[AJCoholic]

I have just started on my next engine project. I have been wanting to design and build a 4 stroke engine for some time, and Ever since I flew an Webra T4-80 a few summers ago, I have thought the rotary valve concept was cool.

Last year in Toledo I picked up a used and abused (but complete) T4-40 for $20. I took the engine apart completely and am using it as a basis for my engine. Mine will be a 1 cubic inch displacement. I like the square head/case look of the Webra and am going for that look.

Here is step #1 to building an engine. A wooden pattern must be made, in this case of the crankcase (all other parts will bemachined from barstock). The pattern is made from various bits and pieces of wood, glued together and shaped. Then painted. Now you are ready to pack the pattern in the molding sand and get a rough casting from it. Hopefully that will be later on this week...

Here is the pattern, and the T4-40 case to show the size comparison...

[AJCoholic]

a second shot:

As I build this engine, I will take pics and post the sequence for anyone who is interested...

[JimBrown]

I'm interested. Not that I'll be building an engine myself (it's not something I'm particularly interested in doing, but I am interested in how it's done.)

Quick question, how do you get the pattern out of the molding sand? Lemme take a guess. You make two mold half's?

I take it this is a different method than the lost wax casting method?

...jim

[AJCoholic]

Jim,
The pattern is split into two halves. You pack one half into the sand, put on the second half that is alligned with dowels, and pack the sand around that part. The box it is packed into is open on both ends and also split and keyed. Then you open up the box and pull out the pattern halves. Cut in a feed gate and put the sand packed box halves back together. Now you have a cavity inside the sand that is the shape of the pattern. Pour the aluminum down the feed and voila!

I did a thread back about a year ago with lots of pictures of me and a friend of mine casting. Here is the thread:

https://www.rccanada.ca/bb/viewtopic....hlight=foundry

Here is a picture of the pattern halves being painted...

Oh yeah, investment casting is completely different. That is where you make a wax pattern (usually in a metal mold) of the part you want to reproduce in metal. Then you coat the apttern with the "investment", a plaster-type material that hardens up and will withstand the heat of molten metal. The investment is heated for a long time in an oven, and this melts the wax and drives off all the gasses and moisture. The metal is then poured into the now empty "plaster mold" and once the aluminum solidifies, the works is dumked in water to shatter the plaster and you have your part. Sand casting is a lot simpler, but limits the amount of detail you can have. I hope someday to get into investment casting, but this requires a sustantial investment in materials and supplies I do not have (thousands of dollars). I have about $1000 invested in my sand casting stuff, and the foundry furnace, propane burner, crucibles, tongs, etc are all home made by me. The only thing I buy is the oil bonded sand (about $1.10 a pound, I have 800 pounds on hand) and the chemicals you need for casting (a degasser and a flux, as well as some parting powder and some crucible cleanser powder).

[JimMoss]

You have way to much time on your hands!!!

Looks good as always though!

[JimBrown]

Thanks for the explanation, Andrew! I didn't know about the two different methods of casting.

Nice to know my guess was pretty close.

Looking forward to further updates.
...jim

[planecrazy]

Very cool Andrew!!

When you get it running (Not IF). See if you have the energy\time\resources etc. to build a replica of a Bristol Centaurus!!!

Chris

[AJCoholic]

today I decided to go in and work on something. I made the head. First you take a bar of aluminum and cut off a hunk

[AJCoholic]

The blank is then sized - machined all 6 sides to the proper dimensions. I like to do this in my 4 jaw chuck on the lather, as my mill is small and I dont flycut too much.

That is the stock Webra T4-40 head for size reference again. I am scaling it up 1.3635 times. That brings the .40 to a 1.0 cubic inch.

[AJCoholic]

then, basically its just some boring, threading, drilling and such for the intake, exhaust, glowplug. Also the bronze bushing for the rotary valve was made and pressed into the head. The combustion chamber was machined and voila!