K161 vs K181 Piston Size?

TEET · #1 10-10-2009, 10:40 PM

Hi all,

I'm in the process of rebuilding the engine on my 73 which is a Kohler K161 7hp. I'm having a bit of a hard time finding a std size "k161" piston, although they are available, they fetch quite a bit more than a std K181 piston. Dont know why??

My question is, since both engines have the exact same bore size, and only differ by rod length, can I use a K181 8hp piston in my K161?

I have an old K181 piston and matched it up to my K161 piston, and they measure up perfectly(with digital calipers), even wrist pin location. I read a while back on another forum that a 8hp piston is a common replacement for the later 7hp engines, but I thought I would throw it out there to get some other opinions.

Thanks!

Jeff (teet)

Yosemite Sam · #2 10-11-2009, 01:00 PM

You are correct, the 161 and the 181 had the same bore, 2.938". It was just the stroke that was different by .25". I believe that you are correct in thinking that you can use an 8 hp piston in a 7 hp motor. Now that I think of it I'm not sure they even make the shorter piston (161) any more.

TEET · #3 10-11-2009, 07:14 PM

Thanks Yosemite Sam, my reserach is leading me to believe its a possible swap as well. I guess theres only one way to find out

Jeff (teet)

Merk · #4 10-11-2009, 08:05 PM

The motor in my 70 has a K181 piston in a K161 block. it has around 30 hours on it since it was rebuilt.

TEET · #5 10-11-2009, 08:13 PM

Quote:

Originally Posted by Merk

The motor in my 70 has a K181 piston in a K161 block. it has around 30 hours on it since it was rebuilt.

Sweet Merk! I thought I was hitting a dead end for a while! Did you use a Kohler brand piston, or aftermarket? Run ito any problems with the rebuild?

Thanks,

Jeff (teet)

Merk · #6 10-11-2009, 10:04 PM

Quote:

by TEET
Did you use a Kohler brand piston, or aftermarket? Run ito any problems with the rebuild?

I used only Kohler parts. Kohler parts do cost do cost a little more....the quality is better.....worth it in my book.
The 70 was used to help pay off a morgage. It was ran hard during the early years of it's life. I plan to work it some...not as hard as it was worked.
The motor throw a rod sometime in it's life. You could tell where the side of the block was repaired. The crank journal was still factory size. The only odd think I found was the cam lobe that opens the points had some major wear on it.
I replaced the following parts:
piston and rings
connecting rod
points plunger rod
valve guides
valves
head bolts
governor gear-it was a plastic one
gaskets and seals

The machine shop orders the parts for me. They have a good source plus they give me break ($$$) on parts.

RPalmer · #7 10-11-2009, 10:11 PM

Quote:

Originally Posted by Merk

The motor in my 70 has a K181 piston in a K161 block. it has around 30 hours on it since it was rebuilt.

Seems like the paint just dried.:biggrin2.gif: 30 hours... seems like alot.

Merk · #8 10-11-2009, 10:33 PM

Quote:

by RPalmer
Seems like the paint just dried. 30 hours... seems like alot.

I had the motor in another Cub that I sold. It is easier to have a motor that runs when you restore a tractor. One less problem to solve. The 70 has around 7 to 8 hours run time on it since it was restored.

chris · #9 10-15-2009, 10:14 PM

i can get you a pretty decent price on your motor parts, www.cubclassics.com

TEET · #10 10-15-2009, 10:53 PM

Hi Chris, Thanks for the help. I measured my bore tonight with an actual bore gauge, and unfortunately I indeed have the 2-7/8" small bore K161. I am planning on trying to get it bored out to 2-15/16" which is the large bore K161 and K181 size. Do you have access to the old style 2-7/8" piston and rings? This is my dillema...they are very hard to find, and quite expensive once found.

Thanks,

Jeff (teet)