# Kerzel's V2 CO2 engine



## kvom (Feb 28, 2009)

After browsing a bit deciding which should be my second model, I found this one. I decided to build it double scale until I found a 2.5x2.5x3 block of aluminum in the school scrap bin. So not it will be *triple scale.* 8)

The block, which will become the crankcase, had been flycut on 5 sides. One side had some "oops cuts, so that side will be the one where the flywheel will live.







Since there is extra material in the Z direction I center drilled the crank location 1/2" higher than the plan would indicate. So the engine will have a thicker base, allowing it to sit level and clearing the flywheel. Once I had a hole to locate with, it was on to the lathe to mount the 4-jaw.

I am now a member of the Maryak fan club having removed large amount of swarf from a block of Al:






I don't trust the flatness of the chuck face, so the bearing was left slightly oversize. I'll drill the hole for the crankshaft on the mill since the opposite side is flycut flat.

I had some steel rod that was a suitable size for the pistons, so I decided to attach these next. They will be .75" x .75". I cut one a couple of thousands too small and the other a couple too large, but since the cylinders will be bored and lapped they can be made to fit.

After turning the diameter, I drilled them .5" deep with a 3/8" bit. Then parted off slightly long:






Finished them at the mill. First I milled to length, then using a 3/8" roughing mill I made the bottom square at .54" deep and then elongated the holes to give clearance for the connecting rod. Finally I drilled and reamed the holes for the wrist pins.






I didn't drill holes for the "valve" pin as I'm not sure what size steel ball I will find for the valve. It will probably be 1/8" drill rod.


----------



## Philjoe5 (Feb 28, 2009)

Nice work. Thanks for the pix and documentation. This engine looks interesting. Do you have a photo of a completed one?

Cheers,
Phil


----------



## kvom (Feb 28, 2009)

http://www.floridaame.org/GalleryPages/g1Non0132.htm


----------



## chuck foster (Feb 28, 2009)

looking good Thm: and thanks for the photo documentation 

chuck


----------



## Philjoe5 (Feb 28, 2009)

Thanks for the link. Here's to your success in this build

Cheers,


Phil


----------



## stevehuckss396 (Mar 1, 2009)

The Co2 powered V8 from last month is based on Davids V1, single cylinder. David is a good designer and generous with his knowlage.

If you have not seen his Co2 powered 9 cylinder, it is worth a peek. It won first place at NAMES last year.


http://www.floridaame.org/GalleryPages/g1Non0218.htm


----------



## kvom (Mar 1, 2009)

I had an hour or so of shop time befor lunch and made a bit more progress. First, I drilled the hole for the crankshaft. It's deep enough (1") so that then the crankcase is bored out it will be through. The shaft is 3/16" steel, but since it will ride on bushings I just used a 3/16 drillbit.






Next I started on the crank. Turned some aluminum rod down to 1-1/8" diameter by 3". Then drilled hole for the crankshaft 11/64 and 4" deep. Then parted off.






On to the mill to ream the crankshaft hole and drill/ream the hole for the crank pin.






Finally cut the shaft and pin and pressed them into the holes. The shaft is a slip fit and will need some loctite. The pin was a tight fit and needed the arbor press to go in.


----------



## Philjoe5 (Mar 1, 2009)

Good work kvom. Thanks for the progress report,

Cheers,
Phil


----------



## chuck foster (Mar 1, 2009)

looking good.............the way you are going it should be running by next weekend :bow:

chuck


----------



## kvom (Mar 1, 2009)

Had another short session in the shop this afternoon. I made the two bushings out of some 1/2" brass rod. Drilled and reamed to 3/16, then lapped with some emery cloth and scotchbrite until they fit over the crankshaft.

Then I cut two discs for the cylinder heads out of some 2" aluminum rod. I turned a portion down to 1.5" and then parted them off. On the first one the tool bound up about halfway in, and I finished the cut with a hacksaw. For the other I made a double width cut with the parting tool until there was only a sliver left, then cut with the hacksaw. I will be glad when I get the bandsaw working. Then I faced both discs flat to length on the mill.

Tomorrow will be a learning experience, as I will use the boltcircle function of the mill DRO to locate the holes for the heads. Kerzel drilled with the heads held in a chuck on the rotary table, equipment I don't have.

I will use 5-40 screws for the head as I bought a box full from Enco.


----------



## kvom (Mar 2, 2009)

For some reason the DRO's bolt circle routine doesn't match the manual (or else isn't present). In any case it was easy to caculate the coords of the 6 holes for the cylinder heads. Then it was crank the table around for center drilling, drilling, and countersinking 12 holes.






