Rebuilt my 66 Starfire 425 over the winter. Basically a stock rebuild with stock parts other than 20 over bore and aluminum pistons. All parts supplied by machine shop and name brands. All clearances and gaps checked, etc. Have about 800 miles on it. Oil pressure is 35 at idle, 50 at 2000 rpm. 18" of vacuum and steady. Leak down test is 90PSI in, holds in mid 80's on all cylinders. Here's the problem: smokes badly while idling, uses over 1/2 quart of every 100 miles. My diagnostics so far: Scoped cylinders, have oil puddled in #8, 7 and 6 cylinders. Scoped head drains (as good as you can) and blew air through them, all clear. Since there is oil on top of the pistons I believe the top end is flooding and oil is being pulled and seeping through the valve guides. Since it was a stock rebuild I didn't do anything with oil returns as they have worked since 1966. Any insight, help, solutions would be appreciated.

 

Were the heads gone thru by a reliable shop?

 

Can you scope the intake valve stems through the carb secondaries? If they are loaded with oil it could be stem seals or an intake sealing problem. Were the heads resurfaced? Stock intake?

 

Had the heads done by what I believe to be a reputable shop 6K miles ago. Had new exhaust seats and valves installed for unleaded fuel and new valve springs. This time, had them hot tanked, magnafluxed, and new seals. Intake valves were a crusty mess of oil when I pulled the heads. When I first started working on current problem I pulled the intake, intake valves are oily but found no evidence of intake leak. It holds steady 18" of vacuum so it seems intake is sealed. Stock heads, stock intake, no machine work. I have not checked valve stem height but am learning its important on non adjustable rockers?

 

Are you sure the rings are seated?

 

I'm wondering about the oil. Try some dino SAE 30 or 20w-50 for a while

 

At this point I'm not sure of anything. Used standard cast rings which typically seat by 800 miles and leak down test was good. Also not seeing ANY improvement in smoking and oil use. It runs fine, just smoking and using oil. Intake valves oily and oil on top of pistons make me think its a top end issue but I've been wrong before.

 

Is PCV hooked into into baffled valve covers?

 

It is. That was one of my first thoughts that It was sucking oil through the pcv valve but valve, hose, intake don't show any sign of it.

 

If it were mine I run it hard enough to be sure the rings have seated. A hard uphill run in second gear, and hard back downhill in second pulling a heavy vacuum with the carb butterflies closed, then repeat at least once. (keeping the oil topped-off)

 

What kind of valve stem seals did the machine shop use. Had a friend who had an oiling issue and found that they used rubber chevy style seals instead of the plastic umbrella style olds use stock. It drank some oil and smoked alot.

 

Who assembled it? If the second ring is in upside down it’ll blow more oil but still have decent leak down. Just an fyi.

 

Modern rings should pretty much be seated as soon as you start the engine. Is there any chance you put the second ring on the piston upside down ? That will cause massive oil consumption like you are getting. Unless something is clogged up in the heads I doubt that the oil is coming down the valve stems.

The only other possibility is the intake gasket leaking along its bottom edge. Disconnect the pcv valve if you have one and see if there is some blowby at the oil fill tube. There should be a little bit. If there is a vacuum there the intake could be leaking. Spray about a 3 second shot of carb cleaner into the oil fill tube with the pcv disconnected. If the idle picks up after a few seconds there is a real good chance it is the intake gasket.

 

Darn, you typed faster than me

 

Lol!

 

Ok, I'll try to answer your replies in order. I live in flatland lol, but I'll try to find a hill and follow the steps suggested. They are umbrella seals. Installed myself and positioned according to service manual. I assembled the engine, installed rings per instructions, I believe they said dot up. I just tried restricted puhrods to cut some flow to top end, initial results appear to be the same. Thanks everyone for your input, eventually we'll get to the answer.

 

Forgot one answer, yes I've pulled the cap with the pcv out. You can see a little smoke swirling around. I'll try the carb cleaner and see what happens.

 

+1 for intake gasket along bottom of intake/head. Stick the borescope down the intake and if some of the runners in the heads have a bunch of oil but the intake is generally clean then that's fairly solid. The guides would need to be in pretty bad shape to move that much oil, but the intake seal can be devilishly hard to get good, especially if the block or heads have been machined.

 

Yes it is! I removed the carb and tried to scope the heads. Could only get to a couple but yes, that's what I saw. pulled intake and reset it carefully, let the sealant cure 20 hrs. No improvement.

 

Could pull the R valve cover to look for differences with the 6 and 8 seals vs. 2 and 4.

Had another brand GM V8 gulp oil severely after an overhaul and it was the valve seals
Don't see how that much got past the guides but it did.

 

What part number rings did you use ? Most rings will have a dot on the second ring. That dot has to face up on the piston. The top rings may or may not have a dot depending on the brand.

I built a Small Block Chevy probably 25 years ago and got just one second ring on upside down. It smoked like crazy and fouled that one plug very quickly. I cant imagine how bad it would be with all of them on wrong.

