Engines > From Kits/Castings

Westbury Seal by Vixen

(1/82) > >>

Vixen:
I've moved parts of the 'Seal Help' topic over to this new ' Westbury Seal by Vixen' topic.

Mike

Jo:
 :pics:

Vixen:
Well you asked for some photos.

On the left is the billet of 6082 T6 I bought as an insurance policy in case the Hemingway casting did not arrive.

With the billet I get 6 potential datum flat surfaces, 12 potential datum edges and 8 potential datum corners to choose from. With the castings, nice thought they are, there is nothing flat or square or dimensionally accurate to measure from. I guess I am going to relearn all the old school marking out tricks.

Vixen:
I measured up and created a three view drawing of the Hemingway casting, which I superimposed over my CAD model of the cylinder block. The casting external features were found to be generously oversize in most places. The internal cored feature, though difficult to measure, appear to be spot on for size.

I maneuvered the internal casting features to be a best fit on the CAD model. I find the upper water jacket area to need about 70 thou" removed from the top, side and end faces. The lower crankcase area needs something like  0.13" removed from both ends and approx 30 thou" from the sides. This will obviously machine off the raised flanges on both ends will disappear.  The bottom (Sump) face needs a massive 0.17" or so, to be removed. There are few parallel faces, even the four mounting lugs have a 5 degree draft angle.

There's a lot of material to remove. When I am finished almost every external surface will have been machined (I may as well have made it from the solid billet). I am considering leaving the lower crankcase oversize so as to have some cast features left.

I think my machining sequence will start with facing off the cylinder head top face slightly undersize and then to bring the water jacket ends and sides to the drawing dimensions. I then propose to finish bore the cylinders, valve pockets and all the stud holes, while everything is set up in this position. I can then use the machined  top and sides of the water jacket as datums for when I invert the casting to do the bottom face and mounting lugs. That should give me a nice square block to hold when I do the crankshaft and cam shaft bores on either end of the casting.







Well that's the plan. and as we all know, most plans will change after the first encounter with the enemy.


Mike

Vixen:
Thanks to all of you for calling in. Good to hear you are all well.

Redrawing the engine in CAD gives a lot more freedom to make slight changes before the build. I have tried to incorporate all the valuable ideas and suggestions so generously provided by our MEM members. I have also read and reread the various build logs and the words of Westbury himself and fed in as many lessons as possible.

I made two big design decisions. First; the pistons should not protrude above the top of the cylinder block. Second; I decided to increase the cylinder bore and crankshaft throw in line with Westbury's suggestions while keeping the conrod length as designed. The engines displacement will now be closer to 20cc instead of 15 cc. Both changes require a slightly taller cylinder block. I also incorporated ChuckKey's advice to increase the tappet diameter to 9/32.

I only ordered the cylinder block and cylinder head castings, I plan to make all the other parts from bar stock as that gives me a little more flexibility to position thinks like the water cooling in/out lets to suite the Bren Carrier's installation. It also avoids the need to reposition bolt holes to fit the poorly positioned bosses of the castings.

First up, was to machine the upper half of the crankcase around the water jacket. I found that the valve gear pocket on the side of the casting was the feature which decided where the engine was positioned within the oversize casting. I set up the raw casting in my new (Christmas present to myself) machine vice, with the mounting lugs sitting on two steel rods acting as parallels. I selected a suitable datum from the drawing of the raw casting superimposed on by CAD drawing. I them machined the top face 0.04" overlength and the four sides of the water jacket to finished size. I now have five square faces and four edges to provide datums for all subsequent machining. You will notice the cast flanges on the water jacket  have been machined completely away. As Jason points out, that will provide greater flexibility for the plumbing.

The Aluminium alloy used for the castings appears to be of good quality and machines easily. I can tell it is softer then the T6 heat treatment normal with billet materials. I hope this softer alloy will not adversely effect it's ability to hold screws and studs.




I think it is about time to start a new build thread of my engine, which is separate from the 'Seal Help' thread.



Mike

Navigation

[0] Message Index

[#] Next page