First Running Engine

[c_mario]

Hi, After almost a year of trying and 4 attempts at different engines I finally got one to run. This one was built from RCM&E Plans for the Whittaker Firefly 46. I finally understood the honeing process and was able to measure the taper in the bore properly.
I still have issues. I cannot not keep it running without the glow starter attached. If I remove it the engine dies. I can reduce the current draw to 1amp and It will run a tank of fuel through. I have run three tanks through with new 16% Nitro fuel and tried 3 Separate newly purchased glow plugs, albeit I did use them on my previous attempts.
Difference from Plan:- I used a needle I made previously from a sewing needle. I made the muffler instead of using the recommended OS version. Actually made for previous engine , just created an adapter for this one.
Here it is.
First Running Engine

 

[minh-thanh]

Your effort and patience have paid off!
Congratulations !

 

[aka9950202]

Well done. What do you plan to do next?

Cheers,

Andrew in Melbourne

 

[c_mario]

Well done. What do you plan to do next?

Cheers,

Andrew in Melbourne

Try to figure out why it stops when glow plug power removed.

 

[scottyp]

The engine looks good. I don’t have the exact answer to your question, but each glow engine likes a certain glow plug best and the amount of nitro in the fuel also comes into play. In general, a high nitro fuel will want a cooler glow plug.

Also, do you have enough compression? If it is low, that could be an issue and I would try a hotter glow plug.

It does sound to me that it is running on the rich side. Too much fuel will keep a glow plug from being able to heat properly.

 

[ZebDog]

Well done on your first running engine

 

[Tim Wescott]

It sounds like it's in a rich four stroke, or it's sick, or it's not broken in yet. Do you have good compression? Is it broken in? What plug are you using?

If it's broken in it should turn freely with the glow plug out. If it still binds at the top of the stroke, then you need more break-in. Assuming it's an iron/steel piston/sleeve combination, patience here will be rewarded - in general the production engines that use that combination either break in fast and wear out fast, or they take forever to break in and then last forever (of note are Enyas, which were notorious for taking hours and hours to break in back in the day, and which are now ubiquitous on eBay because they simply don't wear out).

I couldn't tell from the audio if it's laboring under a too-large prop, isn't broken in yet, or is four-stroking rich. Be sure you're using the prop that's suggested for break-in. Without knowing what the engine was designed for I hesitate to make a recommendation, but if the instructions don't list a break-in prop, go one inch smaller in diameter, or one inch less in pitch, from the recommended flying prop.

If it is broken in, then try leaning it out. You can do this briefly by pinching a fuel line and listening -- if it picks up speed then it was too rich (if it picks up speed and dies you pinched for too long!) Break in techniques differ, but if you don't have break-in instructions and it's iron/steel, then get it running, then alternate 20-second bursts of full speed with a minute or two of running rich until it's loosened up enough to keep a plane in the air -- then go fly, keeping in mind that early in their lives iron/steel engines like to cut out unexpectedly, and richer is always safer than leaner (you are going to go fly this, or run a car, or a boat -- yes?)

If it's broken in, and it won't keep running even if it's leaned out until it's just a bit richer than full speed, then you either need to increase the compression (remove head shims if you made them, otherwise turn the head down a bit), increase nitro (but you're already running 15%, and I get the impression that's a .46 cubic inch engine, so 15% nitro is about the maximum reasonable), or go to a hotter plug.

And if it's an ABC engine or some other combination that's not iron/steel then don't break it in like it's iron/steel -- each piston/cylinder combination needs a different break-in procedure. Ask, or search it out on the web.

 

[c_mario]

Hey Tim,
Thanks for such a detailed response.
Its Steel Sleeve , cast Iron Piston. I have run it for a total of about 25 minutes. When I was a boy (some time ago) I used 10 X 6 props on 40 size engines. This prop is an 8 x 5. It is running rich. I think the precision of my needle is not so good, It only needs about 3/4 of a turn from closed to run. Also it seems to get to a point in the needle where it is leaning off then seems to richen up as I continue to move it ever so slowly toward's being closed. I didn't try the pinch test yet. I was planning to get different plugs to try, the plugs were OS no 6. Not sure how to judge good compression but there is a nice bouncy feeling when flicking the prop without glow heat.

 

[c_mario]

It does sound to me that it is running on the rich side. Too much fuel will keep a glow plug from being able to heat properly.

Thanks Scottyp,
Yes it is running rich, partly on purpose not to over rev a newly built motor but also it seems my needle and seat may not be that great. I can slowly close the needle valve down and can hear the revs increase but as I continue to close , instead of revving harder at one point it starts to go rich again.

 

[Tim Wescott]

I've built several needle valves for RC to CL conversions. If the needle isn't round and centered then you'll get that effect. So I think another needle is in your future -- possibly one that has a longer taper. Post a drawing of your needle design?

As for compression, I'd just take a swipe at increasing it and see what happens -- because I'm not sure how to calculate what the actual number should be for compression chamber volume at TDC should be on a two stroke. I know it's complicated, and I know the symptoms of needing more or less, and that's about as far as my knowledge extends.

I also know that with typical engine construction you can start with high compression and use shims to drop it if you overshoot. Those things we think of as "head gaskets" that come with our RC engines are really compression shims, so that you can tune the engine for the fuel you're using and the prevailing conditions.

 

[Tim Wescott]

"Nice bouncy feeling when flipping the prop" sounds like the engine seal is good, but you could get that with a wide range of compression.

