Dumbo The Flying Elephant

[Dwight Southerland]

Larry -
If you are going to make a flat cut on the head to reduce combustion chamber size, here is an easy way to know exactly how much to cut. Put the head on a stand with the combustion chamber facing up. Shim or adjust the head so the head surface is level in all directions using a level. Then, pour the combustion chamber with the amount specified for minimum volume. Use a dial indicator on a bridge to measure the distance to the surface of the fluid from the head surface. Do that for all cylinders and adjust the numbers to determine how much to cut.
This method will work on any head regardless of combustion chamber shape or size.

[Larry Hill]

Thanks Phil and Dwight, I will fill and check to see if 5cc will be .030''

[Greg West]

Take a piece of graph paper and trace a outline of the combustion chamber shape on the paper. Count the number of squares on the paper that are within the traced area. Do the math to calculate the area of the squares. From there you can calculate the volume. This method will get you close. Double check the volume with your first pass on the mill.

[Mike Gray]

Originally Posted by Larry Hill

Pored alcohol all day and only lost 1/2 a qt. The heads are legal right out of the box. The runners are good and the chamber is big 5 to 6 cc. I will run it that way and then recheck before we make an adjustment.

Does anyone how much to cut to reduce chamber size by 1 cc?

Thanks

Hopefully it wasn't the good stuff and by losing 1/2qt do you mean spilling it or drinking it?

[Larry Hill]

I spilled it, but I did buy a small funnel that fits the burette.

Yesterday was recording day in the "Dumbo" engine book. The engine I got came in several boxes, for me its the only way to get one. Most boxes have the brand name and part numbers. This make replacement parts hunting easier. Other parts are in plane white or brown wrappers without part numbers. Such was case with the spring seats for the head. Exhaust and intake have different seats, valves are not the same length. So I make a drawing of each in case I can't find a vendor. If push comes to shove I will be able to find some in some bar stock.

Since I had the heads out I would see how well the seats fit. They almost fit but would not set flat against the head. The problem was the OD of the chamfer was not large enough to have clearance over the radius on the head. Solution cut chamfer 1/64 bigger than the chamfer on the guide boss. I was surprised as to how soft and easy the spring seats machined.

I wonder how much unwanted aluminum the seats would have shaved of heads and put in the oil?

[Tom Broome]

Originally Posted by Dwight Southerland

Larry -
If you are going to make a flat cut on the head to reduce combustion chamber size, here is an easy way to know exactly how much to cut. Put the head on a stand with the combustion chamber facing up. Shim or adjust the head so the head surface is level in all directions using a level. Then, pour the combustion chamber with the amount specified for minimum volume. Use a dial indicator on a bridge to measure the distance to the surface of the fluid from the head surface. Do that for all cylinders and adjust the numbers to determine how much to cut.
This method will work on any head regardless of combustion chamber shape or size.

Done it this way for decades.

Use a dial indicator and bridge or a depth micrometer and some ground tool stock for parallels. Once the chamber is filled with the specific amount of fluid, lower the tip a thousandth at a time. Watch the tip of the indicator or micrometer, when the tip touches the fluid the surface tension will attach the tip. You can then calculate the amount to remove.
If your surfacing machine is really level, you can do it right there....you're not going to bump the head out of level after it's bolted to the machine.

[Larry Hill]

Since all this gen 3 stuff is new to me I am going to check piston to valve clearance, before I do any cutting. Thanks to you guys I have some direction on doing it correctly.

[Larry Hill]

Just finished cc's on the heads. It should make more power now that I'm done. Growing up I always heard, ''If you want to go fast get some heads that have been cc'd from Racing Head Service.'' Well I sure hope my cc'ing is as good RHS. Time will tell.

[Tim H]

I bet your work is "A-1" and maybe we will say " if you want to go fast, get some heads cc'd from LHS."

[Larry Hill]

Today we start checking installed height, seat pressure, open pressure, and adjusting to make equal. It's going to take a while.