Building for durability a working Mac 850

[rwoods]

I posted on the Mac thread and got no replies. Maybe someone over here will give me some good advice. I have a NOS cylinder for a PM850 (82cc) and will be purchasing a new piston which will be ceramic top coated by JetHot and antifriction coated on skirts. I also will have a NOS SP81 muffler ceramic coated by JetHot (should result in a better chimney effect and remove more heat as well as draw more fuel). My questions are: Should I attempt to cleanup the ports (zero experience) or find someone on this site to do it for me or leave it alone? Will a light coat of flat black paint on the cylinder dissipate more heat than leaving it bare or will I actually be retaining more heat? Within reason is my premise of cooler is better, correct? Thanks in advance. Ron:newbie:

 

[little possum]

I think you should try this in just the chainsaw forum, more likely somebody can help you out over there.

 

[SawGarage]

Ron...answers?

Hey Ron,

did you get some answers? I have some, if you haven't

J

 

[rwoods]

Hey Ron,

did you get some answers? I have some, if you haven't

J

Just saw your question as I changed forums in June. No. I have gotten any answers except leave it alone. This may be a long project as I keep using up my donor parts to repair other "donors"; can't seem to bring myself to give up on an old saw.

Any help you have would be much appreciated. I have a PM800 among my collection of working 82cc Macs that screams and runs like crazy with a 28" bar; yesterday as I was bucking some 24" to 26" red oak, I was asked if it were a race saw. I have no explanation for the marked difference - I may have to pull the muffler and look.

I also noticed a post in the MAC thread of someone saying his father once had a ported PM850 for firewood cutting before he leaned it out.

Thanks in advance,

Ron

 

[WoodyWoodsWood]

Dads saw

My dad has a pm850 I cut about a cord of wood with it yesterday and loved every minute of it. Thats all I got to say. Sorry no advice.

 

[Saw Dr.]

I think the reason people are telling you to leave it alone is because of what it is. Those saws run (as you have already stated) quite well for their weight and vintage. 36" bars are not out of the question. The problem is that top ends are getting more and more scarce every day. If you do any mods on it, you risk ruining another good 800 series cylinder and piston. I would consider modding an 850 akin to racing a Delorean on the vintage car circuit. Sure, you can get parts if you have to, but there are many easier way to go racing.

If you do go ahead with the mods, remember that this is a clamshell engine. There is no way to add compression easily like on the bolt-on cylinder models. I would suggest a conservative widening of the ports and call it good. I would also suggest trying your hand at porting on several $35 craigslist saws before getting into the 850 jug. You cannot send your cylinder to anyone good to get it "ported." All of the respectable builders will want the whole engine to check things like ring ends and squish. Good luck