Homebrew boxer twin prototype

[Lakc]

I fired him off an e-mail looking for some dimensions, so I can finalize the drawings and get back to cutting while waiting for them to arrive. Thanks again Steve! :bow:

 

[Lakc]

Head work continued​

Been busy with the proverbial "other things" that keep coming up. The recent snow shut down most of Detroit, I got to work from home, with high hopes of playing hookey a little to get something done. Of course it was one the busiest days I have ever had. Have been fighting off a bit of a cold as well, not suprising since we have barely had 5 days with the temperature above freezing since well before Christmas. Getting frustrated by the lack of progress, I forced myself to complete one series of operations tonight.

I have a half completed head I want to fin, but a few operations are standing in its way. One, I wasnt looking forward too, but finished tonight, was drilling and counterboring the head bolt holes. The holes are on a 1 3/8 bolt circle, one on the vertical CL, two on either side at 45 degrees, and two below at 60 degrees. I started from the blind side of the cylinder counterbore, the top of the head, and did all operations measuring from the handwheels. Maybe next Christmas I will get that DRO. :'( I first counterbored with a .25" center cutting endmill, followed by a center drill, and then some monotonous pecking away with a #27 drill. I didnt want the bit to wander and force the hole off center.

While the drilling came out good, it left some nasty breakthrough flashing peeled right up against the cylinder counterbore. Knowing I had a little surface chatter on the cylinder counterbore, I chucked up one of the stubs left over from the cylinder operation and spread a little 320 grit clover lapping compound, and lapped the head for a few seconds. I didnt get a full contact but the flashing is gone at least. I will check it against the actual cylinder later. Thats why we use head gaskets.

We are still stuck on the spark plugs, will have to call on them tomorrow if I get the chance, but it is taking shape, albeit slower then I had planned.

 

[Lakc]

Heads taking shape​

Well, its been a busy time here, unfortunatly not all time spent on the engine. As you may have guessed from the lack of updates disaster struck. Zigging when I should have zagged, and not paying attention to how deep to drill the intake and exhaust ports, I sent a 1/4" carbide endmill right through the valve seat.
So I went back at it in production mode this time. Making two at the same time, I was caught back up by last weekend. A few tweaks to the drawing allowed for an easier 30 degree port angle.

Then we drilled for 1/4-32 plugs, backdrilled from the other side 1/2".

Manifold attaching holes and rocker holes were next. Plenty of 4-40 tapping. One casualty, knew it was gonna happen right before I did it. Must make a mental note to switch to decaf coffee before tapping numerous small holes. Everything was done with the X-Y manual handwheels, but I laid the parts out conventionally for a double check.

Then came the fun part, finning the cylinders. I tried it dry, but was getting some AL buildup on the teeth, so I resorted to Astrocut 2000 from my oil can. This was undoubtedly the messiest operation I have ever done on the mill. Coolant spraying everywhere off the 2 1/2" x 1/16" side cutting slitting saw. It worked, beautifully in fact, with reasonable cutting speed despite the thinness of the cutter.

The point where I have to make a mop bucket and mop the shop floor seemed like a good stopping point. In fact thats next on the list of things to do, as there is coolant everywhere. Then I will need to give some thought as to how to remove the one broken tap, although its not entirely necessary. What I am left with, however, looks suprisingly a lot like the assembly drawing.

I have some plans for later today, but I think I will attempt to drill the barrels for the head bolts. Not too much left to do here, its really taking shape.

 

[stevehuckss396]

Sorry to here about the problems. Unfortunitly boo boos are all part of the deal. Heads look great.

 

[Lakc]

Thanks Steve. I did learn a lot on the first attempt, and it was real easy to retrace the steps to get caught back up.
The floor is now mopped up. The corner fins on the heads will take some sort of jig to machine, I will probably forgo them for now. The barrels are next up to drill and tap the head bolt holes, then we need cam followers, pushrods, rocker pivot pins, front cover and a prop drive. Lot of little stuff but were getting pretty close.

 

[stevehuckss396]

Most people dont realize it but 1/2 the work of building an engine is in the heads. Lots of little parts.

 

[metalmad]

Mate
Those heads look great!!
ohhhhhh I want a slitter toooooooooo
Pete

 

[Lakc]

Thanks for the comments guys, glad to see others enjoying the thread. I am having a ball watching this take shape.

Cylinder drilling and SECRET WEAPON​

I tend to think things through too much sometimes. Its nice when things go as planned, but having multiple contingency plans can drive you crazy :-[ But occasionally, those backup plans come in real handy.

