Mitigating valve guide oil leakage
 

I rebuilt the bottom end of my 78 400 during the summer of 2023, new rings and bearings, honed cylinders, cleaned the valves, and replaced the valve stem o-rings plus a few other odds and ends. At the time I noticed what I believe to be excessive clearance between the valves and valve guides, I was able to slightly rock the valves side to side in the guides while they were off the seat. I wanted to install new guides and have the heads milled for wiper seals, but time and money didn't allow it. After the rebuild, it burns some oil but only smokes briefly after startup when it is warm, maybe for a second. I suspect it is due to oil leaking down the valve guides past the o-rings, before the rebuild I figured the mountains of carbon I removed from the back side of the valves kept oil from getting into the cylinders.

Does this sound like what can be causing the brief smoking on warm startup? Also, is there anything I can do to help mitigate the oil in the cylinders for the time being like a different plug heat range or changing the carb mixture? The head work is on my list, but I am in college so I will have to deal with it for now.

Once a valve and or guide wares more then .001" then due to the fact that the valve stem is round and the guide is round you will see .003" of excess clearance and that shows up as the valve rocking.

First off I am assuming that when you assembled the heads you did so the right way .
1) after the spring goes the oil splash shield goes on.

2) then the retainer goes on.

3) then the O ring goes on.

As long as this oil usage issue is not to the point of fouling out your plugs and creating a miss your ok.

That being said oil getting into a chamber and the carbon built up from it can make for hot spots at high throttle openings which will cause the motor to ping and worse yet knock.

As a precaution for now until you get the heads rebuilt I would run a higher octane fuel if you can.

In terms of reducing the oil and smoke issue now the only thing you can do is run a thicker oil and you might investigate if you can get the motor to run cooler.

Adding a Qt of Lucas brand engine oil supliment is what I would try out first though and see if that helps with the hot restart smoke you see.

Adding umbrella seals in addition to the o-rings offer a band aide solution.

What’s the supplier and part number for these umbrella seals?

How much do they reduce the retainer to guide clearance?

Unfortunately to cure the issue you'll have to do new guides, and in a lot of cases the valve stems are worn too and new valves will be needed.

You can try a conglomeration of different seals but in my experience it doesn't cure it. The vacuum created sucks the oil in through the guides anyway while the engine is running. Even positive seals won't stop it if the guides are worn.

Hopefully you can slow it down with tricks mentioned above but it's still an engine you'll have to keep an eye on the oil level on a regular basis. Even if you don't see it while driving there is still oil sneaking past the guides.

I appreciate mentioning the OE valve assembly, I just sat here for 20 minutes trying to remember how I put the heads back together. I don't think I installed the o ring from the top after the splash shield. I think I installed It first, and it just got pushed out of the groove down the stem by everything else. At least we know what the problem is though. :cry:

On the bright side, I work at a shop part-time so I should be able to fix that over a few weekends, hopefully, I can rig something up to do it without removing the heads.

Yes the O ring goes on just before you stuff the keepers on.

Now you will likely need new O rings so have them on hand.
With stock valve springs you can bring the piston up to TDC and stuff nylon rope into the chamber to hold the valves up enough to to the job, or you can fill the cylinder up with compression air.

Im definitely going to do my research on that, I really don't want to drop a valve.

I don't recall ever hearing a miss or anything weird, but at the end of an 1100 mile trip, the plugs were so fouled the engine died as soon as I pulled off of the interstate and pushed in the clutch. It was so bad the engine wouldn't fire at all until I cleaned them, I did find that a little odd because it ran great at all speeds that day with no power loss or miss that I could tell.

Just so I can look out for it in the future, Is it relatively easy to hear a ping, miss or knock, especially at wot? I have heard it is. But with my current understanding of what it is like, I don't think I have heard it in person before, otherwise, I wouldn't be taking the car on long trips. I can pick up on most odd noises, I just want to make sure I'm not missing something obvious.

....can you imagine a head design with positive seals at runner side of the valve stem, for positive lubrication?

Using a tool like the one in my link will make this repair a breeze. Just get the cylinder at TDC, put compressed air in the cylinder and away you go. Takes about an hour to do 16 of them on a typical Pontiac application. Good luck.

https://www.amazon.com/Spring-Compre.../dp/B09KKPWXMJ

Had no idea those were still made, I was just looking at the pictures in the pontiac manual thinking "where the hell am I going to get the gm tool for this"

Most parts stores rent the valve spring remover tools for free, just pay a deposit you get back when you return it, they have different styles but even the smaller screw type will work ok for stock springs. They might have the tool for screwing into the spark plug hole & connect compressed air too... if you cant find one I have one I would loan you.

An additive like lucas oil stabilizer should help with oil burning & consumption but definitely wont stop it if its due to worn valves/guides. A slightly hotter plug may also help prolong the oil fouling but again wont stop it. Use a thicker oil if you dont drive in too cold of weather, 10/40 or a 15/40 diesel oil is ok, dont use 20/50 if you use the lucas though, would be closer to 25/55!

Another budget option for the guides is to have them knurled... this isnt ideal and & wont last as long as doing it right with new guides, but you can get many years of use from a knurled guide and is much cheaper to do, but since you gotta pull the heads anyways then might as well save up to do it right.

Another thing to consider for the oil burning is the home re-ring & hone... if you didnt get the hone crosshatch right or got the rings fully seated after start up they could be part of the oil burning issue, especially if the cylinders were out of round at all. My first engine rebuild at 15 or 16 with my Dad on a SBC in a 77 formula that burned oil pretty bad, it was a garage re ring & new bearings, but had the heads rebuilt by a local shop... got it all back together & it ran great but still burned some oil just nowhere near as bad, likely from the amateur hone & re ring job.

I have one of those and it works great for on motor changes.

I am definitely going to pick up some stabilizer and look at getting the tools, hopefully, I can get this knocked out within a few weeks. You will know how it goes based on whether or not you see a "help I dropped a valve" thread :D

it is definitely possible that the rings are an issue, it was the first time I did a rebuild. Everything looked good when I tore it down and reassembled it, though I do remember the bore was just shy of too large for just a hone and new rings, but the machine shop wasn't an option. Right now all the car has to do is run well until I'm out of school and can do a proper build. I don't race it at all or hoon it around much, so I'm not super concerned about the engine going as long as it doesn't get worse.

When the O rings go bad or are installed wrong as in your case the retainer then acts like both a collector and a funnel to send oil right down the valve stem.

Please don’t go with knurling the guides in lue of just replacing them as that still only gets you 70% of the way to having the oil control needed .

I'm not planning on it, like 78w72 said, it'd be better to wait and save up to do it properly

Enginetech S2882. They won’t help wear but will stop some oil from entering the guide.

Do the heads have to be milled for those seals?