OS Max 15LA Won't Run Upside Down

[Richard Wills 2]

yep the gunge from formula irvine should only be a nice bright red. If it is black that is a sign of something not right, probably the silencer not tight as Martin points out but rectify it before going any further.

[paul d]

Not sure it's been mentioned but try leaving the glow driver connected when you turn the model over, may give a chance to tune it.

Another thought, is the clunk free to move? wonder if it's sticking to the roof of the tank? Oh and "black gunge" doesn't seem right.....

[paul d]

Ignore my clunk comment...just seen you've checked it.

[Jon H]

black is bad. the red klotz oil should break down to a dark brown at worst as the others have suggested.

might be worth stripping the engine to check the liner.

[cymaz]

Is the back plate on tight? At any rate strip it all down and check the inside, new OS f plug. If you have an engine test bench, see if it will fit inverted and try and replicate the poor running on that. Is there anything blocking the pressure nipple?

SPARES

 

RCJAPAN

Edited By cymaz on 06/09/2020 10:13:26

Edited By cymaz on 06/09/2020 10:16:41

[EvilC57]

Posted by cymaz on 06/09/2020 10:09:51:

Is the back plate on tight? At any rate strip it all down and check the inside, new OS f plug. If you have an engine test bench, see if it will fit inverted and try and replicate the poor running on that. Is there anything blocking the pressure nipple?

SPARES

Edited By cymaz on 06/09/2020 10:13:26

Funnily enough, removing the engine again to check the back plate seal was next on my list (I’ll recheck the pressure nipple is clear too). I can mount the engine upside down on the test stand by clamping the stand underneath my Black & Decker workmate bench. My test stand also allows for up & down movement of the fuel tank, so I can see if the engine is sensitive to that too. I’ll stick with changing the plug to an Enya No.3 for now, and see where we go from there...

[Nigel Grant 1]

Hi

I remembered an article I read on the LA 15 which talks about sealing the back plate with silicon. Maybe it is an issue with these engines. Here's the link - https://www.treneffrc.com/LA-15%20Clunk%20Tank%20Secrets.pdf - but dont follow their nitro recommendations! Also a colder plug, which holds the heat better (never understand that naming logic) might be better. I think the No. 8 is "colder"than the no. 6.

That engine has to run so that plane can take to the air - it looks great and hope you'll report how it goes.

Nigel

[Paul C.]

I remember having an LA 40 and it had a nylon back plate , not the smartest move by OS but I was able to buy a aluminium one which solved my rough running problem. Think it was a standard OS part but can't remember from which engine.

[kc]

One of the weird things that happened to one of my engines that was (almost) inverted was that a large chunk of carbon like stuff built up, then moved around & eventually blocked the silencer. Caused intermittent running and then eventually stopped the engine. Probably caused by excess fuel running into the silencer when refuelling then being cooked into a lump of carbon.

When you have eliminated all the likely causes you have to check the most improbable things.....

[Maurice Dyer]

I run inverted two stroke engines on a four stroke OS F plug.

Always works for me.

Maury

[EvilC57]

Posted by Nigel Grant 1 on 06/09/2020 10:43:01:

Hi

I remembered an article I read on the LA 15 which talks about sealing the back plate with silicon. Maybe it is an issue with these engines. Here's the link - https://www.treneffrc.com/LA-15%20Clunk%20Tank%20Secrets.pdf - but dont follow their nitro recommendations! Also a colder plug, which holds the heat better (never understand that naming logic) might be better. I think the No. 8 is "colder"than the no. 6.

That engine has to run so that plane can take to the air - it looks great and hope you'll report how it goes.

Nigel

Right, I have now removed the engine from the model (again). I’ve removed the back plate, removed the old hylomar, degreased it and the back of the crank case where it fits, and sealed it back on with fresh silicone sealant. I’ve changed the OS No.6 plug for an Enya No.3, and mounted it in my test stand ready for another go at test running it - probably tomorrow on our flying field, as it’s a bit anti-social running glow engines in the back garden on a Sunday afternoon.

