Mac 101 muffler fail!!

[Al Smith]

--and another .Tinkering around trying different carbs on my little hot rod Mac 6-10 ,right hand start 70 cc not pm 610 ,lost a screw from the throttle plate .Got sucked into the transfers and jambed it up ..didn't ding,smash anything .That was really lucky .
The carb was built from several having a larger choke butterfly than the throttle body which I think acts like a ram tube .I think it's a Walbro .The butterflys had a little itty bitty screw holding the plates which were supposed to be peened which in my haste I had over looked .S---t happens .

 

[Dub11]

So I got home after work, head back into town and got some groceries,I get back home I decide to fire up the 101 and keep the seals lubed up! LOL
Fired up like normal let it sit there and idle for a good five minutes give her a few revs sounded real good and then boom! Take a look at the saw and the muffler is blown out! I thought maybe something was thrown out of it, pull the muffler and find it sucked a part of the muffler in! Suck!!
View attachment 204529 View attachment 204530Ya I am bumped!

Holy *s-word! You should have a trigger warning on this thread before opening.

I have the sads now.

 

[Lee H]

It’s can be bored, it’s .024 over now, .030 will probably clean it up, and they can be bore .060 easy...will see

Terry Ives has pistons up to .068 over in every .004 increments.

 

[Lee H]

Don't feel bad. I lost a 101 motor in my geardrive saw. It had many tanks through it. At one of
my GTG's I started it and bang it locked up tight. I knew exactly what happened. The wrist pin
moved and the needles came out. It was at 40 already and the block was toast. I now use Terry
Ives over size wrist pins in all my 101's and 797's.

 

[Steve]

Don't feel bad. I lost a 101 motor in my geardrive saw. It had many tanks through it. At one of
my GTG's I started it and bang it locked up tight. I knew exactly what happened. The wrist pin
moved and the needles came out. It was at 40 already and the block was toast. I now use Terry
Ives over size wrist pins in all my 101's and 797's.

Lee, ive heard alot of the wrist pins moving and needling the engines. Could you also use a shorter wrist pin and use two closed bearings like the mini- macs do? Instead of typical Mac one blind, one open bearing?

 

[Steve]

So I got home after work, head back into town and got some groceries,I get back home I decide to fire up the 101 and keep the seals lubed up! LOL
Fired up like normal let it sit there and idle for a good five minutes give her a few revs sounded real good and then boom! Take a look at the saw and the muffler is blown out! I thought maybe something was thrown out of it, pull the muffler and find it sucked a part of the muffler in! Suck!!
View attachment 204529 View attachment 204530Ya I am bumped!

That's real chitty Nathan!


I've come to do the same as you have here anymore. Cuss it, tear ot down, fix it, run it again!

A few years ago i would have been so pissed and discouraged i would have thrown it across the yard and never touched it again!

 

[Al Smith]

In general conversation I feel that design of the bearings in the piston was one of the weak links in that design .I've never had a reed valver loose the bearings but I have rebuilt several of the ten series that have .It wasn't a good idea as far as I'm concerned .
What I don't know is if back in the glory days of two cycle racing if somebody might have made a rod bearing assembly with a caged needle in the rod and circlips on the piston .If not they should have .