John Deere CS71 Olympyk 970 Project: Mild Porting and Port Timing Questions?

[j_franich]

Back in 2006 I purchased a box of John Deere CS71 parts off of eBay, the saw had consumed a circlip and destroyed the cylinder. It was being used commercially and was over a year old so it was no longer under warranty, I'm pretty sure I gave $75.00 for it. Well life happened, I moved to AK and sold the saw to my buddy. This fall I moved back to MI and ended up getting the saw back in the same condition I left it (just covered in more dust). Not wanting to spend a lot of money on this saw I ended up buying a used Olympyk 970 cylinder with a lot of aluminum transfer on it for $40, it looked to be the same minus the compression release. Some muriatic acid, sand paper and a Mako piston (not impressed) and I'm almost in business. I did some work with the dremel and widened the exhaust enough to leave 2mm of piston skirt on either side, widened the intake a bit and did a little grinding on the transfers.

I received my degree wheel this week and decided to see where this saw at, hopefully the numbers I have gathered make sense:

161 degrees Exh dur
145 degrees Int dur
19 degrees blowdown
.026" squish w/ homemade gasket
170 psi compression w/o having been started

If my porting timing numbers look legit(first time w/ a degree wheel on a saw), I would like to know from those that have successfully ported these saws if I am headed in the right direction.

I'm still waiting on a few small parts from Bailey's so I won't be able to start the saw until later in the week.

Thanks for taking a look!View attachment 277181View attachment 277182

 

[j_franich]

Since I had the room I removed the base gasket and used Hondabond 4. I put the degree wheel back on, more to get more practice with it than anything, and here is what I found:

Exhaust Duration 160 degrees
Intake Duration 144.5 degrees
Blow Down 19.5 degrees
Compression 175 psi cold w/o having been started

I had been waiting on a new intake boot and it came in today, final assembly went smooth except for being short a few bolts. Having been a box parts for the last several years this wasn't too surprising. The bolts holding the muffler on were borrowed from an Earthquake CS3816.......Earthquake and Efco seem to get about the same amount of respect on this site so I wasn't too concerned.

I threw on a new 20" Sugihara hard tip bar, a new loop of Oregon 72DP chain and turned the oiler up all of the way. For whatever reason it took quite a while for gas to make it to the carb, and I was beginning to wish I had found a cylinder with a decompression valve. It did eventually start and idled quite smoothly, much smoother than I expected. After a couple of warm-ups and cool-downs I tuned it by ear and put the tach on it, it was sounding quite rich still at 12,300 rpms but I wanted to err on the safe side. The one thing I am really impressed with is the throttle response, it is very crisp.

Since I don't YET have a saw testing log in my front yard I walked back into the woods and found a downed poplar to play with. I ended up leaning it up some more as it was four stroking all of the way through the cut. Since I had never ran the saw before I can't really say how it compares to a completely stock saw, but overall I am quite pleased. It doesn't scream like my ported Echo CS600P (currently tuned just under 14k rpms and still four strokes), but it has fantastic throttle response and good torque.

Now to decide which saw to tackle next; Husqvarna 575xp, Jonsered 670, the stock CS600P, or one of the CS56s. The last pic is of my clutter......I think it is time to build some shelves for the growing saw collection.

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[j_franich]

[video=youtube_share;uQmN3p_cRpg]http://youtu.be/uQmN3p_cRpg[/video]

Here is my first attempt at a video. The frozen poplar cut a lot harder than I expected, I broke out a couple of other saws just to make sure it was actually cutting hard and not something wrong with the saw. The saw is tuned to 12,400 rpms in this video, one tank of gas after the rebuild. Now I can see why this model isn't all that popular, it was at least 2-3 seconds slower in the cut than my Echo CS600P (it took 45 mins to upload this video otherwise I'd add the Echo video for comparison). On the positive side of things this saw started on the second pull after spending the night in the unheated garage. Now I'm on the hunt for a good CS81, 980, 981, or 181 cylinder so I can try out this saw in the 76.5cc configuration.

