Author Topic: Another version of how not to build a model engine  (Read 90334 times)

Offline sorveltaja

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Another version of how not to build a model engine
« on: November 06, 2009, 07:14:49 PM »
This has been my main project for a while:


It's a small four-stroke engine, that is based on my own(borrowed some ideas from E.Westbury) drawings. Bore is ~10 mm and stroke ~12 mm. Compression ratio is something between 3:1 and 5:1 (wild guess).

So far I've encountered countless pitfalls on my design. Anyway, the engine shows signs of life, so rather than desperate, I'm curious about it.

In this topic, I'll do my best to reveal both good and bad things, that I've faced during the project, as most of those are common for everyone, that builds his/her first IC-engine.

Progress might be a bit slow, but more to follow...


 

Offline Bernd

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Re: Another version of how not to build a model engine
« Reply #1 on: November 06, 2009, 09:00:10 PM »
Sounds good. Looking forward to your posts.

Bernd
You can't fix "STUPID".

Offline sbwhart

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Re: Another version of how not to build a model engine
« Reply #2 on: November 07, 2009, 02:35:37 AM »
Looks a good project look  :thumbup: forward to you posts

Stew
A little bit of clearance never got in the road
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Offline Gerhard Olivier

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Re: Another version of how not to build a model engine
« Reply #3 on: November 07, 2009, 03:13:57 AM »
Im hooked already

Send more soon

Gerhard
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bogstandard

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Re: Another version of how not to build a model engine
« Reply #4 on: November 07, 2009, 05:25:07 AM »
Sorveltaja,

I'm just trying to figure out which bit goes with what.

Any chance of a few more views, especially from the side.

Bogs

Offline NickG

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Re: Another version of how not to build a model engine
« Reply #5 on: November 07, 2009, 05:38:49 AM »
Sounds great. Is a compression ratio of 3:1 high enough? Can't wait to see more.

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 #6 on: November 07, 2009, 12:03:46 PM »
Thanks for replies.

An overview of the engine's construction: Base is 5mm aluminum; crankcase and cylinder head are both machined from solid alum.
Cylinder liner's material is some sort of stainless steel. Easily machinable though. I used plenty of time, when lapping it. Glad I did.
---------------------------------------------------------
Pearlitic cast iron is used for the piston. It has no oil grooves or piston rings, as it provides nice tight compression without them. Even without any oil.
It's the material that I highly recommend for pistons/cylinder liners for low-power, slow running engines. No wonder, that Jan Ridders prefers to use it on his engines...
-----------------------------------------------------------
Carburetor on the left side is third or fourth version. Needle is from an ancient .10 glow engine. It still needs tweaking, maybe a new one(fifth version). Tried to make the needle system myself, but lack of lathe's top slide prevents turning any decent taper.
Currently, carb's throat size is 1.2 mm. Engine runs with that, but only at (too)fast speed. Positive thing is that no parts were flying out, when it cranked :clap: .
Testing different carbs with different throat sizes has gave me a hint of what the engine likes. Next version of the carb will have 0.6 mm throat, as it's the smallest drill size, that I have. If it's no go, then drill it to 0.7 mm, and so on. 
----------------------------------------------------------------
Sharp eyes might notice, that left side (inlet)valve doesn't have a tappet. Currently it's spring-loaded, as I ruined inlet cam by over-filing it.
-------------------------------------------------------------
To be continued..



Offline chuck foster

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Re: Another version of how not to build a model engine
« Reply #7 on: November 07, 2009, 12:42:31 PM »
very interesting build  :thumbup:

you can spend allot of time trying to find the right combination of parts.............but when you do  :ddb: :ddb: :ddb:

please keep us posted and let us know how it all turns out  :clap: :clap:

chuck  :wave:
hitting and missing all the way :)

skype:  aermotor8

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Offline NickG

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Re: Another version of how not to build a model engine
« Reply #8 on: November 07, 2009, 01:02:18 PM »
Brilliant effort. Well done for getting it to run.  :bow: An IC engine is not far down my list of projects as it is something I have yet to do.

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 #9 on: November 07, 2009, 01:26:30 PM »
Thanks for kind comments.

The engine ran today, and I was going to shot a video of it. But the breaker points failed again.
I'm going to replace them anyway with proper ones, that's used on cars. I've ordered few sets of those, and expect them to arrive next week. 


Offline sorveltaja

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Re: Another version of how not to build a model engine
« Reply #10 on: November 10, 2009, 04:41:08 PM »
In the meantime, I made another temporary breaker points to continue the testing.

Coil(an ex-transformer), that I used for ignition, stopped working, and made itself useless by sparking inside the coil:

After abusing(and destroying) several ones during the tests, I must admit, that transformer coils are not suitable for an IC ignition purpose. Not only because they can't produce reliable sparks, but they just can't handle repetitive strong current pulses.

