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Tractor Talk Discussion Forum

CRANKCASE BLOWBY

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NEED HELP......

08-20-2004 18:39:20




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how is engine crankcase blow by measured and what is user to do it?




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Tommy D6-8U

08-21-2004 18:14:50




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 Re: CRANKCASE BLOWBY in reply to NEED HELP.........., 08-20-2004 18:39:20  
I run a fair amount of engines on our dynamometer
at work and even with rebuilt engines run at various loads, you will almost always get a fair amount of what looks like excessive blowby. When you actually measure it with the manometer, its only an inch or so of water column. All mfrs figures are different. The first engine I rebuilt myself did fine until I put the 100% load on it and it steamed out the vent like a locomotive for about 5 minutes and then cleared up. It was a 1004 Perkins; I think they say about 2-3 inches is acceptable (not sure about that). All told, I"ve dyno"d Perkins, Kubota, Deutz, Nissan, Yanmar, JD and they all seem to do about the same; it always looks worse than it is. For what its worth!

Tommy

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david val

08-21-2004 03:20:19




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 Re: CRANKCASE BLOWBY in reply to NEED HELP.........., 08-20-2004 18:39:20  
crankcase blowby can be measured by a gas flowmeter.
the measurment has no value unless you have manufecturer specs which you don't find often in the books. otherwise you may learn about the engine from looking at the blowby as mentioned.
david



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RAB

08-21-2004 00:56:35




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 Re: CRANKCASE BLOWBY in reply to NEED HELP.........., 08-20-2004 18:39:20  
A little more information would help to solicit some sensible answers.
Like - how can we help in your particular case? Do you have a problem engine? If so what is it and what are it"s symptoms.
How do you normally operate this engine?
Has the problem arisen very recently or over a long period of use?
Does it consume oil and if so at what rate?
Have you tried a compression test?
Any other information which would make a diagnosis or recommendation, from a distance, more useful?
Regards, RAB

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Joe (Wa)

08-20-2004 21:06:41




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 Re: CRANKCASE BLOWBY in reply to NEED HELP.........., 08-20-2004 18:39:20  
Crankcase pressures are measured with a manometer in inches H2O.

Joe



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BushogPapa

08-20-2004 20:38:44




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 Re: CRANKCASE BLOWBY in reply to NEED HELP.........., 08-20-2004 18:39:20  
That is really a "suggestive" subject...!!

It depends...some tractors will "Breath" quite a bit, until they are really good and hot--as they are eveporating moisture from the crankcase, etc..

If it is still blowing a lot of vapors after a good long hot run, suspect ring-seal, or valve-guides.. Using a "Leak-down" type compression tester will give you a good idea of each cylinder"s condition. Using this method, you can actually hear any leaks from the intake valve, exhaust valve, breather, etc.. What you use is regulated compressed air put in the cylinder at reduced pressure, while the piston is at TDCC.. With an air-flow measurement, you can see how much is leaking out of the cylinder.. Less than 10%leak-down is pretty good..1 or 2% is what you would want in a competition engine BUT..if it still runs good...why fix it if it ain"t broke..??? Ron.

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RAB

08-21-2004 00:48:19




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 Re: CRANKCASE BLOWBY in reply to BushogPapa, 08-20-2004 20:38:44  
Valve guides? I think not, unless it is a) turboed (inlets), or b) has a constricted exhaust and at high speed.
Air flow measurement. Use a stop watch to compare cylinders - pressurise and then turn air off with a valve - simpler. Don"t know what you mean by 10% - it will all leak eventually even from the best engines, won"t it?
RAB



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BushogPapa

08-21-2004 08:51:04




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 Re: CRANKCASE BLOWBY in reply to RAB, 08-21-2004 00:48:19  
A properly set-up Competition engine with "0-Gap" Rings will leak down 2% or Less.. The ring ends are machined to over-lap..leaving NO gap to leak...

Ron.



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TheRealRon

08-21-2004 05:40:49




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 Re: CRANKCASE BLOWBY in reply to RAB, 08-21-2004 00:48:19  
You are correct. When doing a cylinder leakdown test the rate of leakdown is measured. There are different types of testers and they come with instructions on how to conduct the test and how to calculate the percentage of leakdown. Generally, anything over 10% means the engine must be torn down.



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