Kohler Magnum oppy conversion

I currently have a 18hp kohler magnum opposed twin that came off the Craftsman GT. I'm not positive what I want to do with it yet. Maybe a tractor build I don't know but either way I wanna try to convert it to Horizontal. It's currenty vertical but I think the only different components are the intake and the sidecover/base piece. It already has the mounts for if it was horizontal.



If anyone has any info on this please post it up. I was thinking about just buying a side cover and intake on Ebay but if anyone has any Magnum oppy parts lying around they would be willkng tk part with please let me know. Thanks!

Intake manifold and oil dipstick tube are the two parts for sure that need to be changed, but I'm not sure wether the oil pickup does too. Might be in a different spot on the verticals and if you tip it up like a horizontal it might not get oil properly.

Yeah maybe have a look inside and see where the oil pick up is. Even if it's not in the right spot for horizontal, might not be too hard to modify it. Then you'd be good to go I think.

AllisKidD21 wrote:

Intake manifold and oil dipstick tube are the two parts for sure that need to be changed, but I'm not sure wether the oil pickup does too. Might be in a different spot on the verticals and if you tip it up like a horizontal it might not get oil properly.

I'm not overly familiar with pressure lubrication systems but I see how that would create a problem. I should open it up.

Don't forget to post pics if you do

mr.modified wrote:

Don't forget to post pics if you do

I definitely will.

I did some more research and things are looking alittle doubtful. On the horizontals the dipstick tube doesn't go into the side cover so I would have to drill into the block. I doubt anyone here has been inside one of these things but I think I might have to split the halfs to actually look inside it. I might open it up when I get home this weekend if I do I'll make sure to post all the information I obtain.

usually a pain to convert them I think. But do-able if you really wanted to.

mr.modified wrote:

usually a pain to convert them I think. But do-able if you really wanted to.

Well I basically just want a horizontal twin but there so rare in my area. I've only incountered a few and they have all been over priced. Are the briggs oppys easier to convert? I know the pressure lubed ones will present the same issue with the oil pick up but I just wonder if the dipstick situation is less of an issue. I'm gonna look into it because vertical briggs oppys are pretty common in my area.

The Briggs oppy's need a hole drilled for the dipstick tube as well, but some of them have the hole pre-drilled with
a removable plug I believe.

You don't even really need a dip stick I suppose if you have a place to fill it and maybe a check hole in the side at the level you want. Take out a side plug and see if the oil runs out. That will show if it's up to that level or not. But that stuff might be just as much of a pain as putting the dipstick tube back in.

Personally I'd be more worried about getting the oiling to work.

I was just thinking looking at that pic. I wonder if you could keep the dipstick tube in the stock location and weld an elbow to it. It will still fill through there (maybe a bit slower with the bend) and if you get the height right you can still check it with the dip stick. In other words, a 90 degree turn where it goes to the block.

mr.modified wrote:

You don't even really need a dip stick I suppose if you have a place to fill it and maybe a check hole in the side at the level you want. Take out a side plug and see if the oil runs out. That will show if it's up to that level or not. But that stuff might be just as much of a pain as putting the dipstick tube back in.

Personally I'd be more worried about getting the oiling to work.

I was just thinking looking at that pic. I wonder if you could keep the dipstick tube in the stock location and weld an elbow to it. It will still fill through there (maybe a bit slower with the bend) and if you get the height right you can still check it with the dip stick. In other words, a 90 degree turn where it goes to the block.

Good thought with the 90 degree in the dipstick. I assume your oil capasity would be a couple ozs higher.

So I went into work yesterday to ask my boss for advise on this project and he told me he was scrapping this next week and I could have what I wanted from it.




It's a Snapper LT12 and the 12.5hp Briggs oppy is what I'm after. I'll I liked the idea of having the magnum convenience is taking the wheel. After studying mr modified's GTR thread I am considering putting 18hp oppy carb, rods, crank, and pistons in the 12.5hp. If the 12.5hp is indeed a 40ci. My boss tried to tell me that it was a 38ci which I don't think it is. If anyone knows for sure if the really small oppys where still 40ci please let me know. Thanks!

Awesome deal MJ! Should work great!

Also the 12.5hp oppys are indeed 40 c.i. displacement.

Might be better off taking the parts off the 12.5 hp. and put them on the 18 hp. The parts to convert it over to a horizontal that is.

Richie would be all over that snapper haha. I’d try to take the whole tractor if ya can and give him 20 bucks for it. More than he woulda got in scrap. From what I saw last night they’re pretty stout tractors. Neat drivetrain design too

CraftsmanQuad19 wrote:

Richie would be all over that snapper haha. I’d try to take the whole tractor if ya can and give him 20 bucks for it. More than he woulda got in scrap. From what I saw last night they’re pretty stout tractors. Neat drivetrain design too

I thought of Richie as soon as I layed eyes on that cool hood. Although the drive systems are cool they are not that useful for offroad purposes at all. If I was able to take it I might 633a swap it and have a proper tractor.

Or a 2300. But that frame is thick. It’s a proper GT

Nice find! Yeah 40CI should be the smallest ones they made. That's the older ones. Then 42CI is probably the most common I would think. They are maybe 16hp? to 19.5hp. If you find one marked 20-22hp it should be a 46CI. Those are more rare because they only made them for a few years maybe before they stopped making the opposed.

The 40 and 42's are the same block, pistons, heads, and everything else I think. (Cam may be a bit different? Not sure) The only difference being the stroke. So different length rods and different crank. But yeah they all should swap. The carb might have been a bit smaller on the 40CI too vs the 42CI.

The 46CI ones I think are bigger bore. I would assume the same stroke as the 42. Not sure if they use a different crank or what.

Do you have an 18hp to use parts from? I never checked but the horizontal and vertical shaft stuff should be the same on them I would think.

Thanks for the info! The carbs are different from the 40ci to the 42s. I have a 19.5 carb they I am going to put on since the carb on it now is no good. I don't not have a 42ci right now besides the one on the rally mower which I don't really want to take apart. I would not have much trouble locating a 42ci vertical in my area though.

What I always wonder is, what's the difference in the engines which are the same size but listed at different HP? I wonder if there's really that much difference at all. But I could be wrong.

The only thing I can think would be cam differences, but why they would keep messing with the stuff that much over the years I have no idea. It's a little bit strange.