LB7: Excessive blow by

[Sandracer799]

Back in December I was lucky enough to join the cracked piston club.

About a month ago i picked up an 8,000 mile LB7 long block. Got it running this past Sunday. Drove it all week with no issues.

Going down the road today I come to a stoplight. As I am sitting there I notice a little bit of smoke. I assumed it to be stuff still burning off from the install.

Well after I get to my destination I quickly learn it is not burn off.

I pull the oil fill cap and it is blowing out of there and when you pull the dip stick same thing.

The truck is not idling rough at all like it did before when I cracked the piston. It is just blow by.

I need opinions. Stuck ring? Injector not sealed correctly? Cracked piston? :banghead:

Any and all help is appreciated. I am at my whits end with this truck.

 

[blk smoke lb7]

Hey guys any ideas on this 1.I sold this motor to Josh and it ran flawless for me it was never efi live tuned.It sat for 9 years then i bought it,installed it for 6000 miles while my motor was being built.It had absolutly no blow by and was THE quietest motor i have ever heard the rockers where set at 11thou and i had installed arp head studs in it before i installed the motor in my truck.I was saving it for a day i did a car project but it was far to nice of a motor to tear back apart just to build so i finally sold it,josh caught me at just the right moment and i sold it to him.He had called me last week to tell me how impressed he was at how smooth and quiet the motor was.I got the motor from a local guy THAT KNOWS A GUY AT GM,it had dropepd a valve and stuck the valve in the head,the head was replaced with a 25k head new piston and gasket then like i said it was driven for 6000 miles without problems.Thats about it as far as history,anyone have any ideas at all?Stuck ring? valve seat come loose?

 

[ripmf666]

Is it a lot of blow by huffing or alittle haze? I have a little hint most motors have a hint if you look at them puff out. So one that's been parked on the floor could have some more to it. Maybe try a video for us to see.

 

[Sandracer799]

Is it a lot of blow by huffing or alittle haze? I have a little hint most motors have a hint if you look at them puff out. So one that's been parked on the floor could have some more to it. Maybe try a video for us to see.

It is huffing.

Here is a video.

http://www.youtube.com/watch?v=WtRPAvseGBo&feature=youtu.be

 

[Bonestock]

Pcv restricted?

 

[Devon]

Pcv restricted?

My Pcv hose was kinked pretty good causing some blow by..


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[LWATSON]

Fed emissons on the LB7 should have a vac pump correct? all that in working order?

 

[blk smoke lb7]

Fed emissons on the LB7 should have a vac pump correct? all that in working order?

No a cali model would have a vac pump the more i think about it it has to be that pve line being pinched or something because that motor ran so well and with 8000 miles there cant be anything wrong with it and it still runs very well.

Remeber the guy this winter with the Escalde front end thought he had a blown a piston? and come to find out the pvc line was froze over he cleaned it out and no more blow by.
http://www.duramaxdiesels.com/forum/showthread.php?t=45836&highlight=blew+oil+cap

 

[Sandracer799]

I have checked everything and nothing is clogged or pinched. When the oil fill cap and the dip stick are in place the smoke is pouring out of the breather/pcv vent at the bottom of the motor.

 

[workin' diesel]

I have some blowby on mine too. I have never tried taking the filler cap off while it is running. I do notice it at stop signs and I can smell it in the cab once in awhile. Don't think it is that bad though. It is really oily around my vent hose and surrounding area.

 

[blk smoke lb7]

This motor never had any blow by for me or for josh for he 1st week he had it in .

He is going to do a compression test today.Anybody else have any ideas?

 

[Chevy1925]

balance rates? his injectors or yours Scott? brians did this just before he tore it down, it was assumed bad headgasket or pushed cup as it would build too much coolant pressure but didnt make sense to the blow by which me and Simon felt was strange. specially since no pistons were cracked and no bent rods

 

[messejme]

Perhaps the cylinder with the dropped valve had some scoring. A HOTTER tune will accentuate this due to higher cylinder pressures.

 

[Bonestock]

How long did the engine sit? Almost seems like stuck rings not sealing from possible rust or ???

 

[blk smoke lb7]

Iirc he said they were pretty new injectors and he bought a new install kit to reinstall his old injectors.I had revealed the cups before I installed my injectors and they were only in for 6000 miles.When I installed them I used silicone release agent (like vasoline) so the injectors wouldn't pull on the cups when I pulled them back out.I wouldn't think there should be an issue with the injector cups sealing.

Josh is it possible an injector didn't get seated tight enough and/or the I ejector body o ring got sliced and is allowing blow by????

 

[blk smoke lb7]

How long did the engine sit? Almost seems like stuck rings not sealing from possible rust or ???

Since I ran it last it sat for 2 years but if it was a stuck ring wouldn't it show right away after he installed it.I know engines that sit get stuck rings quite a bit but they do it right away most of the time.And yes I agree that's what it acts like because it still runs very good just has blow by.

 

[Chevy1925]

i would suggest doing the compression test, find the low cylinder (if there is one), then do a leak down and pull the upper valve cover. that should pin point it i would think. if its a ring, you should hear air coming out the oil fill cap and not where the injector is

 

[blk smoke lb7]

Ok any suggestions as far as to get it unstuck if this is the case?

On passers we used to Dump a couple quarts of trans fluid in and let it clean the motor then dump it and put in fresh oil and it would run like new.

What about seafoam oil treatment?

 

[dirty_max]

subd

 

[Chevy1925]

Ok any suggestions as far as to get it unstuck if this is the case?

On passers we used to Dump a couple quarts of trans fluid in and let it clean the motor then dump it and put in fresh oil and it would run like new.

What about seafoam oil treatment?

something about putting ATF in a motor just doesnt sit well with me but ive never tried it either.

i dont think its a stuck ring though. knowing you, it was sealed up well while it sat