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DC Sabre Prop/instruction sheet

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Jon - Laser Engines14/07/2017 18:54:10
4789 forum posts
179 photos

In a moment of nostalgia I dusted off some of my old diesels this afternoon and had an ether fueled trip down memory lane. In the pile of castor gummed engines was a pair of DC Sabre engines that ran alright but kept overheating and throwing in the towel. I think the prop was too big but a little search of the interwebs didn't give me anything to go on. I'm guessing it wants an 8x4 or something but if anyone has an instruction sheet it would be interesting to read.

I would have tried a smaller prop than the 9x5 fitted but couldn't find much under about 16''!

Engine Doctor14/07/2017 20:21:43
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2295 forum posts
27 photos

Hello John . Peter Chin test stated 8x4,8x5,8x6 or 9x4 dependant on type of use.Google Scepterflight.net for loads of test reports for old engines from yesterday year.

 

Mike Etheridge 114/07/2017 20:27:47
1519 forum posts
412 photos

Presumably you slackened off the compression screw as the engine was about to stall Jon? Many years ago my DC Super Merlin would act the same as your Sabres and preferred Mercury 8 fuel to run consistently. I did de-gum a DC Sabre in the recent past that was fitted in a control plane I made years ago. However the Sabre I remember was not as good as the PAW 1.49 which was favoured for control line flying.

engine sizes.jpg

Edited By Mike Etheridge 1 on 14/07/2017 20:35:04

brokenenglish14/07/2017 20:59:48
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455 forum posts
29 photos

Jon, I run 1.5 diesels quite a lot, mostly on the bench, but flying them as well.

Everything written above is obviously valid and correct, but IMO, there's an important point that's being missed.

We have a general consensus that the "best" prop is probably an 8x4, OK BUT the Sabre certainly should turn your 9x5 gently and consistently, without undue fuss. If it really won't turn the 9x5 well enough to run out a tank at moderate rpm, then something is wrong somewhere...

I normally use a light (old soft plastic or wood) 9x4 for sport RC flying using a PAW, ED or Oliver 1.5, and the results are superb in terms of engine performance.

Nigel Dell14/07/2017 21:14:15
367 forum posts
27 photos

Hi Jon I agree with above and as Brokenenglish said it should turn the 9" x 5" without too much drama although flying , running in etc would be better on an 8".x 4", I have 4 of them and used them on control line models with a 7" x 6" but even though it was all those years ago I remember running them in on 8" x 4" but tomorrow I will dig the new in box one out and email you the picture of the instruction sheet.

It does sound like it is a touch over compressed if it is overheating but there again I was not there.

Cheers

Nige.

PatMc14/07/2017 21:46:48
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4197 forum posts
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Posted by Jon Harper - Laser Engines on 14/07/2017 18:54:10:

In a moment of nostalgia I dusted off some of my old diesels this afternoon and had an ether fueled trip down memory lane. In the pile of castor gummed engines was a pair of DC Sabre engines that ran alright but kept overheating and throwing in the towel. I think the prop was too big but a little search of the interwebs didn't give me anything to go on. I'm guessing it wants an 8x4 or something but if anyone has an instruction sheet it would be interesting to read.

I would have tried a smaller prop than the 9x5 fitted but couldn't find much under about 16''!

John, if you PM me your email address I send you a PDF file of the DC Quickstart instructions.

BTW the instructions do recommend an 8x4 prop for the Sabre.

onetenor14/07/2017 22:14:25
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1900 forum posts

1If you backed of the comp screw and it still overheated it may be a tight contra piston. Take off head and cylinder then using a brass or alloy drift knock the contra up and down a few times..If this doesn't free it take it out and polish it lightly with 0000 grade steel wool. Lightly

Jon - Laser Engines15/07/2017 02:38:26
4789 forum posts
179 photos

Thanks for the replies. The current prop is some nasty yellow thing and the engines really don't rev out as well as I would like them too. I ran my paw 149 at the same time and it sang as sweetly as ever. If I had thought of it at the time I would have pinched the 8x4 off the paw.

