B J Cicada engine

[Petit]

Hi all, i have a couple of little engines under my belt now, both flame lickers the jan ridders internal valve and the Poppin engine. I wanted to venture away from flame lickers for my next project but was unsure what to do, i didnt want to make a steam/air engine as i dont have a compressed air supply at home. I started looking into ic engines when i then came across the B J Cicada engine. I liked the look of this engine as its a compression start engine so i wont need anything to run it apart from diesel, and also it looks simple enough to make, so ideal for my first steps into IC engines.

This is my first build thread so bare with me, im building it on a full size Colchester lathe... At work on night shifts! I don't have my own lathe or mill yet but i am a maintenance engine by trade and i have all the facilities and materials to build the engines at work! Albeit slightly under the radar hush hush! So here goes!

 

[Petit]

Ok so for those who may not know the bj cicada engine looks like this...
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First on the list to build is the crankcase. I found a scrap of aluminium and roughed it out square on the mill, i then went to the lathe, put it in the 4 jaw chuck and bored out the crank housing.
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I then went back to the mill and cut out the shoulders milled it to finish size and then went about drilling the conrod clearance hole on top.
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The plans call for a 5/8" hole and as luck would have it i found a 5/8" end mill floating about the workshop.

This is the finshed article minus the screw holes etc.

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[Herbiev]

Off to a great start.

 

[Petit]

Thankyou Herbiev, im excited about this engine, after this i may move on to something like an owen mate, who knows?

 

[Petit]

The next part to be made was the crankcase front bearing. I could either make this part out of aluminium round bar and machine the flats square or use square bar and machine the rounds in a 4 jaw. I decided to make it from round bar, use the 3 jaw chuck and turn it to size and machine the flats on the mill. This seemed like a more logical approach but there are many ways to skin a cat as they say.

So firstly i clocked it up in the 3 jaw and turned down the smallest diameter leaving enough meat to produce the radius in the corner where the front bearing meets the mounting face.

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I then ground up a tool to cut the required radius.

After that i then flipped the part around and began turning the otherside.

This was the critical side, as this diameter sits tightly inside the crankcase bore and locates and holds the front bearing square to the case. Therefore i decided to drill the thru hole for the crankshaft from this side rather than the otherside. If i drill it from the otherside there would be a chance that the hole would not be square to the shoulder that locates inside the case, therefore the crankshaft would not run true.

Once this diameter was done i drilled n reamed the crankshaft bore with a 6mm reamer, the plans being imperial call for a 1/4" reamer but i never had one of those, so as long as i make the crankshaft to suit it shouldnt matter.

Once that was done i took the part to the mill to machine the flats on the front mounting face. Sorry for the lack of pictures at this stage i was clearly having to much fun!

This was the finished article

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After that i clamped it to the crankcase and with an m3 tapping drill drilled the fixing holes.

This is the finished item with temporary m3 capheads, i will get some nice shiney slotted screws to finish it off.

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Next up will be the crankshaft, hopefully i will start that this weekend!

 

[werowance]

Petit, I attempted the BJ Cicada with failure (im a newb though)one thing that might help you to know is that the piston rod does not have clearance and will rub the side of the cylinder at the bottom if cut to drawing dimension. another builder found the same thing I did on another forum recently. his post was on model engine maker

that said, I have ideas about why I cant get mine to run, I just havnt gone back to it to try and fix it. I would very much like to see the reamed hole for the crank bearing or front housing cover you just built and also see just how tight of a fit you have with the crank and bearing when you finish your crank. I belive mine is a little to loose and allowing blow through instead of pushing fuel back up to the top of the piston.

that said, I will be following your build so I can learn where all I went wrong and try to re-do mine this winter.

yours is looking great so far.

 

[Petit]

Ok werowance thankyou for the tip ill look out for that, currently the front bearing is a real snug fit in to the crank case, ill hopefully do the crank this weekend and ill post on here. This is the first diesel engine ive done so bit of a learning for me aswell. But we'll see! Would it not be the fit between the piston and barrel thats creating the blow through as you call it. The clearance in the crank and front bearing shouldnt affect it should it? I may be wrong though?
Good luck with your one, did you have a build thread?
Cheers
Joe

 

[werowance]

Well the crank case is pressurized as well it pushes the fuel down around the crank and then back up that 1/4 inch port you mill in the inside of the cylinder. I feel like one of my problems is slight blow by between the crank bearing support or "snout" as I was calling it. My reamer left some swirls in the inside. Along with many other bad cuts I made. By the time I put it on the shelf though I had the cylindar construction down pat after several remakes on it.

