SC52 2stroke issue.

[Paul Marsh]

Posted by Snorbitz on 27/12/2018 23:33:10:
Trust me it wasn't through choice....it would've taken some major reconstruction of the firewall to get it to fit even without the extra peice in the silencer. The glow plug access is on the right. If I have to remove the cowel which I'm a little loathed to do now I'll take a picture of it too just so you can see what I've done.

Go onto Just Engines and buy a silencer. You can't fly it like that and looks silly. As said, you'll get hydrolic locking and if the engine stops you would lose the plane.

Turn the engine over 180 degrees, and see what silencers will fit. I'm suggesting a Pitts Type...

 

https://www.justengines.co.uk/acatalog/Just_Engines_Pitts.html

Edited By Paul Marsh on 28/12/2018 09:20:29

[ken anderson.]

I suppose the engine doesn't know which way up it is....but I've never in 30 years seen and installation like that....

ken anderson...ne...1...intrigued dept.

[alan p]

As the exhaust is above the engine, could it just be a case that any residue in the exhaust is flowing back into the ports and choking the engine at tick over as the pressure is insufficient to clear it at idle revs?

[Former Member]

[This posting has been removed]

[gangster]

Like Ken I have never seen a side mount that way up and can also appreciate the comments about fuel flowing back into the exhausr, that could be a nightmare on starting as well. That cut does not sound like it is leaning out just stopping dead. I cannot from looking at the picture and video work out why it would be major surgery to spin the motor 180 degrees apart from re drilling the mount holes as well as maybe pipe and linkage. If the cowl and/or firewall is too deep it is possible to get extension pieces between the silencer and the manifold to drop it lower.

Might also be worth stripping that new carby and giving it a good wash through. Many years ago I bought a new Irvine 40 carb, the plastic one, I really struggled to tune the engine it got worse the more I tried and eventually I could not get any fuel through even with no needle in. I blew down the fuel inlet, cheeks puffed up and nothing happened, then for some reason I sucked, something flew into the back of my throat, later identified as plastic swarf. Problem sorted many years of reliable operation from they motor followed

Personally my approach would be replumb, different tank, motor other way up and fresh fuel and take it from there.

 

Edited By gangster on 28/12/2018 11:49:40

[Steve Hargreaves - Moderator]

Watching the video I can't help think it's a fuel flow issue....the engine just stops as though it's run out of fuel.

Personally I's agree with Gangsters approach...re-position the motor (you may need a new silencer as the firewall on the Extra is quite deep so you may struggle to get the muffler clear of the firewall...the Pitts type muffler in Pauls post would be my choice) & go through the plumbing with a fine tooth comb.

If there is any doubt about the bearings change 'em....a simple job & less than a tenner....

[Bob Cotsford]

Just Engines also sell silencer extensions that go between the silencer and exhaust port. that should help with mounting it the 'right' way up. Remember the engine doesn't have to be at 90 degrees or inverted, any angle that helps with fitting is ok.

There even used to be a few designs where a rear exhaust engine would have the pipe rising up to the rear inside the fuselage so the exhaust position shouldn't affect the running. Are you sure that the clunk isn't either tangled around the vent or reaching the rear of the tank, either will restrict fuel flow. Ideally the clunk should sit 1/4" clear of the rear wall of the tank.

[Tim Cheal]

If the engine orientation is the issue, what happens when you run the engine with the model upside down? It would tell you whether reversing the engine orientation will solve the issue - at least I would have thought so?

Good luck, I had a similar problem with an OS55AX which would deadstick, there is a thread on here, but I am not sure it will help as mine was an overheating issue.

Tim

[Snorbitz]

I've removed the cowel now and refitted everything up so I'll take some pics for your analysis and try running it upside down...I've also ordered some fresh fuel. That should be with me on Monday. I looked into the exhaust extension but even JE didn't have one as long as I needed.

[Dave Hess]

Try adjusting the mixture screw. I'm surprised that nobody else suggested that. It's normally on the opposite side of the needle valve inside the throttle arm. Screw it out 1/4 turn. If it gets better, screw it some more until it's OK. If it gets worse, screw it the other way.

Edited By Dave Hess on 28/12/2018 21:28:49

[onetenor]

Fuel flow prob use bigger bore tubing

[Martin Harris - Moderator]

Posted by Dave Hess on 28/12/2018 21:27:06:

Try adjusting the mixture screw. I'm surprised that nobody else suggested that.

I think you'll find it was mentioned several times at the beginning of the thread.

Not that it's likely to be the cause of this problem but I had a few head scratching moments helping a clubmate earlier this week - engine started easily, went to full throttle, ran for a few seconds and cut...repeated the exercise and it happened again - just a bit quicker...

