The Craftmans Shop > Model Engineering

Rockerblock engine--something a little different--

<< < (7/10) > >>

Brian Rupnow:
I'm going to get bold here, and do something I haven't done before. Since my crankshaft is built up from individual components pressed, Loctited, and possibly pinned together, I'm going to make up a one piece con-rod and assemble it with the crankshaft. If it works, then great, I'm way ahead of the game. If it doesn't, all I've wasted is a bit of time. Since this is a "demonstration" engine and is not going to see long hard hours of use, I'm not going to run any bearings on the con rod. Aluminum rod running on steel crankshaft lasts a long time if it is kept well lubricated.

Brian Rupnow:
I'm not blazing thru this build like I have some others, but I did manage to get some machining time in today. The con-rod still has to have the center relieved, but at least I did something. I can't assemble the crankshaft until I have the con-rod finished so I thought this had better be a priority.

Brian Rupnow:
I got so tired of bodging up temporary fixtures to relieve the center portion of connecting rods that today I actually took an hour and built a dedicated fixture for it. I will post a clearer picture of it when I get the other side of the rod finished. It works like a charm.

Brian Rupnow:
This is the finished con-rod, along with a shot of the fixture I made for relieving the section of rod between the two end bosses. The round rod in the center is turned to 3/8" x about 0.290" long. The remainder of the round rod is 9/16" diameter and passes thru a 9/16" reamed hole in the flatbar, and is welded a coupe of places on the side which fits into the chuck. The other bolt passes thru the far end of the con-rod and holds it snug against the flatbar, with the help of a flatwasher. The piece of flatbar which sticks out on the other side of center gives the fixture balance and can be tapped anywhere to accept a different length con rod.

Brian Rupnow:
The first stage of crankshaft assembly is completed. There is a lot going on here!! The large shaft is an alignment shaft only, turned to be "size on size" with the largest holes in the web plates---not a press fit, but a damned close sliding fit. The small shaft is a piece of 3/8" drill rod, at about half a thou oversize. It is a hard press fit (with 638 Loctite) into and thru the first web plate (0.3735" hole), then wiped down with solvent, then oiled and fit thru the bore of the con-rod, then wiped down with solvent a second time and coated with Loctite 638, then pressed thru the second web plate.  You don't see it, but there is a "washer" made from cardboard cereal box at 0.018" thickness setting on one side of the con-rod, because the con-rod is squeezed in there very tightly. After an overnight dry, I will make both ends of the crankshaft in one long piece and press it thru all in one blast. After the Loctite on it sets up, I will mill the piece out from between the web plates. Then I will soak the entire thing in water for a couple of hours to dissolve the cardboard washer and give the con-rod some side clearance. One thing to note---When you ream a con-rod to 0.375" diameter, a 0.3755" diameter rod will not fit thru it without pressing. I had to open the bore in the con rod by about .0005" to get a proper fit over the .3755" drill rod. I don't have any oversize reamers, so had to do a lot of persuading to get the bore opened out. This type of "persuading" is accomplished by sanding a taper on a piece of the drill rod in the lathe, coating it with cutting oil, and then CAREFULLY working the rod up and down the taper until it slides over the main diameter.

Navigation

[0] Message Index

[#] Next page

[*] Previous page