I was able to get barely a pop and a little smoke with manual priming the cylindar but again I had so man mistakes it was pretty Imbarrasing. But I did learn a lot from everybody here

I'll post my build and that other persons build about the piston rod fit which I first thought I had just miscut but after a few remakes I figured out that it was correct and the drawings were wrong I didn't put that in my build log though. There were some other minor wrong sizes in the drawings. Or at least one other on threads I believe which is in my build log but it's been about a year now so I don't remember.

Anyway I'll post those other links for u in a bit

Good luck and please show us close up pics of the fits cause I really want to try mine again. From the looks of things you are much more talented than I am. Nice cuts

 

[werowance]

had to switch to laptop to get the links.

here is my miserable attempt at the build
http://www.homemodelenginemachinist.com/showthread.php?t=23533

and her is another build on another site which had the same problem on the rod, I tried his approach first, but the last attempt I just filed down the rod a little and it barely cleared. but he go his running, I did not.

his build has better information than mine.
http://www.modelenginemaker.com/index.php/topic,4868.0.html
most pictures on this site wont load unless you are a member and logged in.

I wish you success and hope to learn from your build.

Bryan

 

[Petit]

Thanks Bryan ill have a look through them soon, i also see wat you mean about the blow through the front bearing now, i forgot about the side port. I havn't looked that far into this engine yet, but once i have made all the componants and piece it together ill start to get my head around it.

I took some photos of the bore the best i could hopefully you get an idea.

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[10K Pete]

Although I've never made a little aero engine, I have worn out a few when
I was a kid.

What I found was that:

1) The crank case must be sealed.
2) This requires that the moving parts, piston and crank shaft bearing,
be very, very, closely fit or...
3) Compression on both ends of the piston is lost and when there is
enough wear there's no starting them. Into the bin.

Looks good!

Pete

 

[Petit]

Thanks Pete this gives me a better understanding of these engines. Ive never made one nor even played with one. The plans don't actually list any tolerances, i was gona make the mating parts as tight as i could get away with but now i am going to take abit more care, especially between the crankshaft and front bearing.

Joe

 

[10K Pete]

Petit, you're welcome! My take on it is that the internal volumes on these
little engines is so small, and the required compression ratios so high,
that any leakage is a killer. And the speed they run.....!!!! It seems to be
a ratio thing; leak rate vs. volume vs. time. ???

The biggest engine I had was a .35 cu. in. and it ran for two or three years.
But most of them were .049 cu. in. and I'd go thru a couple a year.

Good luck,
Pete

 

[Petit]

Thanks for the advice Pete, i will definately bare that in mind.

 

[Petit]

Ok crankshaft was turned up lastnite, pretty pleased with it, still require pressing in the crank pin and putting the m5 thread on the end which i will hopefully do tonight. I work in metric so changed the thread from 10-32unf to m5, closest equivalent.

Spent a while dressing up the shaft to get the best fit i could, used 1200grit wet n dry to essentially hone it. Really lovely fit on the front bearing now, and with abit of light oil the shafts spins very freely. I tried sealing my mouth over the top port and pressurizing the crankcase to check for leak rates. I was very impressed to find that it sealed really well, very very small leak, felt like my head was gona explode blowing into it, so hopefully that should be sufficient enough, i imagine the fuel that is used is thicker than Plus Gas so should seal even better.
I did notice that when pressurizing the case the shaft thrust bearing is forced up against the inside face of the front bearing, as if it is being blown outve the front. I assume that as the bottom end is under compression the small thrust bearing will be forced against the inner face and would act as a mechanical shaft seal. Gona spend sum time polishing up the inner face to help it seal even better. Its one of those things which i dont know if its good untill i try run the engine. Anyway heres some pics.

