2 Stroke deadstick issues

[Robert Welford]

Posted by Russ P on 06/06/2018 22:07:23:

First I went the carb route, as it is the simplest, dismantled and gave it a through clean, checked the O rings which seemed ok. Put it back together, reset the needle valve and hey presto running great again.

I did find a very small piece of debris in the needle/spray bar even though I had previously cleaned it without dismantling.

Thanks again for all your ideas/suggestions.

I'm glad you've got it sorted.

[Engine Doctor]

Posted by Tim Cheal on 06/06/2018 21:33:20:

Here is the corned/crankcase I described above:

Check plating at top of cylinder for flaking by quickly removing Cyl Head. If thats ok then it must be a fuel issue ie air leak or bit of debris in the jet. Try setting carb a little richer to see if it improves . then let us know your findings

[Tim Cheal]

Thanks for the feedback and help guys.

I have stripped the carb (to be honest I didn't know you could break it down so easily by winding the slow running needle in) and there was nothing there. Liner is out and to be honest I am not sure what I am looking for. It's got some scoring, and its not very shiny, see pictures attached:

Any further advice or comments gratefully received - new OS 55 on order!

Thanks again

Tim

[JOHN MOSLEY 2]

Looks badly scored bore, interested in what the piston look like.

Edited By JOHN MOSLEY 2 on 07/06/2018 18:08:29

[Denis Watkins]

The blue patina does indicate that the motor did run very hot, and the piston needs a photo too

[Robert Welford]

It may have got hot because of running lean. It could still be as simple as a carb issue not letting enough fuel at full throttle.

As I stated before you have to completely dismantle these carbs as blowing, or squirting fuel, through them does not dislodge any debris etc.

[onetenor]

There could be a shellac type coating in the spray bar which can be removed with acetone or thinners. Helped by thin string or pipe cleaner passed through it Or a drill of correct size.

[Tim Cheal]

Thanks again guys.

Piston pictures for you Dennis:

Robert and one tenor, I have stripped the carb and can't find anything at all:

All your help much appreciated, I will fit a new one, but would like to understand what happened to this one!

Tim

[Denis Watkins]

I have reassembled and flown motors again after a clean up Tim, with similar signs of the usual wear as yours.

Nail polish remover and cotton wool for starters on the piston and liner inner.

If anything is more stubborn, some would wipe the surfaces with 1200 grit wet and dry, but great care to clean up afterwards.

Your motor just looks used to me.

On reassembly and tightening, you will probably solve any pressure leaks

[onetenor]

Piston looks OK but has a bit of blow by but having been hot that may have cured it self. I'm still suspecting a thin lacquer coating in the spraybay. It may look clean .BUT give it a soak in acetone (nail polish ) overnight then the string /or something pulled through and a Q tip in the wider part .It doesn't take much lacquer nor to clean it either. You may not see anything happen but you could be surprised afterwards when tried again later. Also soak the piston and liner in Acetone/Amyl acetate/ Thinners overnight then quick up and down twisting motion with 0000 grade wire wool. Clean up with a magnet . In case any wire wool bits left behind. Good luck.

John O/T

[Tim Flyer]

For some “stubborn” browned areas carburettor cleaner spray available at car accessory shops works rather well. It’s a much more aggressive solvent than acetone and also obviously is good to remove gum in petrol engine carbs. Obviously with aggressive solvents keep them away from o rings , as some types of o ring or plastic may be degraded by them. In racing nitro engines ( eg Rossi ) there is sometimes a silicon insert near the front of the hollow crankshaft for to aid gas flow . That can be damaged by some solvents. With a good solvent I find cleaning with an old toothbrush normally suffices. 

Edited By Timothy Harris 1 on 08/06/2018 09:45:54

Edited By Timothy Harris 1 on 08/06/2018 09:48:52

Edited By Timothy Harris 1 on 08/06/2018 09:53:04

[onetenor]

I did post re the conrod/crankcase clearance.It LOOKS as though it has been machined just a fraction out. A light touch with a burr in a DREMEL will sort it out. Followed by a thorough washout. I mean a light touch. You never know it might even ease your problemas I'm sure it is making contact under load.Just a thought. How are your bearings.? Or is it plain bearing engine? If so how is the bearing in the crankcase?

[Tim Flyer]

Looking at the corrosion on the crank shaft counterweight I would replace both bearings for the few pounds it costs. It’s hard to feel bad bearings until it’s often too late!

[Tim Cheal]

Thanks to and Tim, I have already changed the bearings. I have just put it back together, so I will run it later today and let you know how I get on (I will take it apart again and try the dremel trick if all else has failed!!).

Thanks again.

Tim

[Tim Cheal]

Hi All

I thought an update would be worthwhile. I rebuilt the engine, cleaning what I could but to be honest no acetone at this stage. I set the engine up on my rig and it ran a full tank through pretty much fine at varying throttle settings (12 X 6 APC prop).

