puppeteer ( Diesel) after a long period of storage, which is circa '20 years old .

Sam then passes the Pup' over to His -Son for a flight or three .

P.A.W 60 I believe . which throttles superbly ( for a diesel )

That is to say , Three generations of the same Family , have now Enjoyed the same Model Aeroplane.

Wind conditions are far worse than appears ( I was there )

No substitute for experience. as they say.

Respect .

[Keith Evans 3]

Hi Dennis

I understand what causes an hydraulic lock ,that is why I am suggesting that the fuel is also cut off at the same time by the bottom end needle being shut thereby cutting the fuel supply off when the carb is fully closed therefore preventing the hydraulic lock .i.e.no fuel ,no lock .,just like pinching the fuel tubing .

When a glow is converted to diesel be it 2 or 4 stroke I understand there is no change to the carb. itself and no special procedures are incorporated to shut the engine down other than the normal procedure of actuating the cut off switch on the TX .Is this correct ?

Could Mr. Harper possibly comment on this on his diesel conversions ?

Thanks .

[Jon H]

Most Diesels use smaller carbs than their glow counterparts but for my versions we didnt change the carbs at all. Everything is the same.

In reference to the concern about a hydro lock i wouldnt worry. Usually the engine will stop long before the carb is fully closed and even if it didnt it wont be an issue as you need quite a lot of fuel in there for it to actually lock

Edited By Jon Harper - Laser Engines on 22/12/2016 16:22:42

[Keith Evans 3]

Thanks Jon ,

That's the answer I was looking for as it will make things a lot more easy for me now !

Does your second paragraph refer to diesel carbs that have only one main needle valve as well ?

Keith

[Mike Etheridge 1]

Interesting topic diesel engines. I felt that years ago I was very competent at starting and running diesels and would agree with others that the running in periods for diesels could depending on the motor take some while. My first engine was a Quickstart DC Super Merlin which compared with a Mills .75 was a pig to start. Also when running it would become over compressed so the compression screw always needed backing off. However once I got used to starting the motor and it was run in and I had the right fuel (Mercury 8 was the best) I felt it was a great little engine. I was reminded recently by an old school mate from over 50 years ago when we had to give class seminars that I started my had held Merlin in front of our class by just squirting fuel into the exhaust port and flipping over the prop.

After a diesel has run I always found that it was necessary to back off the compression slightly, fill up the tank and squirt some fuel into the exhaust port and whilst flipping over the propeller slowly increase the compression till the engine fired. Of course this is not possible with silencers fitted other than the old ineffective Enya types. As for the PAW 1.49 in the past we viewed the engine as absolutely brilliant and my friends and I used one in various control line models. Some years later my nephew used a couple of Blue Head PAW 1.49' s to win a 1/2 A combat competition. I still have at least 4 diesel engines and rate my ED Racer MK 2 as my favourite engine.

.