McCulloch Chain Saws

[heimannm]

Remember that on the primer/purge bulb, the shorter nipple is the vacuum side and the longer nipple is the pressure back to the tank.

Mark

 

[Syncop8r]

One of them was labelled "IN" - I guess that would have been the shorter one?

 

[edju1958]

I have a 38cc Mac Cat (not sure what the exact model name is) that I think is similar. I had trouble figuring out which way the fuel lines go when reassembling it and found a really good video by Steve's Small Engine Saloon that explains how the purge bulb works and which line goes to where. Here's a still from it showing a mock-up he did to explain the process:
View attachment 830609
They key thing is that the bulb doesn't prime the carb with fuel; it purges air (and inevitably some fuel) from the carb. Learning this helped me understand the direction of flow.

Here's a still from someone else's video (for a plastic Mac IIRC) showing the fuel lines and where they go:
View attachment 830610
#1 sucks the air and fuel from the carb, #2 drops the fuel back into the fuel tank and #3 draws fuel from the tank into the carb.

Finally here is a photo of my Mac Cat (up the other way to the above photo) showing the (broken) fuel pick-up line on the left, the line from the carb to the purge bulb (partially hidden and in a backward "S" shape) and the one on the right goes from the purge bulb back to the tank:
View attachment 830611

My apologies if this is stuff you already know.

Thanks for your help,much appreciated! I'm looking to find the correct size fuel line I need for replacement.I usually buy it in 25 ft.coils so I have it on hand.The only piece I have left is about 8 in.long & doesn't have a size stamped on it like most of the other line I have do.

 

[fossil]

I have been having issues with the home computer, keeps telling me "access denied", no problems with e-Bay or the Other Power Enthusiasts site...the computer in the museum office did the same thing once or twice but it's working right now.

I will try to catch up on some comments when I can find time, Mrs. Heimann is celebrating a birthday today.

Many of the earlier 10 Series did not have locating pins for the piston rings, but from the 7-10 and on they seemed to all have them. Without the pins the rings may rotate on their own even though you locate the end gaps correctly when you put the saw together. I usually try to put the gaps around 120 degrees apart in the area on either side of the intake port but I'm not sure if that really helps or not.

There were some saw including the CP125 that used Tillotson HS 43, 70, and 71A carburetors that have the same throttle and venturi size as the smaller SDC's.

Some of the SP125's also had the smaller SDC on them and when I switched one over to the larger carburetor you could easily tell the difference.

More later as time & computers allow...

Mark

Mark,

Out of curiosity because I know there appears to be some substitutions on the SDC carbs,. Is that SDC carb application list from MAC?

I was looking at my 700's, one older, the other the late model with the grey tank, and both have 44A carbs on them

Not sure what to think of the SP80 I have. It's wearing and SDC 18.

Have you seen any SP-80 cylinders with the divided transfers?

 

[edju1958]

Mark,

Out of curiosity because I know there appears to be some substitutions on the SDC carbs,. Is that SDC carb application list from MAC?

I was looking at my 700's, one older, the other the late model with the grey tank, and both have 44A carbs on them

Not sure what to think of the SP80 I have. It's wearing and SDC 18.

Have you seen any SP-80 cylinders with the divided transfers?

Also,the DE80 isn't listed as having an SDC.I don't know what the saw that I got from Mark had on it,but the DE80 I picked up back in Feb.has an SDC on it.BTW,it's getting close to me working on that saw.

 

[Yotaismygame]

Anyone ever machine a longer rod to deal with the huge factory squish? Or a rod from another model? This is for a sp60 squish of .048”

 

[Maintenance supervisor]

Anyone ever machine a longer rod to deal with the huge factory squish? Or a rod from another model? This is for a sp60 squish of .048”
View attachment 830766

It would be easier too offset the crank throw and weld for .020 / .030 , its how the early strokers were done on virtually all car motors.
It's a pretty simple thing and there's lots of literature on it.

