Mcculloch pro mac 610 20" bar is not working - no idea why

merja01 · April 22, 2020, 11:14:44 PM

I have an old Mcculloch pro mac 610 that I have been running with a 16" bar. It also supports a 20" bar so I purchased an Oregon 27850 20-Inch Bar and D70 Chain Combo. Everything seems to match the 16" bar and chain except it is longer. However, when I run the new 20" bar and chain any resistance in the cut and the chain stops moving even though the engine is at full throttle. I played with everything I could think of to address the issue – no success. If I re-install the 16" bar (also Oregon) the saw works great. Any thoughts on why the 20" bar does not work??

Appreciate any insights as I have some large pine logs that I have to cut through from time-to-time

donbj · April 22, 2020, 11:42:59 PM

Chain fit on the drive sprocket properly?

Evanguy · April 23, 2020, 07:42:57 AM

Not sure if this is the case but a very similer thing happened to me.

My new bar was a .050 but my chain was a .043 so it allowed it to move over enough and the bar would rub/ get hung up in the cut. Getting a .050 chain made it cut like new

EDIT: never mind. I just reread it. My chain was spinning the whole time just not cutting. Seems to be a different issue then what i had.

How tight are you running it? Can you easily pull it by hand along the bar? With the longer bar and if it too tight all the engine torque is going into moving the chain not cutting wood.

sawguy21 · April 23, 2020, 10:53:42 AM

Does the engine bog down when the chain stalls? I wonder if the clutch is worn out.

merja01 · April 24, 2020, 05:16:12 PM

Quote from: donbj on April 22, 2020, 11:42:59 PM
Chain fit on the drive sprocket properly?

Best I can tell it does - seems to be the same size as the chain that works on the shorter bar.

merja01 · April 24, 2020, 05:17:51 PM

Quote from: sawguy21 on April 23, 2020, 10:53:42 AM
Does the engine bog down when the chain stalls? I wonder if the clutch is worn out.

No the engine will run at max RPM, but chain stops, but will start to spin again if it is not under load (i.e. I take it out of the cut).

Evanguy · April 24, 2020, 05:29:01 PM

Id say the clutch is gone then. Its slipping under load

merja01 · April 24, 2020, 05:39:07 PM

Quote from: Evanguy on April 23, 2020, 07:42:57 AM
Not sure if this is the case but a very similer thing happened to me.

My new bar was a .050 but my chain was a .043 so it allowed it to move over enough and the bar would rub/ get hung up in the cut. Getting a .050 chain made it cut like new

EDIT: never mind. I just reread it. My chain was spinning the whole time just not cutting. Seems to be a different issue then what i had.

How tight are you running it? Can you easily pull it by hand along the bar? With the longer bar and if it too tight all the engine torque is going into moving the chain not cutting wood.

Thanks I keep looking and it is the same size chain - just with more links they are both marked as Pitch: 3/8", gauge: .050"

merja01 · April 24, 2020, 05:40:46 PM

Quote from: Evanguy on April 24, 2020, 05:29:01 PM
Id say the clutch is gone then. Its slipping under load

Thanks, but with the smaller bar/chain it cuts perfectly find with no slippage.

dougand3 · April 24, 2020, 08:46:40 PM

Does the bar say 200PXDD176? Yes = good. Count the chain Drive Links - should be 70. Driver should have 72 on it.
If you can mount the 20" bar and chain and turn it easily by hand.....this makes little sense. If engine was bogging, it'd still cut but like a dog.
If clutch was slipping, it'd slip at least some on 16".
Are you pinching the bar? A longer bar has more surface area to pinch.

merja01 · June 13, 2020, 09:13:36 PM

Link counts etc. seem fine. I replaced the rim shot because I saw that was chewed up, but it is still mis-behaving with the longer bar. What I noticed is I can move the chain b/f easily until I just start to tighten the cover. I can simulate the problem with the cover off by applying pressure to the bar in the same areas where it would be tightened down. As soon as I push the bar firmly again the body of the chainsaw the chain will start to bind and no longer moves easy b/f. There are a couple "shims" - I think they call it a bar plate that site directly underneath the bar. There are currently 2 of these "bar plates" behind the bar (as it was setup with the smaller bar)....I am wondering if I need more of these bar plates or thicker bar plats to work with the longer bar. Does what I am saying make any sense?

dougand3 · June 13, 2020, 10:45:15 PM

The 610 should have 1 inner bar plate - big, it goes around the clutch crankshaft and 1 smaller outer bar plate. The upper and lower "flaps" should point AWAY from the chain. There is 1 shim washer on the engine side of the rim sprocket.

merja01 · June 14, 2020, 05:17:05 PM

Hmm, that makes a lot of sense. Right now I have both of the plates between the bar and the engine. I have played with moving them around, but I will try to set them as you recommended. Regarding the washer on the engine side of the rim sprocket, I don't have a washer there. All I have is a polished steal surface for the rim sprocket to ride on. - Very much appreciate the sharing of your knowledge!!

dougand3 · June 14, 2020, 07:36:04 PM

If you don't have a washer on the crankshaft (closest to the crank seal)...I don't know how the rim doesn't slide off the clutch drum and bind.
Look how it's supposed to go....
http://s30387.gridserver.com/partsDiagrams/McCulloch%20Pro%20Mac%20610%20and%20650.pdf

merja01 · August 15, 2020, 02:14:07 PM

Thank you for all the replies to this thread - a lot knowledgeable people on this forum.

By correcting the positioning of the plates I did get the chain on the 20' bar to move freely. However, when I try to cut the bar/chain bounces off the cut. I think it is because it is not moving fast enough. Best I can tell is the engine in this McCullough pro mac 610 just doesn't have the power to move the chain on the 20' bar fast enough. Going back to the 16" bar seems to work okay.

In any event, my wife was sick of me playing with it and told me to just buy a new one (couldn't pass up the offer). So, I just purchased a Stihl MS 271 Farm Boss. with a 20" bar. It cuts great and is even a bit lighter than the old McCullough, but I kept the old saw around as a backup and maybe I will fiddle with it some more if I have time.

Thanks again for all the insights!!!

Al_Smith · August 16, 2020, 04:00:05 AM

You've got something hanging up slipping the clutch which must be worn out .If not so it would be bogging the engine .I've got three of that model and it will pull a 24" if you want it to .They might only be 60 cc but they have plenty of power .However for 60 cc they are heavy .
I looked at the IPL and it does have a shim washer inboard from the drum which possibly could allow the drum to move inboard therefore having less surface area contacting the clutch .If so I would think the drum would show excess wear perhaps blue in color from being heated up .
Another rarity might be the drum bearing is so worn out it allows the drum to run eccentric which would cause the drum to round out causing less surface area .If it is any of those it should be visible .
McCulloch made a million of this model under different model numbers and others like Sears and Roebuck sold them under their brand as did Wards K-Mart later sold a basic model on sale for $169.95 with a 16" bar circa 1980 .There is
still a good number still in service and zillion of them sold used in the $50-$75 range .You might find a few in a saw dealers dead pile they would give you for parts . Other than being heavy they are good old saws and really pretty tough all things considered .