Author Topic: 1/4 Scale Cirrus MkI  (Read 21493 times)

Offline cwelkie

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Re: 1/4 Scale Cirrus MkI
« Reply #90 on: March 05, 2018, 03:27:00 AM »
Flash forward a number of shop hours and it's pretty much there from a fabrication perspective.  I plan to have the engine mount and tank stand powder coated for durability (and because I hate painting).  For the curious, I used Caswell blackening solution on the cylinder barrels, rocker arms/supports and crankcase breather bits.

Sadly I got into a groove whilst building the distributor and didn't take any photographs.  It contains a 4-magnet disc to trigger a hall-effect sensor with the usual rotor below the cap to distribute the spark.  Ignition timing is adjustable in sync with the throttle with mechanical linkage.

I've decided to build a universal ignition box for this project.  Previously I'd build a special system for each engine but finally realized that was ... wasteful.  The last photo shows the state of pay in this area so far.  The larger electronic board is the IGBT coil driver from Model Engine Builder magazine.  The smaller board will provide an electronic "buzz-box" input to the coil driver if desired.  (A switch will provide for selecting between single spark and multi-spark modes.)  There is room for an induction input tachometer and a volt/ammeter.  Power and point/hall-effect inputs will be via banana jacks.  H/V output will be through a 'safety' banana jack mounted in an additional insulator on the panel.

Sorry for the lack of updates ... hopefully better late than never.
Charlie

Offline michelko

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Re: 1/4 Scale Cirrus MkI
« Reply #91 on: March 05, 2018, 06:28:45 AM »
Hi charlie,
Very impressive build :ThumbsUp:
I would like to ask what material you used for the rings? And how did you get them over the pistons?
I broke several oil rings, so i left them and run the bugatti without them.

Michael

Offline Roger B

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Re: 1/4 Scale Cirrus MkI
« Reply #92 on: March 05, 2018, 07:57:15 AM »
Excellent  :praise2:  :praise2: Not long now until the first trials  :)

What material did you use for the distributor, Delrin?
Best regards

Roger

Offline cwelkie

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Re: 1/4 Scale Cirrus MkI
« Reply #93 on: March 05, 2018, 02:14:03 PM »
Thanks Michael - I used 12L14 steel for the rings on this engine.  It was something I wanted to try for a change from cast iron.  I must admit to running this engine in for 30 or 40 minutes so far (electric drill drive while contemplating the next move) - it was "tighter" than any other so far.  On previous builds I've had luck expanding cast iron rings on a tapered mandrel to get them started onto the piston and then relying on fingernails to hold them open to get in the lower groove(s).  The large diameter end was slightly larger than the piston OD.  Managed to get all of them on a 9 cylinder Gnome without breaking any and they were cast iron.

Thanks Roger - Yes, it shouldn't be long now, especially when one considers how long ago the journey started.  If only winter would end ... snow banks in March are normally unheard of where I live!  Yes, I used Delrin for the distributor cap and rotor.  It's nice to turn and dimensionally stable enough for something like this.

Charlie

Offline fumopuc

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Re: 1/4 Scale Cirrus MkI
« Reply #94 on: March 05, 2018, 06:01:46 PM »
Hi Charlie, what a beauty.
« Last Edit: March 05, 2018, 06:17:16 PM by fumopuc »
Kind Regards
Achim

Offline petertha

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Re: 1/4 Scale Cirrus MkI
« Reply #95 on: March 06, 2018, 08:09:34 PM »
Looking great Charlie!
Re your 12l14 piston ring comment, are you heat setting them on a pin to a specific opening so they have radial tension once installed in the groove (the Trimble method I guess as its popularly known). Or is this a 'cold' process, turned & gapped?

Offline cwelkie

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Re: 1/4 Scale Cirrus MkI
« Reply #96 on: March 06, 2018, 10:48:41 PM »
Thank you Achim and Peter.

Peter - the piston rings were not annealed as provided for in the "Trimble method" for cast iron rings.  These were machined to an (oversize) outside diameter at the required width so a radial segment could be cut away providing the spring tension and hopefully the correct gap.  Any out-of-round is dealt with by holding the ring on a fixture in a compressed state for a final trim of the outside diameter.  If you look back to a previous post from November 22, 2016 you should see some photographs (if Photobucket hasn't killed access).  The whole process is done "cold"; one without the black art of heating/timing or non-magnetic ferrous phenomenon  :mischief:.

Cheers
Charlie

Offline michelko

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Re: 1/4 Scale Cirrus MkI
« Reply #97 on: March 07, 2018, 08:19:37 AM »
Hi Charlie,
do you have experience with the combination of steel Rings and cylinders?
I made the Cylinders of my Bugatti Typ50 out of ETG100 This is a free turning high strength steel.
Compression Rings are made from GGG60 Iron. As mentioned before the oil controlrings broke on assembly.
So i am thinking of steel rings like you did.
Iam interessted in your ignition Setup. Can you tell me from what Issue of the modelenginebuilder magacine the System is?