I left it overnight and ran it again yesterday. This time, after about 8 minutes, I could hear it start to make what I can only describe as a knocking sound - quite regular and frequent, but definitely a knock and not a buzz! I smelt it getting hot and then it stopped. So, the only thing I can think is that when the engine gets to a certain temperature the parts expand and the conrod starts to hit on the crankcase - does that make sense? If so I might try the Dremel, but to be honest I think it might be best broken down for spares (the new OS55 has arrived and is fitted, run in and awaiting a test flight).

I cant really understand why it would work for 200 flights, then start this, but I guess that’s just wear and tear.

Thanks again.

Tim

[onetenor]

Definitely needs a touch with burr in a "DREMEL£

[Martin Harris - Moderator]

Is there any meaningful play in the con rod big end bearing? That might explain the markings around the area under the con rod at BDC. The knocking could be pre-ignition caused by a slightly lean mixture when it gets properly hot - if you richen the mixture does it go away?

[Tim Cheal]

Hi Martin.

There is no appreciable play in either end of the conrod, all seems pretty sound to my untrained hands!

I have taken my hand file to the crankcase today, (I tried the dremel, but wasn’t brave enough to use it - looks like you would need to be trained dentist to get that to be successful!) and found that I could fold a bit of emery to allow me to work in the indent to smooth it.

So, all rebuilt now and I will run it tomorrow to see what happens!

I did have one other thought though. When I took the rear bearing out there were quite a few bits (of what I don’t know) in the bearing seating. I am wondering if this has stopped the bearing from seating properly and forcing the conrod against the edge of the indent? Is that posssibel?

Tim

[Tim Cheal]

Hi again all. I promised an update.

I ran the engine on the 12th, and although it seemed to run hot it ran a full tank of gas through, most of that time at full throttle. But, I have had this before and so I ran it again yesterday. Another tank of gas, and mostly at full throttle (about 10300 rpm), and full throttle for the last 5 minutes. It was hot, but I am not sure how hot is hot. To be honest it did seem a little "easier" when running and it idled lovely at 2500 rpm.

So, a couple of questions if I may.

1. How hot should it be. After a full throttle run for 5 minutes, would you expect spit to sizzle off, iris that to hit?

2. There appears to be a small drip of fuel from the needle, it's not a lot but the photo below might help. Is that normal, or indication of a leak?

Thanks again.

Tim

[Denis Watkins]

Needle should be dry Tim, the O ring from Just engines or Hobbyking

They do get hot hot, to burn your hand, but always best if you can get it up in the air

Or, needle lean for a minute, then rich for a minute, so on so forth for 5 minutes, then cool down

Best in the air though

[Jon H]

In general the engine should be too hot to hold but not too hot to touch. Around 100'c on the head is not excessive.

If on the other hand you get a 3rd degree burn the moment you touch it then its probably a bit warm!

[Nigel R]

Tim

Concur with Denis, needle shouldn't leak, O rings are cheap for peace of mind.

I would be a little suspicious of the "bits" around the main bearing, which you have now cleaned out.

Does the engine now hold full throttle for a full tank without knocking or going off tune?

BTW, probably asked already elsewhere - what plug are you using?

[TartanMac]

Sounds like an air leak from your last description and agree with Denis it should be dry. My Irvine 40 had similar results. 2,500 rpm is kinda high not for flying but in the bench I would expect around 2,200 with the ability to snap the throttle open with a clean lift off of idle. I should say I have never run an O.S 55AX but from what I've heard it sounds like a good runner and should be able to achieve a lower idle.

Above you can see the engine has an idle of 2,400rpm and touches 2,200rpm. When below 2,400rpm I need to creep the throttle open to keep it running and then it rises up in idle. So 2,400 is the safe number but when left to idle it richens up very slightly and on throttling up you can see it is quite dirty and not very crisp at all. But if I lean the mix the engine wants to die on throttling up quickly but will still throttle up just slightly rich after a while of idling and when you pump the throttle it will respond inconsistently. So you have to set it slightly to rich to make up for the air leak.

Once I fixed the leak you can see it runs super smooth @ 2,100rpm and will drop below it. It would sit at 1,600 if I could hold the throttle steady. But it is clean on throttling up with quick response even under the power band that seems to be around 8,000 rpm.

You can also hear the plug is just on the verge of being too hot for the amount of nitro I'm using as when you take it down below 2,000 it gets a little rough and you can hear the ticking noise. When I used lower nitro it went away and was smoother and when I used a cooler plug the same but the response was lagging just a tad and I think the setup used above is giving best ignition and fuel burn on idle. And keeps the temp up on idle. Maybe you have a similar situation and the rich mix is making the engine knock.