 

[Syncop8r]

I'm looking to find the correct size fuel line I need for replacement.I usually buy it in 25 ft.coils so I have it on hand.The only piece I have left is about 8 in.long & doesn't have a size stamped on it like most of the other line I have do.

I have ID 1/16", OD 3/16" in my head for some reason or that may be for the Mini Macs. I don't think I can get that size here though.
I just used some opaque beige stuff that the guy at my local Stihl Shop said was for McCullochs. I used it for oil line as well, the OD was a bit big though.

Hopefully someone can give you a better answer!

 

[rwoods]

View attachment 830465
Picture of the muffler installed with heat sheild. ...

Pixar could make a real character from that muffler shot. I bet he would be pretty grumpy.

Ron

 

[rwoods]

Some of you may already know this fix, but today with Brian's encouragement I believe I have whipped my old nemesis of chain brakes that won't latch. If yours are like mine, you just need to bend the spring to lengthen the straight portion of the spring on the side that engages the trigger. Not the little tab - the straight portion underneath it. A little extra length will make the tab fit jam tight in the trigger. Wish I had known this years ago. The trigger pivot doesn't even have to be tight.

Thank you, Brian.

Ron

I need to revisit this post after running the 800 today. At times the brake would fire on its own, but as the saw got hot it held well. I believe I need to figure out a way to tighten the trigger pivot. Little JB Weld in the hole or possibly a little hammer work on the hole to close it up a little.

Some Memorial Day cutting with the 800. Trunk of a nice red oak. Probably twice that much wood left to pull out. I cut it all but was too tired to drag it out today plus I had other things to get done today.


Ron

 

[Yotaismygame]

It would be easier too offset the crank throw and weld for .020 / .030 , its how the early strokers were done on virtually all car motors.
It's a pretty simple thing and there's lots of literature on it.

Can you explain that a little better?

 

[rwoods]

Can you explain that a little better?

If I recall correctly my 82cc MAC also had a lot of squish room. Tightening up the squish with a taller piston and including a pop up is how I ended up with too much compression with my experimental saw.

Brian and I have discussed both the offset crank and a different approach if you have the tools - similar to a gasket removal (which of course lowers everything). Just take some off the base of the cylinder and an equal amount off the bearing journals. I don't know how much you can lower it before your port timing gets too screwy.

Ron

 

[Yotaismygame]

On a SP60 is there a specific gasket for the fuel tank? I'm not seeing one in the IPL.

 

[rwoods]

If the SP60 is like the other A/V saws the tank is glued together at the factory. Ron

 

[Yotaismygame]

If the SP60 is like the other A/V saws the tank is glued together at the factory. Ron

I'm thinking that's the case. l already have it torn apart. There was a paper gasket in there with sealant all over it. Probably from the past owner.

 

[Maintenance supervisor]

Can you explain that a little better?

Add material to the long side and remove equivalent amounts from the opposite side as necessary for rod fitment therefore increasing the stroke by offset of the crank.
But like others have said I have no idea how that would affect the timing of the piston ported saws.
This technique used to be referred to as the "poormans stroker" because forged cranks were worth their weight in gold, but since they 90s most of the major metal forging has been farmed out to Asian countries its cheaper to buy then fabricate.

 

[Todd Loosli]

You would have a tuff time with a 2 cycle crank. You have to get the crank hard enough to run a needle bearing on it. Tuff when you are welding on one side and grinding on the other.

 

[Jethro 2t sniffer]

Welding a pop up seems a whole lot easier even machining the bearing bores and dropping the cylinder if need be

 

[Max the Mac Man]

If the SP60 is like the other A/V saws the tank is glued together at the factory. Ron

Yeap and they can be a real pain to separate. I have had a few that i never could get apart. I just got this 8200 tank resealed from a bad fuel leak and painted Saturday. letting her set for a few days to cure. Nothing fancy, just figured new paint would be nice while I had the tank off.

 

[Aaron Rybicki]

Trying to replace a recoil spring on an SP125.
Is there some trick to this? Seems like the housing is on there pretty good with not much to grab on to rotate it off.