I have an older model Craftsman 12hp 6 speed 38", I have a significant amount of smoke coming from the very front of the motor, I think the muffler to be exact. Due to the current economy I decided to try and make it work another year or two.

Whiteish smoke or more blue?

White

Since its white check the crankcase oil for gas contamination and see if its above the full oil level ( overfilled) .

Usually the white smoke is a sign that the crankcase oil is getting contaminated with gas, that is if the Head Gasket is good. That can be check with a compression check to see if the valves and rings are good.

It could be the carburetor needle valve is letting gas leak into the carburetor and flooding the cylinder(s) when the Engine is sitting in time.

The Gas will seep by the rings and get into the crankcase. The oil is to high and thinned and gets by the rings and into the cylinder when you run the engine. We call this "blow By" This is what usually causes white smoke. Put a piece of paper in front of muffler and see if its spitting fluid, spotting the paper.

The white smoke from a lawn mower is like white smoke form a car except a cars white smoke is usually a bad head gasket and the anti freeze is going through the combustion chamber and out the exhaust. The gas in a mowers crankcase is a liquid and evaporates out its muffler like antifreeze does in a car. .

What is the sign of gas in the crankcase oil, and also please explain how to do a compression test.

Crankcase in the oil is easily detected by smell. Oil should smell like oil and not gas.

Since the engine is likely running well, I'm going to nix most of the theories.

Bet your Oil breather needs to be replaced. You can go to Parts & Accessories | Shop & Find Lawn & Garden, Appliance Parts at Sears PartsDirect | SearsPartsDirect.com with the model number and locate it. There is usually a hose to nowhere and it's located on the side of the engine. Replaced from the outside.

This is much like a PCV system in a car, when it ceases to work, you tend to get gas in the crankcase.

You can also get oil in the air filter and along the base of the engine.

Sometimes the oil breather drips oil onto the muffler causing smoke.

How big of a job is replacing the rings on this motor? Do you have any tips and/or recommendations.

Post the model number.

I don't believe it's rings.

I will be able to show you where the oil breather is.

I rebuilt my first small engine when I was probably 12 years old after I threw a rod. Dad said, your going to fix it and so I did.

You may need a few special tools like ring compressor, flywheel puller, feeler gauges, rebuild manual, torque wrench.

You may need a dial caliper to figure out which set of rings to get. They come in standard and oversized versions.

Rebuilding an engine will keep you busy for a while the first time you do one.

I forgot to answer the compression test question:

Remove all plugs. You purchase a "Gauge that screws into the plug hole".

You crank and note compression and uniformity between cylinders.

If compression is bad, you squirt oil in the cylinder. If it improves, then it's usually rings. If not, then head gasket or valves.

The riding lawn mower model # is 917255742

The motor is a Tecumseh motor labeled as Craftsman
It is a 12 hp 4 cycle and the motor model # is 143366202

NIce job on the motor model. I did it the hard way.

Here is the link to the breather and diagram.

CRAFTSMAN | Model #143366202 | CRAFTSMAN 4-CYCLE ENGINE | ENGINE | SearsPartsDirect.com

It's part #83. Best to print the diagram. I can't find it on my screen.

FWIW: Tecumseh closed their small engine division in Dec 2008. There will likely be some aftermarket parts available for some time.

You can do the direct lookups here: Parts & Accessories | Shop & Find Lawn & Garden, Appliance Parts at Sears PartsDirect | SearsPartsDirect.com. Sears is not necessarily the cheapest source, nor the correct source at times, but they are quick.

NIce job on the motor model. I did it the hard way.

Here is the link to the breather and diagram.

http://www.searspartsdirect.com/part...hTerm=breather

It's part #83. Best to print the diagram. I can't find it on my screen.

FWIW: Tecumseh closed their small engine division in Dec 2008. There will likely be some aftermarket parts available for some time.

You can do the direct lookups here: Parts & Accessories | Shop & Find Lawn & Garden, Appliance Parts at Sears PartsDirect | SearsPartsDirect.com. Sears is not necessarily the cheapest source, nor the correct source at times, but they are quick.

I have tried getting the local carquest to order the parts needed and with the info I had it narrowed down to three different ones but I need the s/n of the motor itself. I have the checked the motor, pulled the top motor cover to see if it might be under there and have not found a thing, any suggestions?

So far this is where you can get a cheap manual I'm still looking it up.

For a basic compression test do all cylinders and see how far they are off. If there is one that's a lot higher then the other then the low one is the problem. I will get back to you. In the mean times maybe Kiss has it.
Tecumseh engine manuals, Tecumseh repair manuals, Tecumseh service manuals

I went and got my hair cut and was talking to my stylist and she told me that her dad owned the local lawn mower repair shop. They talked and he told me to bring the motor up to him, I used about five or six cans of brake parts cleaner and took the motor to them, the guy that looked at it noticed that the main gasket where the drive shaft goes throughwas ripped and sticking out and recommended at a total of about five dollars and a couple hours I try that to fix the problem first. So I did and it is all done but I can't get it to go back together all the way. Is there any tips to put it back together?

Have to love the Hair Shop gossip!

The round rubber seal with a metal ring right?

Usually I take them in and out with the base removed. They really need to be pressed into place. Any side to side variation, they don't fit.

They can be tapped into place.

You could try a drilled 2 x for the size of the drive shaft and a piece of pipe that fits over the drive shaft and tap into place with a rubber mallot.

seal, 2 x 4 with hole, pipe, mallot

I removed the shaft it had a bolt in the end, then I removed the bottom from the top with the unit turned upside down as directed by the shop. There was one little gear that was attached to the bottom but the others were still in the motor. I just can't get the last 5/8" to go down so I am guessing that the gears are slightly tilted or out of wack a little. What can I do?

It was probably the plastic impeller. That's the oil pump. It does need to be positioned so it will be in the sump when assembled.

It almost sounds as if your sitting on top of the alignment pins on the base. Are you? There isn't much wiggle room with the pins.

Take a flashlight and peer through the crack.

I got it thanks for all your help I am going to put the motor back on and hook everything back up and will let you guys know how it goes.