Laser Engines - Technical questions

[bert baker]

I did this on my SE5A

[Artto Ilmanen]

hi Jon,

 

I'm adjusting the carbs of my 300V so they are in sync with respect to barrel opening

 

Would you kindly confirm what is the correct length of the 300V carb fixed link rod?

Mine is 72,2mm measured from center to center.

However, if I set the link rod as per your instructions (your email back in 2016 - for some reason I have not attempted to fix the matter until now):

 

"...First the two carbs need to be straight when viewed from front and back of
the engine. Its not going to work if one is leaning towards the other."

-> OK, I adjusted the two carbs according to what you write. However, when straight they are more apart from each other measured from the center of the barrel axle than what is the length of the link rod? Should the link rod be longer?

 

I feel if I get this right I will never ever mess with this!

 

This is your email instructions in full text - as there may be others that appreciate your instructions:

 

"First the two carbs need to be straight when viwed from front and back of
the engine. Its not going to work if one is leaning towards the other.
Then, the throttle arm of the left carb that drives the link rod (viewed
from behind the engine) should be aligned with the fuel inlet nipple
(viewed from above) when the throttle is fully closed. On your carb i
think the nipples both point to the left instead of the newer way where
the left cylinder carb has its nipple point right. If its the older type,
line up the arm to the nipple with the barrel fully closed, if its the
newer type, align it the same way but with the throttle fully open. Then,
fit the other throttle arm to the other carb with the link rod and set the
right carb to full open with the left carb at 1/2 throttle. Gently tighten
the throttle arm on the right carb so that it grabs but can still slip.
Then open the left carb all the way, before closing the barrels and
checking them with a small torch. if they are slightly out just slip the
right hand carb throttle arm a little until they are the same. I set all
of the carbs by eye this way and if the rod is the right length, with the
carbs and arms in the right place it should be almost perfect straight
away"

 

thanks, Artto

Edited By Artto Ilmanen on 30/01/2021 17:33:33

[Jon H]

Hi Artto

If your engine has one of the fixed length link rods i used to make then its fine. As long as the carbs are straight and the link throttle arm of the left hand carb is aligned with the fuel inline nipple at full power (or idle with the older type of carb) then it will all work out. You just need adjust the position of the arm on the right hand carb to make them match at idle.

[Artto Ilmanen]

Posted by Jon - Laser Engines on 01/02/2021 08:30:30:

Hi Artto

If your engine has one of the fixed length link rods i used to make then its fine. As long as the carbs are straight and the link throttle arm of the left hand carb is aligned with the fuel inline nipple at full power (or idle with the older type of carb) then it will all work out. You just need adjust the position of the arm on the right hand carb to make them match at idle.

 

thanks Jon,

the reason for asking is the carbs were not straight as I received the engine - it seems like the "slave carb" was a tad twisted towards the "master carb" as can be seen on the picture? and yes, you made the link rod or at least someone at the factory.. So If I now mount the carbs straight, then, this is not how they were when you assembled the engine.

I'm happy to follow your instruction but as the carb rod is a tad shorter:

I can adjust the barrel opening to be the same when at idle but they won't open linearly. Wether this has any importance in mid/ higher rpm range, I'm not sure though.

Please see picture attached

 

 

Edited By Artto Ilmanen on 01/02/2021 15:39:33

[Jon H]

Hi Artto

Now the forum is fixed i can reply. 

To be honest, i am not sure i understand the problem. If the carbs are vertical and the arms correctly adjusted (have them point straight forward at half throttle) then the whole thing will be correct. To make sure they are correct close the master carb until it is just barely open, then adjust the other to match it. 

[Artto Ilmanen]

13 hours ago, Jon - Laser Engines said:

Hi Artto

Now the forum is fixed i can reply. 

To be honest, i am not sure i understand the problem. If the carbs are vertical and the arms correctly adjusted (have them point straight forward at half throttle) then the whole thing will be correct. To make sure they are correct close the master carb until it is just barely open, then adjust the other to match it. 

Hi Jon,

I appreciate your patience - I certainly do not want to sound stubborn and ignore your very clear instructions. I just honesty believe your design of the link rod is designed to be of the same length as is the distance between the carbs when measured at the center of barrel axles and carbs vertical (straight). Please correct me if I'm wrong?

This is not the case in my situation. The link rod is a tad shorter. -> this means that I can, of course,  adjust the carbs so they both open the same at idle (barely open). But,  they won't match at all barrel opening positions as the arms won't move parallel to each other. 

However, are you saying that slight variance with the link rod length can be cured with just adjusting the carb opening manually as you describe without any issues in half throttle, etc.? 

For some reason my picture of the engine seems to get lost all the time for some reason? Anyways, if I manage to upload the picture you can see that the carbs are not straight as I received the engine.. I wonder if this is to compensate  a tad "shortish" link rod..?