Then I found a piece of 3/8" round steel rod in the bin that was just long enough to make the two connecting rods. Took longer than I expected to do the turning on the lathe. Later in the evening I finished them on the mill. The tricky part was finding just the right combination of parallels to allow them to chuck in the vidr for milling the flats and drilling the holes.

On the final hole the steel apparently work hardened as the drill wouldn't cut the last little bit. I had to turn it over and drill from the other size, making the hole slightly out of round. In any case it won't be visible in the end.






In retrospect using 1/2" al rod would have been easier all around.


----------



## Philjoe5 (Mar 2, 2009)

Looking good Kvom. We all keep a folder labeled "Retrospect". When we do the next project that is where we find many of the instructions ;D

Cheers,
Phil


----------



## kvom (Mar 3, 2009)

I went to my Tuesday machining class tonight and never touched the mill or lathe. Instead I accumulated/borrowed stuff I need to make progress on the engine:

1) Set of 30-60-90 and 45-45-90 angle plates plus some .5" steel plate to make a set of my own. My plan is to mill these tomorrow and use the school surface grinder on the edges on Thursday.

2) Some pieces of 1.5x1.5" aluminum bar to turn the cylinders

3) A boring bar


----------



## kvom (Mar 4, 2009)

I found a nice heavy piece of 12L14 round steel 2.5" in diameter in the school scrap bin, so that becomes the flywheel. Since multiplying dimensions by 3 increases volume by 8 times, this will be approximately 3 times the weight of the flywheel on the original, even if it's smaller than it would be with a straight scale up.

Since my prior engine's "bling" spoked wheel didn't merit nomination for POTM ;D, I decided to go with the classic 6-hole design. Beats 8 hours cranking on the old rotab cutting A2 steel.






I borrowed the set of angle plates from school and used them to make my own copies from some "mystery" steel plate. Enco wants $22 for that set, so it was worth the 30 minutes or so it took to machine them. I will try to surface grind the edges at school, but even as they are they are reasonably accurate.


----------



## kvom (Mar 7, 2009)

I have been trying to make a cylinder, and screwed up the first two tries using 1.5" square aluminum bar. I since discovered that my mill head was out of tram, thanks to a defective cheapo DTI. I retrammed with a better quality DI and seem to be in better shape.

Not having another piece of 1.5x1.5, I decided to use a piece of 2" round stock. Got the profile machined and went to try the new boring bar setup after drilling through with a 41/64" drill. It was a tight fit, but did manage to bore it one of the pistons (a couple of thousand undersized still).






I had purposely machined a 1" round on the end to enable me to chuck the piece in a 5C collet. So with it chucked in the square block I machined the mounting flange (which will now be a rectangle with 2 1.5" sides. Still plenty of room for the mounting screws in the corners. 






Still in the collet block, drilled and tapped the holes for attaching the head:






What do you know, it fits!






Now I transferred it to the hex collet block to drill the 6 exhaust holes






Next time out I will part off and finish milling the bottom flange, plus drill the corner holes.  I hope I can make another one that looks the same.


----------



## chuck foster (Mar 7, 2009)

looking good Thm: 8)

the part i like about your post is "What do you know, it fits!" you make it sound like you had some doubt that it wouldn't fit :big:

keep up the great work

chuck


----------



## ksouers (Mar 7, 2009)

Ain't it a great feeling spending time on parts that are supposed to match, and they do?  ;D

Great job!


Kevin


----------



## kvom (Mar 10, 2009)

I managed to finish boring the crankcase. I started it on the lathe using the Cedge-design boring bar holder, but I found it too difficult to get everything lined up perfectly straight with the 4-jaw chuck. So I bored it to 1" and then mounted it on the mill to finish out to 1.5". With the quild feed at the minimum speed the finish of the bore is very good (although a precision surface isn't needed here).






I also parted off cylinder#1 and turned the bottom surface. It still needs the mounting holes and to chamfer the inner bore at the bottom to clear the piston rod.


----------



## Maryak (Mar 10, 2009)

aermotor8  said:
			
		

> looking good Thm: 8)
> chuck



Me too

Best Regards
Bob


----------



## cfellows (Mar 11, 2009)

Really looking good! Can't wait to see the finished engines (and a video?)!

Chuck


----------



## kvom (Mar 20, 2009)

My new boring bar came from Enco today, so I was able to make some progress, boring the holes in the crankcase for the cylinders:







In setting it up in the vise I found that one of the faces was off by a degree or so. I wonder if it slipped when milling the angle?? It's not too critical and probably not visible without close inspection, but irritating to me.

