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McCulloch PM 605 Chainsaw Repair and other adventures

September 2021

I had to repair my McCulloch PM605 chainsaw. The last time I was using is, I started hearing this clanging while it was running. I thought it sounded like a the clutch was loose, but on inspection, I found the clutch in good order and discovered that the flywheel was loose. The center hub of the flywheel broke loose from the aluminum casting. It eventually dawned on me that while I was cutting wood, I stumbled and fearing that I might fall on the saw, or it fall on me, I threw it. Well, I guess it hit hard enough to break the flywheel.

The original flywheel on the left. The new one (after I cleaned it up) on the right.

The clutch cover and recoil starter after I cleaned them up.
The Finished Saw Here it is, all finished and ready to rock!

One of the really nice things about this saw is that it is part of a family of saws made by McCulloch (PM 605, 610, 650, Eager Beaver, etc) that they sold thousands of, and so there are lots of parts available.

It is a rugged and powerful saw. It is heavy for the horsepower it produces, but maybe that's why its so rugged. I've owned this saw since 1988, and this flywheel issue is the only the second thing I've had to repair. The other was when I broke the chain brake handle, but that was due to my abuse, not a defect or weakness with the saw.

October 8, 2021 - a new Pro Mac 610

I'm going to Columbus today to buy a McCulloch PM 610 for $30. It looks very complete and in decent shape. The seller says it has good compression. I figure it's a source of parts if nothing else, but I'm anticipating being able to run it. We'll see. It's a $30 adventure.

Update 6:05PM - I got home with the saw, pulled the spark plug and it looked brand new around the electrode. Except for the dirt at the base of plug just below the boot, I would have bet that it had never been used. Amazing! Checked for spark and it has a strong spark. I'm getting excited.

I dumped the little bit of fuel in the tank out. I'm pretty sure was diesel fuel. I put in a little bit of new fuel. I splashed some fuel into the top of the carburetor and with a few pulls it fired. With a few more pulls it was running. It smoked a little bit at first, but cleared up in a minute and ran good. Macs are just very reliable.

When I was getting the saw, the seller met me on his front porch and he said, "You don't have to feel obligated to buy it, if you don't want to. That's OK. Don't feel obligated at all. Its OK if you don't want to buy it." I figured that either he knew it was a total wreck and felt guilty about selling it, or he realized what a bargain price he was selling it for and was hoping I would back out. I was betting on the latter.

This new saw has a shorter bar than my PM605 and it came with a chain cover. The air cleaner cover is broken, but still completely functional. It wouldn't have to be replaced, but to make the saw look new, I might get one.

I'll have fun cleaning this all up (it's alreay been a hoot) and I'll have a really nice saw when I'm all done.

October 23, 2021
I'm back on the chainsaw today. I've been working on my new handsaw the past few weeks, and now that I have it in decent working order, I'm getting back to the Pro Mac.

Here's how I clean parts. Take them to the basement and scrub them with soap and water.
I've got it taken down pretty far, and am about done cleaning. Back together soon!

The bar is messed up. I'm not sure how someone did this, and I'm not sure of the impact. I filed it to clean it up. I think I'll get a new 20 inch bar and chain.

Octoer 25, 2021

I was starting to assemble the saw last night. I found that the chain adjuster screw was bent. It wouldn't be hard to do, because you have to line up the dog on the adjuster in the hole in the bar and then put the cover on and tight things up. But when you put the cover on, things want to fall out of place, and so if you start tightening without making sure things are right, you can bend the screw. So I took it out, straightened it and chased the threads. Now it's ready to go.

I also notice that the bar is badly boogered up. I have no idea how you could do this. I cleaned it up with a file, but there's not filling in the chipped out part of the bar. So I'm a little torn. I didn't really want to put any more money in this saw, but it's crying for a new 20 inch bar and chain. No idea why they made the bigger saw with a shorter bar. My 605 has an 18 inch bar. It may have originally come with a 16 inch.

October 25, 2021

Together and running great.

When I look at this, I'm really impressed. It looks great huh?

One last improvement needed: It needs a velcro strap or small bungee cord to hold the chain guard on. It is a very loose fit on the bar and easily slides off.

Oh, the depth gauges need to be filed too. It was not cutting great when I ran it the first time.

I need to order a new air filter for it. I'm waiting to decide if I buy a new bar and chain too.

November 13th, 2021

The PM 605 is back in the shop. I was cutting with it on Friday and toward the end of the work, I heard it rattle-clanking. It sound all too much like the sound I heard when the flywheel was broken (see above). I found that the nut holding the flywheel was loose. The woodruff key is battered so I need a new one. I'm not sure why this happened. The shaft and hub both seemed sort of dirty. Maybe there was dirt that kept the hub from seating on the shaft and as the crud disolved, the nut came loose.
I've ordered a key from eBay. NOS, $5.90 delivered.

November 26th, 20201

I've been tearing my hair out, trying to make the flywheel tight on the shaft. Long story short, I've discovered that the hub is loose on the flywheel. Now I'm wondering if that was the case from the start with this used flywheel. I'm guessing that is the case. So now I have two flywheels with the same problem. I found a video on Youtube where I guy did what I've been pondering, and that is to drill and tap some holes right at the seam of the hub & flywheel and put screws into it. Since I have two bad flywheels, I think I have nothing to lose by giving it a try.

I'm going to run the idea by my dad and see what he thinks.

December 14, 2021

I've drilled and tapped four holes on the perifery of the flywheel hub. And then I filled the holes with LocTite red and ran set screws into the holes, hoping the LocTite would be pushed into the gap between the hub and flywheel. Here's photo and video that explain it.

Youtube version

January 10, 2022

I had a tree to cut up over the weekend and used the Mac PM605 with this repaired flywheel. It held up at least for the work that I did. I didn't go through a full tank of fuel, but probably ran it for 15-20 minutes total. I'm encouraged!