McCulloch 7-10 needs your help (rebuild)

[vizette]

OK I need your help, and by proxy so does the saw.

Background: ebay buy, got it running, idles, about 120lb compression, NO guts. I've got two 10-10 with more grunt and those are ~120 too. I assumed it was exhaust scoring based on what I saw looking down the intake. Took it apart to better evaluate, doesn't look nearly as bad as I expected...

piston/rings/cylinder:

• Rings look OK but will replace anyway since I'm here
• Piston isn't terrible, one not-so-great spot on the top.
  
• Most markings on the cylinder don't feel bad, except for the obvious bad spot at the exhaust port, and even that doesn't feel that bad, except for right down the middle of it. I'm thinking some gunk got sucked in, scraped the top, and then scraped up the exhaust side on the way out.

Bearings and seals:

• Bearings feel good, no slop
• Going to replace seals since I'm here
  
• Any "gotchas" on the seal replacement?

Cosmetic; when you paint, do you use an etching primer? Just shoot it raw? It doesn't need to be a beauty queen, just want to make it look nice again. It'll definitely get used once back together...

Still not sure why it was so weak, unless it's that ugly mark on the exhaust side, but I've seen a lot worse do a lot better. I did check the compression release valve, it's working as expected. Exhaust is new, so no carbon blockage.

tag is: 600052D



Thanks all!!

 

[2broke2ride]

You should post in the Mac sticky. There are a lot of very knowledgeable Mac nuts over there. IMO I would run that piston without hesitiation.
Here is a link to the Mac sticky

https://r.tapatalk.com/shareLink/to...&share_fid=16367&share_type=t&link_source=app

 

[vizette]

You should post in the Mac sticky. There are a lot of very knowledgeable Mac nuts over there. IMO I would run that piston without hesitiation.
Here is a link to the Mac sticky

https://r.tapatalk.com/shareLink/to...&share_fid=16367&share_type=t&link_source=app

Oh I'm definitely familiar with that thread! I guess my debate was visibility, like it would get lost in the 1700+ posts vs something new, but maybe I have it backwards hehe...

Agree the piston isn't bad, still need to check ring gap, but assume they need to be replaced.

Question that I can't answer based on what I see after getting it apart is, why is it so weak? Compression was not horrible, tune was reasonable, idled OK, spun up OK, just no power in a cut...

 

[2broke2ride]

Points not set right causing the timing to be retarded??? Carb not tuned just right???
At 120psi you should still have been making good power. That is getting low but not terrible. These saws make the best power right on the bitter edge of being too lean. If they are set too rich they are slow. They will still cut but they will be slow.

 

[vizette]

I went through the standard tune; lean until runs high, richen until it starts to four-stroke. I tried messing with it a bit in a cut too, it was fairly unimpressive. I have several old Macs and Super XLs that I've got tuned and cutting like madmen, so hopefully I didn't just flub that one!

Honestly though, the compression felt terrible now that I'm thinking about it. The others I can almost pick up by their pull start (sxl's are putting up 150psi). This one, I could spin the magneto with one finger without significant effort - which kind of throws me when it's at 12o psi. That and the scoring are what really instigated the tear down.

Points were something that crossed my mind after the fact unfortunately... Definitely should have checked that! The oil tank needed to be replaced either way, and at that point, you're pretty much at a full tear down anyway. I just don't want to get it back together after all this just to have it fall over again.

 

[rwoods]

The MAC sticky thread is on a 7-10 roll. You are just in time to join the party. Ron

 

[vizette]

You weren't kidding... better to re-post my question in it's entirety in the mac sticky, or link to this thread from there?

 

[Goinwheelin]

Just post your question over there. Copy/paste. Like Ron said, the 7-10 discussion is top shelf right now.