Any new thoughts? Or do you think I'm way too meticulous?

thanks ?

[Ron Gray]

I had the same problem with one of my 160 twins which made for very erratic running. I did what Jon said, slackened off the right hand carb and rotated it to make sure it was vertical, then I slackened off the carb arm clamp and adjusted the arm position so that the barrel was open by the same amount as the master carb (I used some thin copper wire to set the opening gap). I then made sure that the openings were the same at half throttle and full. Clamped up the arm again and all good, the engine now runs perfectly.

[Jon H]

With the carbs upright, master (left) carb throttle arm set to point straight forward at half throttle, and the idle positions matched, it will work fine. Its probably ok as it is even with a slightly wonky carb. 

As we have discussed many times over the years Artto, just fly it. If its running well, just fly it, fly it, and fly it some more. Last i recall it was in your yak54? it seemed to be singing sweetly in the video you sent me all those years ago so unless its now not running sweetly, just fly it and dont worry about it. 

As much as proper maintenance is important try not to get obsessed with minor details if the engine is running correctly. If, like Ron, your engine was misbehaving then clearly it needs attention, but unless i missed something yours was performing well and should probably be left alone. 

[Artto Ilmanen]

Hi Ron & Jon,

 

Ok, it seems I'm too meticulous. I'm just a tad jealous of the way how your & Ron's engine seem to idle as seen in the videos. But anyways, I will set the thing as instructed and check the barrel openings match at idle, half and full throttle. I'll let you know how things proceed.

By the way, thanks for instructions and comments on low speed needle adjustment - was it in this thread when Ron was having some troubles with his 160 twin. Once I get the engine back in the airframe I try to learn to tune the low speed needles the way you adviced Ron with good success

 

The engine is still in the GP Yak 54 - I love the combination

 

thanks again

Artto

[bert baker]

Good morning all, I’d more or less given up find this forum,

[Ron Gray]

44 minutes ago, Artto Ilmanen said:

By the way, thanks for instructions and comments on low speed needle adjustment - was it in this thread when Ron was having some troubles with his 160 twin. Once I get the engine back in the airframe I try to learn to tune the low speed needles the way you adviced Ron with good success

On all things Laser, always listen to Jon, (it's also a good idea to listen to him on other things too - he can sometimes talk a lot of common sense!!!)

[Artto Ilmanen]

Ron,

That's a good piece of advice, I believe ?

 

 

[David Davis]

Not a very technical question for you Jon but something born out of my idle curiosity.

 

Why do all my Laser engines have only one nut holding on the propeller? All of my OS, Thunder Tiger and Magnum four stroke engines have two.

[Chris Walby]

I'll chip in before Jon answer gives the full technical detail as I needed to ask Jon the same question. My club and certain committee members (they have to inspect and sign off the model before use - good thing in my book) say that props have to be double nutted.

 

On one occasion I had to drive home, get another nut and return before I could fly the model. I questioned this with Jon and received the official Laser response, only one nut is recommended. 

 

Anyway Jon said to me, Laser's very rarely if ever back fire and hence its very unlikely to throw a prop (if the correct torque is maintained on the nut) and so only one nut is supplied with each engine.

 

PS - I used to compete with methanol fueled single cylinder 4 strokes motorcycles and only experienced backfire when starting with very advanced ignition timing (we used static) and that was with very wild valve timing. There was a benefit when using over square (bigger bore to stroke) engine configurations than seemed to increase the likelihood  along lower piston crown to gudgeon height.  Another factor that might have had an influence was that we reduced effective flywheel weight, so part engine design and part operator. On the point of operator it was best if once primed that the engine was started with very little throttle opening....one occasion with bike on stand started completely ripped my dads industrial leather glove open (destroyed all the stitching) and off his hand. The alternative was to run at full speed with a pusher (second person) in top gear and dump the clutch (jumping on sidesaddle). Really interesting as it would normally spring to life in one or two engine revolutions  with very fast acceleration in a gear suitable for +60 mph...and nothing for the pusher to be pushing against! 

 

 

[Jon H]

Chris beat me to it but yea, props dont fall off with one nut so why use two? 

 

My saito 45 has a single nut, never thrown a prop, my enya 120 and 155 have single nuts, never thrown a prop in the air (backfire on start sometimes gets the 120), my SC400 radial, ASP160 twin, OS240, 300..none of them have thrown props and that is to say nothing of my Lasers. In fact, when the propeller on my La7 exploded and the hub split in two, the single nut was still hanging on to the prop when i came down.  

 

I think the locknut thing came about, i suspect, following some sort of litigation concern. 'Your engine spat a prop in my face (while i lay down in front of it revving its rod off and trying to touch the crankshaft with my nose) and now im going to sue you for a billion billion moneys' That sort of thing. 

