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15 comments
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Join Date: Jun 2009
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4D56 turbo 2.5 l diesal engine

06/13/2009 8:25 AM

recently i overhauled the engine of my pajero. after 2 months i noticed that there is blow by through the dipstick when pulled out. i also noticed reduction in running and pulling power. i have put genuine rings, overall gasket set, standard crankshaft, pressure tested head and other genuine parts from authorised dealer[nivis motors in fiji for mitsubishi motors]. what are the reasons for this and how can i reduce or stop blow by. i have already fairbit of money so cant overhaul again.please suggest alternatives

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#1

Re: 4D56 turbo 2.5 l diesal engine

06/13/2009 10:06 AM

Two immediate things that come to mind:

1. Did you get the ring "orientation" correct? Usual is something like gap of #1 ring at 12, #2 ring gap at 4, and #3 ring gap at 8 all on a clock face. (just an example)

2. Did you diligently follow breakin for ring seating?

While it is a pain, you can probably re-ring for much less cost than overhaul.

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#2

Re: 4D56 turbo 2.5 l diesal engine

06/13/2009 10:24 AM

From the way you describe this it seems like the lower block is pressurized correct?

Somewhere on the side of the block there is a pipe that will lead to the intake, it is a diesel version of the crank case vent. From what you have said it sounds like it is blocked.

As the pressure in the block builds the efficency of the engine will decrease.

Check it out and let us know.

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#3
In reply to #2

Re: 4D56 turbo 2.5 l diesal engine

06/13/2009 10:31 AM

HAH - excellent snag sir!

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#5
In reply to #3

Re: 4D56 turbo 2.5 l diesal engine

06/13/2009 11:07 AM

why... Thank you sir.

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#9
In reply to #2

Re: 4D56 turbo 2.5 l diesal engine

06/14/2009 3:45 AM

today is sunday. i will check this option on tuesday and let you know. very interesting though

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#14
In reply to #2

Re: 4D56 turbo 2.5 l diesal engine

08/07/2010 7:43 AM

Hi, So im having a really weird problem with my 4D56t. at hi speeds and rpm oil blows out from my dipstick, i thought it was a faulty dipstick so i bought another and i took tape and build it up so that it holds downs more firmly, it does, however the oil is now spraying out from around the engine cap. another thing, the egr vacuum lime and i believe all other vacuum lines are disconnected, my last mechanic didnt hook it back up because he didnt know how to.... apparently also, on the top of the egr valve oil sometimes leak out from there as well(the vacuum line isnt hooked up there as well), but wen i do put on the vacuum line on the egr, the engine pings really loud..... help!!plz!! this engine does not have an intercooler and its in a Mitsubishi L300.

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#4

Re: 4D56 turbo 2.5 l diesal engine

06/13/2009 11:07 AM

i have put genuine rings, overall gasket set, standard crankshaft, pressure tested head and other genuine parts from authorised dealer.

That's good . but what's for pistons and piston cylinders . did you change pistons or you installed new rings for old pistons,did you execute pore polishing for piston cylinders .did you change it by new standard ones . it's different cases leading to different results.

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#6

Re: 4D56 turbo 2.5 l diesal engine

06/13/2009 11:13 PM

Did you check ring gap before installing?

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#7

Re: 4D56 turbo 2.5 l diesal engine

06/13/2009 11:49 PM

The piston rings are not sealing for some reason. Re-check the compression pressure and you will probably find it much lower.

You will probably have to pull it apart to fix it right. Diesels are very unforgiving of fitment errors. Piston ring grooves MUST be clean, square, and not worn, Side clearance specs are critical. End gap of rings is critical. Condition of cylinder bore surface is critical. Usually necessary to re-hone, bore oversize, or replace liner to get satisfactory fit and finish for good ring sealing. New pistons usually required.

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#8

Re: 4D56 turbo 2.5 l diesal engine

06/14/2009 12:22 AM

It is obvious the rings did not seat and you are experiencing considerable "blow by" i.e. leakage of combusion gas past the rings and into the crankcase. I can think of two possible explanations for the problem you described: 1) the cylinder walls were not properly prepared by honing.The hone breaks the cylinder wall glaze and the resulting cracks hold oil to lubricate the new rings so they will seat properly. or 2) The oil pump was not properly primed before restarting the engine so the rings ran in dry cylinder bores for some time before oil was splashed on them.

You need the advice of an experienced engine rebuilder but I can think of no alternative except to disassemble the engine and examine the cylinder bores and rings.

Dennis Waller

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#10

Re: 4D56 turbo 2.5 l diesal engine

06/14/2009 11:00 AM

The most likely reason is (assuming you did not rebore or change the pistons themselves) that you forgot to "rough up" the bores properly. There is a special tool that goes in an electric drill, that needs to be worked up and down each bore before fitting the re-ringed pistons....

There are some other points already mentioned that also need to be checked out fully, I did not feel the need to tell you twice.....

I would do it soon as the rings and pistons are being damaged by the blow by....you may need to replace the rings again as they could have dramatically over heated.....

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#11

Re: 4D56 turbo 2.5 l diesel engine

06/14/2009 11:34 AM

Obviously, you rebuilt the engine because it was worn to the point that there was a lot of oil burning, loss of power or other, right?

Particularly with a high compression diesel engine, the wear on the cylinder walls produces an ovaled geometry. When overhauling, if you don't rebore AND replace pistons, you can't return to the correct cylinder geometry that will allow the rings to seal properly for an extended period of time. In addition, if you don't replace valve guides but instead just have them knurled, oil will be drawn through the guides as the slightly raised knurled surface quickly wears away. The voids produced by the hatch pattern of the knurled surface actually hold little "lakes" of oil just waiting to be pulled into the manifold through the valve stem clearance by vacuum action.

There is no getting around it. If you don't do a 100% job, you can't expect 100% results.

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#12
In reply to #11

Re: 4D56 turbo 2.5 l diesel engine

06/14/2009 1:47 PM

GA from me.

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#13

Re: 4D56 turbo 2.5 l diesal engine

06/15/2009 12:42 PM

Some blowby is normal. With new engines, about 1% of the air mass will get by the rings after it is broken in and the rings are seated. 3% blowby is considered by some as the upper limit (expecially on newer low-emission spark-ignited 3-way catalyst engines). Diesels, however can handle more than 3% blowby and little difference in performance will be noticed.

Anyway, my point is that you have to quantify the blowby. A little bit is normal. And even if it is a bit high, make sure that you check the PCV (positive crankcase ventilation) system to make sure it is properly re-installed. A blocked PCV, as another person commenting here said, can be responsible for your observation of high blowby on the dipstick.

Can you compare the blowby to a known good engine? Maybe it is not the real issue. Ask a good mechanic who has a feel for such problems if possible.

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#15

Re: 4D56 turbo 2.5 l diesal engine

08/07/2010 8:08 AM

What is the state of the engine now. Did you strip down and re-hone the bores as needed?

Please update.

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