Thanks for the link Nigel, but you have confused me now with your suggestions of a colder plug, when other people were suggesting a hotter plug!

I’ll report back again after tomorrow’s bench test run attempts...

[EvilC57]

Posted by Maurice Dyer on 06/09/2020 13:01:07:

I run inverted two stroke engines on a four stroke OS F plug.

Always works for me.

Maury

Thanks Maury, I’ll bear that one in mind.

[cymaz]

Posted by EvilC57 on 06/09/2020 13:20:54:

Posted by Maurice Dyer on 06/09/2020 13:01:07:

I run inverted two stroke engines on a four stroke OS F plug.

Always works for me.

Maury

Thanks Maury, I’ll bear that one in mind.

I’ve been told the same. As the OSf plugs are deeper the fuel that could “pool” does this below the filament.

[Richard Wills 2]

cold plugs are for 'cold'engines, thicker wire keeps heat better and more platuinum surface area for the catalytic reaction with the methanol, and keeps the fire burning. Hot plugs are for 'hot' engines normally smaller ones which don't need the help. They mainly alter the ignition timing depending on where they lie in the heat range.

[PeterF]

Posted by Richard Wills 2 on 06/09/2020 14:15:04:

cold plugs are for 'cold'engines, thicker wire keeps heat better and more platuinum surface area for the catalytic reaction with the methanol, and keeps the fire burning. Hot plugs are for 'hot' engines normally smaller ones which don't need the help. They mainly alter the ignition timing depending on where they lie in the heat range.

Funny, i always thought it was opposite, put a tuned pipe on an engine (make it hotter) and you need a colder plug, the plug runs cooler. Just Engines also believe this to be the case, extract from their website

Glow Plugs

The right choice of plug can make all the difference to engine performance and reliability. The general ‘rule of thumb’ is: Hot engine = Cold plug and Cold/Cool engine = Hot plug.

So, if you have an older, slightly tired engine or you prefer to use straight fuel you should choose a hot plug. If you have a high performance, high revving 2 stroke that is working very hard a cooler plug is a good idea.

Always use four stroke plugs in four stroke engines, and they are also very good in inverted two strokes where starting and running at idle can be difficult.

See Just Engines glow plugs

[EvilC57]

Posted by PeterF on 06/09/2020 15:34:37:

Posted by Richard Wills 2 on 06/09/2020 14:15:04:

cold plugs are for 'cold'engines, thicker wire keeps heat better and more platuinum surface area for the catalytic reaction with the methanol, and keeps the fire burning. Hot plugs are for 'hot' engines normally smaller ones which don't need the help. They mainly alter the ignition timing depending on where they lie in the heat range.

Funny, i always thought it was opposite, put a tuned pipe on an engine (make it hotter) and you need a colder plug, the plug runs cooler. Just Engines also believe this to be the case, extract from their website

Glow Plugs

The right choice of plug can make all the difference to engine performance and reliability. The general ‘rule of thumb’ is: Hot engine = Cold plug and Cold/Cool engine = Hot plug.

So, if you have an older, slightly tired engine or you prefer to use straight fuel you should choose a hot plug. If you have a high performance, high revving 2 stroke that is working very hard a cooler plug is a good idea.

Always use four stroke plugs in four stroke engines, and they are also very good in inverted two strokes where starting and running at idle can be difficult.

See Just Engines glow plugs

Interesting. So my take from this is that with the OS 15LA being what I would call a bog standard, ‘cooking’ engine (i.e. not a sporty one), that it will run cooler than a high performance engine, and therefore need a hotter plug.

Interesting too, that Just Engines should also suggest a four-stroke plug for an inverted two-stroke. I’d not heard of that before I started this thread.

