Glow Engine Theory and General Technical Discussion

[Paul De Tourtoulon]

Hi Jon, can you give me some of your expert advice please, I have an old .90 4 stroke methanol engine with a worn out bronze bearing big end,

as a con rod is not available, and I don't have any bronze, would brass be an option, I have an old brass boat prop shaft handy, or even stainless steel ?.

 Thanks, Paul

[Jon H]

53 minutes ago, Paul De Tourtoulon said:

Hi Jon, can you give me some of your expert advice please, I have an old .90 4 stroke methanol engine with a worn out bronze bearing big end,

as a con rod is not available, and I don't have any bronze, would brass be an option, I have an old brass boat prop shaft handy, or even stainless steel ?.

 Thanks, Paul

 

Define 'worn out'. If its a bit sloppy then just forget it and run the engine. If the engine is old enough to have worn out the big end bush ( being a 90 we discontinued them over 30 years ago so yep, its old) then it is likely the rest is not in brilliant shape either. With no spares available just keep running it until it dies.  

[Paul De Tourtoulon]

Not sloppy but knocking, thanks, but I don't want it to die,🤢 as it will take my PC 9 and its servos with it.

[Jon H]

If it knocks a bit i wouldnt be too concerned. A catastrophic failure is quite unlikely. Give the age, Its more likely to eat a valve than bust the big end. I would also make sure the knocking noise is the rod and not something else as the knock is caused by play in the rod, and if there is no play it cant be knocking. This suggests it might be something else. 

 

However given the age of the engine its clear its days are somewhat numbered and it might be worth swapping it for another engine. The tired one can be fitted into something more relaxed so it can just potter about a little more sedately and prolong its life as much as possible. 

 

I think this would be a better route to take as you risk killing the engine completely if you attempt a repair without the required parts/materials/tools. 

 

This general conversation about trying to save an old engine is one i have had so many times. There is a great reluctance to admit that 'its dead Jim' and move on. It seems to be more of an issue with Laser engines than other brands in my experience as we have an almost mythical reputation for long lived engines. While its true our engines last a long time, there comes a point where even a Laser (the discontinued ones espeically) is worn out and cannot be saved. 

[Paul De Tourtoulon]

It's just I don't have much to do at the moment Jon,,,

[Frank Skilbeck]

Paul, getting back to your original question here's a comparison between phosphor bronze and brass https://www.napenggworks.com/basic-points-of-difference-between-brass-and-phosphor-bronze/.

 

Basically phosphor bronze is much harder than brass so more suited to a bearing material.

[Paul De Tourtoulon]

Yes I know the différance in hardness thanks Frank, but brass is still harder than aluminium, (? ) I have some Saito's without bushes, so I wondered if a brass one would do the job, even for only a couple of years.

[Outrunner]

1 hour ago, Paul De Tourtoulon said:

Yes I know the différance in hardness thanks Frank, but brass is still harder than aluminium, (? ) I have some Saito's without bushes, so I wondered if a brass one would do the job, even for only a couple of years.

Make one and try it.

[Jon H]

35 minutes ago, Outrunner said:

Make one and try it.

 

Or not? If the job is not done properly you risk killing the engine today. Brass will not be satisfactory and as it wears it will shed bits of itself all over the place causing damage to other components. 

 

I cant understand why leaving it alone is not an option. It works, leave it alone!  

 

 

[Paul De Tourtoulon]

Silly me, I just had a brainwave, a mabuchi 540 motor has sintered bronze bearings, all I need is to find one and pull it to pieces.

[Outrunner]

Pau, I've got some lumps of bronze if you can find a way to get it down south.

[Engine Doctor]

I have in the past bushed big ends with brass for people even after explaining that Bronze is far better . Suprisingly they lasted a very long time with no adverse effects. 

As Jon says if it aint broje dont fix it but if bush is loose in the rod then give brass a try. Probably different grades of brass and the lighter the shade the more zinc so avoid that.

