Lawn Tractor engine ID: Boxer?

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PRR

Well-known member
Joined
Jan 30, 2010
Messages
11,143
Location
Maine USA
I've acquired a lawn tractor. Craftsman 18HP, 44", roughly 1980? Model # 917255911

It "runs", only at half-throttle and half-choke, poorly.

Combined with the filthy gas-can found near it, I assume the carb is full of dirt. At its age, if I am mucking it out, I should replace the rubber bits too.

SearsParts has listings for it, and some key parts are still stocked.

The engine is "unavailable". Not that I would buy an engine, but I wish they would say WHAT the engine is so I could find the little bits like carb-kit.

The engine itself has big "Craftsman 18HP" decals, but AFAIK Craftsman never made engines. It must be a re-badge. But of what?

It's air-cooled, flathead, standard lawnmower stuff, albeit horizontal-shaft for tractor belting, BUT: here's the unique part. It is a 2-cylinder horizontal-opposed twin. Not a one-banger, and not the V-twin which has become popular in recent decades.

Who made boxer utility engines a few decades ago? Only Kohler? Or was it Kohler who made boxers?
 
Maybe Kohler, maybe an old briggs or tecumseh.

Chances are you might not be able to get the little bits.  Most engines of that time did not use rubber parts anyway, gaskets were made from paper(which you can get rolls of at the autoparts store and make your own gaskets like this).  I'd carefully start to dissect the engine and see if there are any embossings on the case that might tell you who made it.

Other than that, if the carb has a bowl on it, you might have gasoline solids(varnish) in it.  Usually it dries to the outer part of the bowl and then flakes off when you put new gas in.  It then clogs the jets/ports.  

Get a small can of carb cleaner, not the stuff in the spray can, but the stuff you dip the carbs into, and submerse the carb into it.  You might be able to dissolve some of that varnish and wash it out.

If you do decide to rebuild and can find the parts get some mag wheel cleaner, the stuff with the acid in it, and use that for cleaning.  It'll etch some of the gunk off of the aluminum that the cleaners can't get.  But wear GLOVES! that stuff is nasty.


I found this:

http://sears.pammar.net/id_number.html

http://www.smallenginewarehouse.com/RepowerItems.asp?Brand=Sears&Model=GT-18

http://cgi.ebay.com/Sears-GT18-GT19-9-vintage-garden-tractor-manuals_W0QQitemZ330363064849QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item4ceb2c5211

Looks like a number of engines were used.  Onan, briggs and tecumseh are named.

I see a part on Ebay for the Onan engine that looks like it bolts to a boxer type engine.  I can't find any info on the briggs or tecumseh engines.

 
> the Onan engine

EDIT!!

"Onan" was the name that slipped through the space between my ears.

However one of your links showed me where to dig at the grime. "Briggs & Stratton" and a big long number which does decode to a 43cid horizontal 2-jug made in 1986. The basic model was still in production in 2003, the date on the operator manual B&S posts, but the parts manual is clearly pre-CAD, hand-drawn. Carb kit $19, pump kit $9, carb assembly $200 (whoof!). The carb does not look quite right, but maybe if I take it off (it's quite tight to see in there) it will make sense. Oh, and the notes indicate that my 0721 version takes a different carb, so I guess the picture may be of the generic carb.
 
My machine is Model # 917255911

One of your links http://sears.pammar.net/id_number.html IDs 917.255910 as "Sears GT-18 Twin, 6 Speed Garden Tractor", another says 917.255912 is "1986 Sears GT-18 Twin, 6 Speed". Mine is one digit off either way, and does not say "GT", but is an 18HP twin with 6 speeds.

I found belt-numbers for the ..911 model:
917.255911
Blade................................................ 106381X 6892
Trans................................................ 101342N 6893

This machine is really a Roper. Most Ropers were one-bangers, mounted sideways, and the belt coming off the side to an obscene twist-turn ahead of the front axle. Mine is a bit more rational because the crank is lengthways and the belts drop down from each end of the crank.

One tip-off that this was a DeLuxe machine (aside from the high HP and 2 lungs) is the mower clutch. Not a big lever forcing a belt-idler, but a switch on the dash! Turns out they used the clutch from a car A/C to engage the PTO.

> if the carb has a bowl on it

The carb casting has a place for a fuel bowl, but it is blocked off with a freeze-plug. There is a plastic block on the firewall with a hose to the fuel tank, a hose to the carb, and a hose to the crankcase. It sure looks like a diaphragm. So it appears to be a diaphragmed version of an old float carb casting. And if I can ID that diaphragm, it may be the whole problem.

OTOH: I found a similar Onan with an SU carb from a Mini. They say it runs a lot better. That machine's manifold seemed to come out side-draft, mine is down-draft. Ell? Carb from a 1963 Falcon 170 Six? (NO!)
 
PRR said:
OTOH: I found a similar Onan with an SU carb from a Mini. They say it runs a lot better. That machine's manifold seemed to come out side-draft, mine is down-draft. Ell? Carb from a 1963 Falcon 170 Six? (NO!)

Wow, that sounds like way too much carb for an 18hp motor. That might be the 26hp(?) version that was used in the Westcoaster and Cushman carts. Same general shape but bigger. The 36hp has a cast iron flywheel/cooling fan on the front.

I remember seeing a classic Sears Lawn tractor forum somewhere...

Edit: I was probably thinking of this site - http://www.ytmag.com/gardent/messages/archive270.htm

And if I remember right with Sears, that last digit in the model number refers to the deck size (38", 42", 48", etc...).
 
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