Building a twin cylinder inline i.c. engine

[Vixen]

Jason,

Brian's solid roller is a much better option than a tiny ball race, considering the repetitive shocks experienced by a rocker arm.

Mike

[Brian Rupnow]

The new carb body is finished. All the parts that bolt to it are going to soak overnight in a can of laquer thinners, and then get washed tomorrow with a strong solution of dish detergent and hot water and be scrubbed with an old toothbrush.

[Brian Rupnow]

Jason's work is art. My models will never look as good as his do. I want them to look "good enough" and to function but they will never be as flawless as the stuff Jason makes.---Brian

[Brian Rupnow]

Okay, today we have the new carburetor, which consists of a new main body and all of the old components that were from the carb I built ten years ago. everything fit just fine.

[Brian Rupnow]

I think that the next thing to be tackled will be the gas tank. I really like the octagon shaped gas tank with the glass ends that Andrew Whale of the U.K. built so I will make my gas tank the same. The model of the gas tank isn't finished yet, as I have to add a filler cap and a discharge pipe, but I will do that tomorrow. I have also switched the tank to be at the opposite end from the gearbox. This still leaves the back side of the engine clear for my ignition coil set up.

[Jasonb]

Regarding your Coil Brian, From using ATV coils to make buzz could you need to ground the metal bar that passes through the middle both when testing and in use. I was not using with points so may be different but the bar is what they mount the coil to the snowmobile with and therefore ground it to the structure.

[Brian Rupnow]

I was trying it with the coil mounts both grounded and not grounded. It didn't make any difference.---Brian

[Brian Rupnow]

Today  I built a gas tank. Started at 10:00 and it's 5:00 now. Damned expensive gas tank if I was paying somebody to make it for me.--And, it's not done yet. I saved $10 by starting with a piece of aluminum 2" square, and worked on it 3 hours until is was the shape you see.--$115 worth of work to avoid spending $10.--It has a 31/32" inside diameter, and I still have to counterbore the main tank for the sight glasses and o-rings that keep it from leaking at the ends. I still have to make a filler neck and cap for it, and still have to make and attach a discharge spout, and still have to make the part that mounts the tank to the engine. It will be a $300 gas tank by the time I'm finished.

[Brian Rupnow]

The gas tank mount is finished and the gas tank is in place. I still have to add a filler spout and a discharge spout to the tank itself, and I may machine a scallop into the side of the tank so it doesn't set too close to the cylinder beside it. I'm off now to my tooling supplier to buy a 5/8" fine thread tap.

[Brian Rupnow]

I just went over to my tool supplier and spent the Rupnow fortune on a pair of 5/8" fine thread taps, and the proper drill to use with them. I've just tapped the fuel filler hole and have a 5/8" fine thread bolt screwed in there right now. Have to do a bit of CAD work now to see where I am going with this.---Brian

[Brian Rupnow]

I think this is going to work out fine. I bought a 5/8" x 1" long hex bolt while I was out. It can be modified to match the drawing and screwed into the tank after coating the outer threads with J.B. Weld.

The actual plug which screws into it can be made from a piece of mild steel threaded with 1/2" fine thread on the outside.

[Jasonb]

Does it need the spout? As you are not using your usual cap could just cut the fine 1/2" thread straight into the tank and screw the plug into that.

[Brian Rupnow]

Jason--I could have made it the way you suggest, but I like a separate threaded bezel that is permanently fixed to the tank. Okay--Now we are going to get down to the part that everybody has been asking about---the crankshaft. I just got a price of $9 for a 9" length of 1 1/8" diameter 1144 stress proof steel from my local supplier and will pick it up later today. I've had lots of questions about the one piece crankshaft, so I will post about it as it develops.

[Brian Rupnow]

Okay kiddies--Let the fun begin. This is a piece of 1 1/8" diameter 1144 stress proof steel. My first job will be to cut it to  9.403"" length, then remove a slab from each side until I am left with a "plank" 1/2" wide.  This will involve milling 0.306" from each side of the round. This length is 1" longer than I actually need, because the ends will be center drilled for live and dead centers. Then when I'm all finished I trim 1/2" from each end.

[Brian Rupnow]

So, here we are with the first side of the crankshaft milled flat x 0.300" deep. Did it bow when I took so much from one side? Maybe, but not very much or I would have noticed the endmill taking a heavier or a lighter cut.--Tomorrow I will flip the crankshaft over 180 degrees, put a piece of 1/2" thick tool steel under each end so the flat rests on it, and take 0.300" off the other side. This is the only thing I don't like about stress proof steel---you can only buy it in rounds, then mill it flat yourself.