Luckily I had an appropriate replacement part at hand:


What comes to breaker points, at first I tried several micro-switches:

They seem to fade quite fast.

Besides the temporary breaker points, that I made, today arrived the replacement for those also:

Next thing is to figure out, how to attach that to the engine, as the spring is too stiff for the humble power of small engine.
------------------------------------------------
Short video of the engine:

<a href="http://s323.photobucket.com/albums/nn471/sorveltaja/?action=view&amp;current=01.flv" target="_blank" class="new_win">http://s323.photobucket.com/albums/nn471/sorveltaja/?action=view&amp;current=01.flv</a>

Carburetor needle is extremely sensitive, making the engine behave like a donkey.

Today it ran about half minute, at fast speed, then stopped due to heat expansions, I assume, as the cylinder head was too hot to touch.

bogstandard

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Re: Another version of how not to build a model engine
« Reply #11 on: November 10, 2009, 05:20:53 PM »
I found that a hall effect sensor and a rare earth magnet was much easier and more compact to use. I used the Tim 6 configuration.

Here is a link to other ignition types, the hall sensor takes the place of the contact breakers.

http://www.5bears.com/tim4.htm

Or go with Jan ridders version by using a piezo, which does away with everything, and fires the plug direct.

Here are a couple of pics of the last ic engine I made, after having a long running in session. It is still sitting in my shop in the same condition. I never wanted to, or ever will finish it off after getting it to run OK. It just knocked ic engines completely out of my system, after struggling with such terrible castings. It would have been ten times easier to have made it out of bar stock, as you have done, and how I made previous engines.

The second picture shows the mounted hall sensor and the magnet was mounted in edge of the small ali disc. Those two parts take the place of the points and condenser. No wear, and you can cover it in oil, and it still runs perfectly


Bogs



Offline NickG

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Re: Another version of how not to build a model engine
« Reply #12 on: November 11, 2009, 05:38:03 AM »
sorveltaja,

The car points spring might feel stiff but remember they don't have to move much and it will only be a very small cam throw so it may not cause too much power loss when used in the correct manner - give it a go, I know the webster uses that method.

Jan used the piezo with some success but they sap quite a lot of power. He has also used the coil set up but with a microswitch as you show with success. http://heetgasmodelbouw.ridders.nu/Webpaginas/pagina_drukgestuurde_tweetakt/druktweetakt_frameset.htm

John,

I've never seen that one before, nice engine  :thumbup: what is the coil on it? Why is there an inline switch shown on the Tim 6?

Cheers,

Nick
Location: County Durham (North East England)

bogstandard

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Re: Another version of how not to build a model engine
« Reply #13 on: November 11, 2009, 06:54:01 AM »
The engine is actually the Westbury Whippet, and the castings for it are available from Hemingway. But they are so bad they are almost unusable, especially the head area ones. I had to get a friend to build up areas of the casting with ali weld, just so that I could carry on with it. They were up to 1/8" out in places.

Those coils are now not available, and were made for fitting into model aircraft with 4 stroke petrol engines. They are only about 3/4" diameter.

The inline switch is in fact where you would mount the contact breaker or in my case, the hall sensor.


John

Offline NickG

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Re: Another version of how not to build a model engine
« Reply #14 on: November 11, 2009, 07:54:33 AM »
John,

I thought I recognised it. A friend of mine is building the Chenerey V Twin Aero Engine with castings from Hemingway but he has also had all sorts of problems with the head castings especially. Valve bushes in the wrong place, wrong angle and blow holes everywhere. I think he tried 3 that I know of but then resorted to machining from solid. It looks a much better job and he said it was far easier.

Incidentally, if anybody is interested Hemingway say they supply a similar model electric coil to John's and they supply the TIM 6 in kit form, but they'll cost you an arm and a leg! http://www.hemingwaykits.com/acatalog/Ignition.html

Oh right, I see now, they just haven't shown it in the same way as the TIM4. I don't get TIM 7 ...  :scratch:

What sort of battery did you power yours from? I know Jan uses cordless drill batteries and the like.

Nick

Location: County Durham (North East England)

Offline crankshafter

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Re: Another version of how not to build a model engine
« Reply #15 on: November 11, 2009, 11:24:59 AM »
NickG

"Incidentally, if anybody is interested Hemingway say they supply a similar model electric coil to John's and they supply the TIM 6 in kit form, but they'll cost you an arm and a leg"

The coil they supply is the Exiter.

