Author Topic: Another version of how not to build a model engine  (Read 90294 times)

Offline Stilldrillin

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Re: Another version of how not to build a model engine
« Reply #50 on: November 19, 2009, 03:17:50 AM »
It`s much smaller than I thought too......  :bugeye:

David D
David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!

Offline sorveltaja

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Re: Another version of how not to build a model engine
« Reply #51 on: November 19, 2009, 01:35:18 PM »
What comes to that carb needle -dilemma, it's time to make a needle body, that has grub screw to hold the needle, as it allows testing different needles.

The idea came from this:

Above, the grub screw doesn't actually hold the needle, but instead possible extension piece.

And here is more than enough meat for practicing:


The safety pins are of 1mm wire, so it's possible to use a mini-drill for making different tapers.

bogstandard

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Re: Another version of how not to build a model engine
« Reply #52 on: November 19, 2009, 02:26:18 PM »
S,
Quote
so it's possible to use a mini-drill for making different taper

Are you using a tapered bore in your inlet?

If so, you will not get very good control as you are using two tapers, when they start to open up, they grow apart too quickly. You must only use one taper (the needle) to get good results.

Please see C-o-C.

Bogs

Offline sorveltaja

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Re: Another version of how not to build a model engine
« Reply #53 on: November 19, 2009, 02:49:33 PM »
Bogs, thanks for demonstration. Anyway, I intend to use the taper on needle only, to keep things simple.

I'm not even quite sure, how to make a decent tapered bore, so I have kept myself away from it.

bogstandard

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Re: Another version of how not to build a model engine
« Reply #54 on: November 19, 2009, 03:11:32 PM »
S,

I found that sewing needles had a much longer taper, so aiding much finer adjustment, and they were stuck into the threaded holder with Loctite. If you need to go up a size, just warm the holder up and the loctite will give way, allowing another needle to be fitted.


Bogs

Offline sorveltaja

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Re: Another version of how not to build a model engine
« Reply #55 on: November 19, 2009, 03:56:43 PM »
Bogs, the Loctite thing is a fast thing for sure, but it would require cleaning, when changing the needle.

So I'll stick with that grub screw -schema stubbornly .

Ready for needle shaping:



And the finished needle:





Offline NickG

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Re: Another version of how not to build a model engine
« Reply #56 on: November 19, 2009, 05:50:21 PM »
S,

Don't know whether it's the camera playing tricks but that needle looks parallel except for a very short tapered section on the end. If you used a sewing needle as bogs said you'd be sure to get a finer adjustment. Worth a try.

Nick

ps on compression ratios, from looking at Jan ridders designs he seems to aim for about 6:1. I know 6:1 is low for a 4 stroke auto engine these days so it might pay to go through some recognised plans and see what they come out at?

Location: County Durham (North East England)

Offline sorveltaja

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Re: Another version of how not to build a model engine
« Reply #57 on: November 20, 2009, 12:47:42 PM »
Nick, it wasn't the camera, needle in the pic had a short taper.

Here is the needle with longer taper, after some polishing, and the needle body with grub screw:




Offline NickG

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Re: Another version of how not to build a model engine
« Reply #58 on: November 20, 2009, 06:40:55 PM »
That looks much better, fingers crossed.
Location: County Durham (North East England)

Offline sorveltaja

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Re: Another version of how not to build a model engine
« Reply #59 on: November 21, 2009, 06:08:05 PM »
So I got the engine assembled, but as always, at least in my case, it was(is) quite challenging(despairing) to get the spark timing even close to position, where the engine starts to show signs of life.

I'm quite sure, that I need to make a spark tester, that shows exactly when the spark occurs.

There is a fine example on Jan Ridder's page: http://heetgasmodelbouw.ridders.nu/Webpaginas/pagina_vonktester/vonkentester_frameset.htm



 

Offline sorveltaja

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Re: Another version of how not to build a model engine
« Reply #60 on: November 23, 2009, 02:12:48 PM »
My previous post's problem was caused indeed by the temporary breaker points, that I made :wack:.

As I looked back the replies, there was good suggestions, such as using TIM4, or piezo igniter.

