LMM injector o-ring function

[camcojb]

I searched and found threads on LB7's and they said the o-ring didn't seal compression. I'm wondering if that's different on an LMM.

I just finished up the engine swap on my truck; bought a low mileage LBZ engine and swapped everything from the LMM to that, including the injectors. My local dealer didn't have any new o-rings so I just re-used my old ones.

Got the truck running and when I came back from a short drive I can hear what sounds like a small compression leak on the passenger side of the engine, in time with the engine. When I shut off the engine you could hear the psssssssshhhhhhhh of what sounds like compression bleeding off for 2-3 seconds.

I immediately thought it was an injector o-ring, but searching only found LB7 info, and on that they said the o-ring doesn't seal compression. Is it (hopefully) different on and LMM/LBZ? If not, any ideas what it might be?

Jody

 

[SIKDMAX]

I beleive it would be different on LLY/LBZ/LMMs because of how the LB7s are different in that they are under the valve covers. Maybe with the movement of the injectors they also changed in how they seal?

Everything else go ok with the swap? What was the most difficult part of putting the new engine in? Thats what Im most worried about.

 

[camcojb]

I beleive it would be different on LLY/LBZ/LMMs because of how the LB7s are different in that they are under the valve covers. Maybe with the movement of the injectors they also changed in how they seal?

Everything else go ok with the swap? What was the most difficult part of putting the new engine in? Thats what Im most worried about.

none of it is particularly difficult, just time consuming. Since I had to completely strip both engines it was like a puzzle getting all the brackets and hard lines back, as in some cases they have to go in a particular order or the next item can't be bolted on. I am glad I did it though, as I have a much better understanding of how the engine works from seeing it blown apart.

The twin install went pretty easy, easier on certain items like the drain line because I could do them with the engine out of the truck. Some of the install pics could be bigger and a couple other pics of certain steps would have helped a lot, saved me some time in figuring it out. But figure it out I did, and the kit fit perfectly. Very nice quality from Nathan. Haven't really put my foot into it, kinda sorting the whole new combo out, checking for leaks, etc.

Jody

 

[dmaxvaz]

I would look at all the glowplugs, make sure they are tight

 

[Dzlnut]

Jody..my truck makes a similar sound right after shut down ..i think it is the a/c system ..which is running while the defrost is on.

Just a thought..

 

[camcojb]

Jody..my truck makes a similar sound right after shut down ..i think it is the a/c system ..which is running while the defrost is on.

Just a thought..

yeah, I've heard that before too, but this is different. For one, the a/c is completely off as I haven't charged the system yet. Two, it makes a sound of compression escaping all the time. You can only hear it with the hood up, sounds like someone pushing the end of a valve stem on an inflated tire, in rhythm with the idle speed. Then you shut off the engine and the compression in that cylinder bleeds off.

I looked again at the old LBZ injectors, and it appears that the o-ring must seal compression. Can anyone verify?

Jody

 

[Iceman56]

Are you sure the air isn't coming from the twin setup, loose clamps ect.?

 

[JoshH]

I don't think they do. I'm pretty sure the copper washer is what seals compression.

 

[camcojb]

I don't think they do. I'm pretty sure the copper washer is what seals compression.

I think you're right. Maybe it's a loose glowplug, doubt it though.

 

[LBZrcks]

I don't think they do. I'm pretty sure the copper washer is what seals compression.

X2, I would think that also. Only the tips get black/soot on them, the bottom half of the body below the o-ring and above the washer stay clean.

 

[camcojb]

Are you sure the air isn't coming from the twin setup, loose clamps ect.?

It sounds like it's a single cylinder that's loosing compression, pretty small amount but you can hear it with the hood up. It didn't do it when I first fired the engine, so somethings come loose. Seems like if it was a loose clamp or something with the twin kit it wouldn't have the on/off hiss noise.

 

[IOWA LLY]

O-rings are only there to keep moisture out. Are you sure you installed all the copper washers?

 

[IdahoRob]

O-rings are only there to keep moisture out. Are you sure you installed all the copper washers?

Exactly, the copper washers are the key. The orings just keep the crude out of the injector bores.

The big charger will huff a bit after the engine is turned off, but if you hear the noise while running, then I'd say either the injector seal is not tight, or a glow plus is loose. Check balance rates, not sure if compression would be off enough to read a difference, but won't hurt to try.

 

[camcojb]

Exactly, the copper washers are the key. The orings just keep the crude out of the injector bores.

The big charger will huff a bit after the engine is turned off, but if you hear the noise while running, then I'd say either the injector seal is not tight, or a glow plus is loose. Check balance rates, not sure if compression would be off enough to read a difference, but won't hurt to try.

when I started this post I never saw the copper washer; yes, that's definitely the sealing item. Since I've never seen an injector before swapping this engine I didn't look to see if all of them had their washers. I would assume they do as the old LBZ injectors all have them, and they don't just fall off.

Did a balance test, all 8 less than 1 in park and drive. I tried feeling all over around the injectors, exhaust, all clamps were re-snugged, etc. All injectors seem fully seated, all glowplugs tight. Can't determine what the noise is. Best description is a chugging, like an old steam train. Sounds like a small combustion leak. Reminds me of the noise of the blown engine that I just pulled out, except much quieter and without the smoke and missing, etc. Then again, this morning it almost sounded like a slightly out of adjustment rocker arm.

I may remove the fan brace enough to be able to get a socket on the crank bolt and turn the engine over by hand and see if I hear the leakage. That would at least verify if it is indeed compression or not.

 

[MMLMM]

what about a compression test gauge?

leakdown test?

 

[SteveFord]

What about an exhaust leak?

 

[camcojb]

What about an exhaust leak?

it's possible, I sure can't find it though. I'm still looking. I had the fenderwell out with it running, couldn't feel or hear any leaks. Put it up in the air on the lift running also, but you can barely hear it underneath. Sounds like it's coming from the valve cover area, passenger side, one of the two rear cylinders (5 and 7 I believe on these Dmaxes).

Jody

 

[IOWA LLY]

Pull the injectors on the passenger side. I'll bet your missing a copper washer.

 

[camcojb]

Pull the injectors on the passenger side. I'll bet your missing a copper washer.

close........................ It seemed like it was quieter if I pushed a rag around the #5 (third one back on the passenger side) injector. So I removed the injector and could see it had a washer, but there was combustion leakage past it, and a bit of fuel residue on the valve cover around the injector hole. So i swapped the washer for one of the LBZ ones and just fired it back, perfect, no leakage.

Thanks guys, really appreciate the help. It's got to where I rarely post tech questions on the "other " board, Pat and crew have this one going so well.

Jody

 

[JoshH]

Glad to hear you got it figured out.