Author Topic: Kohler K181S  (Read 8702 times)

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Kohler K181S
« on: September 26, 2006, 11:31:45 pm »
Hi guys, I have an old 70s model Wheel Horse mower, it has a Kohler K181S engine which is an 8HP single cylinder horizontal shaft flathead engine with a cast iron block and aluminum head.

This mower has been parked for ages due to having run the motor low on oil. I decided to pull it apart to fix it and I got to thinking about maybe hot rodding it. Just wondering a few things, firstly how strong is the stock rod and how high could I safely rev it after disabling/removing the governor? Will a Briggs rod interchange? (My dad says this engine has been bored something like .070" over and has a Briggs piston fitted, with the rod reamed out to accept the larger Briggs wrist pin.) What about valve springs, what are the options there? What do you guys think about these motors in general?

The transaxle in this thing is a three speed with reverse, with a strange H (turned sideways) shift pattern and a low-high speed selector. It is driven by a large pulley on the right side and is obviously very low geared. The brake is built into the transaxle, it has a rotating drum on the opposite side of the drive pulley with a brake band that wraps around it. On the back of the transaxle there is a tag that says "Uni-Drive"; gotta look over the thing more closely and see if there are any more markings. Any idea how strong this transaxle is and ideas as to its suitability for racing?

If I build this thing, basically what I want to do is just build a kick a$$ 1/8 mile or 1/4 mile drag racer out of it, but still have the capability of driving it around at part throttle and with decent driveability. I have heard these small engines can be supercharged with a smog pump and I would like to try that. I am also not opposed to running methanol as I believe there could be considerable advantages to doing so. I am pretty well equipped to do most types of fabrication, and intelligent/knowledgeable enough to take on this project, just extremely short of funds so this will all have to be done for CHEAP using whatever parts I can scrounge up or get for cheap.

This is my first time really messing with a small engine but I learn quick so no worries. :) Thanks for any help you guys can provide!

Offline FlatheadPuller

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Use a 10-14hp kohler instead.
« Reply #1 on: September 29, 2006, 09:09:39 pm »
I pull garden tractors and know quite a bit about the kohler singles. You do NOT want to rev the 8hp very high with a stock rod and flywheel. You will cash the rod in before the flywheel but it WILL come apart and not take long to do so. If you want something reliable use a 10-12-14 hp kohler single. You can use the rod from a 16hp or a 18hpohv kohler. Both those rods are stronger then the factory 10-14 hp rods. Have the big end of the rod machined for a bearing insert. (shell bearing). If you don't do that it will pound the aluminum rod until it breaks. The sock flywheel is very pourus cast iron. It WILL come apart and hurt you or someone else if it sees more than 4000 rpm on a regular basis. There are a few places making performance parts for the kohler singles. Its not cheap to make it last if you wnat to rev it but if you keep the rpm down around 4000 and have a 18ohv rod machined it will last a long time.
Dennis Bazzett
Grandville Michigan

Offline offroadwhatever8

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Re: Kohler K181S
« Reply #2 on: October 29, 2006, 07:04:59 pm »
i have a kohler k-241 10hp in my old 69 cub cadet, that thing is so powerful for a 10 hp. Ive been thinking about finding another one of these engines to make into a racer becouse they are so powerful.

Offline money89tractors

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Re: Kohler K181S
« Reply #3 on: January 08, 2007, 06:13:18 pm »


theyll have about everything youll need to make a very strong engine out of the already strong kohler.

..."I used that motto to keep going, keep pushing, keep digging to
find a way around, or through to find a hole, some kind of break that
would allow some space. Once something broke thru, I could be there to
take advantage. Then I would finish 7th instead of 10th." - Dubba G


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Re: Kohler K181S
« Reply #4 on: November 24, 2007, 07:21:43 am »
I supercharged mine.. 

Offline amcchevy1

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Re: Kohler K181S
« Reply #5 on: November 24, 2007, 10:58:38 am »
that looks good with the air pump on it. how much does it actually help?
2007, 2008 amra member.  modified flathead
2008-2010 arma member.  sportsman
If you build it, it should fly.
take it out and let it eat...


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Re: Kohler K181S
« Reply #6 on: November 24, 2007, 01:01:32 pm »
This air pump was too large and pushed too much air. The engine would actually start to stall the pump. I'm gonna try it with a smaller pump or a smaller pulley to see how it would work.

With this much boost it was hard to get the idle and high speed mixtures right... I took it back off until i find a smaller pump. This one was free so I tried it out..

The engine just got a massive overhaul at the machine shop.. so I'll tune it without the pump, break it in, then add it back on to check out the difference..

Offline George Herrin

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Re: Kohler K181S
« Reply #7 on: November 24, 2007, 01:44:13 pm »
This not being a pulling site nor any sanctioned rules I know of do not allow this type of mods (super charging) please dicuss this in pm's or some other form. We already been thruough this once and we are not gonna go thru it again. Thank you for your understanding.
George Herrin #6
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My other racer is a 1/5th scale Dirt Late Model!!!!


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Re: Kohler K181S
« Reply #8 on: November 24, 2007, 02:07:42 pm »
Ok.. I didn't know...  :(