operation fix mc10

[David Luciani]

terry, we never did i.d. the piston but best guess was aftermarket.
wasn't a quick time as far as i know.
had a slightly domed top though so possibly a moss piston.

currently i am considering replacing the old style piston and rod with a mc91 piston and conn rod.
can't find my muriotic acid so i may have to buy more before i can proceed.

d

[ted johnson]

Dave, Moss Precise Lite pistons were flat top with two scallop cuts on the intake sides, not domed. We used to our own at the kart shop. I sold dozens of Moss. Good quality stuff. TJ

[David Luciani]

ted,
i have a couple of that king of moss piston really nice parts.
i was told they also made a slightly domed piston but that i guess is wrong.
so who the heck made the domes piston.

on a different note i got alot done with money work already this week. 
my best help isn't available tomorrow so i have hopes of digging out replacement parts from my stash.
i hope to get my little mc10 going again.
funnily enough while getting the big tray cleared out for build i came accros a project motor i forgot about.
i think it's a mc72 saw motor that i'd stopped on because it wouldn't fit up the mc10 style points set up.
is a mint little motor should've just been finished with mc20 points.
but may build it as a space mc10 9 port clone with electronic ignition..
bwa ha ha

d

[ted johnson]

Don't know. Maybe the domed piston came along after we closed the shop in '63. They must've had to turn a corresponding female dome in the head. We never had more than .020 clearance flat piston to flat head!
We're still busy trying to find someone who'll make the super 260KSI tensile West Bend rod screws. Dave B. doesn't even have one pair of spares he can sell me. TJ

[David Luciani]

i inspected the piston again as the damaged area is making me insane. 
in the ruined section the aluminum seems to have "sugared" in the ring area and gotten brittle.
there's also dragged aluminum on the pistons lower skirt.
the weird part is it happened at the back intake port not anywhere near the exhaust ports.
only thing i know of that could've caused this would be lost lubrication but can't figure out how that happened only on those three ports.
but i'm also leaning towards a sudden air leak overheating the piston .
 i was adding high needle flow at the time but it still went away on the straight towards the end .
finally it could just be the piston was worn out and started chipping on the edge  and over heated.
i've rarely run a mcculloch as long as i ran the mc10 and the piston was used when i got it so i might've just worn out the piston.

i'm trying to figureout what went wrong so i don't get an instant replay.
so i am researching reading piston damage .
here are some neat links.

reading piston damage link to pix and text

another link similar text better pix

good text mostly

this next link is excellent good pix and lots of text
both two and fouyr stroke piston reading of damage

really good pix and text on piston failure

   

i'm gonna try this on the new piston may be a bad idea on mcculloch.
but i will never know if i don't try it!
exhaust bridge lube hole on piston

d

[ted johnson]

I've seen more than one stick other than at the exhaust. How I love alky/castor! I have NEVER lost a piston other than just having it wear out from use, when running castor/alky. Last engine I stuck was my brand new George Pollack open Atlas 1 back in '78. I thought I'd just break it in with the stock HR on gas and oil. Whoops! Didn't hurt the bore at all, but ruined the brand new piston.  That's the engine Charlie Craibe still has on his Black Widow. It's still STOCK BORE!  TJ

[Paul Hunter]

Don't know. Maybe the domed piston came along after we closed the shop in '63. They must've had to turn a corresponding female dome in the head. We never had more than .020 clearance flat piston to flat head!
We're still busy trying to find someone who'll make the super 260KSI tensile West Bend rod screws. Dave B. doesn't even have one pair of spares he can sell me. TJ

Ted - I thought kprecision was good to go on the rod bolts for west bend, sounds like you know otherwise. Whats up?
Thanks Paul

[ted johnson]

Hey, Paul. Kurt Bogerman got some bolts from K Precision, and shortened them for use in his Mac. They went in the rod a bit hard, but screwed in OK when oiled. When he went to actually assemble things, the head just popped off one bolt with almost no torque on it. Jeff Kniseley will examine the bolt when it arrives at his shop. I hope he can get things solved. I think Jeff's an honorable guy-these screws just take an awful beating in our engines. I had a chat with Dave B. last night, and he's concerned about a few issues there. if we could get one of the small-batch aerospace firms interested, we know the proper alloy to use, so a screw could be manufactured that'd be like the old US Motor Power screws that Dave designed. If USMP would install the screws in every engine they sell, the cost could be amortized over the product line. Now, if you're running a Mac, you can get the 101 spline head screws from Chuck Giacobbe, and they'll be fine. They just won't be safe in a West Bend because of the length. Ted

[Paul Hunter]

Thanks for the info Ted, and I agree with you on Jeff. He has some cool performance parts for WB on his site and I appreciate what he is offering us.
Paul

[Michael Burke]

ARP has already done the engineering to make the bolt we need. Unfortunately since they found that they didn't already have the tooling and material for 10-32 threads the cost went up to a little over $20 per bolt in a 1000 bolt production run. I worked with them for a couple of months off and on since I live about 1 mile from their plant and I know a member of their staff. If enough people want to put together an order they will make the bolts. I didn't pursue it further because I was told no one would pay that much and then everyone seemed willing to pay the same price for the new bolts that apparently are having some initial problems. I wasn't going to be selling bolts. All I was doing was trying to get them made.