Mac 10-10 piston help.

[wstan101]

Howdy men, I am working on a Mac 10-10 auto and the exhaust port is one without the bridge which I understand is for pistons with locating pins.
The piston I have does not have these pins so would it be safe to assume the rings could potentially get caught in the exhaust port?
I've searched high and low for reference to this issue and a part number for the pinned piston but to no avail. Any advice/help would assure your acceptance into heaven. LOL Thank you

 

[heimannm]

I am going to go out on a limb and guess someone has switched the short block in your 10-10 Auto to a 57cc version with the oval exhaust and pinned rings. The 54cc models are all 1.750" bore and the 57cc models are 1.813" bore. Measure the piston or the bore diameter to confirm.

So far I have never encountered a 54cc model with anything other than the two hole bridged exhaust. That last Piston/Cylinder list that I have is dated 1982 and they show all models including the Pro10-10 as using the same piston and rings.



Of course with McCulloch, exceptions are the rule...

There is at least one Pro Mac 10-10 IPL published in January 1983 (93711-R6) that calls out the 1.813" piston/ring combination for a 600014 model but I think it was accidentally carried over from a 10-10S version and did not actually reflect a bigger bore PM10-10. Since yours in a 10-10A it should have the smaller bore and bridged exhaust.

Mark

 

[wstan101]

Thank you Mark, upon further and closer inspection it appears someone has removed the bridge in exhaust port and did a stellar job of it. I measured the bore and it is indeed 44.44 mm +/- thou. and 1.749. Now the question being what are my options piston wise given the bridge is gone. thanks a million!