Here's the crankcase with both holes bored:






And with a preliminary test fit to get an idea of how it will look:


----------



## BMyers (Mar 20, 2009)

Very nice, It always amazes me the small scale some of you work in.


----------



## kvom (Mar 23, 2009)

After overboring the second cylinder I decided to make a new piston to fit. I had a 2" piece of 1" dia brass round that I turned down to the bore diameter, parted off, and machined much as I did the other steel piston.

After dinner I made a couple of wrist pins from 3/16" drill rod and pressed them through the piston and rods. A test fit onto the crank pin looks OK. I still need to clearance the piston rod from the bottom of the cylinder as it binds when the crank is at the top.

Yesterday I glued the crankshaft bushings into the block with locktite, so the assembly is starting to come together. I did discover that I will need a separate base as the weight of the steel flywheel is enough to tip the rest.

I still need to find a couple of steel balls for the valves. I will likely need 3/8" balls. There's a seller on eBay that has a wide variety of balls in fairly small quantities.


----------



## kvom (Mar 25, 2009)

I found some steel balls at the local Ace harware store. Drilled and chamfered the valve seat and put the pieces together for a poser shot. I need to drill the air inlets on the cylinder heads and the pins on the pistons, and it will be ready for a test.


----------



## Maryak (Mar 26, 2009)

kvom,

Looking very good :bow:

Best Regards
Bob


----------



## kvom (Mar 28, 2009)

Yesterday I bored/drilled one of the cylinder heads. For the air inlet I will thread it 1/4-20 and fabricate a screw-in attachment so that the air feed can be removed from the head. I also threaded the hole for the pin in the top of the piston 5-40. To determine the length of the pin needed I used a 5-40 SHCS and shortened it until the ball ceased to hit the top of the head. So I will cut and thread a piece of 1/8" drill rod the same length as the screw.

I also got the second piston to have a good fit with the cylinder by lapping with toothpaste. At first it was too tight to turn the crankshaft by hand. So I clamped the crankcase in the vise and clamped the crankshaft with a 5C collet in a collet block. Then I was able to turn it by hand holding the collet block. "Booty fab!" After a few minutes of this with the toothpaste it was turning pretty freely. I took off the collet and ran it for about 30 seconds with the electric drill. It now turns easily by hand.

A few more small parts and I can try to run it on one cylinder.


----------



## itowbig (Mar 28, 2009)

i started to make this engine but it made me mad cause it was so small . put it in a box until i could get the patience to finish it. I'm watching this build with intrest so maybe your build will reinspire me. great job. thank you for showing your build


----------



## kvom (Mar 28, 2009)

I cobbled together everything needed to mount one of the cylinders. The air inlet I made is too small to clamp securely with the plastic feed tube, so that will need to be redone.

I applied compressed air anyway and found that it became very hard to turn the flywheel, indicating that the cylinder bore was pressurized. Since the cross sectional area is .44 square inches, 60 PSI air means a resistance of 26.5 pounnds. Of course this is good news and bad news. The good news is that the piston/cylinder bore is relatively air tight. The bad news is that I should not get pressurized air into the cylinder bore until the ball valve lifts, so I have a leak between the cylinder head and the bore. Either the ball is not seated properly or the valve seat is not seated closely enough in the cylinder.

So the next step is to make a more secure inlet tube and also to lap the valve seat both to the cylinder and to the ball.


----------



## stevehuckss396 (Mar 28, 2009)

When I made my Co2 engine, I made a test fixture for the ball seats. It's a simple mock up of the block and head to apply air and listen. The ball can be poked off the seat with a piece of rod from the bottom.

You might give it a try.

Also remember that with a tight piston, when moving toward top dead center, the piston will compress air until the ball is lifted. This compression will need to be overcome with higher air pressure. My engine needed 65lbs to sustain a run.


----------



## kvom (Mar 30, 2009)

Made some more "progress" this afternoon. First I needed to fab an inlet tube that would sustain higher pressure without blowing off the tube. From a piece of 1/2" brass rod I turned one end down and threaded it 1/4-20 to match the threaded hole in the head. The other end I turned to .325 and used the compound to cut three tapered barbs. This turns out to work well with the hose clamp. I still have some leakage around the threads as they are not tapered, but that's OK for now.

