Echo 21cc Trimmer Mods (SRM-210SB, GT-2000, etc)

[steve316]

just subscribing

 

[slipknot]

I think the mantis engine is 25cc....my bad.

 

[slipknot]

c'mon fellas this thread aint done yet..there's more to know.

 

[Miles86]

I could see getting the power up to 2.5 to 3.0 hp. The Zenoah G230RC is 22.5 cc and is available from RC shops rated at:

quote from an RC website:

"Available in factory black finish or with aftermarket chrome shroud, fancover, etc pre-installed.
Engine Stats: Displacement: 22.5cc. Power: 2.8HP @14,000 RPM. Torque: 1.32 ft/lbs @10,000 RPM. Timing:30 degrees BTDC @ 8,000 RPM. Compression Ratio: 9.2:1. Fuel: 95 octane or higher mixed 25:1 with 2-stroke oil."

How long these Zenoahs' last is ????:msp_unsure:

 

[Team FAST]

I've seen simliar info. I've been looking at what the Zenoah folks have been doing for modifications (RC cars, boats, and also scooters). I've also found some people who are modifying these echo string trimmer engines for use on R/C aircraft.

My plan to get more power is to raise the exhaust port for more rpm, open up the transfers, and try and get a decent combustion chamber setup (squish and volume). And install a bigger carb for better breathing. Something else I am cosidering is building a pipe. Howe cool would THAT be?

The holy grail would be a programmable ignition with a non-linear advance curve. The fixed timing on these engines really holds them back.


I've got some more stuff to post, just need to find the time....

I could see getting the power up to 2.5 to 3.0 hp. The Zenoah G230RC is 22.5 cc and is available from RC shops rated at:

quote from an RC website:

"Available in factory black finish or with aftermarket chrome shroud, fancover, etc pre-installed.
Engine Stats: Displacement: 22.5cc. Power: 2.8HP @14,000 RPM. Torque: 1.32 ft/lbs @10,000 RPM. Timing:30 degrees BTDC @ 8,000 RPM. Compression Ratio: 9.2:1. Fuel: 95 octane or higher mixed 25:1 with 2-stroke oil."

How long these Zenoahs' last is ????:msp_unsure:

 

[Miles86]

Team:

Like the module on the CS-370? They state it is a slope advancing unit, not sure how that works, does it retard for starting then variable advance through the rpm range? Or just wham-full advance at x rpm? My cs-370 is just a little rev machine, very happy with that saw.

I need to order some of those 21 cc muffler outlets for my other echos.

 

[Team FAST]

Interesting idea!

I will have to look into the CD-370 ignition module. Never thought of that! I have a pair of CS-400 saws, so I wonder if they have a similar module. I will have to hook up a degree wheel and a timing light and see if there is a timing curve built into that module.

If it works, I may be in the hunt for a CS-370 ignition module....

 

[PLMCRZY]

Just curious are you retired?


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[Team FAST]

Just curious are you retired?


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Not even close! Why?

 

[PLMCRZY]

Not even close! Why?

How the hell do you have time for this stuff lol? I think it's cool for sure but you put a lot of time into your stuff it seems.


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[Team FAST]

I decided to get a bit radical. I think the biggest limitation to getting decent port timing and squish settings in trimmer and chainsaw style engines is the fact that these are one piece cylinders with the cylinder head cast into the top. If you start raising up the cylinder to get better exhaust port timing, you increase the squish...not a good thing.

So I decided to get radical and try something I haven't seen done a lot on here on this board.

First I machined a mandrel from 6061 bar stock so I could conduct machining operations to the cylinder in my lathe:

Here's a pic with it installed in the cylinder. It's slip fit into the bore.

Then, I took the GT-2000 cylinder and cut the top off using my bandsaw:

Next, I mounted the cylinder onto the mandrel and then installed it into my lathe using a 5C collet chuck. I designed the mandrel so that the stock bolt holes could be used to support and attached the cylinder to the base flange. I machined the actual mandrel to be a close tolerance slip fit to the stock bore. Here's how it looked with the cylinder installed (before I cut off the top)

OK. So once I cut off the top, I used the mandrel in my lathe to machine the top of the cylinder smooth and square. At this point, I don't know how much to take off, so I machine it to only clean up the top of the cylinder. Later, when I go to set the port timing, and eventually the squish clearance, I will take more off as needed.

