Efco 62cc woods port

The little John Deere (Efco) CS62 has become my pet firewood saw in the 1 1/2 years that I've owned it. Today it is getting a woods port, because why not ?

A paper degree wheel was glued to the flywheel with a few globs of Seal-All. Baling wire served as a pointer.


OEM Specs recorded before modding:

144 psi (equivalent to 169 psi at sea level, so that is very, very good)
0.038" squish
154 degrees exhaust duration measured with a degree wheel
150 degrees intake duration
11 degrees blowdown
5 CC zero squish chamber volume
9.1:1 UCCR (if Efco can do it, why can't the Stihl 660?)
0.008" + 0.0012" ring gap
57 mm long con rod
12 mm diameter wrist pin
3.6 mm top land
38 mm tall piston
21.5 mm deck height
0.160" skirt either side of exhaust port

OEM port map.


For comparison, I also calculated the durations based on the port map. As always, the port map durations are a bit higher because the map "sees" the far edge of the port bevel. I figure both methods are half right and I'm comfortable using either method, just be aware that the results are slightly biased.

159 degrees exhaust duration calculated from port map
153 degrees intake duration
13 degrees blowdown

Specs are nearly identical to its 81cc big brother. It appears that Efco uses a cookie cutter approach to designing its pro saws. I like the conservative specs -- these Efcos are much easier to hot rod than the wacky Stihl 660 specs.

The piston uses the same eared clips as the 81cc saw. These are the wimpiest clips ever -- if you tried, you could probably remove/install them using only your fingers. But, they seem to work.


Placement of the ring locating pins is a bit odd. One pin is smack in the middle of the intake.


The intake port has a partial bridge to support the pin.

The other pin is on the exhaust side of the piston, believe it or not !


Pretty conventional exhaust port. Cylinder is in fine shape, good plating all the way to the very top (why can't NWP cylinders be like that ?).


Like its big brother, the 62cc jug's transfers leave little room for improvement. The size is generous and the upper transfer is swept toward the intake side.


The tentative plan for a conservative woods port:

-- 0.025" squish (gives me some wiggle room to fine tune)
-- pop-up piston just enough to achieve 10.5:1 UCCR, which should produce 165 psi.
-- dropping jug will unavoidably increase intake duration a few degrees
-- raise exhaust port just enough to maintain existing exhaust duration
-- widen exhaust port 0.06" each side (10% increase), leaving 0.100" skirt either side of port
-- widen intake port 10% (same % as exhaust)
-- open up piston windows

Wow, very short blowdown, certainly would not want to raise the transfers any.

Actually lowering them by dropping the jug and raising the exhaust back up should help with torque up higher in the powerband.

timberwolf said:

Wow, very short blowdown, certainly would not want to raise the transfers any.

Actually lowering them by dropping the jug and raising the exhaust back up should help with torque up higher in the powerband.

Click to expand...

Thanks for the input, Timberwolf.

I wondered about the short blowdown ? Not much can be done about it, except, as you point out, it will pick up a degree or two of blowdown after dropping the jug.

Actually, this saw cuts very, very well in stock form. Rarely bogs, not fussy about RPM, yet cuts fast for its size. It came with a 20" .325" bar, but I will be trying a 24" x 3/8" after the woods port. I'm thinking the modded saw will pull a 24" in softwoods, and I could use the extra length for those occasional "big" trees (big by 2nd growth standards).

If you are always using the saw at elevation there should be room to go after all the compression you can easily get.

Watch the ring end on the exhaust side when you widen the exhaust, 361 stihl is simmilar and there is very little room to widen the exhaust towards the flywheel side where the lower ring end pin is located.

Used solder to measure the profile of the chamber dome, then wrote a CNC program to follow the shape of the dome. Taking a 0.020" deep cut.




A very gradual taper, no sharp steps. Still plenty of meat left on the top land (0.120"). Life is good.


Thrice measured zero squish chamber volume with new pop-up. 4.2, 4.3, 4.4 CC. Call it 4.3 CC.