I hadn't thought this before -- is the engine designed for that size plug? If the head is designed for long plugs then a short plug like the OS will be severely shrouded by the glow plug hole. Its action would be compromised. When the plug is all the way in, its business end should be flush with the head surface. I suppose it could stick in a bit if it's not hitting the pistion (probably tending to cause detonation if it were too much -- but that's not your problem). If it's recessed by more than a couple of threads you definitely need a longer reach plug, or you need to modify the head. If it's recessed by 1/8" or more I'm going to move it up to the most likely cause for your problem on my personal list.

 

[vederstein]

Any runner is a success!

 

[xtal_01]

That is fantastic !!!!!!!!!!!

OK ... for a newbee here ..... how exactly does a glow engine work? Is it a diesel with the glow plug just helping to vaporize the fuel on a cold start? Or does the heat from the engine cause the small wire to continue glowing while it is running and thus aid in ignition?

I guess another question ... what is the difference then between a glow engine and a diesel? I know the glow has a glow plug and the diesel has a variable compression (the contra-piston). But as the glow does not have a spark plug, are they both not diesels in a sense?

Thanks .... Mike

 

[Willyb]

Congratulations. And good job for sticking with it. Lots of people would have given up after the first engine.

 

[Tim Wescott]

...

OK ... for a newbee here ..... how exactly does a glow engine work? Is it a diesel with the glow plug just helping to vaporize the fuel on a cold start? Or does the heat from the engine cause the small wire to continue glowing while it is running and thus aid in ignition?

I guess another question ... what is the difference then between a glow engine and a diesel? I know the glow has a glow plug and the diesel has a variable compression (the contra-piston). But as the glow does not have a spark plug, are they both not diesels in a sense?
...

With apologies to Mario if this is unacceptable thread drift (but it kinda sorta bears on the problem, so...)

I'm going to make this complicated.

A true Diesel engine works because the air is compressed an insane amount (20:1 or something like that). This gets it so hot that when fuel is injected into the combustion chamber, it self-ignites, even if it's crappy fuel in other ways (like diesel oil).

Model Diesel engines work sort of like a true Diesel, but the engine works on a fuel-air mix, the compression is lower, and ether is added to the fuel mix because it self-ignites at a lower temperature than diesel oil. Usually there's some diesel oil (or kerosine) in the mix because the ether will kick it off.

Glow engines work sort of like a true Diesel, too, but the engine works on a fuel-air mix, the compression is even lower than with a model diesel (which is why conversions from glow to diesel can be iffy -- diesel cranks and crankcases need to be stouter), and because the glow plug wire is platinum or some other suitable metal. The platinum element actually catalyzes the methanol-oxygen reaction, kicking off combustion at a much lower temperature than it would happen without it. Basically it's the same chemistry as a catalytic converter.

So if the glow plug isn't getting a good fuel-air mix because it's shrouded (see how I brought this on topic?!?) it'll heat the mix in its vicinity, but it won't get enough methanol to catalyze.

Note that because of this catalytic effect, glow engines can actually start without a battery, on a good (or very bad, depending on the circumstances) day. I've had this effect actually start an engine on me just once (at a contest, where it caused me some grief), but I've felt that "I want to start" bump a few times on an engine without a battery.

 

[xtal_01]

Awesome!

Thanks for the explanation. I've flown glow engines some 40 years ago but never thought to ask "why".

Diesel made sense ... I looked up a few youtube videos. Glow seems to be the odd one out ... I could not figure on how the glow plug fit in with a lower compression engine.

Thanks .... Mike

 

[c_mario]

I hadn't thought this before -- is the engine designed for that size plug? If the head is designed for long plugs then a short plug like the OS will be severely shrouded by the glow plug hole. Its action would be compromised. When the plug is all the way in, its business end should be flush with the head surface.

Mate thanks again for your insight.
Yes In my mind I did question the plug length. It is recessed into the plug hole which I thought was strange. Also the plans actual do say to just buy an OS needle and gave the part number, but since I had already made one I used it. I will try to reduce the plug hole depth, I.e. machine the recess deeper (from the top side) meaning the plug will go deeper into the head, and try another needle.

 

[stackerjack]

Try to figure out why it stops when glow plug power removed.

Well Done making the engine pal. The fact that it stops when you remove power from the plug is nearly always the plug itself. Have you tried an idle-bar plug?
Is it running on pressure from the tank?
If so, try removing the pressure pipe, and opening the needle a little.
Reading lower down this thread, you need to sort out the needle valve before you do anything else.

 

[Donnyo65]

New to the site but not new to glow plug engines! If all the above suggestions have been ruled out, try a hotter glow plug or a long reach glow plug or both. When experimenting with a new engine I always have a selection to try with as different engines can be very sensitive to glow plug type. a word of caution - if trying a long reach plug. Turn the engine over slowly by hand with the plug installed but no fuel or battery connected - some engines will allow the piston to strike a long reach plug! If all is fine, connect everything and have a go. Another thing to try is using a fuel with about 15% nitro - I don't like this as the engine needs to be run dry at the end of a session and thoroughly oiled as the nitro residue forms an acid with moisture in the air but it does help with (Mask!) a lot of engine problems.

 

[Tim Wescott]

If you just bung a longer plug in there you definitely want to check for clearance before flipping the prop. I suspect it was just designed for a long reach plug, though.