Both of the sabres struggled to get through their integral tank as they overheated and died half way through. I was unable to decompress them beyond a certain point as the contra piston did get stuck when the engine was above a certain temperature. In the end I resorted to running them undercompressed to begin with and as they heated up they came on song but still were not happy. One engine also has massive end float and I think the wrong prop driver so this needs looking at anyway. I may fetch the wire wool and have at the contra pistons while I am at it. I don't want to go mad though. I know from the laser diesels that the fit is quite critical.

The final engine I ran was a PAW 60 (10cc) which was a bit of a monster. For a start it vibrated like hell as the balance on the crank is really not that good. I also had issues with the contra piston falling down the bore and getting stuck to the piston. With the engine running It made an awful sound and It happened a few times so I took it to bits and found a slight leak round the contra piston. This was filling the chamber above with pressure and eventually blew the contra piston down the bore. To confirm my theory I drilled a discrete 1mm hole in the head to relieve the pressure and the problem vanished. It runs well now but the balance really is poor which is a bit of a shame really as it hits a resonance at certain rpm and its just a blur. It also throws out more goo than any engine I have ever known. Smells nice though

Next time I run them I will try the 8x4 and see if they run cooler and let the contra piston move. I still have an AM10 and ED Pep to fire up so I might have a go tomorrow.

Mark Lubbock20/07/2017 21:45:27
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313 forum posts
13 photos

DC Sabre was my first engine way back in '72-'73! I have a number of these engines now and a 7x6 is best for control line and an 8x4 for FF/RC. they will swing a 9x4 but the power output is not good at these revs.

onetenor20/07/2017 23:55:22
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1900 forum posts

Jon Go easy with the wire wool and use nothing coarser than oooo grade,Very often it is just a lacquer coating on the contra piston causing it to stick. A soak in thinners will often be all that is needed to free it off .so try that first. Castor oil lacquer can be surprisingly hard but thinners usually shifts it. Try it before the steel wool. If still tight try metal polish before the steel wool.Regarding the PAW 60 send it back for them to check out. It shouldn't vibrate etc like that ,Mine is very smooth I would have assumed you would know all this already Jon

Jon - Laser Engines21/07/2017 18:51:05
4789 forum posts
179 photos

I actually did some more diesel running and got my AM10 going. It went like the clappers on a 7x5, its was really good. We also fired up my dads ED Pep and I had another go with one of the sabre's.

It ran better this time but still had issues with the compression. My gut feeling is that its mostly castor gunk causing the trouble so I will take it to work at some stage, press the contra piston out and then soak it for a little while before some very light abrasion.

As for the PAW 60 it is clerarly not right. My hole in the head treatment has fixed it to a point but the little hole emits a trail of smoke/oil, the engine runs hot and is really tricky to work out the settings. I think PAW do a service/re-bore so I might give that a shot. Or just turn up a few new bits on the lathe at work As for the vibration, its still outrageous. I think its hitting a harmonic with the falling apart test bench I use and the whole thing is going mad. It still makes one hell of a mess too.

Tenor what prop do you use on your 60 and what rpm do you see from it?

Engine Doctor21/07/2017 19:42:44
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2295 forum posts
27 photos

Hello John . Re the loose contract piston on you PAW 60. Have you considered the ball bearing trick ? If smoke and oil is coming from the hole you drilled then it's obviously very loose. Remove contra piston and lay on a flat metal surface / anvil/ thick metal plate. Choose a ball bearing that sits in the recess in the top and hit it with a hammer . Check fit if still loose then repeat until it expands enough to be a good fit . Take care not to over do it . Have done this many times with old diesels and never fails to restore the fit and seal.

E.D.

Jon - Laser Engines22/07/2017 08:38:00
4789 forum posts
179 photos

Hi ED

I have not tried that I have to say but might give it a go. I have no many engines to sort out (of all types) that it takes me a while to get through them all. As none are in daily use I am not in a desperate hurry.