Too lean? No

Tank venting problem? No

Glow plug problem? No

It occurred to me that he had a Futaba 2.4 Rx fitted - what do they do when they detect a low battery voltage?

Yep - they shut the throttle (which still needed setting up for idle).

After a close call a couple of weeks before when his battery went flat 30 seconds or so after taxying back from a short test flight, my first question before we started was "is the battery fully charged?" and the answer was yes.

On further questioning after the engine runs and confirming the other control surfaces were dead but he said he'd charged it fully and even put it on a hand held tester which confirmed 98% full. I asked him "98% of what - I'm a bit wary of those devices." He told me it was definitely on the NiMH setting.

We extracted the receiver battery.

It was a 5 cell pack.

The charger and checker were both set for 4 cells...

Edited By Martin Harris on 30/12/2018 02:30:59

[Jon H]

we had a chap once who kept having batteries go flat so he bought some larger capacity packs. As this made the problem worse he was quite perplexed and finally asked for help.

After some investigation it turned out he was using one of the 100mah chargers that came with his futaba gear and would only ever charge them for 'an hour or two'. We explained that his higher capacity batteries would probably need about 24 hours on this for a full charge and recommended a delta peak job instead.

He was a little red faced by the error...especially when we pointed out that the charge time was written on the battery from the get go!

[Geoff S]

Posted by Paul Marsh on 28/12/2018 09:17:38:

Posted by Snorbitz on 27/12/2018 23:33:10:
Trust me it wasn't through choice....it would've taken some major reconstruction of the firewall to get it to fit even without the extra peice in the silencer. The glow plug access is on the right. If I have to remove the cowel which I'm a little loathed to do now I'll take a picture of it too just so you can see what I've done.

Go onto Just Engines and buy a silencer. You can't fly it like that and looks silly. As said, you'll get hydrolic locking and if the engine stops you would lose the plane.

Turn the engine over 180 degrees, and see what silencers will fit. I'm suggesting a Pitts Type...

**LINK**

Edited By Paul Marsh on 28/12/2018 09:20:29

The only problem with those Pitts silencers is that they're useless as silencers compared to the ones supplied with the engine. I had one fitted to a GP Ultimate I built with an Irvine 53 engine. I hated the noise so much I ended up cutting away part of the fuselage to make room for the Irvine silencer. Didn't look so neat but it was much, much quieter.

I still have it somewhere.

Geoff

[Martin Harris - Moderator]

I was teaching a new flyer some years ago - bright chap, ran an electrical control engineering company. His batteries kept going flat early - he eventually mentioned that each time he'd charged his batteries on the genuine Futaba charger supplied with his radio outfit it was for a full hour...

[Denis Watkins]

Apologies, wrong thread

Edited By Denis Watkins on 30/12/2018 12:27:43

[Martin Harris - Moderator]

Back on topic - I'm not sure whether you've actually managed to get it started again - did the video pre-date the starting problem?

One thing to check is the backplate - crankcase sealing is critical on a 2 stroke and it isn't unknown for the securing screws to work loose. You could do worse than removing the engine to check it - and have a look inside at the rear bearing while you're at it (don't lose the clear sealing gasket while you're doing this!) to check for rusting.

If the bearing is rusty (or in the process of breaking up) particles of rust/metal can pass through the engine and damage the glow plug element. It's possible that the plug element is platinum alloy plated rather than solid and if this coating is damaged, can glow with power applied but fail to support combustion with the lead removed.

Can you arrange to run the engine with the model inverted? This is the easy way to eliminate the unusual orientation. I see no reason why this should prevent it running though - sustained inverted circuits have never bothered any of my side mounted 2 strokes - but it will be more prone to hydraulic locking while starting it.

Can you see the fuel pipe with the engine running? Check for any sign of air bubbles as vibration can cause fuel frothing if the tank isn't full - packing the tank bay with foam can help here. Make sure fuel is actually being drawn through while the engine is turning. This is the reason I always use (and advise) clear tubing to the carburettor.

How long is the clunk pipe? If it's a little too long the clunk can get stuck at the top of the tank, allowing a start on a full tank but early cut due to sucking air.

You are sure the carburettor isn't plumbed to one of the tank vents? You wouldn't be the first to wonder why an engine would start on a full tank but cut out soon after it was running!

Edited By Martin Harris on 30/12/2018 12:52:09

[Doug Campbell]

Why not just open the main needle a couple more turns before you try anything drastic.

[Snorbitz]

[Snorbitz]

[Martin Harris - Moderator]

From these and an earlier picture, I don't think you have an optimal fuel feed. First, the tank seems a long way from the engine but possibly more significant is the pipe clipped to the engine. The long run, coupled with vibration applied directly to the pipe from the engine may be encouraging the formation of air bubbles at increasing rpm - possibly causing the sudden cuts.

