Jump to content

Garden Tractors and Parts on eBay

- - - - -

Question about boring an kohler engine ?

  • Please log in to reply
4 replies to this topic

#1 propane1 ONLINE  

  • Senior Member
  • Member No: 54307
  • 8,709 Thanks
  • 4,123 posts
  • Location: Charlottetown, Prince Edward Island, Canada

Posted December 12, 2014 - 05:24 PM

I have a 12 hp Kohler engine that split the piston at the oil ring groove last summer, which 

I have not taken apart yet other than the base off to look in. Some of you may remember that. So I am wondering, that when I take it apart to see what damage there is to the cylinder wall, that if there is some and have to bore it out to repair it, could I bore it to the size of a 14 hp Kohler engine. Why have a 12 if I can make It into a 14.  Just wondering what you think,   Noel

#2 glgrumpy OFFLINE  


    Getting Out!

  • Senior Member
  • -GTt Supporter-
  • Member No: 8360
  • 8,604 Thanks
  • 7,909 posts
  • Location: Huntington, IN 46750 North East in State

Posted December 12, 2014 - 08:00 PM

First one needs to find how big it NEEDS to be able to clean up the scores or oval or whatever problem it may have. Kinda thinking .030 is about the biggest bore and to find a piston for, I might be wrong tho. I think for more power you might need bigger bore carb, maybe shave the head some, do some cam work or replace with another?  There are pulling engine sites that deal with hop-up items, might wanna see what things are changed there?  Myself, don't realy see where you would tell you had the extra horsepower until you put big money in it. Those 12hp are very strong engines, think stock should be keeping you happy for most work.

  • propane1 said thank you

#3 superaben OFFLINE  


    Con Man

  • Senior Member
  • Contributor
  • Member No: 11204
  • 7,668 Thanks
  • 5,677 posts
  • Location: Shenandoah Valley, VA

Posted December 12, 2014 - 08:52 PM

Keep in mind that although you probably could hop up the block to the next HP level, you will also need to consider the other parts you will need to upgrade along with just the bore.  I understand that the crankshaft setup is different.  It will need to be counterbalanced differently and timed differently.  You would need a 14hp crank if what I am seeing is correct.


For what it is worth, Kohler did offer up to .040 along the way.  They can be rough to find, though, for some models.


Ben W.

  • propane1 said thank you

#4 JDBrian OFFLINE  


    Super Moderator

  • Super Moderator
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 2507
  • 9,624 Thanks
  • 14,150 posts
  • Location: Hubley, Nova Scotia - Canada

Posted December 12, 2014 - 09:09 PM

Noel, check this out. He gets 16+ HP out of this K301 engine. http://www.kirkengin...ohlerPartII.pdf

  • DH1, LilysDad and propane1 have said thanks

#5 dodge trucker ONLINE  

dodge trucker
  • Senior Member
  • Member No: 19314
  • 2,421 Thanks
  • 3,114 posts
  • Location: kankakee

Posted December 13, 2014 - 09:46 AM

you might be able to bore it to the 14HP size (well we are at it why not go 14HP + 0.040" over)

but the truth is there are 2 reasons NOT to;  1) with everything else left the same simply boring an engine to the next oversize, by itself will not make an appreciable difference in power.... it might seem to but really you just restore a tired worn out motor to original clearances.... all that does is to restore the power that a particular engine had new.

and 2) especially with an air cooled engine the thicker you can leave the cylinder walls the better. Thinner walls distort more when heated meaning power will actually go down and it may well eat oil....

there are other things that can be done to increase an engine's power though in the world of these engines, it is kinda rare other than in the tractor pulling world.

  • propane1 said thank you