Leaking Valve Stem Seals?

[Ruben]

What are the symptoms of leaking or bad valve stem seals?

 

The engine in my 240Z had been sitting for couple years before I got it running. It appears to be running fine except for some white smoke that comes out of the exhaust. The engine is a Nissan rebuilt L28 (N47/F54) with only ~25,000 miles. I have heard that white smoke among other things could be a result of leaking valve stem seals. It does not appear to be a blown head gasket and compression is 160psi on all cylinders.

 

I suppose it could still be leaky rings but I'm hoping it's the valve stem seals.

 

Any thoughts?

 

Ruben

'72 240Z

[Z-Gad]

Usually when there's white smoke right after sart-up and shortly after goes away, is usually a symptom of valve stem seals...

Run a compression check dry and then wet to check the rings.

G-luck, Mike

[Guest Anonymous]

Mike nailed that one. You'll get smoke on startup because the oil was up in the head and ran right down the valve stem past the guides and into the cylinder. Instant oil injection on the cylinder, bingo, smoke.

 

I havn't seen the L28 (or L24 or 26) head to see if it can be done on the car. I've done some AMC's and some Chevy's by using a sparkplug fiting that you hook air up to.

 

You air up the cylinder and then compress the valve spring and keepers, remove the retainer and pull the valve seal and replace. You then recompress the valve spring and put on the retainer. Its time consuming, but on some engines can be done on the car. You do have to be careful when sliding the seals on to not push the valve open otherwise it likes to slide down into the cylinder. (I don't think it would go all the way, but I paniced when I saw the first on do it.)

 

Good luck with it,

 

Lone

[Ruben]

Thanks guys. That's exactly when I'm getting the white smoke. I did a dry compression check, so I'll do a wet test next. Maybe the rings are also leaking.

 

Ruben

'72 240Z

[Careless]

resurrecting this sucker.

 

my z31 always burned a little oil after doing the valve job on the head at home (ported, never touched the guides at all, was very careful, and lapped the seats by hand, had the heads decked too).

 

I used Fel-Pro seals that came in the kit with my Top-End gasket kit. It was for an 88 turbo, as for some reason the 87 turbo kit was not listed, and I know I had the W series heads (therefore I purchased the 88 turbo kit to be sure I got the W series gaskets).

 

SO anyways. I started the car and I've been driving it for a while. On start-up it has a large puff of blue-ish smoke.

 

On Idle not so much... During acceleration while under load, it smokes quite a bit.

 

I did a compression test, and got exactly 150 on all the cylinders before I even turned the engine over. well, actually I had removed the turbo because of a fear that it was leaking a lot of oil and causing a lot of smoke to blow, so I pulled the turbo and did a compression test while the turbo was being repaired. The car had not started for 2 weeks at that time, so it was dry for sure, and I returned my broken gauge and got a new one just to be sure.

 

perhaps I've installed the valve seals wrong? I did install them as I have on other engines, but what got me worried was that I ordered a back-up set for the weekend that I planned to install them, just because I KNOW that sometimes it can go wrong... and When I opened the box, the part numbers were the same (Fel Pro) but the valve seals were definately different. Neither looked exactly like the Nissan ones, really.

 

Now, the worst part is, the car was misfiring a lot due to fuel dumpage, so I decided to remove the O2 sensor plug and it was running great, However, it did smoke a lot still... so I figured I would just sea-foam the car, as I have done on a pathfinder with the same engine, and it ran noticeably smoother...

 

After doing that, the car now idles sometimes at 700rpm or so (digital gauge), and it rocks back and forth pretty badly, and even has a slight knocking sound if I turn the lights on... If I don't turn the lights on, it bumps the idle up to 800 and the knock goes away. The car revs up very hesitantly up to 1800, but passed that it revs up nicely, and now it burns a lot of oil.

 

I noticed when replacing my turbo seals that my passenger side rear exhaust port, and my driver side front exhaust port were covered in sooty black residue, that may or may not have been wet due to the misfires I was getting. The other ports were lightly coated in some sort of residue, but not black and thick and hard to whipe off my hands. Also, the turbine housing had some of the same black thick type of oil in behind the backing plate for the turbine wheel, but the rebuilder said the turbo checked out fine both times, and he replaced the bearing a second time for me just in case.

 

So now I'm not sure what to expect. I mean, can a valve seal have popped off or the rubber ripped off the metal casing? the exhaust ones have a positive lock, so those are hard to screw up, I'd say... but could it be that the intake ones that were different than the nissan ones popped off or are not sealing correctly, and would that cause A LOT of oil to come through. I'm going through quite a bit of oil here...

 

I know a hand-check of the valve guides is not an accurate measure, but the valves were pretty darn tight in there, i'd say... and the car DID NOT smoke before I did all this work. It did have an exhaust leak but I've since fixed the crossover pipe leak...

 

Could the seafoam have cleaned any carbon that was sealing the piston oil control rings? Could it have coked the oil control ring on the turbo shaft? I've kinda had it with this engine and I'm thinking of getting another $300 88 N/A motor with 140km on the clock and putting my turbo stuff on there.

 

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