[Richard Wills 2]

Posted by PeterF on 06/09/2020 15:34:37:

Posted by Richard Wills 2 on 06/09/2020 14:15:04:

cold plugs are for 'cold'engines, thicker wire keeps heat better and more platuinum surface area for the catalytic reaction with the methanol, and keeps the fire burning. Hot plugs are for 'hot' engines normally smaller ones which don't need the help. They mainly alter the ignition timing depending on where they lie in the heat range.

My expanation leaves a lot to be desired, just read it back. Makes sense to me but does not translate well in words! Ignore.

[Maurice Dyer]

As I originally said: never had a problem running an inverted two banger on OS F plugs.😊

Maurice

[EvilC57]

Posted by Maurice Dyer on 06/09/2020 16:09:03:

As I originally said: never had a problem running an inverted two banger on OS F plugs.😊

Maurice

I shall take one with me to the field tomorrow, in case the engine doesn’t get on with new new Enya No.3 I’ve fitted.

[Engine Doctor]

If your engine runs fine when upright and set correctly then plays up when turned inverted I would suspect the tank set up or possibly the plumbing in the tank . If it as anything to do with the plug it would behave the same upright .

[paul d]

Totally agree Doc.

[EvilC57]

Posted by Engine Doctor on 06/09/2020 17:29:09:

If your engine runs fine when upright and set correctly then plays up when turned inverted I would suspect the tank set up or possibly the plumbing in the tank . If it as anything to do with the plug it would behave the same upright .

I’ll add a different tank to the list of things to take with me for my bench tests at the field tomorrow. It’s something else to be eliminated from the list of possible causes.

[Robin Colbourne]

When the model is inverted and the tank upright, the clunk tube will be diagonal across the tank, so further from the back wall compared to when the model is the right way up. I have also found that the clunk tube can stretch when sucking fuel, so may be longer than in the static position. A slot cut across the inlet on the metal clunk would makes sure it can't suck itself to the back of the tank.

The silencer looks quite long; does it have a baffle in it? Could oil, unburnt fuel or lumps of congealed castor oil be collecting on the engine side of it and blocking the tank pressure pipe?

Check each silicone tube for transverse cuts & pinholes, particularly where they come of the tank tubes and nipples. When you turn the model over, this could be opening or shutting a hole which will affect the mixture.

Make sure the tube going to the carburettor is long enough to not touch the crankcase. This can sometimes cause bubbles in the pipe.

The front of the silencer appears to be touching the cowl cheek.  This could be increasing vibration in the model and also contributing to fretting at the exhaust port silencer interface.  Pressing something convex against the cowl cheek  whilst supporting the inner face may be sufficient to indent it enough not to touch the silencer.

Finally, is there any foam around the tank? If not, could the fuel be frothing when one way up?

Edited By Robin Colbourne on 06/09/2020 23:46:03

[EvilC57]

Update:

New Enya No.3 plug fitted (as per my earlier post), crankcase back plate newly resealed with silicone, exhaust pressure nipple checked to be clear. Tank dismantled, clunk and other pipework checked to be correct. Tank reassembled.

------

Turned up at the field and had to wait in the car for 30 minutes for the rain to stop.

Engine right way up on the stand started first spin on the starter, and ran OK up to maximum RPM after a minor tweek of the needle (bearing in mind I'd had to remove the needle in order to remove the engine from the model).

Stopped the engine, and turned it upside down by clamping the test mount to the underside of my B&D Workmate bench, turning the tank right side up in the process.

Engine reluctantly restarted and run up to full RPM for most of the remaining tank's worth of fuel.

Thought I'd try the OS F four-stroke plug as suggested by a number of people here (after carefully checking that the piston cleared it at TDC). Engine wouldn't run at more than about 1/2 throttle, so went back to the Enya No.3, with which the engine would also now not run at more than 1/2 throttle.

I took a spare tank with me to try (as per earlier suggestions), but never got a chance as by this time the rain was coming down again, so gave up and came home for a cup of tea.

All a bit inconclusive really.

[J D 8]

What was the exhaust like?