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New user seeking the collective wisdom of this forum

#1

D

dunlin182

Hello! I'm new to the forum. I have a 20+ year old MTD yard machine with a14.5hp Briggs and Stratton under the hood. I am having trouble with it and could use some help diagnosing the issue.

After running for a minute or two, motor hot, I see a white haze from the exhaust. It sounds fine and runs smooth, but the longer it runs the more smoke (always white) billows out the exhaust. After a few minutes it begins to run rough, then it goes old faithful on me out the intake filter, specifically the tube coming from the crank case. The liquid fountaining out it's dark gray. Not brown like the clean oil, or clear/amber like the gas. It does smell a bit like gas, but I'm not sure what it is. If I had to guess I'd say it is a mix of oil and gas (I realize there are only two options and that's a real stretch of an assumption...).

I could use your wisdom and experience at this point. Where do I start? Is there a common failure that causes what I'm seeing?

By way of introduction, I'm a mechanical engineer with a passion for fixing things. I lack knowledge on this small engines but have years of experience maintaining and repairing my cars over the last two or so decades. I'm confident enough to attempt any repair but cautious enough to enlist expert help when I lack knowledge or experience in the matter at hand, like this mower problem.

Thanks for reading and for any comments!


#2

Boobala

Boobala

dunlin182 said:
Hello! I'm new to the forum. I have a 20+ year old MTD yard machine with a14.5hp Briggs and Stratton under the hood. I am having trouble with it and could use some help diagnosing the issue.

After running for a minute or two, motor hot, I see a white haze from the exhaust. It sounds fine and runs smooth, but the longer it runs the more smoke (always white) billows out the exhaust. After a few minutes it begins to run rough, then it goes old faithful on me out the intake filter, specifically the tube coming from the crank case. The liquid fountaining out it's dark gray. Not brown like the clean oil, or clear/amber like the gas. It does smell a bit like gas, but I'm not sure what it is. If I had to guess I'd say it is a mix of oil and gas (I realize there are only two options and that's a real stretch of an assumption...).

I could use your wisdom and experience at this point. Where do I start? Is there a common failure that causes what I'm seeing?

By way of introduction, I'm a mechanical engineer with a passion for fixing things. I lack knowledge on this small engines but have years of experience maintaining and repairing my cars over the last two or so decades. I'm confident enough to attempt any repair but cautious enough to enlist expert help when I lack knowledge or experience in the matter at hand, like this mower problem.

Thanks for reading and for any comments!
Click to expand...

My summation would lead me to thinking of a compression check , ..it sounds like the piston rings are
gone on vacation ..permanently ...:2cents:


#3

D

dunlin182

I have a compression tester and intend to test soon. Does anyone know the nominal compression (and tolerance) for these engines?


#4

I

ILENGINE

Lets start with the model and type of the engine so we can see what engine you are working on.


#5

D

dunlin182

IMG_20170425_174615.jpg

I hope the image comes through. It shows the top cover, and the requested codes.


#6

I

ILENGINE

My first suspicion would be a head gasket working on going south. When the engine heats up the burnt opening between the cylinder wall and the push rod cavity is allowing compression, unburnt fuel, etc to enter the crankcase, as well as oil is drawn into the cylinder on the down stroke.


#7

D

dunlin182

I agree with you and thought the head gasket may be my issue as well. Would a compression test show head gasket failure? Is there any other check/inspection to isolate head gasket failure?


#8

I

ILENGINE

Compression test might show compression issues, but since there is no published specifications for compression on briggs engine, we don't know what is normal. A cylinder leakdown test would be the correct test to determine that issue, but there is still no way to determine if it is rings or head gasket, because both will show up the same on the leakdown test. From your description of the issue you are getting crankcase pressure build up, so those are about your only two things that can cause it.


#9

D

dunlin182

Thanks again to everyone that responded. I had some other priorities to work but have finally gotten back to this issue. I pulled the cylinder head and the head gasket looked great.... until I pulled it off. On the back side i noticed the beginnings of cracking and a thin section. Seems like the gasket failure was just beginning and thermal expansion was required to show symptoms.

In summary, after a new head gasket, valve cover gasket, valve clearance adjustment, and oil change, it's fixed and running better than ever. The problem was definitely the head gasket. I didn't realize how hard it was to start until making that valve clearance adjustments, it now cranks over when starting with little effort from the starter.

Thanks again to all that contributed! Below are some pictures of what I found, enjoy.

IMG_20170526_094641.jpgIMG_20170526_094656.jpgIMG_20170526_094257.jpgIMG_20170526_094146.jpgIMG_20170526_100125.jpgIMG_20170526_101609.jpg


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