SPI engine

Surfer_kris wrote:Sounds like you are comparing a four-stroke with a two-stroke engine. When you turn a cox engine over TDC and it has compression you will not hear any click as the rod is constantly under compression.

Here is a picture of the wear the rod can make in the piston (there is no flat spot, just a wear on the piston);

I am comparing the two as they both rotate 360 degrees. True loads and stresses may differ but, esentially they are the same.

What I was trying to point out is that rod knock in a 4 cycle is a product of wear on the bearing surface as is ball wear in our little Cox engines.

That picture looks to be a well used piston. Keep in mind it is possible for the rod ball to wear evenly and still wear through the piston as long as the socket was reset throughout the life of the piston. If the socket was never reset I bet the ball would look a lot different once it broke through the crown.

At any rate none of this matters much anyway. I was just suggesting a theory as to why the SPI gap decreases after a reset.

microflitedude wrote:

John Goddard wrote:I might be wrong Matt but I think Joe was after it all connected up.

I put the set on an engine, and got it exactly at TDC. The removed it and took the picture.

That is an SPI piston from Bernie.

That's why it's such a huge gap. The short SPI pistons with the old type SPI cylinders combine to make an excessively large gap. SPI used to be created by lowering the bottom of the exhaust port, like a #1 BW. The newer SPI is created by the short piston skirt. The combination makes what I would think is too much, like double SPI. So, how does it run like that? Is it hard to start? Hard to needle?
Even though I shortened my BW piston, it's still taller than an SPI piston.

RknRusty wrote:

microflitedude wrote:

John Goddard wrote:I might be wrong Matt but I think Joe was after it all connected up.

I put the set on an engine, and got it exactly at TDC. The removed it and took the picture.

That is an SPI piston from Bernie.

That's why it's such a huge gap. The short SPI pistons with the old type SPI cylinders combine to make an excessively large gap. SPI used to be created by lowering the bottom of the exhaust port, like a #1 BW. The newer SPI is created by the short piston skirt. The combination makes what I would think is too much, like double SPI. So, how does it run like that? Is it hard to start? Hard to needle?
Even though I shortened my BW piston, it's still taller than an SPI piston.

I have not run the combo yet.

I test ran that Babe Bee as a Diesel today and it works AWESOME! It is technically my first successful Cox Diesel. I had one before, but the Pylinder was worn out and it had to be started with a Norvel Starter that likes to take the prop off. The engine ran like crap and I had to have the comp WAY up to get it to run.

The Bee ran real nice. It puts out a lot of air with a 6x3. I will get the Texaco 8x4 and see what it does. I know that is over propping it but I am curious and would like to try it. I apparently was running it rich today because when it died it really took off. I am not real experienced in diesels. But hopefully this will help. The first two times I ran it and the last time I got it in three flips. The middle times I had taken it apart to move the bowl around because of a leak.

What kind of crankshaft are you using?

I am using the Killer Bee Crankshaft. The Cylinder is a #2.