Thanks in advance

Michael
« Last Edit: March 07, 2018, 01:23:12 PM by michelko »

Offline PJPickard

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Re: 1/4 Scale Cirrus MkI
« Reply #98 on: March 07, 2018, 12:06:37 PM »
That thing is beeeyootiifuuull!
I'd love to build one of those someday, then I found out what the castings(if you can find them) cost!

Offline cwelkie

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Re: 1/4 Scale Cirrus MkI
« Reply #99 on: March 07, 2018, 01:41:53 PM »
Thanks PJ

Michael - No, I do not have any experience with steel rings.  I was curious about how they would work and the process of making them.  I'm led to believe that steel is used in many (most?) modern full size engines so why not try it here(?) ... that was my only rationale.

The ignition control board I'm using was detailed in Model Engine Builder, issue #34.  The article was by Dave Sage and John Gedde (with writing assistance from Mike Rehmus).  It inspired me to try an automotive "coil-over-plug" ignition coil.  The first bench test of the circuit startled me with the ferocious spark when triggered.  The rest of the "system" is just my attempt to build a universal ignition box for use on multiple engines, granted with more bells and whistles normally found in my usual rag-tag, last minute lash-up.  Once the rest of the components arrive on the slow boat from China (literally) perhaps I'll post some additional information on a separate thread.

Offline michelko

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Re: 1/4 Scale Cirrus MkI
« Reply #100 on: April 02, 2018, 08:50:57 AM »
Flash forward a number of shop hours and it's pretty much there from a fabrication perspective.  I plan to have the engine mount and tank stand powder coated for durability (and because I hate painting).  For the curious, I used Caswell blackening solution on the cylinder barrels, rocker arms/supports and crankcase breather bits.

Sadly I got into a groove whilst building the distributor and didn't take any photographs.  It contains a 4-magnet disc to trigger a hall-effect sensor with the usual rotor below the cap to distribute the spark.  Ignition timing is adjustable in sync with the throttle with mechanical linkage.

I've decided to build a universal ignition box for this project.  Previously I'd build a special system for each engine but finally realized that was ... wasteful.  The last photo shows the state of pay in this area so far.  The larger electronic board is the IGBT coil driver from Model Engine Builder magazine.  The smaller board will provide an electronic "buzz-box" input to the coil driver if desired.  (A switch will provide for selecting between single spark and multi-spark modes.)  There is room for an induction input tachometer and a volt/ammeter.  Power and point/hall-effect inputs will be via banana jacks.  H/V output will be through a 'safety' banana jack mounted in an additional insulator on the panel.

Sorry for the lack of updates ... hopefully better late than never.
Charlie
Hi charlie
Could you post some pics of the distributor cap internals and rotor?
Thanks michael

I also build the ignition circuit. Works realy nice with an 12v automotive coil.

Offline cwelkie

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Re: 1/4 Scale Cirrus MkI
« Reply #101 on: April 05, 2018, 01:51:10 AM »
Hi Michael - here are some photos as requested.

The rotor is a "hand" press fit onto a socket head cap screw that attaches the rotor shaft to the camshaft.  The knurling on the capscrew is used to hold, index and drive the rotor.  Under the rotor is the magnet disk and under that is the hall effect mount.

The hall effect mount started as an ring with an annular groove in it.  That was trimmed down and the left over piece was used to make the top cover.  The sensor is sandwiched between the top and bottom, inside the groove.

The hall effect is fastened to the bottom of the distributor housing which moves (i.e., rotates) with the mechanical linkage to the carb for timing changes with throttle setting.  The magnetic disk is held to the above mentioned rotor shaft with a couple setscrews to allow for setting the timing of hall effect activation.

The distributor cap leads run through holes from the top (for the spark plugs) and bottom (for the coil).  There are socket head cap screws that make contact with the wire end and pass through to the rotor on the inside of the cap.

Hope this all makes sense ...
Charlie

Offline Art K

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Re: 1/4 Scale Cirrus MkI
« Reply #102 on: April 05, 2018, 03:18:49 AM »
Charlie,
The Cirrus is looking quite impressive. I like the distributor set up. I think the mechanical advance is a great idea. What sort of advance curve are you using?
Art.
"The beautiful thing about learning is that no one can take it away from you" B.B. King

Offline cwelkie

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Re: 1/4 Scale Cirrus MkI
« Reply #103 on: April 05, 2018, 04:23:25 AM »
Hi Art - thanks for the kind feedback.
I'm planning to start with 1 or 2 degrees BTDC at idle and adjust the linkage for 18 to 20 degrees BTDC at WOT (wide open throttle).  I'm not aiming for "wild and crazy" performance ... reckon it will run and I can fiddle with it from there.  Having variable timing was more about easier starting and limiting the likelihood of getting whacked by that wooden club :)
(It's a bit like putting a lawnmower on its side and then flipping the blade to start it!)
Charlie

Offline Art K

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Re: 1/4 Scale Cirrus MkI
« Reply #104 on: April 05, 2018, 12:01:38 PM »
Quote
It's a bit like putting a lawnmower on its side and then flipping the blade to start it!
This reminds me of one of the log splitters that came up when Brian was building his. A flywheel with the wedge sticking out.
Art
"The beautiful thing about learning is that no one can take it away from you" B.B. King