Homebrew boxer twin prototype

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Hello Lakc!

How do you plan to temper your rings? If you want you could use my oven. Bring them over in the fixture and we can cook them at 950 for an hour or so. Sure beats the old torch and brick trick.

 
Thanks for the offer Steve, I will very likely take you up on it.
I probably have enough materials to make a furnace, but thats a project for another day, unless a PLC suddenly drops in my lap.
 
Jeff, this looks an intersting build - nice work so far. Will definitely be watching.

Nick
 
Thanks Nick, glad to have you along.

I have a piston, and it is reasonably close to print, but it needs a design change. I am not happy with bisecting #60 drill holes with the oil ring groove, there is just not enough hole there. It doesnt look right in the engineering sense, like those subconscious "back of the envelope" calculations are saying noo way. I learned a long time ago to trust that instinct, so its back to the drawing board for now. Hopefully, we will get something together over the upcoming holiday.
 
Pistons

I am back at it, finally. The Thanksgiving holiday was filled with wallpaper removal and ressurecting a boarded up and plastered over laundry chute. The wife is happy, and I did the near impossible, loosing weight over the holiday, despite eating everything in sight.

I tweaked the drawing a little, adding .1" to the piston in various places above the wrist pin, and shrunk the connecting rod by .1". I also ordered a piece of A2 to make a ring groove cutter, and picked up a reduced shank 9/16 drill bit. Minor tooling additions, but they made a big difference.

I start with two pieces of 2024 about 1-3/4". It is a bit of a waste for a part just under 3/4" but there is no substitute for having a decent piece of stock to grip on, and a little clearance from the chuck jaws helps a lot too. The stock is squared up in the 3jaw with a dial indicator and gentle taps of a plastic hammer, then faced off to make a measuring datum and drilled .662 deep with a 9/16 drill.





Now the fun really begins. I move the drilled and faced blanks over to the 5C spindex, which has had a little attention paid to its lateral play since the last attempt. It was rather ,so it was greased up, and tightened up, best as I could. The wrist pin hole is drilled and reamed under power, .351" from the face. Then we move up to .478 and drill the 16 .0625" oil drain holes in 140 degree arcs between the wrist pins. I used a parabolic flute drill, and after bringing the drill bit to just spot itself, it was drilled under power from the quill. These holes just broke into the shoulder of the earlier 9/16 drill hole. This worked wonderfully, and the power downfeed probably saved me a drill bit or two because I couldnt get impatient. :)





Back at the lathe we do the same centering trick with the plastic mallet and dial indicator, helped a bit by keeping the written bar identification under the same #1 chuck jaw each time, we sucessfully recentered the part in the 3 jaw with under .001 runout. Then we turned a minimal amount of skin of the 1" bar to the .948 diameter.



The piece of A2 tool steel was earlier machined down to .037" width and hardened. I carefully aligned it to center and optically zero'ed it to the earlier faced off bottom of the piston. The carriage was moved so that the bottom side of the tool was bisecting the oil holes and the oil ring groove was cut .045 deep. It cut like butter and I couldnt have been happier. :) No further drama ensued as I stepped up another .070 to cut the compression ring groove .039 deep. This was a great relief as my earlier hand ground form tools did not leave the ring groove square and wandered around a bit. These grooves came out quite clean and square. Cleaning up the work from this side of the piston, we bored the bottom interior .23" to .886" id.







This piston has a 15 degree crown, and previously I attempted to part it off only to shatter a toolbit and give up, hacking it off semi flat. This time I centered the work with the 4 jaw and using the crosslide set to 15 degrees, I ran the lathe in reverse and trimmed the part from the backside. This left me with only one problem, that I could not measure the overall length of the part with the other side firmly in the chuck. I scribed a line .611" from the face where the crown starts, then I used a small measuring pocket microscope to determine how much to move the carriage. I can happily say that one part was only .002 too short, and the other .006. Close enough for that measurement in my book.







Now I have two happy pistons. :) Identical enough in every respect, I am pleased and quite relieved it is all over. I will likely take a ball mill to the inside later, when I set the rotary table up, but that falls under the "pretty" heading more so then a functional one.

As always, feel free to chime in if I am doing something the wrong or hard way, or especially if I am ignoring the obvious. I am self taught from a lot of reading, but not a lot of doing. I have learned a lot on this forum and others, so if you see a teaching moment, dive right in.

Next up? These pistons look a little naked, so I will probably make the jigs to heat treat and skim the rings. I likely wont do a write up on the wrist pins themselves, but its getting time to finalize the connecting rod drawings and they will likely be the next major pieces.


 
Ring treating fixture

Well, I am pleased as can be to still make progress, so here is a little update on where I am today.