 

Some of the early 4 strokes were more prone to throwing props. My dad's 48 surpass was a nightmare, but operating that same engine today it never throws props so perhaps it was always a handling issue? 

 

Not sure, but we do not need or recommend double nutting our props as it serves no purpose. 

[Bruce Collinson]

Jon,

 

Sorry if this is repetition but can I run a BNIB Laser 80 in a Wot 4 on low oil fuel, and still a 14x6 for running in?   Anything more to add?

 

Bruce.

[Jon H]

3 hours ago, Bruce Collinson said:

Jon,

 

Sorry if this is repetition but can I run a BNIB Laser 80 in a Wot 4 on low oil fuel, and still a 14x6 for running in?   Anything more to add?

 

Bruce.

 

yep, all fine. dont run it rich. Set needle 3/4 turn open from closed and tune from there

[Martin Harris - Moderator]

I've seen numerous props come off - many while being started and many of them fitted with lock nuts.  The odd thing is that they don't seem to come off after I offer to tighten the nuts for the owners with a suitably sized spanner.

 

Chris has touched on a definite cause of many problems - the use of lightweight propellers.  Many years ago, I put a lovely looking but very light wooden prop on an old 40 Surpass fitted to my Puppeteer and go a smidgeon too lean when tuning and there'd be a rattle of pre-ignition and off would come the propeller. Plonking an APC on the front made it behave normally - diagnosis, lack of flywheel effect.

 

I see the use of a manufacturer's designed locking system as a wise precaution rather than an absolute requirement. I don't think I've ever sent Chris home to get a locknut but I may have advised that it would be better to fit one...

[John Stainforth]

I think whenever I have had a prop throw, the culprit has not been the prop nut(s) but the screw holding on the front casing of the spinner. If that comes loose, the electric starter twists the spinner housing against the prop and the extra leverage on the prop then undoes the prop nut(s). At least, I think that's the problem.

[Jon H]

8 hours ago, Martin Harris - Moderator said:

 

 

Chris has touched on a definite cause of many problems - the use of lightweight propellers.  Many years ago, I put a lovely looking but very light wooden prop on an old 40 Surpass fitted to my Puppeteer and go a smidgeon too lean when tuning and there'd be a rattle of pre-ignition and off would come the propeller. Plonking an APC on the front made it behave normally - diagnosis, lack of flywheel effect.

 

 

 

This is commonly talked about but it is not the whole truth. 

 

The OS40fs is quite prone to throwing props i have to admit. My surpass example threw an 11x5 master across the yard at work when i was fiddling with it once but wooden props tend to be more vulnerable. 

 

The reason is not their weight but the shear strength of the hub. When the prop is tightened down the hub conforms to the knurled face of the prop driver. In the case of a knock, the engine wants to slow down suddenly but the prop is quite keen on keeping going. With a nylon prop, the material in the key between the prop and driver is strong enough for the momentum of the prop to drag the engine in the direction it should be going but with a wooden prop, the wood fibres are not strong enough and shear. This not only gives us the engine and prop now rotating opposite to each other but also the shearing turns a portion of the hub rear face into saw dust which loosens the nut due to the removed material. The rest, we know. Clearly this all happens very fast but its not the weight causing the problem as much as it is the properties of the material. 

 

 

Most of our engines need very little flywheel in order to run with 2 inch dia thin aluminium flywheels being enough for 2 strokes in model cars and we have used similar small/light flywheels on Laser 70's fitted to helicopters and tanks.  

 

The main reason for props flying off is exactly as Martin suggests. The nut wasnt tight in the first place. That can be down to incorrect spanner choice, or just ignoring it for years. In the case of a wooden prop nut need regular checking as the wood shrinks/expands with moisture etc. If this is not done they come loose and fly off. It should also be noted that the bit above about the shear strength of the material is also impacted by the mounting pressure. Less pressure gives less bite and more room for the prop to slip slightly, and gain just enough momentum to overcome the strength of the wood. Throwing props on startup? likely to hot on the glow or hydraulic locking...or it just wasnt tight. 

 

My saito 45 has used very light wooden props the whole time i have used it in my flair nieuport. It has never thrown one and is generally very well behaved. That ruined OS40fs i rebuilt recently ran fine on an 11x6 wood and didnt throw it off. I use wooden props on my OS240 and all my big lasers. I just have to keep an eye on them from time to time.

 

 

[J D 8]

 I agree with Martin, seen it many times prop nuts simply not tightened up enough.  When one has been doing engineering jobs for many years you just get know how much to lean on a certain size bolt so it is tight but not overloaded. But this is not the case for many and they tend to err on the slack side worried about snapping the thing. 

  Perhaps using a torque wrench may be a good thing for some.  Don't know if any engine makers have a torque setting in the instructions though.

