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Discussion Starter · #1 ·
Hi, greetings from Norway!

I'm usually a member of the Frontera Owners Group, but as we with the Frontera share engines and components with you guys I thought I should try to give my problem a try here at the Planet!

I have recently done an engine rebuild with new pistons, liners, rings, oil pump, valves, bearings, seals etch. Put it all back in the car on Sunday and have only been doing small trips to run it in after that. Problem is the engine oil is running out the rear crank seal and I can actually see oil smoke blowing out there. The crankcase pressure is pretty extensive so to say.. Probably the crank seal is blown and the rubber has got scorched like my old one from the combustion gas heat. Had the same problem before the rebuild and I thought the crankcase pressure was due to worn liners (which gave me to big end gaps on the rings).

Now I think that the problem might be elsewhere as it has not improved a bit with the rebuild. I did not touch the valve cover in the rebuild and I came to think of the breather valves. On this model 2.8 there is only a baffle plate space in the top of the cover, on "ball in cage" valve which is visible on the inside of the cover and there is one diaphragm valve in the top. Both valves seem OK, no gunk or sludge. Breather hose is also fine. Can I remove the valves for a while just to check if they are malfunctioning and that's why I get all this pressure in the crankcase?
 

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Crankcase pressure is not going to come from much else than the combustion chambers.

Specifically the rings on the pistons must be allowing so much compression past them that they are pressurizing the crankcase. There can be no other option.

The valves are not going to cause pressure in the system either, unless their failed integrity means that they are not working correctly and not holding pressure inside the combustion chamber for the time they are required to do so. In essence they are apparently doing their job at least somewhat correctly.

So - I'd forget about the valve train causing this problem at all.

As for the KV and CV side of the crankcase emission control package, they CAN be a problem, but this situation is too large to be their problem alone.

When you replaced the rings, did you mic the cylinders for taper? Seems to me that you've got a worn out block and new internal parts that cannot comply with badly worn wall surfaces in the cylinders.

EDIT:::

I just went back and re-read your post and you say you replaced the 'liners' on the engine. I am not sure Isuzus use a liner'd engine. That's very expensive!

Is this problem in an Isuzu or some other engine that has liners for rebuilds - like a Peugeot?

Further - did you used an anaerobic sealer on the outer periphery of the rear main seal?

Still though ----- fire and heat coming outta the rear seal is kinda condemnatory for the rings not holding pressure.
 

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yes the isuzu Diesel does use chrome liners wich its one of the reasons that they last soo long.

you have a very weird situation, of you replace everything at the block theres no reason to have a los of pressure, but well could be a piston ring not installed in the correct way or that something its just not how it should be, are you sure that the breather hose has no obstruction? did you see fumes getting out by the hose? do you have a oil catch can installed?
 

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That much pressure has to come from the combustion chambers.

Missed the 'diesel' part - sorry
 

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Discussion Starter · #5 ·
Thanks for the replies, guys! I have been on a short holiday. Haven't been able to troubleshoot the truck more, but have ordered a new valve cover and a new rear seal. Will try to run a new hose, remove the diaphragm valve in the valve cover and then replace the seal again. Fingers crossed... With all new parts, liners and rings I suppose there could be some blow by until they are well seated, but not this much :( Rings are installed according to Isuzu workshop manual. Don't think they should have moved much during installation.
 

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id give replacing the seal a shot and be 100% sure the valve cover can vent freely. may have just been a bad seal or it tore on startup. youll definately have a little excessive blowby untill the rings seat, but its best to get the engine under a full load sooner for short distances but without revving too high to seat the rings faster. theres really nowhere else for crankcase pressure to come from other than compression passing the rings... could the exhaust system be plugged up or badly restricted somewhere by chance?
 

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Discussion Starter · #7 ·
Yep, has to be blow-by that's causing this. Even with my newly rebuilt engine :-( I have replaced the exhaust with straight through mufflers and welded up with 2,5" pipes, so that should be completely open with no restrictions.

The guy at the shop that replaced the liners told me they never came out completely straight after pressing them in and that they usually drilled and honed them afterwards to make sure they got completely circular and straight. The Isuzu ones are very thin, already chrome plated and honed, so there is not much to do but to install them and hope they get reasonably straight... Mine came out a little off, a fraction of a mm but they told me it should be OK, just a little increased oil consumption on one or two cylinders. They are supposed to be good, rebuilding a lot of race engines and also heavy duty diesel engines. And as the block has to be heated, the liners cooled with dry ice and then pressed in with a bench press I decided not to take upon that task in my own tiny garage.

Now it's done and I think I'll have to live with it. Hopefully it will develop a tighter seal when properly run in!

In the meantime, would it be a good idea to remove the internals (ball-in-cage, diaphragm valve) of the valvecover and the just let it breathe through a catch can with suction from the air filter box? Go old school and just forget the "modern" PCV stuff?
 

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Discussion Starter · #8 ·
I just received a new rocker cover. It's definitely an Isuzu genuine, but a bit different from the one I have on the engine now. It seems to have two outlets. How are these two meant to be routed? Are they both in use on your engines?
Pics of the cover here:
http://db.tt/aF1JsqM
http://db.tt/kKFeqrk
 

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Discussion Starter · #9 ·
Result!

At least I think so... Took down the gearbox again this Sunday to replace the seal for the fourth time... Really took my time investigating a bit further this time and removed both the aluminium spacer and the steel backplate of the engine. Oil everywhere, but when the plate was off I noticed to small holes, on each side of where the sump pan meets the engine and the crankshaft bearing cap, see pictures below. I put an air hose down the dipstick tube and tried to inject some air into the crankcase to test and, wow! A fair breeze out of the two openings. No wonder I have been loosing oil....! I could actually see all the way into the crankcase. When the backplate is on these two openings are hidden and the oil seems to come from the shaft seal itself. The workshop manual describes how one should not use too much of the silicone sealant when sealing the sump, so I did. No place it is noted that one has to add liberal amounts where the rubber strip seals over the crankcase bearing caps meets the engine block. So much for me replacing all these oil seals, when it all along has been leaking directly from the sump/block connection...

I should really have had the engine out again to seal the sump properly this time, but I have no time for that now. So for the time it's bodged up with a thick smear of silicone sealant applied from the outside. I degreased properly with break cleaner first so hopefully this quick fix will stand and seal up for the summer vacation road trips.



 
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