Porting an Echo 352

[Nutball]

I'm about to modify my 352. Any suggestions for a small engine like this? I saw a short thread about a ported 310. The engine looks the same, but this one is slightly larger. I assume both have a 38mm piston, so far I have only measured stroke on the 352 to be 30mm, so that means 38mm bore for 34cc.

I have an aftermarket 200t cylinder, if their port designs are any good I could reference from it. The ports on the 352 currently look smaller all around; mainly shorter in duration and possibly less width too. So if the 200t is good, this appears to have easy room for improvement. 1.75hp stock. I roughly figured the intake timing to be around 65-70, and the exhaust to be around 110 maybe lower.

I am going to try sanding the base down some for more compression, and sanding the bearing slots to match that change. I'll rely on a sealer to correct any flaws in my grinding of the bearing slots. It started with 140psi cold and having sat for a week. 170psi with oil.

 

[Nutball]

The lower transfers seem better than on the 310 seen here http://opeforum.com/threads/echo-cs-310-build.5046/page-2 but the shapes are seemingly random. A "V" shape can act as a vortex generator for better flow around the sharp bend, the middle rectangular ones seem designed for straight flow into them. Uppers are small and have very little blow down.

Is it normal for the piston to outweigh the crank counter weights? I'd assume this would add vibration. I guess I'll try lightening the piston and maybe the rod too until it balances. In lightening the rod I'd sharpen it to be more aerodynamic since it is really square.

 

[Redfin]

I would try to find a piston with a taller comp height before I would mess with the base and bearing pockets.

 

[Piston Skirt]

I'm about to modify my 352. Any suggestions for a small engine like this? I saw a short thread about a ported 310. The engine looks the same, but this one is slightly larger. I assume both have a 38mm piston, so far I have only measured stroke on the 352 to be 30mm, so that means 38mm bore for 34cc.

I have an aftermarket 200t cylinder, if their port designs are any good I could reference from it. The ports on the 352 currently look smaller all around; mainly shorter in duration and possibly less width too. So if the 200t is good, this appears to have easy room for improvement. 1.75hp stock. I roughly figured the intake timing to be around 65-70, and the exhaust to be around 110 maybe lower.

I am going to try sanding the base down some for more compression, and sanding the bearing slots to match that change. I'll rely on a sealer to correct any flaws in my grinding of the bearing slots. It started with 140psi cold and having sat for a week. 170psi with oil.

Easiest way is to get a 353 engine. It's made for non-emission countries from 352 with factory porting, upgraded crank and forged conrod.

 

[Nutball]

I see, the 353 already has roughly the HP I hope to get. I'd like to know how much different the emissions are relative to the power output. A bigger chainsaw will put out more power and emissions, so why not just call a high powered small saw a "bigger" one so it goes by the same standards. But then I guess they are looking at the kind of toxic emissions? Maybe a 2.5hp 35cc saw puts out more toxic gas than a 2.5hp 50cc saw.

 

[Piston Skirt]

I see, the 353 already has roughly the HP I hope to get. I'd like to know how much different the emissions are relative to the power output. A bigger chainsaw will put out more power and emissions, so why not just call a high powered small saw a "bigger" one so it goes by the same standards. But then I guess they are looking at the kind of toxic emissions? Maybe a 2.5hp 35cc saw puts out more toxic gas than a 2.5hp 50cc saw.

When they squeeze the engines into a permitted "window" of emissions (in this case it's 30-50cc) there is a limit of CO/NOx. Go too lean - NOx jumps up. Go too rich - CO pops up. There are way more factors those two being the simpliest. With non emmision units it all doesn't matter. You can spit unburnt fuel drops if you want Imagine what an engineer does when he just needs to find a sweet spot between power and reliability without no further thinking

 

[Nutball]

I looked around HL for a differen't 38mm piston, but I don't think any there will work better. I just ended up buying a 660 kit instead. I'll give sanding the base a shot. There's hardly anything on the upper block half holding the bearings, it's mostly just the seals getting support, so I think I'll manage to get it to work.

 

[Nutball]

Why is there commonly a hole in the top of oem pistons?

The 352 has over 3mm more stroke before opening the exhaust over the 200t. Squeesh is .040. Here's a picture of right when the transfers start to open on the 352 and 200t

 

[Nutball]

It took a while, but I got the base sanded about 1mm, and the bearing slots matched back up pretty well. I won't do that again though, that sucked. Now that I know the compression mod should work out ok I can start porting. I'm thinking to keep with the torque theme of Echos in general, raising the exhaust 2mm which should still leave it roughly 2mm lower than a 200t for comparison, so hopefully more torque on top of the extra stock stroke. Widen intake a little, the base sanding will have advanced it by 1mm, raise the lower transfers, lighten the piston, and maybe bore the ventury a smidge.

 

[Nutball]

Exhaust so far

 

[Nutball]

Done. 177psi right after an oily assembly, but we'll see after it cuts. It did fire up, so that's good. Squish is about .008-10ish. I've found my solder no not be reliable, so I had to pre smash it into a feeler gauge.

 

[Nutball]

It felt like a real hot saw today cutting 6" cedar with a .043 chain. It was even impressive how well it handled a full depth noodle cut. I think the 16" bar only reaches about 15" right now. Very wide power band, I had hoped to keep the low end torque high, and you can really lean on it. The 4+ month old ash logs for timed cuts are pretty hard though, lots of vibration, not as smooth a slice as cedar. >30% cut speed gains. I'm very happy with it. 155psi coming from 140psi. I just need to sand a bit more off the ignition coil since when I assembled it it wasn't touching the flywheel, but there was practically no gap. Now it's scraping it.

 

[Nutball]

I just thought to check, the lightly broken in (1-2 tanks of gas) 352 is cutting 1 second faster than a new MM 355t in the same log. I assume minor port work to the 355t will then match it, hopefully exceed it.

Note the above posted video does not show the fastest cut time with the 352 on that log.

 

[Nutball]

What's the best way to remove the engine? I forgot. I remember it wasn't easy, and just now it seemed near impossible. The divider the boot goes through can't come off the boot till it slides up, but it can't slide up till the engine does, but the engine can't slide straight up cuz the shaft hits the case, and is already a super tight fit to get out.

 

[Nutball]

 

[Nutball]

 

[thedude74]

Pretty cool build man. Before I picked up my 490 I had considered the 352 due to it being a lightweight saw (8.8 lbs iirc). Also considered the cs400 but @10 lbs it's nearly as heavy as the 490 and gives up 10cc. At some point in the future think I'll have to get a 352 . It looks like a a good saw for my son to learn on and for the wife as well. Besides, I've gotta feed my CAD somehow! Lol. Appreciate you taking the time to post your build thread. Have you thought about advancing the timing to see how it responds?

 

[Nutball]

I have not. I've heard Echos tend to not need timing advance, though the gap was reduced between ignition and flywheel due to the compression mod, so that effectively advances timing a very slight amount. I had to back it off slightly as it ended up scraping, maybe due to stretch at high rpm.

 

[Nutball]

Stock numbers
EX 111.5
TR 126.5
IN 68

The inner exhaust deflector on the 2 piece unit is what causes the most restriction.

 

[Nutball]

Piston stopper for finding TDC.

I screw it in all the way and center the degree wheel with an equal number of degrees on each side of 0, then visually confirm that the piston stops rising right at 0. Movement is actually visually undetectable for around 4 degrees before and after TDC.