[Paul De Tourtoulon]

I stripped it, 0.5mm+ play in it🤢, I phoned a friend who made live stem engines, and he has some bronze, so off to see him this evening, thanks to all,,,

[Jon H]

1 hour ago, Paul De Tourtoulon said:

Silly me, I just had a brainwave, a mabuchi 540 motor has sintered bronze bearings, all I need is to find one and pull it to pieces.

 

No. Stop. Sintered bronze does not respond well to impact loads and a conrod will see significant impact load. Your motor will only see rotational load, which sintered bushes are good at.

 

 

So, we are going to try this one last time before i completely loose my cool. 

 

Leave it alone. You risk causing greater damage by doing a bodge job repair with the wrong materials and tools.

 

4 minutes ago, Paul De Tourtoulon said:

I stripped it, 0.5mm+ play in it🤢, I phoned a friend who made live stem engines, and he has some bronze, so off to see him this evening, thanks to all,,,

 

Is .5mm too much? Do you know what the clearance was when it was made? 90's have soft EN24 cranks and ran higher big end clearance than current engines. Exactly what that was i dont know, its not relevant in my day to day work so will have to look it up, but the point is it might not be as far out of spec as you think. In any case, some big ends of that era do not have oil holes and instead have a helical oil way turned into the bush itself. Will you be able to recrate that? And the bronze you are getting. What is it? Ali bronze? Phosphor? Silicon..? They are not all the same and not all of them are suitable. Even if you source the correct material its really not a good plan without the required tooling and knowledge so stop guessing, put it all back together, and leave it alone. 

 

You asked my advice as the manufacturer and that is it. Leave it alone. 

 

 

[Don Fry]

I don’t understand all this interest in motors. Install correctly, feed it nice fuel, and feed it a glow plug every couple of years, thereafter you don’t have to take much notice, unless you actually have to dig it out of the ground, why the interest. Not interested in chain saw motors, car engines either. 

Edited October 12, 2023 by Don Fry

[Paul De Tourtoulon]

I love any sort of engine, and I made it my bread winner, boat engines, inboard and outboard, 2/4 stroke petrol paraffin and diesel, cars and then onto agricultural machinery, motorbikes all along the road with garden equipment( my VAP 2 stroke chain saw is still running after 43 years ) and of course my toys,

I look after our garden gear at the club, mowers etc, and all that is left is my toys, which I love repairing and even improving some of them, got to go, I have the garden tools and chain saw to sharpen 😆

[Chris Walby]

IMO every post that is not directly related to Laser Engines technical questions should be deleted including this one.

 

Set up a dedicated page for bodging, knackering things and not following manufactures guidance and I'll be the first to unsubscribe from it 

[Paul De Tourtoulon]

How can you delete any post, even your own ?.

[GrumpyGnome]

You can't - only mods can.

[Simon Bulk]

Hi Laser-Guys. 
 

One question does not let me sleep and I did not find anything about that on the internet. 

 

Can the (not longer available) Laser Diesel Engines be run on Synth Oil? 
 

Or is Castor still the ultimate choice due to the higher combustion temperature or  for whatever reason? 
 

thanks for an Info and best regards 

Simon

[Jon H]

Synthetic is fine and the recommended recipe is:

 

15% oil

30% ether

2% ipn or 2ehn

balance as paraffin/kerosene etc

 

Modern synthetic oil is superior to castor and even PAW recommend a fuel with a synthetic alternative now. 

[Simon Bulk]

Hi Jon. Thanks for clarification. 
 

another question regarding the Glow World. Maybe that has already been discussed before, but I didn’t find clear references…

 

What is the design secret behind Lasers zero-Nitro philosophy? Is it the combustion chamber design (cylindrical) with a moderate compression ratio? 
 

OS has a similar design (parallel valves) and they run also well on moderate use of nitro (5%).

 

Saito’s design with the hemispherical head integrated in the whole cylinder as one piece with a high compression ratio seems to make a difference here. They run well on >10% or more nitro. Even Saito itself recommends that, maybe for power improvements.
 