And here is the finished product from this operation:

Now this is starting to look like a real cylinder! Something that I can work with to accomplish good porting, tuning and lots of horsepower!

 

[Team FAST]

Here's what going to be installed on top of the now open cylinder:

This head has a nominal 3cc volume (total volume above the piston) with a 15 deg squishband. Best part is that it is a hemi chamber with a centered open spark plug. The stock head has an asymetric chamber with a very shrouded spark plug.

Making the leap from "virtual" CAD to "actual" metal here is the starting point. I sawed the billet from .625" 6061 plate

Machining the edges:

Finished the mounting holes. Notice there are four holes. The Echo cylinder is attached to the crankcases be only two bolts. More on that detail later

Now with a M14x1.25 spark plug hole:

Machining the cooling fins. Takes MANY passes with a .125 diameter ball nose carbide endmill! All the edges were also machined with radius cutters (corner rounding endmills)

 

[Team FAST]

Finished cylinder head

And here is the finished product:

Here's what the combustion chamber looks like. This is actually a prototype head I made. On the first attempt, I messed up on the dimensions of the mounting holes, but I went ahead and finished it. I also had a problem with the spark plug threads, so I installed a thread insert. Otherwise, this is identical to the second part I made. So you are looking at my "Revision A" of my cylinder head design

I still have to machine a counterbore on the sparkplug hole to properly set the depth of the plug. I am going to wait to do this until I get the squish set properly and the cylinder ported.


Next, I will show how I modified the crankcases to the entire assembly will fit together.

 

[dboyd351]

That's awesome!!! I agree the one piece cylinder head is a real limiting factor. Love to see you machining up your own solution. This is going to be an amazing thread to follow. I also like the other extreme, with the bolt on muffler mod. A little bit of something for everyone!

 

[Team FAST]

Thanks! I think when I am done I hope it's going to be a piped snarling fire breathing monster. I haven't ruled out running alky and nitro to get the most power.....


Yeah I know, its a weed eater....:tongue2:

 

[Team FAST]

Design time again. I needed to make another fixture. This time I got two for one. This fixture allows me to mount each crankcase half against a reference surface. Turns out that the good folks at Echo designed their cankcases to allow provisions for two additional cylinder attach locations. The bosses are cast into the crankcases, but they aren't drilled or tapped. So after much measuring and layout, I reverse engineered the bolt pattern for the cylinder base, and established the locations for the additional holes. The new head needs four strong attach locations to clamp everything together to seal it.

The second thing this fixture does is provide an accurate way to bolt up the cylinder so I can drill the extra holes for the attach bolts through the fins.

Also turns out I can mount the cylinder on this plate sideways and directly machine the exhaust port in the mill. Haven't done that operation yet, so stay tuned....

Here's the CAD layout:

Here's a set of cases set up on the mill with the new holes drilled and tapped:

Here's what the cylinder looks like installed (sort of). I made up some studs, which are shown here, but later I decided to purchase M5x65mm socket head cap screws.

Also, having the cylinder open on top makes it a CINCH to measure and set port timing (as it should be).

 

[cujet]

I'd love to know what port timing specs were stock and what you end up with. Also, your predicted HP.

Obviously, a well tuned pipe would be best, but there are compact alternatives that may produce more power than a modified stock muffler.

I had considered trying a larger volume muffler, with internal standpipe to reduce noise levels.

 

[Team FAST]

Let's see....port timing for the Type Ie cylinder (which is what I am going to use to modify) stock is:

Inlets open at 65 deg BTDC with 130 deg duration
Transfers open at 48 BBDC with 99 deg duration
Exhaust opens at 115 ATDC with 135 deg duration

The exhaust port timing is super low. I'm going to raise the exhaust significantly. That's why I had to cut the top off the cylinder and machine my own cylinder head.


I haven't had time to do any porting yet, so I welcome any inputs for where to put the ports.

 

[cujet]

Can I suggest 196 degrees exhaust port timing and 135 degree transfer port duration. You have no "guts" if you don't go this radical, ha ha. Of course, that would require a properly tuned chamber and case reed induction. What fun.

I am totally impressed with your modification plan. Very cool indeed.

 

[Miles86]

TeamFast;

Great job as usual!

How are you going to stop the head from warping? Maybe use the stud method with a spacer collar to act as a limit stop? (The cylinder fins are not uniform in their shape at the top of the cylinder, maybe it doesn't matter.) Thanks again for sharing.