I recently lost one of my legs/hands  :bugeye::lol:
cs

Offline NickG

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Re: Another version of how not to build a model engine
« Reply #16 on: November 11, 2009, 11:27:49 AM »
 :lol:

But as long as your model engine works it was worth it right?!  :thumbup:

Nick
Location: County Durham (North East England)

Offline crankshafter

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Re: Another version of how not to build a model engine
« Reply #17 on: November 11, 2009, 11:53:56 AM »
NickG
Time will show. The coil and TIM6 will be used on a Hoglet Twin that I have under construction. You can see some of the parts of it at my Avatar.
Hope to have it running before newyear.
cs

bogstandard

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Re: Another version of how not to build a model engine
« Reply #18 on: November 11, 2009, 12:09:04 PM »
Nick,

I think they are supposed to run off 3.6 volts, but I used a small 6volt 4ah sealed lead acid, and they give out around 7volts, and I had no trouble with them at all. The engine would run for hours using that battery.

I actually bought a Tim 6 circuit board kit from the US, half the price, and made up some of the cards myself. Made about a dozen of the units for friends for about 2 squid each. I gave all the rest of the bits to make them to a friend not too long ago. I think the coil was about 20 squid, again from the US.

If anyone is interested in making their own coils and magnetos, the late Bob Shores book (of which I have a copy), Ignition Coils and Magnetos in Miniature is a must. It tells you how to make them from scratch, at very small cost.


John

Offline crankshafter

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Re: Another version of how not to build a model engine
« Reply #19 on: November 11, 2009, 12:55:07 PM »
John.
You are rigth. The Tim4 is for up to 4 volt and the Tim6 up to 6volt batt.
Actually Hemmingway kits get them from US of A. ( made by the well known Jerry Howell)
CS

Offline sorveltaja

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Re: Another version of how not to build a model engine
« Reply #20 on: November 11, 2009, 03:13:49 PM »
Thanks for replies!

Today I made a new carburetor, and tested it. First was 0.7mm throat, then bored it to 1.0, and finally to 1.5mm. None of them brought the engine alive. Most likely reason for that is the fuel that I used - it was an unopened can of well known brand lighter fluid.

I have used that succesfully before, but this time even the odor was different. It smells more like teen spirit mouth-wash, than gasoline.
Did the burning test on a small steel cup with it, and the amount of smoke and smell told already, that it was something else/heavier, than pure gasoline.

To keep the engine's fuel thing straight, avoid lighter fluids, unless you are sure, what you get. 

Anyway, next I'm going to obtain real gasoline. And start the carburetor testing -phase from the start.

Learning curve might be quite steep, but I'm getting used to it. Having the engine, that really wants to run, is the source of inspiration :thumbup:.

bogstandard

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Re: Another version of how not to build a model engine
« Reply #21 on: November 11, 2009, 05:25:40 PM »
How are you starting it S?

If you look at the pic of the back of my engine (opposite to flywheel),  you will see a lump of bar with a hole in it.

That holds a one way clutch bearing. Stick a bit of 6mm rod in my drill, put it into the bearing and turn on. When the engine fires and runs, the rod just pulls out. It saved hours of finger aching starting during setting up trials.


Bogs

Offline sorveltaja

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Re: Another version of how not to build a model engine
« Reply #22 on: November 12, 2009, 04:13:05 PM »
Bogs, at the earlier stage I used a Dremel with rubber wheel against flywheel for starting.

Recently it hasn't been necessary, since the engine starts easier. If it doesn't even kick, I know it isn't going to run. During this project, I have learned, what the general faults are, that prevent running. Mostly it's flooded spark plug, or failing breaker points.
Earlier the biggest problem was the cylinder head cover not being leak proof, due to my somewhat faulty design. But more of that later.

One by one, I've managed to stomp the bugs as they appear.

On the left is previous needle system, that snapped right where the needle tip comes out. In the middle is newest carburetor body with 1.5mm throat.
On the right side is a new needle, that I made off of compass needle. It however might need some tweaking. 



bogstandard

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Re: Another version of how not to build a model engine
« Reply #23 on: November 12, 2009, 04:20:15 PM »
S,

A lot of people use sewing or darning needles in their carbs.

Cheap and cheerful, but very accurate.


Bogs

Offline sorveltaja

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Re: Another version of how not to build a model engine
« Reply #24 on: November 13, 2009, 01:26:29 PM »
I tested the new carb, and it floods the engine too easily. Most likely reason for that is the M3 thread, that holds the needle,
being too coarse(0.5 mm pitch), preventing any tuning.

The glow engine needle, that I used earlier, has 0.35mm pitch on its thread. It seems that even finer thread (~0.1-0.2mm) pitch would be better in this case.

I can make that fine thread on the lathe, at least outer thread. Small diameter inner threading is more of a problem. It would require threading tap.
Is there any other way to accomplish that?

Easiest way could be to buy a whole new needle system. But not yet.

In the meantime, I'm going to make a vapor carburetor, as it surely can't flood the engine :dremel:.