I lapped the valve seat a bit with toothpaste and hooked it all up, but there is still high pressure air bleeding into the cylinder. I'm not sure if it's around the ball or the perimeter of the seat or both. If I can't get it to seal I think I will bore out the top of the cylinder to make a wider rim for the seat, and make a new seat to fit.

I took the cylinder off the crankcase and will use it in a manner similar to Steve's test rig, hoipefully. I also tok the crankshaft off and will cut a flat for the flywheel setscrew.


----------



## Maryak (Mar 30, 2009)

kvom,

Did you give the balls a light tap with a soft dolly and hammer? This helps to bed them properly to the seat.

Hope this helps.

Best Regards
Bob.


----------



## kvom (Mar 30, 2009)

Sounds like something to try, Bob. Thanks.

I made a number of tries with the cylinder+ head only. I put a bit of way oil in the bore, which had it easy to see where air was leaking around the ball. Tried lapping a few times, and then decided to try the other valve seat

I polished it with steel wool as well as some toothpaste lapping. Then I butoned it up, and seemed to have it air tight. So I put in the piston and screwed the cylinder onto the crankcase. I turn on the air and don't hear leaking from the cylinder. Tried to start it by turning the flywheel, but then I get loud air leak noise. Off with the air, then back on, and all is quiet.  So now I'm guessing that the ball is deformed or scratched and seals in one position but not others. Took a break.

Next time out in the shop I'll try it with another ball, and will try the tap-to-seat method as well.


----------



## kvom (Mar 31, 2009)

Still frustrated today. I tried Bob's idea of tapping the ball into the seat with a plastic hammer, but no go. The cylinder is air-tight when air is first applied, but once the ball lifts the first time it ceases to be, as if the ball doesn't reseat. I did notice when experimenting with just the cylinder and head, that when the cylinder is inverted and air is applied, the ball doesn't seat. Rather it spins around the inverted cone at a high rate. I think this is what might be happening.

One thought: in Kerzel's build he used a center drill to make the valve seat, meaning a 60-degree countersink. I used a 90-degree countersink since I needed a larger hole. I wonder if the angle is too shallow. If so, I should be able to make a seat with a steeper angle using a boring bar and the compound.

I decided to take a break and start the rebuild on my bandsaw until the frustration recedes.  :'(


----------



## kvom (Apr 2, 2009)

I did some calculations today preparatory to making a new valve seat. My conclusion is that the 3/8" ball is probably too big. If anyone cares to comment on these calculations please feel free.

The original version uses a 3/32" ball. Ignoring the difference due to the taper, the ball has an effective area of .007 square inches, and at 60 psi would be held by .414 pounds of force. My 3/8" ball would have an area 16 times greater and hence a force of 6.6 pounds. To maintain rotation, the flywheel would need sufficient angular momentum to deliver this kind of force.

I measured the motion of the piston as well. At the point where the piston closes the exhaust holes, the depth from the top of the cylinder is 1.144 inches. When the lift pin clears the bottom of the seat the depth is .556 inches. This gives a ratio of about 2, a bit less than Kerzel's figure of 2.5. This means that the cylinder bore would be pressurized at 28 psi, and hence the engine ought to run at 30 psi or so.

My conclusion is that I am going to cut the seat at 60 degrees to hopefully enable a better seal, and try smaller ball(s).


----------



## stevehuckss396 (Apr 2, 2009)

If you scaled up 2X then I would try a ball 2X and not 4X the size of the original. A #3 center drill is close to 2X the size of a #1. The lift on the ball is critical. .010 - .015 is the range.

If it were me, I would try the following first.

.1875 (3/16) ball
#3 center drill
.020 - .025 lift on the ball at TDC
Build the seat exactly as the plan at 2X including measuring the top of the ball to the bottom of the seat at .202 inches +- a few thou.


----------



## kvom (Apr 2, 2009)

I scaled up 3X.


----------



## stevehuckss396 (Apr 2, 2009)

kvom  said:
			
		

> I scaled up 3X.



Then you need a .281 ball. Maybe a .250 would work better or go up to a .3125


----------



## kvom (Apr 7, 2009)

My glasses broke this weekend and I'm not going to operate any machinery until the new ones are in and I can see what I'm doing.

I asked my school instructor about the best way to cut a 60-degree countersink in brass, and he says to run the lathe at the slowest speed possible. The 10ee will go really slow, so I will try that. I also borrowed a 60-degree countersink plus a #4 and #5 center drill. The #5 looks too big.  I'll see how it works out. I'll also get some smaller balls to try.