Nitro serves as detonator and should not be used vastly in engines with a high compression rate. But that’s the point where my theory does not work in Saito’s world. 
 

Can someone help here? Especially regarding laser? 
 

Best 

Simon

Edited October 16, 2023 by Simon Bulk

[Andy Stephenson]

My Saito82 runs more than adequately on Laser 5% std oil. It even seems more powerful than other higher nitro fuels I've used. This may be due to the increased methanol content. I even use this fuel in my 2 stroke engines.

[David Davis]

I have always run my OS four-strokes on fuel containing 10-15% nitro and my old Lasers on 5% nitro, 15% oil in both mixes. One day I went to the field and forgot to pack the OS fuel. I filled the fuel tank with 5% nitro fuel and the engine, an OS 52 Surpass, ran beautifully.

Edited October 16, 2023 by David Davis

[Jon H]

All glow engines will run on methanol and oil, you do not need more than that. Years ago I used straight fuel in some ASP 52 2 strokes i had and they ran just fine. 

 

Nitro is included to increase power and make needle settings less critical. This happens as the nitro releases oxygen as it is burned, so you open the needle to allow more fuel in to keep the mixture balanced. This is why high nitro engines guzzle fuel like it is going out of style. Anyway, the larger opening of the needle (number of turns) means that a tuning error of a click or two is a smaller percentage of the whole and so the tuning is less critical. The effect of the nitro also makes the 'optimum' tuning range broader in the first place. Much of the above is over simplified, but i dont have all day or a degree in chemistry to really drill down into it 🙂

 

In the case of saito part of their request for high nitro is so they can use the fuel as an upper cylinder coolant before they burn it. Spill glow fuel on your hand and its cold, touch the carby of your running 4 stroke and it will also be cold. WWII aircraft engines used water methanol injection to cool charge air, etc. 

 

This all matters as the ignition timing of the fuel charge is governed by a balance of things like compression ratio, plug temperature, charge temperature etc. if you increase the temperature of the plug or charge, you advance the ignition. Higher comp ratios increase charge temperature and this can cause knocking when the mixture is leaned for peak power, so you have to cool the thing down. I know some have shimmed their saito engines to reduce the compression ratio and they run very well on straight fuel and use much less of it. 

 

All that said, i run my saito 45's on 5% and they are no bother. I test ran a new saito 82 for someone the other day and it ran fine on 5%. It wouldnt hold full power long as it heated up and knocked, but it was new so cant hold that against it too much. I also used to own a saito 450r3 radial and saw the same or increased performance on 5% as rcu forum members in the US running 20%. Mine would also idle fine without glow support but theirs would not. Running lower nitro means the engine will run hotter at idle which helps keep the plug alight. Also with the engine at idle and a rich mix there is lots of the fuel soaking heat out of the engine causing unreliability. 

 

To summarise. All standard 2 and 4 stroke engines from any brand use 5% nitro and 15% synth oil. Its literally the only fuel in the world as far as i care. 

 

The exceptions in fixed wing are things like ducted fan, pylon or other highly tuned engines. or tiny engines like the old cox motors, or YS supercharged engines. Heli's, cars, boats etc again there are different operational requirements so they fuel requirement changes to match. 

 

The primary reason for the 'high nitro better' debate is because slow run needles are left sad and alone having never been adjusted from the factory setting. You must adjust your slow running needle as it governs the mixture up to around half throttle. They are deliberately set very rich from the factory as most manufacturers do not test run their engines and they set them rich to guarantee an engine will start. If you do not lean it off (sometimes several turns) the engine will be too rich and run badly. Adding nitro 'fixes' the problem as the mixture is closer to being right, but its not fixed it really, its just tuned better. The same or better result would have been possible with 5%. 

 

Oh and it wouldnt be one of my posts without mentioning tank placement. Top of the tank in line with the centre of the carb. Get that wrong and the engine will be impossible to tune correctly anyway.