I have an old lawn tractor (forgot the name of it but I think its an Lawn Chief) from around 1987. Anyway it has the 12hp briggs and stratton i/c engine on it.

About 3 years ago, I was using it and I think i threw a rod. It actually kept runing but was banging badly and when I turned it off, i could rock the cylinder back and forth and feel it hitting something.

I have not used it since then.

I want to get it runing again. I have found on ebay a dealer sellling this engine (he has multiple auctions):
http://cgi.ebay.com/BRIGGS-STRATTON-15-5-HP-465-cc-GAS-ENGINE_W0QQitemZ280017572287QQihZ018QQcategoryZ295 20QQcmdZViewItem

Its a 15.5 hp i/c engine that is quite a bit newer. I'm not too worried about the wiring (I have seen info on the web to properly mate older and newer types of charging circuits) but I'm just wondering how compatible the mounting bosses and shafts are?

I would much rather spend a little over 300 dollars (including shipping) for a 15.5 hp long block with everything (carb/etc) instead of 400 plus shipping that my local dealer says my 12hp short block would cost from him (just the short block, no head/carb/etc).

It would be nice to have a bit of extra hp and a whole newer engine instead of using my old head and other stuff, so whats the deal with repowering tractors with slightly different engines?

BTW the overall look of this engine is quite simliar to my old engine.

Other then the wiring everything should match up to bolt down to frame, the spec's to check are for the crank. Most engines of this size use a fairly standard 3-5/32" crankshaft with a straight key way and drilled and tapped for a 7/16" mtg bolt. But check yours and the new engine to be sure.

Thanks for the info!!

I actually wouldn't bother with this old tractor except for the fact that I have a big ole snow blower attachment for it. Because of that, I want to still use this tractor. I doubt that the snower blower attachments are standardized parts.

Will I run into any issues with the fact that this new engine is nearly 4 hp more than the stocker?

Might want to fit it with a seat belt, so you don't flip of the seat when you let the clutch out. With all that extra power ya know....... :dude:

LOL.. funny guy!!

Maybe a set of slicks too??

No, I don't think you will get the traction you need for pushing snow with slicks...

I am thinking may studded tires.......... :p

Did the same thing with my old noma..... 12hp I/C briggs..... , replaced her with a big ol 18hp apposed twin (not I/C but with cast iron cylinder liners)

Except for the monkey wiring I had to replace with the wiring from the 18hp engine..., bolted up and the old stack pulley would have fit..... but some how (must've been from the previous owner) the stackpulleys key was partway sheared... and the stack pulley cracked!! and it wouldn't fit right... luckily the old stack pulley was almost similar to the old one... just a wee bit higher, and the drive pulley for the trans was a tad smaller.... but it will do for now till I find a bigger one.
Now 18hp? That 39 inch deck is nothing to power, doesn't even bog the engine engaging, or mowing.....
soon to come next is a better transaxle as the old is worn out and slipping... Have two to go in, a shift on the go (but needs moding) or a standard 7 speed peerless like it already has in it.

Whats the "Stack Pulley"?

You have now brought up something else I was wondering about. What if the transaxle on my mower ever goes? Is it something that can be rigged with one from a different make? I doubt very much that I could get a new or rebuilt transaxle for my almost 20 year old tractor.

Stack pulley, its two pulleys on one cylinder stack..... the upper is for the trans, the lower for the deck....

As for the trans...., I'm sure you could find one... as the trans in that one right now is 17 years old..... getting replaced with a few years older but less used one.

yeah i think you should be fine, although trans may be a little worn.....you could find a used one for cheap im sure. hell i had one and threw it out.

Happy Wrenching!!

Ok, now I'm getting kind of curious about this whole project. I found another engine on eBay that I'm interested in. Its a 31P700 series 18.5 Intek single cylinder engine. It appears to have the same mounting dimensions as the engine I listed above (the 15.5hp). Would that engine work as well?

as long as the mounting holes match up, along with the stack pulley....

It should....., unless they changed something which they shouldn't have...., like I said above.... that 18 hp apposed was huge compared to that 12, mounting holes fit right up... just don't expect everything else to agree..... In order to keep the original steel hood (i hate plastic, could have used it and it would have been fine) I had to cut the sides so the cylinders could fit through the sides..., vent slots up top had to be hammered up and out in order for the air cleaner nuts to not catch.... (might cut em out later... was in a hurry) though the 18.5 single intek maybe? will fit right in place of the 12.... be a little taller I beleive though, of course longer due to the ohv cover.

Thanks for the info. My tractor has a plastic hood and I'm not afraid to use a die grinder to "make" things fit.

:)

How di dyou put a metal hood inplace of the plastic hood. Are hoods very model specific?

Me? the mower that engine went on, came off the very same (little differences, and alot younger) noma frame....
That frame I put the engine on, already had the steel hood..., just that hood was made for a single cylinder.., the plastic one off the newer frame would have fit... and fit fine, I just hate plastic, that frame was badly rusted on the rear end..., wouldn't have been long before it would have broken something..., so I used the better of the two frames..
The metal hood had louvers near the front end up top... this caught the wing nuts that held the air filter cover on, the bottom half of the sides of the hood were removable by a couple screws but I cut em to fit with tin snips to be more closed in towards the front and leave a little stability basically to the hood, so the cylinders wouldn't get hit and scrape the paint job I did to the shroud..., and catch the fuel line.. on the right side.. and the throttle cable and wires on the left.

Course this model had a couple extra louvered panels that needed to be removed also... they were mostly for show.

I'd actually bet you.... if you measure, and can find one just about the same length across (where they bolt up to the frame at the hinge) it may fit with a little modification...
This noma was a old lowes... course in those ugly lowes colors and the whole thing got painted simple flat black.. engine covers flat red.