First things first. We need a place for the head bolts to go on the cylinders. We pull out the old secret weapon and center inside the bore. I left the cylinders bolted to the case halves which simplified workholding and put the main offset direction along the good leadscrew. I have a new Rohm chuck with R8-6JT adaptor and its a pleasure to work with. My old Jacobs was a good chuck, but its runout was getting pretty bad, and it was only a 33JT-1/2" which isnt as sturdy, and has a nasty habit of falling out of the collet when loosened. New Jacobs chucks proudly proclaimed they were .004 runout, which seemed like a whole lot to me, and they wanted $91 for the R8-6JT adaptor. This Rohm seems better then the Jacobs was when it was new.

Once centered, we simply wound the one axis over to drill the one headbolt at the top of the cylinder. The centering tool is pretty tall so I used an extra long center drill to start the hole.

With the first headbolt drilled, I attached the head and used a transfer punch down the remaining 4 head bolt holes. These punch marks served as sanity checks in case I lost track of a dial turn somewhere. I still laid out the holes with the manual handwheels, and was happy the center punch marks and the handwheels agreed. The heads now had a place to go and it felt good!

The next secret weapon​

I wanted to follow modern full size practice with press in valve seats. One disappointing part is the chatter I had when cutting the seat area with a 90 degree countersink.

And here is where I had already overthought this one to death. If you have ever ground a full size valve seat, you know the seat grinder tool is quite a nice piece of kit. Hex ball driven full bearinged carrier for screw on grinding stones with a diamond dresser, and a selection of tapered pilots to drive into the valve guide. Obviously, a well thought out tool and perfect for the job, but not really scalable. With the guides ready to install and the seats all pressed in, it was time to try a mini version with as few compromises as possible. First stop, Home Depot, for a fresh fine Dremel grindstone, shank dia .1240.

Setting the cross slide over 45 degrees, I clamped a small dressing stone (Dremel circa 1981) in the toolholder and turned (ground, dressed, broke?) a rough edge on the backside of the grinding stone.

I have had this idea for a while, so over a year ago I was looking through my favorite toy catalog (Mcmaster) and found the cheapest diamond dressing bit they had, $7 today, used to dress a convex radius on stones. A quickie adaptor for my toolholder and a last second tightening of the cross slide gibs, I dressed a perfectly flat 45 degree angle on the bottom of the stone.

Now I am at the point where I goofed up when I went metric on the valve stems. I couldnt use the stone on the finish 3.5mm guides so I made one special guide with a .125 hole for the grinding stone stem. Using some Vactra for lube there was no discernable play between the guide and stone stem. The stone was inserted in the head and a dremel used to drive the stone at a relatively low speed (~2krpm).

You definately dont need to lay into it, you hold the stone off the seat, turn on the dremel and let it get up to speed, and just peck backwards 4-5 times letting the stone do the work. It was a lot of work to create a tool that did the job very quickly. If I wanted to dress some more stones at 30 and 60 degree angles, I could do a "3 angle valve job". All valve jobs have 3 angles, thats one of my pet peeves.
Did it work? Let me know what you think.

 

[stevehuckss396]

I use the boring bar for my seats. Micro100 has tiny bars that are razor sharp. You get an almost mirror finish in brass. Then I make a special tool to press them in so there will be no damage.


It's starting to look like something now. You must be getting a bit stoked.

 

[Lakc]

It's starting to look like something now. You must be getting a bit stoked.

Yes I am, but trying to keep my eye on the prize here, it has to make noise.

 

[Lakc]

Ring finishing​

The final sizing of the piston rings required a mandrel to hold the rings collapsed and shave the last .002 to make a perfect circle in the proper bore size. I turned a quick cast iron mandrel by cutting a stub on one side, reversing it and turning an outside diameter equal to the bore, and an inside diameter .005 in length shorter then the ring and a diameter equal to the rings inside diameter. A quick lid was constructed and turned down to just under bore size. The rings were clamped up one at a time, using a Sherline 4 jaw to hold tension, and slowly brought to a diameter that kept the ring gap closed when inserted into the bore. I reused the jig to make the rocker arm stands to file the gap, and checked it with a measuring microscope.

With no headgasket and unlapped valves it still had great compression, and rather low drag.

Progress is progress​

Well, in the effort to get something done we have been jumping all around doing a lot of little bits. Tonight I worked on bearing clearances a bit and made some quick and dirty cam followers. I had planned on using titanium actually, to save on the moving mass and suprisingly affordable in smaller sizes. However it was simpler to make some out of brass I had in stock, the trick parts can wait until I know it wont blow itself to bits when it starts up. The goal here is to make noise, so even if it does self destruct I will consider it a success.

