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Revisit Timing Gear Train I spent today revisiting my choice of 48DP gears for the timing gear train. 48 DP means that a 48 tooth gear will be 1 inch in diameter (really the theoretical pitch circle is 1 inch, the tangent circles where the gears mesh). The alternative is to use Module .5...

Rear Motor Mount and Bell housing Today I turn my attention to the rear of the engine. I started to work on the bell housing/clutch assembly, but then realized the bell housing attaches through the rear motor mount and extends beyond the sides of the crankcase. So I start with the motor mount...

Peter. You make an excellent point. I "thought" I read that the midget had an 88 degree included angle between the banks of valves, but just now I have not been able to put my finger on it. I measured several drawings and I "confirmed" the 88 degrees. But now I am wondering if it was...

Side Covers The side covers are very distinctive feature of the Off and will be fun to model. The crankcase breathers are afixed to the top. I start by importing a picture with a side view, scale it and overlaying the outline. Here is a side view showing how the middle is raised above the...

Front Cover Today I will be working on the front cover, this is indicated by the arrow in the picture below: The early Midget Offy's like the one above hard mounted the front engine mounting plate to the engine as can be seen above indicated by the red circles. The flat plat with the wings...

Front Timing Gear Tower and Bearings The front timing cover at first glance looks like a mirror copy of the rear timing cover, but on closer inspection one can identify some features we would like to include in our model. The front timing cover is thinner than the rear timing cover as well...

You are correct, the gear ratios did not change, but the displacement/bore/stroke frequently were custom, so the height of the gear tower, thus the size of the gears was changed. That was a lot of work. The ease of changing the bolck and gear tower height is one advantage of using a chain...

I have never seen either of these built by a company, but that is not definitive proof they were not. Ron Colona is retired and no longer sells his plans, the Wittle V8 plans and kits are sold by Hemmingways. (Hemingway Kits The V8 Aero Engine - Eric Whittle). Your dad has a 1/4 scale Merlin...

Wow, that is quite a find. The Offy really looks nice. If you have Ron's plans you will see that he did not use castings but machined from the solid. Good luck getting her to run, I want to see it!

Inside Timing Gear Tower I import pictures and drawings into my CAD program (SolidWorks) and scale them to my working scale, this includes rotating them to establish some horizontal and vertical reference points. Most photos and drawings are not very good representations of a part as there is...

Gear Train I need to define the gear train that drives the camshafts and magneto (distributor) from the crankshaft. My goal is to define the pitch and tooth count of all the gears. Below is a picture of the Midget Offy's gear train. Source: The constraints for the gear train include: I...

I am going to try my hand at developing plans for an Offenhauser Mighty Midget Racing Engine. There were many variations manufactured through the decades and my version will likely end up being an amalgamation of many of those. I will also be taking liberties for ease of manufacture/assembly...

Bob, Have you seen this for aligning the lathe? worked for me:

Machining the lobes of the Camshaft The machining of the Camshaft lobes is done using a 4th Axis on the CNC. The Camshaft is cut from 5/16" drill rod and uses the OD as the bearing surfaces. There are bearing surfaces at each end and between each cylinder. The cylinders alternate between...

Yes, I did temper after heat treat, but just a bit, a very light straw. I am willing to get a bit more hardness and live with a bit more brittleness. A camshaft does not experience the "striking" blows that a cutter does so I figured this was a good balance.

The final step is to heat treat. I take the camshaft and wrap it up in wire as shown below, I then make a slurry of isopropyl alcohol and boric acid. I heat the camshaft and dip it in the slurry, reheating and dipping a few times until I have a nice coating of boric acid on the part. Then I...

Several Pictures at the lathe:

This is an update on the progress machining the new Chinese camshaft. It took me a couple of days to create and test the G code program. I cut several cam profiles from wooden dowel before I used the drill rod (silver steel) seen below. A couple of things of note in the machining: the 1/8"...

I don't disagree, however, I have been tasked with fabricating a replacement hardened camshaft. I do not have the engine with its lifters and so do not feel I would be able to redesign the lifter/camshaft geometry to incorporate the desired valve lifter rotation you describe.

I have measured the camshaft and created a drawing. The dimensions with three significant digits are actual measurements, while the ones with one significant digit are estimated. I think I will be able to create a functional part using 5/16" drill rod with hardening and tempering. I could not...