Today though I might have a go at my PAW 249 and dry out an OS 20fp I accidentally left in the rain....

oops

brokenenglish22/07/2017 08:59:15
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455 forum posts
29 photos

Jon,

My PAW 60 is a superb engine.

I did a video showing its running qualities.

It's an old video in an old format, but the engine is superb. The prop is a 16x5 wood.

The ball bearing trick works but I would prefer to send the engine to PAW.

You might find the old video interesting, it's here:

**LINK**

Jon - Laser Engines22/07/2017 13:10:14
4789 forum posts
179 photos

I watched that video after faffing about with mine the first time. Mine behaved nothing like that, and most of the time I use an electric starter to get it going, especially when its hot as it refuses to go otherwise. It also makes so much mess compared to yours even though I am running with lower oil fuel.

My only hesitation with sending it back is that I don't really care that much about it. I don't really intend to fly the engine and bought it 2nd hand fairly cheaply just for a bit of a play. I will think about it for a bit and see how I go.

On the bright side though I was able to sort out the 249 and it ran well despite being totally shot. It leaks fuel from the front when running but as it runs, and is also unlikely to be flying any time soon, I don't really care

Robin Colbourne22/07/2017 21:51:13
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415 forum posts
4 photos

In July 1970, Peter Chinn wrote a review of the DC Sabre for Aeromodeller:

**LINK**

Its worth bearing in mind that if you are using, or did use, the yellow Tornado or Graupner props or the white Keil Kraft ones, that they are unreinforced nylon and the tips have a tendency to pitch down to neutral or negative pitch under load (washout). As a result the effective diameter of the prop will be less than the actual. This means that if you fit a glass filled nylon prop such as a grey Graupner, its going to try and produce more thrust and therefore run slower.

The advantage of the unreinforced props is that being more flexible, they are less likely to bend or break a crankshaft.

Edited By Robin Colbourne on 22/07/2017 21:52:24

Tom Sharp 224/07/2017 03:28:45
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3514 forum posts
18 photos

A picture for Jon.

oldfuel.jpg

Still with some fuel in them. Circa 1955

Edited By Tom Sharp 2 on 24/07/2017 03:32:10

Edited By Tom Sharp 2 on 24/07/2017 03:40:32

extra slim24/07/2017 10:31:59
448 forum posts
48 photos

Hi Jon, Nice to see I'm not the only one... I have recently been playing around alot with diesels having never really used them, other than watching my dad do it years ago. A good few members of our club are of an age where they are mustard with diesels and so I have been leeching the knowledge... I have really enjoyed it and am now pretty good with them, and have built up a little collection..

I had a little merlin with the exact same issues you refer to... my old fella knocked the contra out, put it in the lathe, spun it up and applied 20 seconds light pressure with finest grade paper or brasso I think.. and it totally cured it... castor lacquer is pretty hard... Then on a DC spitfire the contra wouldnt back off, same thing done, same result.. superb running engines both of them.

Got a few vids on my channel

My sabre was aquired boxed for a song, and is seen here

 

 

Edited By extra slim on 24/07/2017 10:33:51

Edited By extra slim on 24/07/2017 10:34:09

Jon - Laser Engines24/07/2017 13:28:59
4789 forum posts
179 photos

Robin, the yellow tornado prop is what came fitted with the sabre. I did tach it but i have forgotten what it was....must be the ether.

Tom, i bet all the ether has leaked out. If not it might still go!

Slim, the wonderful sound of an open exhaust. I hope the residue wont contaminate the burgers on the bbq!

I will be taking the two sabres apart soon and giving them some more love. i need to work out what is causing the huge end float on one of the engines and see if i can stop it. I can gently tickle the contra pistons at the same time.

I seem to be in full nostalgia mode at the moment as have also dug out my old mamod steam engine for some restoration work. i think im getting old

Tom Sharp 224/07/2017 18:24:52
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3514 forum posts
18 photos

One thing about the old stuff, it makes you appreciate the new stuff.

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