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Blow-by assessment - opinions needed!

brianp454

Member
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Portland, OR
The way it makes a distinct puff that seems to be at the frequency of one cylinder makes me think you have a hole or crack in one piston. I don't see an injector adding blowby, but I think a compression check may be helpful.
 

skinnyR1

Member
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Location
Burlington CT
Ran my truck today and pulled the oil cap to see the blowby. My truck has about the same blowby as seen in the video.

Runs great. Source of blowby unknown.
 

WillWagner

The Person You Were Warned About As A Child
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Here's a tip on "blow-by". First, you can't tell if an engine, any engine, has high CC pressure by just the smoke out the filler cap or road draft tube. The pressure needs to be measured with the proper tool, a manometer, and by the proper method, different manufacturers have different methods of checking, like plugging the road draft tube and running the pressure out of an orificed fitting, leaving the road draft tube open and putting a tool on the filler, or just measuring the pressure straight out of the road draft tube. You can't guess unless the air/smoke out the tube is whistling like a teapot, then it is probably fair to assume the engine has excessive cc pressure. Every engine is different. They might be consecutive s/n engines off of an assembly line or two of the same engines rebuilt buy the same guy using identical parts, they will be different in their performance, smoke out the tailpipe, cc pressure, etc. Injectors and the valve set can't cause excessive cc pressure, I take that back, an injector can cause high blow by if, in the case of a bosch pintle style injector, which the multi is, fails in the open position. It can burn a hole in the piston, but there will be other symptoms evident BEFORE you even think about looking at blow by. If an air compressor is causing high cc pressure, you will see excessive oil in the tanks at your post trip inspection...you are doing that, correct? Excessive cc pressure is usually indicated by having big oil leaks at places that are weak links, the pressure trying to vent itself will follow the path of least resistance, usually front and rear main seals, tappit cover gaskets and valve cover gaskets. Bottom line, if the engine is not using oil, remember, the multi does not like to idle, it WILL slobber out the manifold and drip all over the side of the engine, run them hard, they like that, you don't have massive recurring oil leaks or there isn't an issue in the way the engine is running, like missing and lots of smoke that smells of oil out the pipe, you 95% do NOT have high blow by.

Here's something to throw out there on smoke out the breather. A spun bearing will cause heavy white smoke out the road draft tube or filler. It will not make pressure, just lots of smoke. I have seen, I don't know, 20? engines come in with a complaint of smoke out the breather and found that a cam bushing or main bearing was spun. No other symptoms in the way of engine operation, no unusual knocking, nothing. Sometimes these engines have been running thousands of miles before this was found. I went out on an industrial 855 once that was in a mobile drill rig. It had a complaint of a smell coming from the engine that was making the operator feel sick. A main was spun. The operator told me it had been like that for a YEAR but they couldn't put the machine down until I went out to look at it.

Just a seed to plant :grin:
 

Jeepsinker

Well-known member
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Dry Creek, Louisiana
Also note that I've put 25,000 miles on my truck this year driving all over the place. My truck is a good runner. I don't believe I have a cracked piston or anything like that. Ymmv.
 

Wildchild467

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Any updates on this blow by situation? I am thinking I need new rings in my deuce soon so I am trying to gather as much info as I can before start the job. Thank you.
 

skinnyR1

Member
423
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18
Location
Burlington CT
Any updates on this blow by situation? I am thinking I need new rings in my deuce soon so I am trying to gather as much info as I can before start the job. Thank you.
I posted here in this thread at one point. I had alot of blowby, and ended up replacing my motor.

After extensive troubleshooting, my blowby was discovered to actually be mostly of coolant. I pressure checked everything, and no coolant was making its way into any combustion chamber, so with what I could see, I had a cracked block somewhere. The possibility of a cracked head was there, but that would probably have put it into the combustion chamber during a leak down test. Very little coolant was going into the case, it was all coming out of the slobber tube.

None the less, the truck always ran great even like this. I just opted to put in a new crate motor for peace of mind.
 

cattlerepairman

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Same blow-by. No issues. Runs fine and has not changed.
Have an injector or valve clearance issue that needs to be sorted right now.
 

Valence

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Davis County, UT
As asked in the other thread, are you able to provide more information? Over the course of 4 months it went from:
Same blow-by. No issues. Runs fine and has not changed.
Have an injector or valve clearance issue that needs to be sorted right now.
To this:
This progressed to engine defect/failure. Engine swap time, then rebuild.
 
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