5bears's TIM4 has the Hall IC, HAL506UA, that has became obsolete. Nowadays it seems to be a 'hard to find' -part. Couldn't find the replacement either :scratch:.

The piezo ignition is ruled out, because it requires far too much force to make a spark. With bigger engines, that have the grunt, it wouldn't be any problem though.

What's left, is to fit an automotive points to the engine:

Offline sorveltaja

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Re: Another version of how not to build a model engine
« Reply #61 on: November 24, 2009, 10:59:59 AM »
Dark piece in the middle is roughly cut piece of 1.5mm mild steel.  


Here with holes to attach the contact breaker. Aluminum part is for tightening the assembly to crankcase backplate:


...and yes it fits!! ::):


The steel plate has some excess material in it, so after before cropping, it looks like this:
« Last Edit: November 24, 2009, 04:35:36 PM by sorveltaja »

Offline NickG

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Re: Another version of how not to build a model engine
« Reply #62 on: November 25, 2009, 05:27:59 AM »
S,

Looking good, what sort of cam are you going to use? I know the webster engine uses car points and he just has a cylinder of metal with a flat milled on it - seems to work well.

Nick
Location: County Durham (North East England)

Offline sorveltaja

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Re: Another version of how not to build a model engine
« Reply #63 on: November 25, 2009, 01:01:37 PM »
Nick, I was going to make a roller for ignition cam, but it would have been too complex. Simpler the better :beer:.

Brass was used for the cam, and polished it a bit:

Offline sorveltaja

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Re: Another version of how not to build a model engine
« Reply #64 on: November 25, 2009, 03:53:35 PM »
Addition: After previous testing, that was made using ethanol, the engine had couple days of rest.

When it was time to fit the breaker points to it, I noticed that the crankshaft was really stiff to rotate.

So I sprayed some wd-40 from spark plug hole, and gave it spinning. Stiffness was gone. I should have done that right after testing.

That problem never occurred after using pure gasoline...

Correct me if I'm wrong, but ethanol, if I dare to say, is water based liquid :scratch:. If even small amount of it is left inside the engine, rust and corrosion is to be expected :wack:.
« Last Edit: November 25, 2009, 03:56:53 PM by sorveltaja »

Russel

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Re: Another version of how not to build a model engine
« Reply #65 on: November 25, 2009, 11:02:18 PM »
Even if it is pure ethanol, it will tend to draw moisture out of the air if there is any humidity. That can be a big problem with chainsaws and gasoline that has a small amount of alcohol in it.

Russ

Offline sorveltaja

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Re: Another version of how not to build a model engine
« Reply #66 on: November 27, 2009, 02:49:37 PM »
Russel, thanks for the information. That's what I was after. Not water-based, but that ethanol absorbs water from the environment  :beer:.

After installing new breaker points/cam -combo, they seem to work just fine. At first I had a doubt, if the breaker's spring was too stiff, but it doesn't affect the engine's behavior.

When testing, once the engine fired, it ran at fast speed for a short time. I noticed by the ear, that something was preventing it to run longer.
At earlier stage, I had to kill the spark to stop the revving.

But anyway, I checked the ignition system(numerous times), and it was ok. Although the compression felt quite right, there was something wrong.

I have avoided opening the cylinder head, because I've finally managed to get it airtight; But no other way to check the valves.

Most excellent chance to reveal the interior of the head also.

I couldn't get the gasket off willingly, so I'll let it be:



Above pics show the major flaw in my design; middle holes are far too close to the ignition chamber; or the cavity is too wide.
Making a gasket for that is an adventurous thing.

Cylinder head:


As this picture shows, there is a brass button to increase the compression ratio. It has something to do with earlier cylinder head sealing problems.


Valves as they are; far from being similar to each other:


Cylinder liner, made of stainless steel, having two brass parts silver soldered to it:






    
« Last Edit: November 27, 2009, 02:55:11 PM by sorveltaja »

bogstandard

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Re: Another version of how not to build a model engine
« Reply #67 on: November 27, 2009, 05:26:15 PM »
S,

Very interesting design for a side valve.

If you don't mind me giving you a suggestion which you might benefit from.

Even a basic bit of gas flow design might help with the problems you are experiencing.