  Mini torque wrench's for bicycles are available. 30-40 pounds for a tidy one. 

 

 Started this before Jon set his post. 

Edited February 23, 2021 by J D 8
see above

[Martin Harris - Moderator]

I have to say that in quite a few decades of tightening prop nuts with appropriate spanners to my "eyes bulging" inbuilt torque setting, I've yet to strip a thread on any crankshaft or supplied nut(s), from an MDS to a Laser...and I think I've encompassed just about every engine maker in common use.

[f-krist]

With reference to 4-strokes throwing props:

There is probably no general cure for this covering all kind of glow 4-stokes, plugs, glow-fuels in use and end users... but:

On startup:

Sure, a YS fuel injected supercharged glow engine will throw the prop into your face all day long until you decide to follow common practice through experience as:

Use a time delayed glow-driver that allows you to spin engine up with the electric starter before plug is slowly lit by such purpose made glow-driver. Engine then comes in and fires very softly into a steady idle without any problems. This procedure is relatively bullet proof and was practiced for decades in the F3A society before they more or less all went electric...

As the above mentioned supercharged fuel-injected YS engine-example might be the most critical in such respect, this same procedure will normally cure whatever similar nasty tendency of any other glow 4-stroke brand unless stupidly rich primed before putting the starter to it.

In more or less the opposite end of the scale, a Laser might tolerate immense stupidity and inexperience both glow and prime-wise upon startup as opposed to the YS, and for such reason, prop-throwing un-known to the Laser-operator does not comply to the world in which an YS-experienced pilot (airport security-police?) decide to comment negative on a single prop-nut... however such negative comment irrelevant for different technology in use... 

Then, for the brave starting heavily primed say Saito or Laser with a backflip, there is a trick disregarding any gorilla prop-nut tightening as follows: From a leather-glove or similar, use a say small Lexan-car-body scissor (Kyosho-scissor normally performs nice, or similar having curved miniature cutting-blades) and cut a "Leather-washer" and place that washer between the aluminium prop-driver and propeller. This will normally produce massive increased friction between engine and prop, even for "slippery"/non-ideal prop-structures. Further, the leather is normally not sensitive to fuel/oil-spillage/soaking as increased friction is maintained regardless.

Then, with respect to glow-fuel in use, always use fresh fuel of a well reputed brand as say aged fuel left in the shed with say poor sealing etc. might easily extract and absorb water from surrounding air-moisture... and filling such poor fuel to your tank might prevent you from having a correct engine tune-up as the feedback from the engine might be increasingly meaningless caused by bad fuel, fooling you to place top and bottom needles in incorrect positions and worst case resulting in pre-ignition/prop-throwing etc .regardless a rich or lean setting for non-trivial reasons outside normal perception cased by poor/watery fuel alone...

Prop-throwing in the air:

Might be caused by:

Too big prop / engine overload / Lean top-end needle ground setting, and/or engine coming on continous more heavy prolonged load / extended verticals / engine demanding aerobatics, overheating resulting in pre-ignition and goodbye everything from prop-driver and forwards. 

Possible cure might be: Increase cooling like say engine-baffling-remedies and better air-extraction rear of engine.

Do not try to cure by richening top-end alone if cause is abovementioned overload/overheating and not actually an incorrect original needle-setting...

If happened in the air after hours of accumulated use: Remove engine top and inspect for carbon buildup. Heavy carbon buildup will glow on heavy load disregarding whatever glowplug in use and cause pre-ignition, so you must clean out that carbon-dirt from top of piston / Carbonized-valve-"beard"/Valve-seats/head, and anyway reject that corresponding contaminated glow plug. And if running high nitro, you will have smoother in-air engine-characteristics if you force yourself to renew your OS-F plug typical each approx gallon of fuel through your engine ( actual intervals according your accumulated experience with your level of nitro and engine-type in use...)

If you cannot resist overloading your Engine for the model in question, use bigger engine or build more light-weight model or similar less-load-remedy... and dont forget to throttle back, you usually never need full throttle for the whole flight.

Yes, there must be many more reasons for throwing props on glow-engines, but above possibly covers the majority? Where are you Martin McIntosh, some wise words please...

 

Fritz Kristoffersen (No(r)-way)

 

 

 

 

 

 

 

 

[thebluemax]

Hello from across the pond.  I am putting a Laser 180 in a ESM BU-181.  Have any of you guys have used the Model Technics SuperCat 4 stroke glow plugs in your Lasers?  If so how are they?  thanks for your time.

Bill

 

 

 

Edited March 14, 2021 by thebluemax

[Jon H]

Not a fan of that plug. Tested one in a 150 some years back and it rn really slow, overheated, and then stopped. I didnt test it much further! 

 

Use the OS F plug. Easy to get and they work. They also seem to last forever, some of my engines have plugs more than 5 years old.