0.025" squish will bring total volume up to 5.5 CC, UCCR up to 11.3:1. Wow.

Yes, I could take off more, but let's give this a try. It's possible that the saw may see occasional use at lower elevations, so I don't want to make the compression ratio too crazy.

It's easy to hop up these Efcos. They already have a tight combustion chamber, so people at lower elevations will get plenty of compression just by setting minimal squish. Why can't Stihl be that way ?

You seem to be talking 4 stroke uncorrected compression ratios, if you calculate the compression ration on the trapped volume when the exhaust port closes you will get a more meaning full number more in the 6:1 to 7:1 range.

Problem with the uncorrected compression ratio is it does not take into count the exhaust port being open and not truely starting to compress until it closes. There is dynamic compression, but thats a whole other thread.

Nice work on the crown! But I still think there is a good bit left on the table if you want to gain a little more on tightening it up.

timberwolf said:

You seem to be talking 4 stroke uncorrected compression ratios

Click to expand...

Correct. Trapped volume is more accurate, but UCCR seems to correlate well to real life compression results with typical work saw port timing (assuming the rings seal decently). I'm thinking a 10.5:1 UCCR is required to get 165 psi at my altitude.

I haven't calculated the compression ratio based on volume above the exhaust port, but one of these days I should do that.

Is there a particular compression ratio that you like to aim for ? Do you go by static CR or dynamic ? I'm familiar with dynamic CR for 4 strokes, but haven't run across a formula to calculate it for 2-strokes ?

Nice work on the crown! But I still think there is a good bit left on the table if you want to gain a little more on tightening it up.

Click to expand...

It is tempting to make a 0.040" pop-up, isn't it ?

My thinking is that I can always remove more metal later, but it is tough to put it back on ! ! !

I'd like to be able to run regular pump gas, if the need arises, though I did pick up a jug of premium for my newly hopped up saw. All the gas here is ethanol, and sometimes it's pretty questionable stuff, especially after it has sat in my 55 gallon gas drum for 6 months or more.

I have been using corrected CR then applying a trapping efficency to get at cranking compression.

Trouble with uncorrected is based on that method as saw with a 155 deg exhaust duration would have the same cranking compression if the exhaust was raised to 195 deg. Working uncorrected is good as long as no drastic changes are going on with exhaust durration keeping it near 160.

Also I'm looking a peek cylinder pressure as another indicator of what can be tollerated as a work or race saw. Some factoring in needs to be done as a 50 cc small bore longer stroke saw can handle a good bit more cylinder pressure than a way oversquare big bore 100 cc 066.

Looking at the location of the lower ring end pin it is well outside the skirt so no worries of it dropping into the exhaust port like on the 361.

Nice to see other brands getting some play time. I have a new 156 here and have been thinking of getting a 162 head for it.

Might as well take advantage of the .120 crown and cut a .020 popup. I'd set the squish at .018-.020 too. If you don't want the compression that gives you, you can raise the exhaust and buy yourself some additional blowdown.

blsnelling said:

Might as well take advantage of the .120 crown and cut a .020 popup.

Click to expand...

The 0.120" top land is after a 0.020" pop-up was cut.

Yes, I could cut another 0.020" and still have a safe 0.100" top land. The UCCR would be around 13.3:1

This is totally different than working on a Stihl 660 where you have to fight tooth and nail for good compression.

But, I like the personality of this saw's powerband, and don't want to change it too much. I just want more of the same. If it'll pull a 24" bar comfortably, I'll be happy.

I'd set the squish at .018-.020 too. If you don't want the compression that gives you, you can raise the exhaust and buy yourself some additional blowdown.

Click to expand...

That is a possibility.

The nice thing about the Efcos is that you do have all these different choices for tuning. You're not boxed into a corner like you are with the 660.

StihlCrazy said:

I have a new 156 here and have been thinking of getting a 162 head for it.

Click to expand...