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[Petit]

Crank pin and m5 thread added on sunday night. Pin was drilled n pressed into the cam with abit of loctite retaining compound, used 4mm tool steel for the pin. Crank shaft is now complete.

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[Billitmotors]

G'day Petit
Your build so far looks good.
Your crankshaft fit sounds fine, you need a small bit of play for lubrication.
When you get to your piston and Contrapiston to cylinder liner fit is when you need to get a good fit.
Rob.

 

[Petit]

Cheers Rob, yeah ive no idea how im going to acheive the fit between the piston and barrel yet, did contemplate using a viton o-ring but i think im going to give the original method a go first. Do u have any recommendations for honing the bore? I guess i may need to make a tool up for it?
Cheers
Joe

 

[Billitmotors]

G’day Werowance
The viton Oring idea is a dud. if nothing else as it goes past the ports they will eat your Orings
Laps are very easy things to make. Just get a piece of brass that is bigger than the final size required and machine it down till it is .001” to .002”smaller than the bore of your cylinder, your cylinder is approximately 1.6” long so make the machined length of the brass 2” long plus your chucking length.
Once you have machined the parallel 2” length centre drill using a No 2 or No3 centre drill. then drill with a 5.1 drill or 13/64” drill around 1.5” deep. Then using a ¼” BSW or 1/4” UNC TAPER tap, only let the tap enter for 16mm or 5/8” of an inch. Next get your hacksaw and cut down the axis of the lap for about 1". Run your tap in again to the same depth, remove it and using a fine file remove the burrs from the outside. Then screw in a 1/4" allen headed cap screw until it just starts nipping up.
You can either use diamond past or aluminium oxide lapping paste, I prefer the diamond paste which you can buy cheaply on Ebay.
To load the diamond paste onto the lap put a small amount (it goes a long way) on a flat piece of steel preferably high speed steel and while pressing the lap hard against the flat steel roll the lap over the paste.
Cover your lathe bed with plastic and put the lap back in the chuck leaving a small amount of the chucking piece protruding from the chuck jaws or put a large plastic washer on the lap adjacent to the jaws so that the cylinder can't touch it without marking the it.
Set your lathe to run slowly and slide the cylinder, head first onto the lap, use kerosene as your lubricant and turn the lathe on. It is always worth making a shroud that the cylinder is attached to so it protects your hands. Grasp the shrouded cylinder and slide it back and forth along the lap. Your aim is to get a fine even finish cross hatched surface finish over the entire length of the bore. You will need to keep incrementally tightening the screw as the lap wears and the bore size increases and becomes round and straight.
When you first start use coarser grit paste and once the bore gets an even matt finish over the entire length go to a finer grit. It is worth having a second lap prepared to use with the finer grit. Once you are happy with the finish of the bore wash and scrub it clean of any grit before you try and fit your piston and contrapiston. I purchased a small cheap ultrasonic cleaner which does a great job of final cleaning all the parts.
When you make your contrapiston use the DCO method which you can find on Ron Churnich's Model engine news web site which is invaluable reading if your making engines. The problem with this site is I end up spending more time reading than building, it really works well. Just go to the finder section and type in DCO method.
I hope that this helps.
Rob.

 

[werowance]

I agree, I made several cylindars and pistons when I was making mine, albeit mine did not run, I was only able to achieve high good compression after doing the brass lap method Bilitmotors is suggesting, I was amazed at how well it worked and how easy it was to make, drill, tap with taper through tap, to the bad saw and make a slot down it, when you put the screw in because the threads are tapered, it causes the slot to expand, the diamond compound is cheap on ebay and a little went a very long way. (sorry for pretty much repeating your post Billitmotors but I agree completely, you posted the same in my build and results were great I was just to lazy and stuborn to try it your way to begin with)

after using this method, it was the only cylinder make that wasn't tapered at the top and bottom, I had good tight fit all the way

then on the contra piston, another member posted in my build log about cutting it at a taper, 1 deg or less, and cutting the back side of the piston wall thin so they will compress in as the piston is shoved in the cylinder, worked good on mine. and that was after multiple tries.

after several attempts, those 3 things - piston, cylinder and contra piston are about the only things that were in reall good almost perfect for me tolerances. all the other ways I tried resulted in crappy fits and finishes.

hope that helps.