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Bobcat 873f 1999 - blows smoke and oil out exhaust

A-aron

Member
Joined
Jun 3, 2023
Messages
7
Location
Minnesota
3100hrs
Duetz 1011

Short story - billows smoke and oil vapor out exhaust, starts great, runs great otherwise.

Long story - recently purchased machine. Was used by landscaping company and fleet maintained till 2019. Owner sold company and kept machine for home use. Less than 5hrs since little or no maintenance during home use. Had oil leaks from rocker cover, lh side front and rh side from oil fill cap down. Cap appeared to have hole drilled complete thru cap...? Machine had light smoke but ran well and sounds solid. Machine starts quick, runs smooth and had power.

after significant cleaning needs lots of maintenance items.

first thing I replaced was oil dipstick as had old ribbed one and the oil cap. As soon as oil cap was replaced machine had near constant billowing smoke and heavy oil residue from exhaust. I removed the vent tube from valve cover to turbo inlet and it was clean and clear.

since the only thing that changed was redirecting the crank case vapor to the intake and therein increasing case pressure slightly I'm tryin to figure out the next diagnostic step.

I suspect there is either a head gasket leak to the pushrod tube, engine is out of time(skipped a timing belt tooth) or the engine is tired. Any additional ideas are welcome.

Plan to compression test and check timing as next steps.
 

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spitzair

Senior Member
Joined
May 4, 2007
Messages
1,008
Location
Squamish BC (Home), Slave Lake, AB (Work)
My guess is your head gasket is pooched, very common issue on these engines. Our 873 had the same thing happen, not a very hard job to change it. There are 3 different styles of head gasket, our bobcat dealer sent us all 3 and we returned the 2 that we didn’t use…
 

A-aron

Member
Joined
Jun 3, 2023
Messages
7
Location
Minnesota
My guess is your head gasket is pooched, very common issue on these engines. Our 873 had the same thing happen, not a very hard job to change it. There are 3 different styles of head gasket, our bobcat dealer sent us all 3 and we returned the 2 that we didn’t use…
I agree it's the most likely but is there any way to test it/confirm short of tearing the head off?
 

A-aron

Member
Joined
Jun 3, 2023
Messages
7
Location
Minnesota
Update

Pulled the airbox and tubes. Little to no oil in intake.

Ran compression test - cranked 5-6 strokes
(counting From front of engine)
Cyl1 - 300
Cyl2 - 410
Cyl3 - 410
Cyl4 - 410
(All built 200psi on first stroke)

Ran engine and if I remove the oil cap engine doesn't smoke from exhaust, as soon as I put the cap on in about 7-10seconds it starts smoking like crazy. Removing cap releases pressure and smoke stops.

Leak down test - rigged up pressure line and applied 100psi to cylinders individually each at there respective TDC. There was leakage to the crankcase but all seemed similar in sound/leakage.


Trying to understand how a cylinder head gasket could be the cause?

Could the timing belt have slipped a tooth? Out of time?
 

willie59

Administrator
Joined
Dec 21, 2008
Messages
13,479
Location
Knoxville TN
Occupation
Service Manager
Trying to understand how a cylinder head gasket could be the cause?

Because the engine is cooled by engine oil, not typical antifreeze/coolant. When the head gasket on those engines go south they leak engine oil (the coolant) into the combustion chambers, which causes the white oil smell smoke and oil droplets coming out of the exhaust. Very typical for those engines. Problem is, you have to tear it down to actually identify the gasket. The gasket has notch marks on it the denote which gasket to use, serial number won't identify the gasket.
 

A-aron

Member
Joined
Jun 3, 2023
Messages
7
Location
Minnesota
Because the engine is cooled by engine oil, not typical antifreeze/coolant. When the head gasket on those engines go south they leak engine oil (the coolant) into the combustion chambers, which causes the white oil smell smoke and oil droplets coming out of the exhaust. Very typical for those engines. Problem is, you have to tear it down to actually identify the gasket. The gasket has notch marks on it the denote which gasket to use, serial number won't identify the gasket.
That makes sense to me, but what I'm getting lost on is How does the head gasket cause what is presenting as excessive blowby/crankcase pressure?
 

willie59

Administrator
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Dec 21, 2008
Messages
13,479
Location
Knoxville TN
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Service Manager
That makes sense to me, but what I'm getting lost on is How does the head gasket cause what is presenting as excessive blowby/crankcase pressure?

No way for anyone to know that's what's causing the excessive crankcase pressure, that could be a different issue altogether, all things are possible. But if you have a failure of the head gasket fire ring then compression can leak by into the ports that return lubricating oil from the head to the sump which will cause crankcase pressure. Only way to know is take it apart.
 

A-aron

Member
Joined
Jun 3, 2023
Messages
7
Location
Minnesota
Well the heads off.

Unfortunately I don't see anything obvious.

There's carbon buildup at the top of each bore and around the intake valves but the head gasket and sealing surfaces appear consistent. There's not anywhere that it looks "blown out"
 

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A-aron

Member
Joined
Jun 3, 2023
Messages
7
Location
Minnesota
More photos
 

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willie59

Administrator
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Dec 21, 2008
Messages
13,479
Location
Knoxville TN
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Service Manager
Yes, no obvious failures there, but that head looks suspect, some spots are shiny where the fire ring sat, but other spots are discolored, like carbon is sneaking under the fire ring. You might consider having that head shaved. The block deck and top of cylinders look good and shiny, don't see a problem there, but that head, I dunno. Looks like you have a one notch head gasket, there's always a possibility someone in the past fitted the wrong gasket, don't know a way to confirm that myself. For what it's worth, I had a 1011F in a Genie that was smoking and spitting oil, pulled it apart, like yours, head gasket really didn't look that bad. Put it back together with new gasket, no more smoke or oil spitting. Yes, weird.
 

A-aron

Member
Joined
Jun 3, 2023
Messages
7
Location
Minnesota
****Repair resolution*****

The final consensus was there were several things going on.
1. Most notably the crank case vent passage in the cylinder head that runs from valve cover vent to front of the head was completely plugged with carbon and oily residue.
2. Valve stem seals were out of position and had slid up the stems to the bottom of the valve spring retainers.
3. Cylinder 1 (actually 4 but front of engine) with the lower compression had much larger ring gap than other 3. We suspect there was a fuel injector failure at some point that washed the cylinder causing the wear.
4. Heavy oil residue on intake runners, valves and exhaust runners on cylinder 2&3

Failure points - engine has blow-by from cylinder 1 and valve seals, sealed crank case causing it to pressurize due to vent passage, heavy smoke was due to turbo drain back becoming pressurized and pushing oil into intake side of engine and being burned. This is why when we opened the oil cap the smoke would stop when case pressure was relieved turbo stopped pushing oil into intake.

Since the engine ran fine prior to tear down we decided to roll the dice on the cylinder wear and see how it goes. Lapped all the valves and replaced the valve seals. Cleaned the vent passage with wire brushes and acetone before reassembling with a new set of injectors and glow plugs for good measure.

So far (1 hour) engine runs great, starts instantly, still has some light smoke from the blow-by but is manageable.
 

willie59

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Messages
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Location
Knoxville TN
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At least you found some problems to address. Heck, it might run for many more years now.
 
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