Atkinson Differential

[Gordon]

I am building the Atkinson Differential engine and I have a question for anyone who has built this engine using the Gingery book.

On the oscillating arms it locates the bore in the crank boss and the pivot boss but the hole in the piston rod boss is shown on a 2 7/16 radius arc but it does not show any other location. I assume that this location would be fairly important but I cannot find any other location.

Gordon

 

[mohavegun]

Correct me if I am wrong because I did not take the time to re-read the book before making this reply but as I recall Gingery made a comment concerning location of the cylinder assembly before mounting and adjusting bolt holes with respect to the position of the pistons in the various stroke position. Perhaps he wanted to allow freedom of final placement of the pin. I am currently finishing up my patterns and getting ready to cast parts for my engine from this design and will take some time and locate the exact point of his discussion about locating the cylinder, it is one page either side of the photo of him clamping the cylinder before drilling the holes

 

[Gordon]

I reread that section and it just tells how to layout and drill the holes but it does not say anything about locating the piston rod pivot later. As a matter of fact it tells you to drill all three holes with the same setup. There is a discussion about possibly having to adjust the linkages to obtain correct piston location. I guess that you could just drill it and adjust the connecting rod later if required. The thing which makes it confusing is that the drawing shows the hole not centered in the boss.

Actually at this point I am redrawing the drawings in CAD since I am finding the drawings in the book kind of hard to follow since details are scattered on different pages. Some are on the pattern and some are on the detail page. At this point I am waiting for the castings. I made the patterns and there is a small job shop foundry making the actual castings.

 

[Gordon]

OK. Still working on this engine. I am looking for someone who has built this engine using the Gingery plans. So far I have run into two rather serious problems. As stated above the position of the pin in the connecting rod boss of the oscillating arm is not really specified. I built it offsetting the hole 1/8"from center as near as I could determine from the drawing. It ended up that it should have been at the center of the boss not 1/8" forward. I ended up having to remake the connecting rod at 1/8" shorter because the pistons hit inside the cylinder. Also I had to shorten the bottom of the oscillating arm 1/16" because it hit the bottom of the cylinder bore. Everything now seems to be working but now I am making the intake and there is not enough room for the valve stem. It hits the bottom of oscillating arm. In looking at the you tube video by Dave Gingery it looks like he had the same problem. As near as I can tell by pausing the video he ended up cutting a piece off from the right hand arm to obtain the clearance. I have been over my build trying to see if I screwed up but it looks like I have it built per the drawings.

Has anyone else experienced the same problems and am I in for more surprises? I have looked at all the images I could find on Google but none of them show the area I want to see. Most of the images are not actually of the Gingery design but variations of his design. It seems strange that with all of the engines which have been made that there is not more discussion of what are errors in the original drawings or folks who made the same errors that I may have made.

Gordon