If the 56cc head is still good, I'd keep it, but make a custom gasket to drop squish down to 0.020". Mild woods port, bigger muffler exit. Efco left a lot of power on the table for you to take advantage of.

Yesss!

About frikin time somebody do up an EFCO. Thank you! Too bad Im not smart enough to contribute to the valuable info contained in this one.opcorn: but im here to learn on my brand of saws.

Exhaust port after porting and sanding. Not nearly as pretty as some of the work that has been posted on AS, but it's an improvement over my previous jobs.


Exhaust after porting.


Muffler and muffler gasket get port matched.

Knocked a lip off the bottom of the lower transfers, but otherwise left the transfers alone.


I wasn't happy with my work on the intake. I intended to make it 10% wider, but it ended up 14% wider. I intended to merely flatten the bottom of the port, but ended up lowering it about 0.3mm. It's not 100% symmetrical, either, but I'm not going to take off even
more in the name of symmetry. More practice and more patience is required ......:newbie:

Your port work is looking fine, especially the exhaust port. I'd recommend squaring up the intake a little more though. Make those sides as straight as possible. That way you get maximum area ASAP.

Flashing ground off piston windows and windows widened slightly. The Efco piston was pretty good as it came from the factory, so there wasn't much room for improvement.

Nice work! Glad to see someone do an Efco. Imho their pro saws are the most under rated saws on the market. We used the pizz out of our CS 56 and have been extrmely happy. The five year consumer/two year commercial isn't a bad warranty either. One thing is for sure, with their filter setup your going to get plently of air through the saw.

Earlier, I claimed that the cylinder bore had good plating all the way to the top. After cleaning up the jug and examining it closer, I have to take that back. This jug has a gouge at the top of the bore. It's not the worse gouge I've ever seen, but it's there, and I can "catch" it with a piece of bent copper wire.

The gouge is accidentally made by the boring bar that machines the squish band. It's not unusual, even on OEM jugs (it's even less unusual on aftermarket jugs.)

As best I can measure, the defective bore extends down 0.100" - 0.120" max. The piston has a 0.120"+ top land, plus 0.025" squish, so the top ring should remain on good bore. I wouldn't dare drop the jug any more than what is already planned, though.


Just recently, I gave Grande Dog a hard time because a couple of his NWP jugs had defects at the very top of the bore, so if Grande Dog is reading this, he's probably feeling a little bit better right now. But hey, Grande Dog, at least the Efco jug is still 100% usable for both rings, even with a pop-up.

In other news ...... machining a 48 mm sleeve for the modular mandrel.


Cleaning the old fibre gasket off the base. Works better than a putty knife.

After several final tweaks to the squish and port timing, here is how it ended up:

0.025" - 0.028" squish (one of those squish bands that tapers all the way to the very edge, lotsa luck getting consistent squish measurements)
157 degrees exhaust duration, measured with degree wheel
156 degrees intake duration
12.5 degrees blowdown
5.52 cc total chamber volume, including squish
11.1:1 UCCR

Final port map.


For comparison, the port map calc spits out 161 ex/ 155 in/ 15 blowdown. The port map numbers are sexier, but the degree wheel measurements are probably more accurate.

When I went to install new NWP pin clips in place of the cheesy OEM clips, I noticed the Efco piston has no cut-out for installing/removing clips. Further complicating matters, the OEM clips seem to be made of thinner wire than most other 12mm clips, so a thicker clip would not fit in the groove, anyway. You are pretty much stuck with the OEM clips. I haven't had the slightest problem with the wimpy clips, but Olyman mentioned that one of his Efco's spit a clip.

I'm going to call it a night. Tomorrow, I'd like to fab a new deflector for the muffler outlet, which could take some time. The Efco might be cutting wood by tomorrow noon.

Anyone care to guess how much she'll blow ? We started out at 144 psi and 9.1 UCCR. The exhaust port was only raised 1/2 mm, and now the UCCR is 11.1. opcorn: