Give the flywheel a quick flip backwards by hand, if it stops and bounces back compression is fine. Unless the connecting rod broke and wrecked the block it is likely salvageable.

WHich engine would be helpful. Remove the spark plug and feel w/ a screwdriver, pencil etc if the piston is traveling as the engine is rotated by hand. Valve seats can come out of place - holding a valve open. Model and type #s off the engine will at least get us looking at the same engine. Changing from one engine to the next requires moderate skill if they are exactly the same. Different engines takes a greater skill to adapt them.

Here's the Engine numbers:

B&S Model 286707 Type 0437 01 Code 920060411 I/C Gold

It looks like the Engine in this Ebay ad.

The engine turns over fine and tries to start, but doesn't. It rotates normally
with the same resistance you expect for the compression cycle.

Thanks for your help!

Jim

Here is a link that might be useful: 12.5 HP B&S Engine

James: From your questions, and self made answers, i really think you should just go out and buy a new machine, and forget about trying to fix the old one! It is quite obvious that you are not well educated in the care, operation, or repair of small engines. It will save time, money and countless questions about how to make your present machine run and operate.
Then, if and when you get the new machine--spend a couple evenings reading the instruction booklets, on the care and feeding of the new machine, and stick to those instructions as much as possible.
But, if you "run it hard, and put it away wet" as it seems your present machinery has been treated, you will eventually ruin it, too.
Also--mowing 6 acres with a light weight lawn tractor is sure to hasten its demise! You need a larger machine for that kind of mowing. Its like sending a kid out to do a man's job! JMHO: Rusty Jones

The title of your post says NO COMPRESSION and then you say-

It rotates normally with the same resistance you expect for the compression cycle.

You really have to make up your mind!

There's 1000's of Briggs that "look like" your engine.
As tomplum said-
"Changing from one engine to the next requires moderate skill if they are exactly the same. Different engines takes a greater skill to adapt them."

Dear Rusty: "James: From your questions, and self made answers, i really think you should just go out and buy a new machine, and forget about trying to fix the old one! It is quite obvious that you are not well educated in the care, operation, or repair of small engines. It will save time, money and countless questions about how to make your present machine run and operate. "

Well, I beg to differ with you. #1: I run a farm. I can't afford to spend $2,000, $5,000 or $10,000 on a big shiny new mower. I generally buy old
mowers from homeowners that have something wrong with them, fix them up
and keep using them and fixing them as needed, untill they won't go any
more. I'm aware that I ask a lot from them, but I don't do *too* badly; I
generally get 2-3 years out of an old mower that I bought for a couple
hundred bucks.

I've never opened up a small engine to do repairs, but I've done everything
else. I did some research, and read in these forums about how to reset valve
seat etc. I thought maybe someone here could give me a few pointers, and
I'd give it a shot. Maybe I was wrong, but I'm not afraid to try!

Dear Bill: "The title of your post says NO COMPRESSION and then you say
It rotates normally with the same resistance you expect for the compression
cycle. You really have to make up your mind!"

I was responding to ROMORE who suggested that the connecting rod might
be snapped; in which case there would literally be no compression

As I mentioned before...

This particular mower I got from a friend who was moving. It died shortly
after I started using it. A local 'mower repair' guy said it had no compression;
I didn't particularly trust his opinion, and I hoped to be able to repair it.

I just tested it with a compression guage, and it reads 30 lbs compression,
not very much is it? The mower makes a kind of wheezing sound when you
try to start it...

Bill: "There's 1000's of Briggs that "look like" your engine. As tomplum said-
"Changing from one engine to the next requires moderate skill if they are
exactly the same. Different engines takes a greater skill to adapt them.""

Did you miss the engine numbers I included in that post? Some asked for the
engine numbers, so I provided them.

Again, I was talking about swapping two seemingly identical engines from two
seemingly identical Craftsman LT4000 riding mowers. I was hoping for a
little more information...

Thanks for your time, Jim.

JamesBeam, I encourage you to go on and pull the head off the engine to see what the damage is.
If a valve seat has loosened or the exhaust valve burned, there is hope for repairing the engine......unless you are just set on replacing it as an assembly.
Don't get too riled at the curmudgeonly comments. It is after all a free forum with free speech.
As you surely have learned by now some folks are terse or curt in life but not necessarily "mean people".
Endure the remarks and glean the info. This is forum is like a "bull session" sometimes. Sharp remarks are often part of making sure everybody pays attention and knows what the down sides might be.
We are not all preaching from the same book here, so expect an individual "flair" to accompany comments.

I was responding to YOUR statement-
"It looks like the Engine in this Ebay ad."

Don't worry, there will be no more confusion from me.

I learned, early on in life--if ya walk around with a chip on yer shoulder--somebody is sure to knock it off!
So, i'm going to follow old Bill, and skip out! Rustyj

Is pulling th head off as simple as unscrewing the head bolts?

The Repair manual I found seemed to imply that parts of the valve train might
jump out at me, and be hard to put back together...

What should I be looking for when pull the head? How will I know if the problem is with the valves or the rings?

Opinions? I'll try to include the URL to the manual...

Here is a link that might be useful: B & S 12.5 HP Repair Manual

JamesBeam,
I admire your willingness to learn and understand your interest in avoiding cost. But I don't see where this is going. Some things can be explained by correspondence, but other things can only be taught in person. I mean no offense to you, but have you ever rebuilt an engine of any kind? If not it's going to be very difficult for you to understand advice given to you by written correspondence. Once you get the head off do you have access to a torque wrench to put the head back on? Once you get the head off and discover it is a bad valve seat, do you have the tools to compress the valve spring so you can have a new seat pressed in? If the valves are not the problem and it is the rings, do you have the tools needed to compress the new rings so that you can get the piston back in? If you don't you are not going to be able to repair the engine.
BUT this is an oportunity to disassemble an engine that is worthless to you and learn how it is put together and what parts are involved--learn by doing. Figure out how to remove a valve and figure out what is involved in putting it back in and the next time you'll have some hands on experience. What is there to lose and there is knowledge to be had.
If you have an identicle model engine that is running you could certainly try to swap engines. You'll need to trace all wires and mark them so you know what to hook up to what. If the mounting holes do not line up or they have different shaft lengths you've got problems (but then they wouldn't be identical would they?) and you are going to need to know what a keeper key is and how to remove and instal one so you can remove and replace the pulley--but that will be easier than a rebuild.

To answer your question: Detatch the intake and the exhaust manifolds from the head.Remove the valve cover(s). Remove the rocker arms. Remove the push rods. Remove the head bolts. Remove the head.

"To answer your question: Detatch the intake and the exhaust manifolds from the head.Remove the valve cover(s). Remove the rocker arms. Remove the push rods. Remove the head bolts. Remove the head"

You may want to rethink that.

"Is pulling th head off as simple as unscrewing the head bolts?"

Yes, remove the cooling shroud then head bolts. Look for a valve seat out of its' recess holding the valve open.

Walt Conner

If it has NO compression, follow the above advice. If it has normal compression and attempts to start, check the flywheel key.

If you can find TDC on the compression stroke, turn the flywheel so the piston moves another 1/4" downward. Lock the flywheel at that point. Use a socket or other strong device. Apply 20# of air to the spark plug hole. If you hear alot of air escaping, you'll know if it's thru the exhaust or intake. Careful. If the flywheel isn't secure, it can turn suddenly without warning and injure you.

If you hear no major loss of air and the flywheel wants to forcefully turn, your valves are probably OK. Check the flywheel key.

With the proper leak down equipment, you can go up to 60+ pounds to do this test. If you don't do it properly, you can be seriously hurt or killed by flying objects.