Mcculloch 850 Pro Mac build.

[Steve]

Look real good!

 

[TJ the Chainsaw Mechanic]

Thanks @Steve! Got the piston assy in today to!

 

[Steve]

Great! Is it running yet?

 

[TJ the Chainsaw Mechanic]

Great! Is it running yet?

I wish lol Lot's more parts to paint and then I gotta get new nuts an bolts. Taking the cylinder to the shop tomorrow to clean and port.

 

[TreeLife]

Excited to see the jug get ported, I love old Mac's.

 

[PogoInTheWoods]

Not much porting to do on a PM850 'cept mebbe polish the exhaust.

That OSHA yellow looks like a real nice McMatch. I used Rustoleum Sunburst Yellow on my SP81 and it's close, but the OSHA looks closer. And if you need decals/stickers, I'd recommend Joe Salva at Sugar Creek Supply. Lots of his stuff is on Chainsawr also.

Gotta say I'm pretty envious of your project. Been scrounging for a PM850 for a while now and the closest I've come so far is a buddy in S. Carolina says he has a box full of what he thinks is one and wants my super nice Homelite 1050A in a straight-up trade. Yeah, he's nuts.

Good luck with it and keep the pics coming.

 

[Sleeper]

Not much porting to do on a PM 850 'cept mebbe polish the exhaust port.

That's what I said to him. Plus, leave the step that is cast into the exhaust port... that is there for a reason. When I ported my 850, I took that out. Probably didn't help it run any better.

Plus these are getting harder to find, no reason to risk buggering up a good cylinder by screwing up a port job.

 

[TJ the Chainsaw Mechanic]

Not exactly sure what porting was done, but this guy did something to wake this puppy up. Unless it was just not tuned right before. I noticed you couldn't do all that much so I was gonna open things up a tad and call it good. Be a first port job anyhow so figured I start with something simple. Cylinder may not clean up anyhow as it does have some transfer so we'll see. If anything I wanna polish off the carbon build up on the exhaust cause it's perrty bad.

Ported McCulloch pro mac 850 - YouTube

 

[TJ the Chainsaw Mechanic]

That's what I said to him. Plus, leave the step that is cast into the exhaust port... that is there for a reason. When I ported my 850, I took that out. Probably didn't help it run any better.

Plus these are getting harder to find, no reason to risk buggering up a good cylinder by screwing up a port job.

What's the step for? Sorry if that's a stupid question, just never seen it yet.

 

[Frank bierce]

Looks like a nice project!!

 

[Sleeper]

What's the step for? Sorry if that's a stupid question, just never seen it yet.

The theory is the step causes the gasses to pull the exhaust out stronger, kind of like stepped headers on a drag car. It changes the velocity as the gasses exit and go over the step. Think of a waterfall, it causes turbulence in the port, tumbling, really. So the flow is rolling over the edge of the step.

The step should be all the way around the port, at the cylinder wall, and it extends into the port about 1/8" or so. If I still had my 850's that I took apart, I would post a picture showing that more clearly. But those went to another member here.

 

[PogoInTheWoods]

Not exactly sure what porting was done, but this guy did something to wake this puppy up. Unless it was just not tuned right before.

Just looks like how one should run to me. He posted another vid today of a ported vs. non-ported PM850. The non-ported wasn't too bad and the ported one just sounded like a way leaned out 850. Definitely ran, but didn't look like a true/fair comparison to me. Would like to see pics of his port work on that saw.

 

[TJ the Chainsaw Mechanic]

Slowly getting parts painted up. A co worker of mine is gonna clean up the cylinder for me as he's been working on those macs since they were new. haha He offered...hell why not! Gonna work on getting all the parts cleaned and painted today. Hoping to get this thing back together soon. Wanna let er cut some wood.

 

[Al Smith]

Step??? Are you talking about the "eye brow" in the top of the Ex. port? Lot's of talk about what they were for .Some say it acts like a boost port,some say it was for noise .Others including myself say it acted like a pressure relief at cranking speeds .I'm not certain if all of them had those or if that was a later innovation .

 

[Sleeper]

Step??? Are you talking about the "eye brow" in the top of the Ex. port? Lot's of talk about what they were for .Some say it acts like a boost port,some say it was for noise .Others including myself say it acted like a pressure relief at cranking speeds .I'm not certain if all of them had those or if that was a later innovation .

No, not the 'Q' port... the step on the 850 goes all the way around the port... kind of looks like casting flash, but it is not... it is to help extract the exhaust gasses from the cylinder. 850 has a decomp in the top of the cylinder, so no notch or "eye brow" in the top of the exhaust port. I believe it was the 800's that had this, not sure what other 82cc Macs had this.

 

[PogoInTheWoods]

PM8200

​

 

[Lee H]

PM8200

View attachment 86728​

If this is what a 800 has then now I know why my 850 will give it
a severe arse whippin. My 800 is a dog stuck in a pen. Hope my
Double Eagle 80 don't have this. Haven't run it since I bought it.

 

[Lee H]

I also have a 805 in pieces. Gonna have to take a look at that
one. If it has it, It is going to get welded up and a replate.

 

[Warped5]

Lee, according to my notes here the following saws models have that Q-Port cylinder: PM800 .. PM805 .. Super PM850 ... Double Eagle 80

The PM8200 has a different part number for the cylinder, but the same Q-Port feature.

 

[Al Smith]

I've got both an 805 cylinder and a later model 850 .I think they both have a Q but I'll check tomorrow .It's kind of dark in the shed this late .
I don't remember if the earlier model 850 I have inside of the 805 shrouding had a Q or not .I don't recall the ones with a Q if it were that large .They both had decomp valves and it's chore to pull them over without using same .As for the other 5 cuber,an SP 81 I have no idea .All I did to that one was replace the ignition system .
The SP 81 is the one that closed the decomp on a drop start and walked to rope on me .Scared the chit out of me.never ever again did I toss a larger displacement saw after that .That SOB could have taken my arm off if it had fired .no no no ,not good .