First step was to split the rings. Start with a carbide scriber from McMaster Carr for <10$ to give a nice initial groove for the file to bite into. Then using the corner of the square file we make a couple passes and lay the groove made opposite an Enco scraper. Thumb pressure from the same hand holding the scraper easily parted the rings with no casualties.


This picture I couldnt resist titling Pile of Perfectly Parted Piston rings, try and say that 3 times fast. :)



A chunk of 1 3/8 cast iron was spotted on center in the lathe. Moving to the mill a 3/16 hole was reamed .477 inches from center. A piece of 3/16 cold rolled steel rod had its shoulder turned down to .164 inches to provide the proper gap for the rings during stress relieving.


Back in the lathe the center of the holder is drilled to tap 1/4-20 and turned down .905 diameter for a length .005 less then the entire stack of rings.



A cover is turned basically freehand with the only dimension critical being the depth, same .005 less then the stack of rings, and an F drill center hole for bolt clearance. The cover will hold the rings compressed flat for heat treating.





Things are looking up, the list of remaining items is getting smaller, and while free time is never much in excess, the holidays should provide enough to make some serious headway. :) It would be nice to get the connecting rods done next to complete the reciprocating assembly.
 
Nice work on the pistons and rings Jeff. Must have a fairly high compression this engine does it?

Your work on the rings will make a nice tutorial for anybody else wanting to make cast iron piston rings.

:bow:

Nick
 
NickG said:
Nice work on the pistons and rings Jeff. Must have a fairly high compression this engine does it?

I have not actually settled on a compression ratio yet, but 8:1 may be a stretch for a model and that was kind of a stretch goal.
Your work on the rings will make a nice tutorial for anybody else wanting to make cast iron piston rings.
Nick

Thanks Nick! I do not remember ever seeing it done in tutorial form before. I am sure its probably not the first, but rare enough I wanted to include it.
 
Jeff,

I only guessed it may be because of the domed piston crowns but I don't know what the combustion chamer is like!

I'll certainly be looking this back up when I do them.

Cheers

Nick
 
I am glad you brought that up Nick, I ran the compression ratio calculations, and it was a measly 4.9:1! So I spent some time and wrote up a spreadsheet, added back the .1 inch I took off the connecting rod when I stretched the piston, and got 8.3:1 compression. With a .950 bore and .694 stroke making a bit of an oversquare engine, it was really sensitive to the tdc position.
 
Connecting rods n stuff

Well, today we finish off the recriprocating parts of the engine. evil :big:

First we grab a bar of .250x.750 2024 aluminum and skinny it up to .690. We part off the two rods 1.58" length and two caps of only .220 length. I dont have a stop for my vise, so I used a 1-2-3 block across the end and drill 4-40 clearance holes in the caps and tap threads in the rods. Bolt the pieces together and it comes out reasonably square. There is going to be a bit of filing going on regardless so I am not too worried about a perfect fit at this time. These are simple rods, compact, and probably a bit on the bleeding edge thin towards the caps. They barely miss the opposite cylinder liner at bdc, so I cant make them any larger without adding some relief. They should be strong enough, if not, its only a couple inches of bar stock. :)

For contouring the rods I broke out an old friend. I made this jig for another motor that had slightly larger rods and hoped to adapt it. Being slightly offsize it proved just slightly a pain in the @$$ to work with, and I deceided against using it. The other motor needed 6 rods, but I can get by without the jig for only two. I find the center of the rod and lock down that axis, using my edge finder to locate off the cap end to bore the big end of the rod and finish ream .344" Then I run a 1/8 ball end mill .100 deep towards the small end and bore and ream the little end .1875. Next I hang it off the side to come in with a 1/2 cutter and put the shoulder radius in, then flip it on its side and mill up the the radius leaving ~ .290" wide beam.

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Nothing too complicated there, pretty straightforward stuff. We took a variety of files to the rods to clean them up and skinny them up a little, as they invariably have clearance issues because I never seem to make the journals wide enough on the crankshaft. Next we break out another hotrod alloy steel for the wrist pins, 8620. Not much to show there I just drilled them hollow, polished it up with emory cloth and parted it off .850 long.
100_0429.jpg

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With a couple simple jobs under my belt I started to get the itch to try something fancy. Ill just let the pics do the talking for a change.

