# Craftsman lawn tractor burning oil



## bkenobi (Oct 18, 2015)

I have a second hand Craftsman lawn tractor from the 90's (AFAIK). The tractor has always used a bit of oil but the last season it has started to use significantly more. When I started it yesterday, it ran ok (small amount of smoke) but after a few minutes (around the time I engaged the mower deck) it started blowing a massive cloud thick enough it was hard to see through. The motor still sounded fine, so I continued working. I ran for 1-1.5 hours until it started acting like it was out of fuel. I topped off but that didn't fix things. After some basic diagnostics, I found that the plug was fouled.

In the past, I've had a little smoke when cold but it runs fine thereafter. I started checking oil level more regularly and realized that it was probably being run low, so I've been checking/topping off every time I use it. Currently, I have to fill the oil reservoir prior to running it or if I run for an extended period of time or else I'll have basically no oil.

I cleaned up the motor, performed a compression test, and replaced the spark plug a few months ago. At that time, I had good compression. I checked the compression today and I still have 70 psi. As I mentioned, after it stopped running, the plug was completely fouled with a crusty buildup. There are 3 areas that seem to have some oil build up outside the engine.

Small amount on lower half of valve cover.
Some oil/dirt build up around the oil fill/drain tube. This is also where the split in the engine (sump/cylinder) is located, so could be a leak in the gasket.
Some build up on the block near the throttle cable/carburetor (governor bolt?)

There is no evidence of any leak under the tractor, on the frame, or on the mower deck. It appears to me that since there's no significant leak/puddle (nothing compared to what I put into the engine each time) that the oil must be getting burned especially since the spark plug was so crusty and I'm always running with a bit of smoke.

I'm not sure what I should be looking for at the moment. I spoke to a local repair shop and they suggested that it could be a head gasket leak, but if I have good compression, that doesn't make sense. I would think it would be more likely a leak in the valves if compression is good. When I pulled the valve cover off, there was a puddle of oil at the bottom of the compartment. I turned the motor over and there was some spray of oil that appeared to be sourced from the lower push rod, but that could just be splatter from the puddle.

Mower details:
Craftsman 917.270723
Serial # 071999B 003832

Motor:
Briggs Inotek 17HP OHV turbo cooled vertical shaft
Model 311707
Type 0132-E1
Code 990714ZE


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## HarveyW (Sep 15, 2014)

Hello bkenobi,

Welcome to the tractor forum.

Does the engine have a crankcase ventilation tube that goes to the air filter/ carburetor? If so, pull the tube off at the carburetor and see if it is blowing a lot of blow-by gas and oil out of the tube. The engine has to burn/recycle this discharge. That would explain the fouled plug and smoke. 

I normally replace an engine when I see this, but others on this forum may have a better solution. Obviously, combustion gas is getting past the piston rings. The cylinder wall is probably worn, maybe scored, which would contribute to the problem. 

I think you can get a (new) replacement engine for around $400-$500. Check out mower supply shops, internet sources, ebay.


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## bkenobi (Oct 18, 2015)

I'm not sure about the ventilation tube. I looked at the manual and it doesn't go into that level of detail. It shows parts, but not details of the castings so I don't know if that feature is present.

I drained the oil I installed a couple days ago which had maybe 15 minutes of run time on it. I was only able to capture 20oz though it should have 3.5 pints/1.75 qts/56 oz. The fluid was black as if it had been in there for ages. I only had 1 qt so I couldn't completely fill it up but I figured that would be enough to test it for a minute or so. With low oil, I can run it fine with no load. If I try to engage the deck, it quickly chokes and then stops. I'll get more oil today but I wouldn't have expected that low oil would keep the engine from running for a few seconds.


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## bkenobi (Oct 18, 2015)

I pulled the head last night (a bigger pain than expected due to all the accessories they hooked to the block through the guards). The gasket was blown in the typical spot between the crank case port and the piston. Prior to removal, I tested compression again and found that it was between 90-95psi in 3 tests. After cleaning with brake cleaner all surfaces look really good. The piston walls are nice and shiny so with good compression I'm assuming a new gasket will get me back up and running.


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## bkenobi (Oct 18, 2015)

After rebuilding the head, I now have 120psi compression! I killed the battery by leaving the key in the wrong position while working on the engine, so I had to charge it last night. This morning it started with plenty of pep and had no problem engaging the deck with just a small puff of exhaust. Looks like I'm back up and running!


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## jhngardner367 (Apr 5, 2011)

Glad you got it fixed !
These engines were so bad about blowing gaskets,that iIused to keep a dozen on hand,when I had my shop !
The early,single-cylinder engines also had a problem with the crank case bolts coming loose.
They were made about 3/16" too long,and the sump would work loose,and twist!
Common cure was to shave 1/4 " off the ends of the bolts,replace the sump gasket, and torque it to specs.


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## bkenobi (Oct 18, 2015)

The motor seems to run great after it warms up. Prior to the gasket failure (the large plume), I could turn the mower on and engage the deck immediately if desired. Now if I don't let it run for a couple minutes the motor will bog down and try to die. After it's been run for a few minutes, I haven't seen any issues.

I checked the spark plug and it has black on the sides but not the spark points. I haven't done anything to the carb, but I'm wondering if somehow it could have been bumped enough to require tuning? Black soot to me suggests it's running rich but I don't see any exhaust so I expected it to be a clean plug. Perhaps these engines have some small amount of soot even when running clean?


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## bkenobi (Oct 18, 2015)

Updating this based on a new incident. I replaced the head gasket in 2015 and everything was running smoothly for years. I noticed the oil was low recently and topped it off. I checked again a couple mowing sessions later and it was low again. I topped it off so I could get to work and then changed the oil later. Yesterday I mowed the 2nd time on fresh oil and started getting the smoke screen affect. After a bit, it was pretty thick so clearly something is wrong. I'm going to have to pull the head off again to see if the head gasket failed again. I didn't do anything with the breather tube last time around because I wasn't able to find a tube running to the air box. After reviewing the engine schematic more closely, I see that the breather is a separate box that doesn't communicate with the air box and instead just mounts to the side of the crankcase. I didn't see it last time because it's got a thick coating of dust. I'll also have to confirm that the rings are still good since as far as I can see a faulty breather valve/clogged breather assembly could put extra pressure on both head gasket and rings.

I tested compression and it's showing 145psi so I'm pretty perplexed since last time the head gasket failed it was holding 70psi or less and only produced 120psi after replacement. I suppose if the breather if plugged solid, there could be extra compression available through the crankcase side of the engine? I've gotten lots of life from this second hand lawn tractor but I'm hoping to keep her going a while longer!


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