Simplified design, I used a radius cutter to narrow the contact patch, which effectively lowers the duration and overlap of the cam. Both can be increased later with a flat or mushroom style tappet. Then a 1/8 ball mill makes a cup in the other end

Lots more little stuff to do, but it feels good the list is getting smaller.

 

[Lakc]

Odds and ends​

Always busy here, but not often on fun things. I am getting excited to be nearing the end here.

For starters we needed a gear cover. I made a drawing but really only for cutting the stock to length. Its a simple 1/4" plate of anodized 6061 with a 3/8 hole for the crankshaft, a counterbore for the front crank X-ring, and a counterbore inside for the cam gear attching hardware. Two holes for screws were put in the cover, drilled and tapped the block, and the block casting outline was scribed on the backside once the cover was secure. This was then taken over to the bandsaw and roughed out, finished with the small disc sander and buffing wheel. The painters tape was there to protect the anodized surface.

Next, we changed tack slightly by making some shims for the cylinder heads, using a transfer punch, and a hand punch. These were used to take the space of head gaskets while I worked up the proper dimensions for valve clearance. No spark plugs yet so I used some 4 cycle glow plugs, were close enough to running that the first pops will hopefully be on them. I am running out of the patience I mentioned when I started this thread.

Back to the basic block, it was stripped bare and a third cross bolt was added to each side below the cam centerline. They are not symmetric due to one crank oiling hole but were placed on center of the meat of the block halves for some good clamping pressure. Two 4-40 screws were added to the top lip of the block for additional holding pressure. A hole was drilled and tapped into the bottom of the block for an oil return outlet.

Rounding out the block updates, I drilled and tapped 4 #8 screw holes into the back for mounting purposes.

Next everything was cleaned and put back together like it was going to run. This pic shows the extremely complicated way I manufactured the pads for the wrist pins. A fair amount of drag with piston rings installed but felt good enough to motor on the lathe for some break in, and break in it did, quite a bit of very fine metal particles came out of the oil return port, mostly ferrous in nature. Even without head gaskets, the intake ports sucked and the exhaust ports blew, leading to a very happy home model engine machinist, if I can call myself that yet. ;D

Now I was at the point where I could generate some ideas for intake manifolds. A prop was procured and a prop drive washer was made, but isnt present in these pictures. Here is how she sits now.

 

[metalmad]

Its a Beast !!
looking fantastic
Pete

 

[Artie]

leading to a very happy home model engine machinist, if I can call myself that yet. ;D

You most certainly CAN! As Pete says, its a Beast mate! Been closely scrutinising your progress and enjoying every step of the way.... :bow:

 

[nfk]

WOW!
It looks amazing!
I cant wait to hear it!

 

[Lakc]

Thanks for the comments guys. If I fired it up right now it would probably have a bad rod knock, at it looks like I tweaked one connecting rod big end slightly in the vise. There are still a bunch of odd and ends to handle, and I had plans of doing much of it this morning, but I wake up and the power is out. My next project should be some type of steam generator, or at least a stem powered coffee grinder so I can have a cup of coffee. No idea on how long its going to take to restore power.

I did get the prop drive done, as well as the intake tube adaptors. Big thanks to Marv Klotz for his ogive program to make the prop nut. I leave you with a tiny teaser, hopefully before this laptop battery dies on me.

 

[RManley]

I have been following this build from the start and have to say its looking really, really good. I have a soft spot for boxer twins as that is what my motorcycle has, in fact its what the Douglas motorcycle firm specialised in. Their engines got used for all sorts and your last photograph remineded me of some photos that I saw on the Douglas MCC forum.

(taken from http://www.douglasmotorcycles.net/index.php?topic=1849.0)

Keep up the good work - I can't wait to hear it start.

Rob :bow:

 

[Lakc]

Thanks Rob. Those pics are one of my great fears, starting on mid size projects and combining with the sport pilot rules. ;D It would be great fun, right up until the divorce, or life insurance payment for enough coverage to allow me to stay married.

 

[stevehuckss396]

I did get the prop drive done, as well as the intake tube adaptors.

I had no idea that it was going to be an aero engine!! Very nice job on the prop drive. Love the long nosed prop nut!

 

[Lakc]

I had no idea that it was going to be an aero engine!!

Not necessarily, but its the easiest way to start out imho. No need for a complicated starter system, and the formulas for determining horsepower via rpm and propeller combinations have already been worked out. Keeping a weight budget in the back of your mind sorta forces you think things through a bit more as well. I have been doing R/C stuff for many years, the usages for any small powerplant are only limited by your imagination.

Very nice job on the prop drive. Love the long nosed prop nut!

Thanks, but the credit goes to Marv Klotz, it would have took me a month of Sundays to figgure out how to step cut it like that.