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Anonymous Poster #1

Engine

11/14/2018 6:10 AM

After overhauling a 4m40 engine,still oil is blown from the breather pipe. What could be the problem. Piston sleeves and rings all new
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HiTekRedNek
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#1

Re: Engine

11/14/2018 6:58 AM

Inadequate or defective,clogged or out-of-spec crankcase ventilation system.

All engines have some "blow by" that gets past the pistons.

Crankcase ventilation is required to handle this to prevent a pressurized crankcase from blowing oil out of the breather.

Check your engine specs for the type,location and specifications of your crankcase ventilation system.

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SolarEagle
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#2

Re: Engine

11/14/2018 11:38 AM

This is a common problem with these engines...

..."After the new rings were installed did you follow the break in procedures? This information is normally in the engine manual & typically calls for the use of a specific engine oil (normally a non-detergent) for a specific number of miles. If the rings don't break in during this period they will never break in. Never use a synthetic oil until after things are completely worn in. After the break in period a synthetic would be your best choice for longevity of the engine. J.Conway"...

Not properly broken in piston rings...

https://cr4.globalspec.com/thread/32608/1994-Mitsubishi-4M40-Engine-Breather-Blows-Oil

https://www.woltergroupllc.com/breaking-in-a-diesel-engine/

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#3

Re: Engine

11/14/2018 5:09 PM

How is it running otherwise?

Have you double checked the oil level when the engine is cold flat and level?

Have you done a compression test to compare the cylinders?

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Nitz
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#4

Re: Engine

11/14/2018 10:59 PM

Has nothing to do with using a synthetic oil to breakin a new or freshly rebuilt engine. Been working for synthetic manufacturers for 3 1/2 decades and this is a myth - not a reality. It is commonly not done by engine builders due to the cost difference and that a 'short' break - in interval makes it hard to justify the added cost of a synthetic over a conventional mineral oil running for less than an hour in some cases.

If it was a problem, the major oil companies supplying synthetic oil would have an issue in the Corvettes, Cadillacs, Vipers, Mercedes and numerous other marques that start with a synthetic oil from the essential cranking.

Poor ring sealing is a likely suspect - but not just due to ring sealing but also due to ovality (out of roundness) of the cylinder bores. Hard to get a round piston ring to seal in an oval cylinder or a tapered cylinder.

Perform a leak down test - not just a compression check of each cylinder - as it will identify the condition of the intake and exhaust valves sealing as well.
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SolarEagle
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#5
In reply to #4

Re: Engine

11/14/2018 11:51 PM

Are new piston sleeves likely to be oval or tapered? ....Agree that synthetic can be used as a break-in oil, but it's a waste of money ....

https://www.enginebuildermag.com/2014/10/break-in-oils-and-assembly-lube-needs/

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Oomborrie
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#6

Re: Engine

11/15/2018 5:15 AM

Why would anyone with a problem like this post Anonymous?

The System to control the pressure in the sump is dependent on 1. Is there enough space in the sump to take the pressure created by the downward movement of the pistons. Normally dependent on the OIL LEVEL. 2. How much oil is in the sump air, normally controlled by the OIL LEVEL. The crank should not hit and splash the oil up into the crancase cavity. 3. The vacuum system that control the pressure in the sump. Normally a return pype connected to the inlet manifold.

Most engines that also leaking oil can be traced back to presure in the sump.

if you use the engine with pressure in the sump or to high an oil level it will deposit oil on the sleeves below the pistons and will glaze the sleeves that will lead oil burning and low compression.

if the Engine was renewed because it had this problem before, best is to start with the dipstick and make sure the engine is not over filled.

Please come back and answer some of the questions.

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Mandale
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#7
In reply to #6

Re: Engine

11/15/2018 7:31 AM

Thanks for your comment. This problem was not there before,the problem was with crankshaft. I changed another crankshaft together with the linnerkit .
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Oomborrie
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#8
In reply to #7

Re: Engine

11/15/2018 8:00 AM

Mandale are you the poster with the problem?

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Mandale
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#9
In reply to #8

Re: Engine

11/15/2018 8:08 AM

Yes I am
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Oomborrie
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#12
In reply to #9

Re: Engine

11/15/2018 10:06 AM

Can you answer the questions posted at response #3

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lrsheldon
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#10

Re: Engine

11/15/2018 8:44 AM

possibly one or more broken rings.
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Mandale
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#11
In reply to #10

Re: Engine

11/15/2018 9:48 AM

I have dismantled again the engine everything is in order no broken ring. But the problem is the same
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SolarEagle
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#13
In reply to #11

Re: Engine

11/15/2018 10:40 AM

Were the rings properly installed and broken in, and are they properly seated? what tests have you done? Did you do a compression test before disassembly? Is the oil pressure normal? Checked for oil leaks? All you can do is keep looking, you'll find it...

https://itstillruns.com/check-rings-bad-valves-leaking-5931673.html

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wrenchtwirler
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#14

Re: Engine

11/16/2018 10:05 AM

This is an older thread (2009) which seems to have the exact same

problem and also has discovered a cause and the solution.

https://cr4.globalspec.com/thread/32608/1994-Mitsubishi-4M40-Engine-Breather-Blows-Oil
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HiTekRedNek (1); lrsheldon (1); Mandale (3); Nitz (1); Oomborrie (3); SolarEagle (3); truth is not a compromise (1); wrenchtwirler (1)

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