----------



## kvom (Apr 15, 2009)

I got my new glasses yesterday, as well as an assortment of ball sizes. I machined two new valve seats using the 60-degree countersink at 50 rpm, and the first test with a 5/16" ball showed no leaks in the seat. However, the first try with one cylinder failed to run, so I will be trying various combinations of ball size, lift, and pressure.


----------



## kvom (Apr 15, 2009)

I suspect I may be running into some physical limits here. At 40 psi and higher it takes considerable force to lift the ball against the gas pressure. and even when I can force it by turning the flywheel I do not get much in the way of downward force on the piston. In fact, it's not even enough to rotate the crankshaft a full turn.

I have tried several ball sizes and different lift amounts, but none are even close. ???

Perhaps I need more air volume entering the piston, in which case I might need a large hole in the valve seat and/or a larger chamber in the head.


----------



## stevehuckss396 (Apr 15, 2009)

How high is the ball being lifted off the seat? At one to one scale the ball is lifted .010. At 3X I think I would start with .025 and maybe decrease it some depending on if it seems to want to go. The fact that it seems to be kicking back and locking up would make me check the lift.


----------



## kvom (Apr 16, 2009)

I bought a height gauge recently on eBay. When it arrives I'll try to get a good measurement.


----------



## kvom (Apr 18, 2009)

I decided to use my smallest ball (3/16") to reduce the amount of force needed to lift the ball.. Since I needed to bore the other cylinder and make a new piston to fit, I did that today. I also made a new valve seat to fit the smaller ball. Testing with the head I get a good seal, so once I get the new piston lapped in I can try it. out. I will need to turn a smaller lift pin in order to leave room for the gas to enter the cylinder.


----------



## kvom (Apr 21, 2009)

I assembled the cylinder, head, valve seat, and small ball today. The assembly is airtight but still doesn't run. However, I haven't tweeked the lift yet. I did get my height gauge, but the top of the ball is below the level of the valve seat, so measuring the total lift is a challenge I haven't solved.

I was getting some binding between the piston rod and the crank pin, as my crankshaft bushings weren't absolutely straight. So I turned, drilled, and reamed a 1-piece bushing from some brass rod to get a tight press fit with the crankcase. That certainly loosened up the mechanism. It appears to me that any tightness anywhere will inhibit the engine from running.

The entire process is challenging, but frustrating as well.

Tomorrow I'm on an all day trip to help a friend pick up a Bridgeport mill he found in NC.


----------



## ksouers (Apr 21, 2009)

kvom  said:
			
		

> However, I haven't tweeked the lift yet. I did get my height gauge, but the top of the ball is below the level of the valve seat, so measuring the total lift is a challenge I haven't solved.



How bout a dial indicator?


----------



## kvom (Apr 28, 2009)

I am going to abandon his project for at least the time being, as I suspect the physics may be against me.

I did find a way to measure the lift and it was .045. With some filing on the pin I reduced it to .02, but no improvement. Even at 80 psi there does not seem to be enough force on the piston to complete a revolution. It might work with a much more massive flywheel and higher pressure still, but I have reached my frustration level for the moment.


----------



## vlmarshall (Apr 29, 2009)

Do you think that testing with CO2 instead of air would help? Perhaps CO2's continuous expansion from liquid to gas as it warms would help your engine get over the 'hump'.

Just a thought. Great build so far, I hate to see ya quit.  :-\


----------



## kvom (Apr 29, 2009)

Here are the issues as I see them:

1) The ball has to be small, otherwise the pressure acting on it will be too great for the pin to lift

2) If the ball is small, the the inlet hole is also small, limiting the input gas flow into the chamber.

3) The lift has to be small. If it's too high then the gas enters to early in the cycle and kicks the piston opposite the way it needs to go. But when it's low then issues 1 and 2 come into play.

The 3x scaling problems are these:

1) The chamber diameter is now 3**3 larger, or 27 times the volume of the original scale. That means 27x more gas needs to enter to result in the same pressure.

2) If I could scale up the ball and hole 3x then it would allow 8x the flow. But I would also have 8x the force acting on the ball.

3) The mass of the piston/crank assembly is also 27x the original, meaning the for a given pressure in the chamber I would have a smaller velocity.

The only "solution" that would seem to have a chance is to have an extremely heavy flywheel whose momentum could carry the cycle around, and the pressure would likely need to be quite high as well.

I have a pretty heavy round piece of steel that I could use to try it at some point, but the esthetics of the engine would be poor.


----------



## radfordc (May 4, 2009)

In the past I constructed a 2X version of Kerzel's Mini V1. It never has run well....I think I know why now.

Charlie


----------