Easy enough to prove or disprove - just run up the engine with the cowl off and watch whether bubbles are being formed and entering the carb.

P.S. I tend to agree with Jon's observation in an earlier reply about some worrying noises (difficult to be sure on a video soundtrack) so if you're not keen on removing the engine and its backplate to check, at least please try rocking the prop sideways in a couple of places - any noticeable play would indicate failing bearings and the need for further investigation.

Edited By Martin Harris on 01/01/2019 11:03:22

[Steve Hargreaves - Moderator]

Interesting pics & they answer a question I had in my mind which was "How do you get at the needle valve as it must be underneath the model?"

I see however that you've "solved" that by turning the carb through 180 degrees. My question now is how do you adjust it without burning your fingers on the muffler....

Again never seen or done this so no real experience but I wonder if the reverse opening of the carb could affect the airflow & hence throttle response.

I am also concerned that the very sharp angle through which you have forced the fuel feed pipe has kinked it slightly thus limiting the fuel flow. Even if not kinked at rest I wonder if the airflow from the prop when running could be pushing the fuel tube back & kinking it?

Personally I still think it's a fuel flow issue....for some reason the engine cannot get enough fuel to run at higher speeds. Find & eliminate the cause & you will solve the problem IMHO.

[Snorbitz]

Ok..first of all Happy New Year to everyone. I have a semi-happy conclusion to share with you all. Someone mentioned about running the engine upside down..that would prove/disprove if the inverted installation was the issue. This started me thinking...so just to recap the engine originally started and ran fine then would cut out at WOT...it would then not restart. On my older Pulse XT40 after flying i remembered i always picked up my model in such a way that the oil residue in the exhaust would drain out onto the floor while it was still hot as i walked back from the flight line. It always started like a dream. So if this residue was now draining back into the combustion chamber because of the orientation there's no way the humble glow plug could burn this all off and fire. Turning the plane upside down did indeed make it start everytime...however it was running incredibly rich and still struggled at WOT.....as you can see in the photos the proximity of the needle screw is too close for easy adjustment while running so after a 2 tanks of fuel and many stop/starts i got the mixture screw in from 2.5 turns out to only 3/4 of a turn out and it was running just sweet. Time to turn the plane back the right way up. It also ran the just great even at WOT and this is still on the old fuel (new stuff wasn't delivered on Monday) . I checked the bearings as suggested and all good there with no rust or free play. So i decided that i could live live with the quirk and after flying in future i'd store it upside down for a short while to drain the residue out. No great drama.

So this morning i refitted the engine cowl and decided the weather was maiden friendly. I mowed my strip to within an inch of its life in the paddock and set up my restraints. Went through the last minute checks and paranoid checks again and again and took her out to the flight line. All good so far. Its been a while sine i've flown (Radian Pro aside) so i was understandably a tadge nervous. Did a few practice runs down the strip....she ran nice and true so all good......headed her into the wind and went for it. Climb out ok gained some height and got round 2 gentle circuits. Running level on about 1/3 throttle so no great changes to struggle with this time i thought and i was just starting to relax when the engine note faded and i was dead stick on a maiden with an unfamiliar plane not knowing how far it will be able to glide. I had in my mind that i had read somewhere these Extras don't do gliding very well...this is true!!!...it took a split second to realize it was never going to make it back to the strip so i opted for a long grass field next to ours. It came in quite heavy on the wheels and bent the undercarriage a bit but somehow its otherwise intact.

Inquiry time...Remember i said that the needle screw was only 3/4 out . Well i'd marked it with a paint pen when i was fiddling with it and had refitted it 3/4 out so i knew exactly where the paint mark should be. It had wound itself right in!!!!. How...well i think it was just rubbing on the cowl which of course wasn't there all through the engine running yesterday. Plan is to open the hole out where it sticks through the cowl and put a length of silicon pipe (unless there is a better solution) tightly over the top to stop it turning once set again and try again. Phew i consider myself very lucky. So all that remains is to say a big thank you to you all for your input. It was much appreciated. I'm sorry if you don't like the look of the exhaust sticking out the top but in this case i'll live with it.

[cymaz]

Pressure test the tank.....pin hole in the clunk feed pipe inside the tank?

[Paul C.]

Just did a quick search for the manual to see how seagull fit the engine, unfortunately they only show 4 stroke or electric pictures nothing for 2 stroke. I wonder if your best bet it to mount the engine as per the manual, remove the silencer extension to keep it inside the cowl, then cut out the box section to clear the silencer and then reinforce the box section. Others will hopefully come up with other options to sort the installation.

Paul.