Here is an of Echo thread condensed:

BME 23.6cc

Most of you guys probably know that Echo was our base engine for most of our engines and no one probably knows them better than I do. If you want to get the most out of your little weedeater engines please follow my directions exactly. Forget the 21cc and the 25.4cc echo and buy the 23.6cc. The older the model the better. They changed the transfers on the later models that did not work well. The first thing you need to do is machine the cylider base down as far as you can. The piston should very lightly bump the head but when you recut the piston crown it should clear again. You want about .015-.020 squish clearance. After this take a dremel and a degree wheel. You want the exhaust to open at 98 degrees ATDC and you want the intake to open at 108 degrees ABDC. Cut the exhaust port a little wider or as wide as the port is at the outermost edge. Work slowly and and check your progress many times so that you dont go to far. After you cut the ports be sure to radius the inside edge so it wont hang the ring. We have done hundreds of these conversions and with the battery ignitions they are turning 8500 on a 17x8 APC.

Keith
BME

When cutting the piston you want to match the radius on the squish area of the combustion chamber. We do not cut the entire top of piston but mostly cut the outer edge. The piston ends up with a smaller radius or higher dome. You want all the compression you can get. I dont know the compression ratio but it runs fine on 87 octane gasoline. You can check the match fit from piston to head by turning and pushing the piston against the head. It will leave marks on the piston where it rubs and you will know where to cut the piston down at. As for the intake side(bottom skirt) we have cut the port on the cylinder on some and we have simply cut the piston skirt on the intake side only on others to obtain the 108 degree ABDC intake opening. These mods can be done on most any conversion engine if you intend on running it above 8000 rpm. If you want to run below 8000 rpm dont raise the exhaust port. Leave it at about 105 dgrees ATDC. I dont know about the different gaskets on the cylinder but I dont think you would want the ones with just holes in them. The good cylinders will have a transfer port opening that is the same size as the opening on the crankcase. Later models will have that opening smaller and it does not match the crankcase opening. I will see if I have time to do a conversion and take pictures for you guys.

I forgot to mention that the only difference between the 21cc echo and the 23.6cc echo is the piston and cylinder.

Keith
BME

Hey guys I am doing a new conversion hop up on the Echo 23.6cc engine. I have installed a crank shaft and piston from a 25.4cc engine in the 23.6cc crankcase and cylinder with the timing mods I mentioned before. This new crank gives the engine a 2mm stroke increase which is just right after you modify the piston to give maximum compression and now it will still travel down to the bottom edge of the exhaust port. I hope to gain as much as 400 rpm more with this set up as compaired to the standard stroke 23.6cc engine which is turning a 17x8 APC at 8500 rpm.


Keith
BME

You could do the same mods to the 25.4cc engine and gain power over the stock form. In my experience no mods I did to the 25.4cc equaled the power of the 23.6cc. When you drop the cylinder down to raise the compression you are also giving up your port time area. You gain it back by cutting the exhaust and intake but your transfers have lost area. With a stroke increase you can get this back plus gain some cc's and power.



Keith
BME

Well I have converted the Echo 23.6cc engine with the longer stroke crankshaft. I did gain some power but I was hoping for more. The engine weighs 1lb 15 ounces and it turns the 16x8 APC at 9100 rpm on the first run up. It should get about 200 more with break-in. Funny but I find they dont want more than about 25-26 degrees timing. I am going to try a bigger carb and see if it gains more.

Ran the stroked 23.6cc Echo again today. I put the carb from a g-23 on it and gained some power. Its now turning a 16x8 APC at 9300. Vibration is starting to show up at this rpm. It needs more counterweight on the crank to spin this fast. I think I will go to the 17x8 APC to drop the rpm down and pick up some thrust. These figures are with a stock box style muffler.


Keith
BME


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