It seems that the fuel might be being held around the valve area instead of the charge being sucked down into the cylinder.

If you look at the C-o-C that I have attached, I think just cutting the corner off the brass slug, like in the two top pics, would improve the gas flow a lot to give a more efficient burn.

If you ever needed to make a new head, the bottom picture shows how it could be improved even further, by shaping the head a little more, and moving the plug a little more into the corner of the cylinder.


John

Offline 75Plus

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Re: Another version of how not to build a model engine
« Reply #68 on: November 27, 2009, 06:12:53 PM »
S, The head gasket can be made of copper foil which should contain the heat and pressure. I don't know about your location but here in the US copper foil can be found in stores that carry craft supplies.

Joe

Offline sorveltaja

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Re: Another version of how not to build a model engine
« Reply #69 on: November 28, 2009, 06:55:15 AM »
Bogs, thanks again for the demonstration :thumbup:. The reason for the spark plug placement is, that I originally was going to add 'dieselish' compression screw(and contra piston) to cylinder head cover.

I'm not sure yet, what to do with that brass button. Maybe I'll bevel it.

In the meantime, to replace the M2 screws, I drilled cylinder head's 2mm holes to 2.5mm, and made an M3 threads to them:


My M3 threading tap has snapped, thus being so short. About 2mm too short for the head. I took an M3 screw, and ground there a bevel, so with that I got the threads finished:


Joe, I actually have 0.1mm(~0.04") copper sheet. Don't know if that is thin enough, but I'll give it a try:
« Last Edit: November 28, 2009, 07:05:04 AM by sorveltaja »

Offline sorveltaja

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Re: Another version of how not to build a model engine
« Reply #70 on: November 29, 2009, 06:26:09 AM »
I made a bevel to brass button, and copper gasket also, and re-lapped the valve seats. With M3 screws it's possible to apply more fastening force to the head cover, than with earlier M2 screws:


So it's about time to assemble rest of the engine.

Offline sorveltaja

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Re: Another version of how not to build a model engine
« Reply #71 on: November 29, 2009, 10:38:21 AM »
At this stage, head cover is fastened, and spark plug in place. I flooded the engine a bit with wd-40, and gave it a spin, to find possible leaks.

The head cover seems to be ok, and valves seem to seal ok.


But there is a leak, where the cylinder and head meet:


I was tempted to put some loctite there, but instead I used 'high temperature instant gasket' paste, that vulcanizes at room temperature.
Head screws were opened just enough to get the stuff between the parts, and then tightened:


When the paste is cured, it's like a soft rubber, making it easy to remove the excess material with a sharp knife.

But anyways, if the gasket paste fails under pressure, I'll get back to that loctite-schema :ddb:.

Offline sorveltaja

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Re: Another version of how not to build a model engine
« Reply #72 on: November 29, 2009, 02:25:37 PM »
During the acid running tests, there hasn't been leak problems so far.

Current setup:


To save my fingers, I used trusty Dremel with rubber wheel to spin the engine:


After some fiddling, the engine fired. Short high speed runs, no response for the carb's needle, just as it did before. Fuel was ethanol.

Next thing was to test with gasoline. At first, the engine had same running habit, that it had with ethanol. I kept on trying, but letting the engine to cool down between the tests.

At first time in its history, the engine started to show even faint response to carb needle :bugeye:.

Carburetor has 1.9mm throat, but with 1.5mm ptfe plug, it worked better.

So there is a new carby to be made...




Offline sorveltaja

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Re: Another version of how not to build a model engine
« Reply #73 on: December 01, 2009, 06:35:37 AM »
I made a new carburetor, that differs from previous ones, so that it doesn't have the needle going across the throat. Parts are ready to be soft soldered together:

Offline NickG

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Re: Another version of how not to build a model engine
« Reply #74 on: December 01, 2009, 07:31:56 AM »
S,

Nice work on that carb  :scratch: I don't really understand it but it looks good! Just wondered - have you considered Jan Ridders petrol vapour carb? That could solve your mixture issues drawing in a pre-mixed vapour, just a thought. Even if you didn't want to pursue that route, or felt it was cheating or something at least it would give an indication as to where the problem lies.

Nick
Location: County Durham (North East England)