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SC52 Destroying plugs and quitting!

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Howard Tomlin15/08/2008 09:10:00
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69 forum posts

Hi y'all,

 My trusty SC52 2 stroke has recently taken a turn for the worst and I am running out of ideas as to what could be the problem.

The issue is that it goes through glow plugs about every 4th flight ( i've tried OS F plugs to  firepower F5's etc), they all last the same time!

 I've never had an engine which has been so hungry for plugs.

 I'm running a 13x4 prop and I always try to run my engines a click or two rich.

 ALSO

 When the model is in a dive (at idle or 1/4) it has always made the noise of an over- running two stroke motorbike- the sort of "ran dang dang dang" noise.????

 Its now taken to spluttering when levelling from a dive unless the engine is kept on a high throttle setting (not what you need in a 3 d model).

 I have removed the tank, changed all the tubes in the tank, tried the engine with and without the remote filler, and changed the tube between the needle valve and the carb - its a rear needle version.

I was thinking that it might be a carb o-ring, does anyone reckon that might cure the running problems.

 As for the glow plug eating tendency then I have little to no idea, I've also tried irvine contest 10 and the other model technics fuel which is a sort of apricot colour (10 %)

 At the minute the model stays home until I can find a resolve as its a source of great frustration making frequent trips into the corn field although its honed my dead stick spot landing skills somewhat.

simon barr15/08/2008 14:58:00
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1033 forum posts
16 photos

Hello Howard,

Just a thought, have you got a shim (washer) on the plug, it may be sitting too low in the head without one.

Martin Harris15/08/2008 16:56:00
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8790 forum posts
215 photos
Could be the bearings starting to break up - tiny metal particles get carried up from the crankcase to the combustion chamber and then hammer the filament and/or create hot spots - either way the result is a blown plug.
Peter Miller15/08/2008 18:48:00
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10152 forum posts
1192 photos
10 articles

An air leak from the carb is a possibility. Try pouring some fuel over the joint while the engine is running, if there is a leak it will run rich for a moment. Sailto Engines were very bad in that respect.

The metal bouncing round as Martin says.

Try Taylor Std long reach plugs. They work perfectly, last well and only cost about £2.50 or less. I have used nothing else for about 30 years in everything from .10 to .91 FS.

Engine Doctor19/08/2008 09:50:00
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2295 forum posts
27 photos

Hello Howard , Does the motor feel ok ? as bearings breaking up will leave the engine feeling gritty and ntochy.  If its ok it may be that the first plug that blew let a bit of the element fall into the cylinder ;  insert through the  plug hole with the engine inverted and flsh out the combustion chamber . Catch the fuel that comes out in a clean container and allow to settle to see if any particles are washed out . Any metalic bits should be investigated . Failing that its a strip down to see whats going on . Hope it helps .

E.D

Engine Doctor19/08/2008 09:56:00
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2295 forum posts
27 photos

Hello Howard , I dont know what happened with my last posting but it seems to have deleted some of it ? I t should read Try filling a sqeezy bottle with clean fuel and put some fuel tubing on the nozzle and insert this through the plug thread /hole .............etc .

E.D

Eric Bray19/08/2008 12:40:00
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6600 forum posts
2 photos
That happened to me in a different thread, some of what I typed disappeared and turned the rest to gibberish!
Tim Mackey19/08/2008 14:35:00
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20919 forum posts
304 photos
15 articles
some excuse Eric !
Eric Bray20/08/2008 12:00:00
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6600 forum posts
2 photos
And I'm sticking to it!
Tim Mackey20/08/2008 17:25:00
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20919 forum posts
304 photos
15 articles
Ooooh stickies
Howard Tomlin03/09/2008 16:52:00
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69 forum posts

UPDATE!!

 I replaced all of the seals on the engine, including the back plate seal (which wasnt fitted in the first place!) and pressure tested the tank, took the plane up the field and it was no different enqine quitting and a few trips into the corn.

 So i had a think about what I'd done to the tank and fuel line over the year or so that I've had it and I remembered that I had changed the very thin fuel pick up hose for a thicker fuel line hose as it had a habit of allowing the clunk to get stuck forward. What I hadnt changed was the clunk and after doing some comparitive tests using heavier clunks I realised that the clunk wasnt following the fuel in the tank as the new fuel line was too stiff!!!

I raided a spare tank which had a heavier clunk and the same diameter fuel pick up as i had recently installed and hey presto the fault has gone away, no more quitting!!!.

 Now all i have to do is monitor how long plugs last for as I havent come to any conclusions about that as yet.

Mark Lubbock05/09/2008 10:58:00
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313 forum posts
13 photos

When an otherwise good engine suddenly starts to blow plugs, it is normally caused by debris remaining after the first faliure damaging the new plug & so the cycle continues. It will sometimes clear by itself, but with the price of plugs & the possibility of bits of metal causing more damage it would be a good idea to remove the head & backplate & give the engine a good flush out with fuel.

This assumes the bearings etc are in good condition, if they are breking up you should be able to tell straight away by rotating the shaft & feeling for any notches or roughness.

hope this helps

Howard Tomlin05/09/2008 11:10:00
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69 forum posts
is there a gasket for the head, if so do i need a new one when I remove the head?
Mark Lubbock05/09/2008 11:17:00
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313 forum posts
13 photos

Most engines use an aluminium gasket which can be reused if not damaged, if it remains stuck to one of the components, leave it there. The same applies to composite gaskets, but these are more easily damaged.

Take care to mark the way the head fits & tighten the screws evenly, working across the head to opposing bolts, a bit at a time.

Andy Gates30/09/2008 19:31:00
636 forum posts
19 photos

My SC52 (same rear needle model) does the same "dang dang dang" noise at low throttle on over run. Just seems to be the way this motor runs.

As for plugs, mine seems to prefer A3 plugs to the No.8, not burned one out yet using Contest 10 fuel.

I use 12x6 APC sport prop, but I need something slower to slow up my plane.

Dusty02/10/2008 10:14:00
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1632 forum posts
560 photos

Anyone know where to get spares for SC52? I got one with a front needle valve, I have called a few places but no luck...

I need a new carb, the threads in the current one are worn.

Tim Mackey02/10/2008 10:23:00
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20919 forum posts
304 photos
15 articles
pretty much identical to the ASP range which JE carry.
Dusty02/10/2008 10:39:00
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1632 forum posts
560 photos
Thanks timbo I will have a look.
Howard Tomlin02/10/2008 11:07:00
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69 forum posts
Galaxy models is where I got my gaskets for the sc from.
Peter 'Ivanna Crashalot' Savage02/10/2008 15:10:00
1557 forum posts
58 photos
i have my dad's 15 year old sc53 in my vietnamese artf (the accipiter ) and when i went to the flying field it would conk out as soon as the plane left the ground, twice so my dad tuned it and it ran alright eventually, i don't think we have ever had any real problems despite its age

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