Thumper---A new 1 3/8" bore i.c. engine

[brian Rupnow]

I have developed the concept and plans for this engine over the last couple of days, under a thread titled "A different engine configuration". Now that the plans are 95% blocked out, I am going to create this new thread dealing with the actual fabrication of the engine. You are all invited to follow along, and assuming this engine is a success, I will be selling the plans after I am finished.---Brian Rupnow

[754]

I have some 1.8 inch cast iron round, what are you making the cylinder from ?

[brian Rupnow]

Cylinder from 2 1/2" diameter cast iron. When you buy it, it comes in about 0.100" oversize.

[nickel-city-fab]

Interested, will be watching this one. I hate to think of having to pay for 2-1/2" Durabar!

[brian Rupnow]

Just so ya know----I'm going a bit beyond my comfort zone here. I haven't made an engine over 1" bore before. All rotating shafts will be on sealed ball bearings except the big and small end of the con rods (both of them). I'm done with bronze bushings. The Rockerblock style is tried and proven on one of my previous builds. I will be using purchased cast iron rings (because I really suck at making them). My ignition will be the old tried and true Chrysler ignition points, and my CM6 sparkplug has a 10mm threaded end and can be purchased at an auto parts store. The cylinder will be made from grey cast iron, and virtually everything else except the shafts will be made from bar stock aluminum. The flywheels will be fabricated from mild steel, and I hope to make them using my new TIG welder that I bought this week. My ultimate goal is to build an engine powerful enough to drive my edger. A piston of 1 3/8" diameter has almost twice the surface area that a 1" diameter piston has.

[nickel-city-fab]

Wow I can't imagine that. My comfort zone goes in the opposite direction -- I've never bored an engine smaller than 3 inches!

[Cuttings]

Looks like this is going to be a good strong engine. I like the name. Have you given a name to any of your other engines ?

[brian Rupnow]

Yes, the twin opposed engine that I worked on for the past two months and couldn't get working is called a dirty Son of a @#$%.

[aostling]

Have you decided on a compression ratio for Thumper?

[brian Rupnow]

Not really. It will be 1 3/8" stroke by 1 3/8" bore. The head has a cavity 1 3/8" diameter by .094" deep, and there is a gasket .031" thick. If I've done the math right , then its .6875 x 6.875 x 3.1416 x 1.5=2.227 cu. inch capacity with piston at bottom dead center and .6875 x .6875 x 3.1416 x.125=.1856 cubic inches with piston at top dead center. 2.227 divided by .1856=12:1 compression. If I've done this right. No allowance has been given for the fact that the valve heads intrude a bit into the cylinder head. That sounds a bit high to me. I might change the cylinder height a bit and aim for about 10:1

[brian Rupnow]

This morning's work was to add in all the other things you need to have with an i.c. engine, namely the gas tank and a way to support it, some shafts, and a whole bunch of drilled and tapped holes with matching counterbored holes. There are more elegant ways to support a gas tank, but this is simple and gives you the capability of raising or lowering the gas tank. (which can have an effect on the way the engine runs).

[brian Rupnow]

I've spent most of the afternoon making detail drawings of the new engine. It has snowed here for the last 48 hours and it's still snowing. It's the biggest snowstorm I've seen in years. There is a rather zen like peacefulness in making detail drawings. All of the heavy lifting gets done during the in initial design process. I have to go down street Monday and buy material. My new welder hasn't showed up here yet, so I guess I won't see it until Monday. I've spoken to the people at Canadian Bearings in Barrie and the have the two sizes of sealed ball bearings that I need---Monday. I've spoken to the fellow who makes rings for model engines and he has the piston rings I need for $5 each, and I'll probably order them on Monday.---Monday may be a busy day!!!

[brian Rupnow]

I just snapped this picture of my truck in the driveway--I'm waiting for the plow to come. They are calling for more snow tonight, tomorrow and tomorrow evening.

[nickel-city-fab]

You too? Buffalo/Niagara is a bit better than that, but not by much. Snow all night yesterday, more coming tonight. 24F(-4C) and we have a 35 MPH cross wind. I'm staying in this weekend, trying to re-learn CAD.

[PStechPaul]

Today we had a few flurries, probably not enough to count as even a trace at the official airport station. This would be the first time in recorded history that we have NOT had any snow in February. I think old Punxutawney Phil was right about leaving his burrow not being scared of his shadow.