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These .015 hard brass bearings were hammerformed with a plastic mallet and the actual rod. Will brass work? I have an idea it wont, even with pressurized oiling. I plan on electroplating babbit on the surface to get the proper clearances. Now you see the reason for the custom .344 chucking reamer. Even if it doesnt work, I have seen silver used for bearings in this same manner, and what fun is building an engine if you dont have to take care of it every now and then. :)

I have reached a moment of truth, as they say, one of many such moments coming up. With suitable bearings to fit the rods to crank we spent a good hour filing spots here and there to make everything fit nicely. Then I spent a good half hour cleaning the engine for assembly. Lubed up and this is what we got!

 
I would probably forgo the rod bearings altogether. There are many model airplane engines using rod without bronze bushings in the big end. With pressure feed oil I think it would be OK without bearing inserts. I've been following from the beginning. It's an awesome build. Will you be flying it?

Greg
 
loving this mate.... something about conrods and pistons... looks fantastic..... :bow:

Im with dieselpilot.... dont fix it if it isnt broken....

Awaiting the next instalment...
 
For thin bearing shells such as you are trying to make the only thing I have ever heard of being used successfully is silver. You can purchase it in strip form from jewelery suppliers.
gbritnell
 
Thanks for the explanation Jeff, 8.3 sounds good, same as my old mini! Will it be hard to turn over? Should be ok I would guess.

More great looking work there. That jig looks handy.

Nick
 
I like your method of cutting the brass strips with the wood and slitting saw. I will have to try that one day.


IronHorse
 
Thanks for all the great comments guys!

Steve: Thanks, I still owe you a visit to bake some rings. I can only assume that your holiday schedule is as hectic as mine, and the fact they gave up salting our roads wont make it easier either. :mad: Ill ship you off an e-mail when I begin to see the light at the end of the tunnel.

Greg/Artie: If I keep the clearances tight enough so they dont hammer it may work, but straight AL on steel would have worked as well. I am overcomplicating things a bit here. None of these parts are so big/complicated/expensive that it would hurt to remake them.

George: I dont remember the issue, but at my first NAMES show, I bought my first issues of SIC from George himself. I think there was a boxxer engine in those books that used silver for bearing material, and I have been scouting out jeweler supplier's ever since.

Nick: If I do everything right I am counting on healthy thump. :)

IH: Thats something I did because I didnt want to stress/bend the metal via my usual method, the paper cutter. It left some nasty sharp rolled edges of kerf and I resorted to deburring it by holding it between two flat files, which worked rather well.

I am going to continue playing a bit with the recriprocating assembly, finalizing the oil flow, etc. Then its on to the cylinder heads!
 
Meanwhile, back at the ranch..
Subtitled, dotting the i's and crossing the t's​

The #2 rod is a little tighter then I would like to see, I suspect I didnt give the cutter enough "wiggle" at the final rod journal diameter and its a bit tight near the crankpin. All the fighting the #1 crankpin gave me its got plenty of clearance. It took a whole lot of file work to get it to fit in the first place, just some more of the fitting in of the reciprocating parts.

I deceided it was time to see if the oil pump works. This required grooving and drilling the main bearings and two cross drilled passages narrowly avoiding one case attaching screw just behind the timing gears. I fumpled around and found my 3/8 expanding arbor and turned the main bearings to final size. The marked up photo's show the front oil drilling. I got a bit smarter and just used a slitting saw to groove the case for the rear bearing oil flow. You can also see the rear oil seal, a 3/8x1/2 "X" ring that I will try out.
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I roughed out a pressure relief valve and a pair of nipples for the oil feed and return lines. Dug around and found some old fuel tubing and cut the top off of a McMaster pipette to use as an impromptu oil tank. Low and behold the darn thing worked!
100_0440.jpg



Along the way I also managed to make some nylon bushings to keep the wrist pins off the cylinder walls, and few other little jobs that were necessary but didnt deserve mention.

I have also begun revisiting the cylinder head design. Using solid modelling, I am redrawing it as it would be machined to help visualize the steps to making it. I have a decision to make regarding how to proceed with the valve seats. I origionally thought of trying the cage method, and followed the recent discussions with Brian's hit and miss and George's cutting tool with much interest.

My only problem with the cage method is my lack of experiance with it. Since I am drawing this from scratch, that leaves me in somewhat shaky territory. I am very familiar with full size, shrunken fit, valve seats, and I wonder if that technology could be duplicated in model size? I had already begun exploring ways to grind valve seats ala full scale motors.

Because the holiday season and resulting committments have so far prevented me from taking Steve up on his gracious offer of a ring bake, I did put a ridiculously low bid and won this:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=200552413213
I already had most of the remaining components to make an oven on hand, so next I will try to cobble up a functional heat treat furnace, not just for a ring bake, but to more properly process all this tool steel I have acquired. A seat cutter like George's design comes to mind immiediately, but a seat cutter without teeth would be a valve seat installing arbor.......
 

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