175 blow-by

[JBMac]

I know you guys have followed me through several trials and tribulations over the past year with the old girl (175 diesel). I've got a question on blow-by: When the tractor warms up, it's got a steady smoke out of the puke tube. When it's working hard, it's really steady. Theres barely any smoke out of the exhaust, doesn't use any oil to speak of and seems to have plenty of power. I've got to pull the fuel tank for a repair, so I could pull the head. Is blowby caused by worn valve train components or piston/ring issues? It already seeps a little oil from the head gasket so I could kill two birds. What say yall?

 

[Anonymous-0]

There are experts on here with far more knowledge than I, but I can start off with this.
You ask: "Is blowby caused by worn valve train components or piston/ring issues?"
Blow-by refers to blowing by the rings/pistons, thus excessively pressuring the crankcase.
Worn valve train components usually result in oil burning and smoking out exhaust.
Tom

 

[Masseynut(Australia)]

Well now, there's a couple of questions here.
Has the engine done a lot of work, or could it be just "glazed" from lack of hard work, or a heavy loading, for a period of time.
The "blow-by" can be caused by both the reasons you have nominated. Excessive valve guide and/or valve stem wear can cause crank-case compression, remedied by lifting the head, and renewing either or both.
Crankcase compression can also be caused by an insufficient seal between the compression rings, and the cylinder bores. This can occur at the same time that the oil control rings are functioning as they should. This often explains how an engine uses no oil, but has excessive crankcase pressure.
If you are "pulling the head", I would get the cylinder head checked out, and, drop the sump and remove the piston assemblies. It's not a lot more work to do this. Check the bore for wear, remove a top compression ring, slip it into the bore, about an inch down from the top, and check the "gap". Ring gap for a "good" engine should be, as a rule, .003" for every inch of diameter of bore size. Anything greater than this will give you "crankcase compression" to a degree.

Somethings to think about, regards,
Evan.

 

[Masseynut(Australia)]

Tom makes a good point here, and I'll clarify what I said a little more.
Excessive valve or guide wear will be associated with excessive "blue" smoke on initial start up. This occurs when an engine is left to sit for a period of time, when, the engine oil has time to enter the combustion chambers via the "worn" valves or guides.
This oil is then "burnt off" at start up, and clears as the engine warms up. But the cylinder "compression" can, and is, still escaping thru the worn valve stems and guides as the engine is running, as so, oil can no longer enter the cylinders, but the compression then "pressurises" the crankcase, resulting in a plume of "vapor" from the breather pipe.

Evan.

 

[Anonymous-0]

A couple of fairly easy ways to check for ex. valve vs. ring wear problems. First, if you can pull the engine over slowly by hand, give a listen to the exhaust stack on the compression stroke for each cyl. If you can hear an air leak from the exhaust stack during compression, it's a valve.

Second do a differential leak-down test on each cyl. If the cyl holds pressure within 10 lbs at the top and the bottom of the stroke, you're in good shape. If the bottom leaks down at a much faster rate, either cyl or rings are worn.

 

[jogl]

I just rebuilt our 175 this past winter, it is running great for the first time in many years.

If the tractor is making good power and is not burning oil or leaking excessive amounts of any fluid I would just keep running it.

Ours was burning a quart of oil per 8 to 10 hour day of light duty work. We could see oil running down the valve stems when we took the manifolds off. It would run rough at any engine speed over 1400 rpm. It smoked constantly. It had 6600 hrs on it, many of them hard hours from the '60's and '70's when my dad used to plow 250 acres every year with it. When Ken, at the machine shop, saw the rings and sleeves he said just as much oil had to be going by them as was dripping down the valve stems.

Enough of the gore, the long and short is: I wouldn't worry about a little blow by. I'd just fix the fuel tank and put her back in service.

Good Day,
JP.

 

[AWoods]

I have this same problem After having rebuild and head work. My question is will this harm my engine if I run it much befor I fix it? It uses no oil just will spit some out the dip stick if you pull it out. Mine is 275 With A-248

 

[Bob N.Y.]

My 65 diesel had a lot of fog coming out of the breather when I bought it. I had to overhaul it after a few years. The cause of the fogging turned out to be a blown head gasket from # 2 cylinder to where the oil drains down from the valves.

 

[Danperkins]

There is always windage in the crankase when the engine is running, thats usually what causes some of the oil spitting that you see when pulling the dipstick. Also, if the engine never really gets warmed up, moisture can build up, the fogging out of the breather can be just moisture steaming out of the engine when it finally gets worked hard enought to heat up and vaporize condensation in the oil and engine. If the engine doesn't use any oil, I would leave it alone.