 

[Hedgerow]

That's a good looking saw!!!
Did you lower the intake floor to to open the intake sooner??? Also, these saws like a lot of compression... Like 200lbs +.
They sturdy runners though...
And sexy in JD Green!!!
Rep your way!!!

 

[j_franich]

That's a good looking saw!!!
Did you lower the intake floor to to open the intake sooner??? Also, these saws like a lot of compression... Like 200lbs +.
They sturdy runners though...
And sexy in JD Green!!!
Rep your way!!!

I agree about the color, I probably would have never given an Efco saw a second look if it weren't for the JD Green......now I have a fleet of them. The intake is currently opening at 72.5 degrees BTDC. This is only the fourth saw I've been into so I've been fairly conservative w/ the grinding. I have a couple of lathes, but I have yet to uncrate them since the big move.......I trying to hold out until I *hopefully* build a new garage this summer.

Here is the video of my Echo CS-600P in the same wood for comparison.

[video=youtube_share;jBxH50SlSHk]http://youtu.be/jBxH50SlSHk[/video]

 

[Hedgerow]

People underestimate the cs600...
focus on increasing your intake duration on that Deere.
Also, if you're looking for a few more RPM's, you can remove the bottom ring...

Is it snowing up there right now???

 

[j_franich]

It is snowing lightly right now, we've probably gotten 2-3" in the last 24 hrs. Overall we have not received very much snow this winter, certainly not enough to bring the levels of the lakes back up.

I really enjoy the CS600P, I bought one new and then ended up with another one that needed a piston. My plan is too keep the new one stock for as long as I can so I have something to compare my modded one too as it progresses. We'll see how long I can leave it alone!

 

[Jacob J.]

The Olympyks are typically tuned to make their power at a lower RPM range. It's a holdover trait from when they mainly manufactured concrete saws. From what I can tell, your exhaust duration is near to good. I'd give it more intake an a little less blow-down.

 

[Hedgerow]

It is snowing lightly right now, we've probably gotten 2-3" in the last 24 hrs. Overall we have not received very much snow this winter, certainly not enough to bring the levels of the lakes back up.

I really enjoy the CS600P, I bought one new and then ended up with another one that needed a piston. My plan is too keep the new one stock for as long as I can so I have something to compare my modded one too as it progresses. We'll see how long I can leave it alone!

I picked up a cs600 in a trade deal. New in box... Immediately removed the tabs and tuned it fat... Let my nephew take it and try it...
By tank 5 he bought it from me, by tank 39, we re- tuned closer to where it should be...
He sold his Stihl... :msp_sneaky:

 

[j_franich]

I appreciate the input from you both. I've always loved working on engines, when I was about 7 or 8 my grandfather gave me a complete Briggs & Stratton WM engine to tear apart. I took the wood sides off of my little red wagon and turned it into a work bench, the engine never ran again (that isn't to say that it won't someday) but it was a great learning experience. It has only been in the last couple of years that I have become patient enough to experiment with different engine/fuel management modifications, rather than just repair and ride. Up until the last few months it has been primarily on motorcycles, but I've really grown to appreciate the more manageable size and cost of chainsaws. I have less into my dozen or so chainsaws than I do into one of my used enduro bikes.

I'll plan on running a few more tanks of gas through this saw before I tear it back down and revisit the ports. I'll keep posting updates and asking questions.......I've learned a lot from lurking on this site and I still have a lot to learn. Hopefully someone will find these projects useful or at least entertaining.

Thanks again!

 

[j_franich]

No new videos today, but I did revisit the frozen poplar log with the CS71. I leaned it up a bit on the L and H sides, and it is currently turning 12,800 rpms. The plug was still nice and brown, and the saw seemed to be running stronger. After a few cuts I switched over to the 24" bar and full skip chain, and did some free-hand milling......the saw is definitely running stronger.

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[Hedgerow]

Get a few more tanks through it... It's still a sexy looking saw, in my opinion...
Tune it after 15 or 20 tanks and see what it wants to run for RPM's...
Is it snowing yet???