Valve stem seals' impact on oil consumption

[ganda1f]

I am trying to figure out a few things about oil consumption related to fried valve stem seals. From what I have read on this forum oil consumption can be attributed to a couple of things, with fried valve stem seals being one of them.
Car in question is a '95 Rolla, 4AFE with 170k miles on it.
1. After taking the valvetrain apart and removing the lifters from their bores, it appears that whatever oil that ends up in the bore has nowhere to go. I assume that some of it is sucked past the valve stem seal and into the combustion chamber in the form of oily mist, that is supposed to lubricate the cylinder walls. Now, if the seal is fried and hardened, then an excessive amount of oil would get past it and be burnt or thrown into the exhaust. Is this reasonable?

2. The car uses about 1/3rd quart of oil every 600 miles, pretty much regardless of type or weight of oil (anything from 0w-40 to 15w-50, both synthetic and mineral). Daily commute 50 miles both ways, no city traffic, driven gently.
But on a long highway trip (900 miles) driven rather gently (50-70mph) it only used half of it, that is 1/6th quart over 600 miles.
Could the difference be explained by oil leaking past the valve stem seals when the car is parked overnight? I cannot see blue smoke on startups though. However, spark plugs do have quite a lot of soot on them when examined right after startup. See pic below:

The spark plugs look all right (brownish tan) when examined after a longer drive.

Any thoughts on either 1 or 2?
I suppose this oil consumption does not really justify taking apart the engine yet, but I am a bit curious as to what could be causing the difference.
PCV valve did not change anything.

[speedy25]

You are right that your plugs do show excessive oil consumption.

The MOST leakage past VSS (valve stem seals) is under vacuum. On startup you have all that cold puddled oil laying in the head and getting sucked into the combustion chamber at the high vacuum of idle. Of course after 100k those seals are hard as a rock. Rubber of any compounding can only stay pliable for so long.

The next place oil goes is past the rings under load. As compression gases leak past the rings it pressurizes the oil in the crankcase and it goes anywhere it wants. If it doesnt leak out past seals than it goes in the combustion chamber.

Changing the VSS will lower your oil comsumption but if your driving isnt all stop and go then I think most of your consumption is past the rings.

ALso make sure your PCV valve is OK. If its blocked it will cause oil consumption too.

-SP

[ganda1f]

OK thanks. That brings me to another question.
Would a compression test tell me if the oil is likely to leak past the rings as well? The engine runs great otherwise, so I sort of do not expect poor compression numbers.

[speedy25]

Personally I consider a compression test useless. A leakdown test will tell you MUCH more about your engines internals. It will tell you how much is leaking and you can find out if that leakage is ring related.

-SP

[demonics12]

ive got the same issue, but my plugs look okay?

did a full tuneup, pcv valve, seems to have gotten worse over the past 20k miles or so, now at about 225k

im thinking about having the head rebuilt completely.

car still runs strong, though i bet a bit stronger if i got the head redone and did the timing best service.

[ganda1f]

Would it be possible to change the VSS without taking off the head? I thought that maybe if one put the piston at TDC to prevent the valves from dropping down into the cylinder, the valve springs could be safely removed and the VSS pulled off along the valve stem. I could not have a look myself because I do not have a suitable tool to compress the springs and remove the keepers and springs.
Or do the valves have to be taken out before the VSS can replaced?

[speedy25]

Yes, you can replace the seals without head removal and there are a bunch of different ways to do it. The mosy popular is putting air in the cylider at TDC. R&R of the valve keepers is the hard part of the job. Sometimes getting the old seals off is difficult since they will be hard as a rock. The new ones can alost push on! Some I've removed just broke into pieces.

Demonics- If the oil isnt deposited on your plugs then its going somewhere else.

-SP

[demonics12]

likely out the exhaust then...ugh

anyone have any ideas if and how much is safe to mill the head down? i figured while i got the work done, id bump up the c/r

[ganda1f]

Thanks for the tips speedy. Just to confirm, that I got this right, the valves cannot fall into the cylinder with piston at TDC, right? It will always be possible to pull them up by the stems, correct? Pressurized air in the cylinder is just to keep the valves closed for the installation of the keepers?
I would really hate to have to remove the head just because I drop a valve in the cylinder.

[speedy25]

Originally Posted by demonics12

anyone have any ideas if and how much is safe to mill the head down? i figured while i got the work done, id bump up the c/r

Milling to bump up the CR is useless. The only reason to do it is to have a flat surface.

-SP

[speedy25]

Originally Posted by ganda1f

Just to confirm, that I got this right, the valves cannot fall into the cylinder with piston at TDC, right? It will always be possible to pull them up by the stems, correct? Pressurized air in the cylinder is just to keep the valves closed for the installation of the keepers?
I would really hate to have to remove the head just because I drop a valve in the cylinder.

Yes the valve will fall into the cylinder. It wont fall out of the guide. You need the valve stem extended out as far as it can go so you can put the keepers back on.

By your questions, either have someone else do it, or get someone to help you. I dint want you to screw up and make a mess of your engine.

-SP

[cabbe2]

Would it be possible to change the VSS without taking off the head? I thought that maybe if one put the piston at TDC to prevent the valves from dropping down into the cylinder, the valve springs could be safely removed and the VSS pulled off along the valve stem. I could not have a look myself because I do not have a suitable tool to compress the springs and remove the keepers and springs.
Or do the valves have to be taken out before the VSS can replaced?

Hey ganda1f I know what it is to do this job to my car. I wanted to replace the VSS myself but found it hard to find the suitable tools to compress the valve springs afterwards and when I did find one it was in 200 price range. So what I did was take out the head and sent it to a machine shop and they did all the work for me. Afterwards I put the head back in with 65 pounds of pressure I think it was on the torque screws with a torque-metro, oiled of the rods and put it all back together.

[ganda1f]

All right, thanks for the advice guys.
I wanted to avoid taking off the head since that involves unbolting the exhaust manifold. And I'd rather not risk breaking off the studs for the manifold, which are quite rusty.
As for the tool to compress the springs I was hoping to be able to rent it some place.
Oh well, guess maybe this one is a bit too much for me to handle myself.

[demonics12]

Originally Posted by speedy25

Milling to bump up the CR is useless. The only reason to do it is to have a flat surface.

-SP

if you pull enough material out, it would bump up c/r as the combustion chamber would be reduced.

[speedy25]

Sure, it will, and what will you get?

Umm lets see.... more headaches? Have to use premium fuel? More knock? and 100 horsepower gain. OOPS! Bad math! Thats really 1.00.

There are much better ways to get horsepower gain.

In your case a new converter would probably be best depending on your mileage because of CA emissions testing.

-SP