Mc-10 kart pistons

[steve cox]

i have a question about  mc 10 pistons ,mc 49 pistons and mc 20 pistons . i understand  that they all have  different displacements . here is the confusing part when i google  or search  overbore  mc 10 pistons  like 030  i get  things like  fits 5,6,10,20  last year i ran a mc-10 with a mc49 thin ring piston  i was going to convert  another  mc-10 to thin ring  and found a mc-49 030 # 53926  it said it would fit mc10 and 20  am i missing something i am no expert by any means i would just like to learn something

[steve cox]

i am assuming that mc-49 and mc 20 have different pin heights

[Terry Sullivan]

i am assuming  that mc-49 and mc 20 have different  pin heights

Steve,
All of the engines you mentioned have the same bore.
The 20 has a longer stroke, but I'm not sure about the pin height.
I am in Florida right now, or I would go to the barn and measure a 20 piston.
The 53926 piston you bought from me has the same pin height as the stock 10 piston, so it will work fine.

terry

[steve cox]

i am assuming  that mc-49 and mc 20 have different  pin heights

Steve,
All of the engines you mentioned have the same bore.
The 20 has a longer stroke, but I'm not sure about the pin height.
I am in Florida right now, or I would go to the barn and measure a 20 piston.
The 53926 piston you bought from me has the same pin height as the stock 10 piston, so it will work fine.

terry i am not complaining . just a bit confused  i have a  mc 10  with a 010 thin ring piston 53924  works great  the  i did a search on the  53924 and it came up with  mc-49 and mc 20 i am curious  because mc 6,10,49 have  pin to crown  1.00  and the  mc 20 is 1.06 wondering how they have the same  part numbers    

hi terr

[doug tenney]

Footnote...as I recall, that handy chart was originally published by our esteemed colleague, Scott Kneisel!
circa 3/2016

(possibly in collaboration with esteemed colleagues, such as Terry Sullivan!)

Your mileage may vary.  Batteries not included.  After taking this placebo, if you somehow have an dereliction lasting more than four hours, you'll know you bought the right stuff.

[David Luciani]

you need to look at the math and you'll see the answer.
mc5,6,10,49 all have a pin to crown of 1.00.
mc20 has a pin to crown of 1.06.

so a mc20 can run a mc5,6,10,49 piston because the earlier style piston has a shorter pin to crown ht.
the top ring land will be nowhere near the top of the bore.
this is because the mc20 block is taller than the mc10 block it evolved from.
the piston might be a little low in the bore (.06) so the compression will suffer a tiny bit.
but that's not a deal breaker to make the engine run and the port timing possibly might be a little better.

reversed mc20 piston in mc5,6,10 block will not work. the ring land would clear the bore top and end up hanging the rings.
mc20 piston in a mc49 block is possibly doable because i'm pretty sure there's more crush space in the mc49 block.

easiest way to see is assemble piston,rod assembly , assemble short block without torquing rod bolts but tight , turn the piston 360 degrees through full stroke and return. if the top ring doesn't come clear you are fine. if the top bit of piston comes clear you'll need to add the correct gauge head gasket to compensate.
hope this helps
d

[Terry Sullivan]

Some of the MC-20 pistons have the lower pin height and some don't.
I have a McCulloch document that shows the 53926 as a MC-20 piston, but when measured, it has the same pin height as the standard MC-10 piston.
I have a Wiseco MC-20 piston with the lower pin height.
Dave's explanation is correct.  You can use the 'high' (1.00) pin height in a 10 or a 20, but a piston with a 'low' (1.06) pin height will cause a problem in a 10. 
Between the chainsaws and the kart engines, there are many pistons and other parts that can be interchanged.  I often wonder who was keeping track of the different parts and part numbers.  Seems like there was a lot of needless duplication.

t

[steve cox]

thank you terry and David for the information