 

Tried the carb cleaner into the oil fill tube. Idle stayed the same. All the valve stem seals are correct. I'm not beyond making a mistake but firmly believe the rings were installed correctly. My theory is It's flooding the top end with oil up and over the valve guides and the vacuum is pulling oil through the guides and into the cylinders. The back cylinders are the worst as the engine tilts that way. Installed a standard volume pump but is it possible its moving too much oil?

 

I dont buy it. I know others will argue but I have been doing this long enough to feel pretty good about saying that. That is if it is indeed using as much oil as you said in your initial post. If it was coming down the valve stems you would see it in the exhaust port too.

The oil pump can only move as much oil as the passages it is going through allows. I dont think that is your problem either. If the engine was running ok and not using a ton of oil before the work was done, then something that was done is causing the problem. The valve seals were the same type. The parts that bring oil up to the top of the engine are the same so unless you have 200 psi of oil pressure, the oil isnt getting up there from that.

You have to remember that a lot of engines have pretty much no valve stem seals at all and dont really use any oil. Big and Small block Chevys from that period just had a simple o-ring to sling most of the oil off the valve stem. They really did not use much oil I did a 425 a couple of years ago and used pretty much the same parts that you did, except for Moly faced rings, and as far as I know it has not used a drop of oil.

Since you have a bore gauge, take the spark plugs out and disable the ignition. Turn the engine over for 15 seconds or so and see if the second ring is wiping the oil down off the cylinder walls.

What part number rings were they ??

 

The ring part # on my parts list is P2187020. I don't disagree with anything you said other than the exhaust valves. The intake stroke is when the cylinders create vacuum and could pull flooded oil through the guide. I know it sounds far fetched but I'm going bats**t crazy trying to figure this out. The last time I had the intake off after the rebuild (last week) the intake ports were oily and the intake valve stems had crusty oil on them. I'm not stuck on my theory just throwing it out there to keep getting feedback like yours. Theres a whole lot of collective knowledge out there from people smarter than me. I'll try scoping the cylinders and see what I see. Thats how I found the oil puddled in the cylinders. Again, THANKS everyone, please don't loose patience with me or my problem.

 

Ok, here's what I know: oil pressure is normal, vacuum holds steady at about 18", sprayed carb cleaner down oil fill tube with no change in idle, installed restrictors in push rods to cut oil flow to top end, oil drains from heads to valley are clear, tried uphill downhill to seat the rings. Still smokes badly. Only thing left is rings so the engine is coming out. Thank you all for your input and advice. It helped me logically think it through.

 

Please take us along in your discovery, most often we never learn of the culprit, or the cure!

 

Will do

 

One of the things I do: Use a spark plug hole air hose adapter from your compression or leak down gauge set and apply abt 100psi to each cylinder with that and each cylinder at TDC firing (not overlap) with the engine warm or hot after some operation. Observe crankcase breather for large amounts of smoke concurrent with the air pressure to each cylinder. If it is all cylinders then I also would look for a rings issue. If its really loud on one or more cylinders then immediately time for a teardown. This check is irrespective of your leak down test.

This experience comes mostly from the late seventies-early eighties small block chevy engines which would begin at some higher mileage interval to INHALE oil through a factory machining mismatch of intake port and intake manifold runner out of the lifter valley, with cyls 6-7-8. Would oil foul plugs quickly even after high speed WOT blasts. I don't at this point suggest the same cause with your 425 but rule out what you can with tests before starting to throw work and parts at the job. Good luck ~

 

As mentioned, flooding the top end is actually pretty hard. The Olds head layout is a bit crazy which does lead to the oil having to crawl uphill a bit in order to drain, so there's always some oil along the head/valve cover gap. But enough to actually overtop the valve stems? No, that would be a massive problem.

The problem with intake/head gaps is not an installation problem. Doing it again won't fix that. If the head and intake don't line up *just* right then it takes quite a bit of work to get a good seal.
If you're using separate composite gaskets then you can pull them after removing the intake and see if there's signs of good compression on top and bottom. Sometimes you can even see signs of oil being pulled through the gap - the head will be smeared with oil right under the ports. It's harder to tell what's going on with the metal gaskets.
I always drop the intake onto the long block without a gasket and very carefully check all along the top with a 2 thou feeler gauge. You can't check the bottom, but you can check the corners at the front and back. If everything is flat with a good flat edge then any increased gap at the bottom of the front/back corners will lead to a leak. I usually have to machine an offset into the intake to match the block. The last build even drove me nuts enough to get the BHJ valley checking block and - surprise! - the heads were tilted over a few degrees past 45.

You can do that check without removing the engine - you've already done an intake R&R once.
If it really is the valve stems, then you'd need to pull the heads, remove the springs, and check for excess play in the valves. The stems provide the real seal - not the umbrellas. It shouldn't pull a noticeable amount of oil though the stem even with no seal. You can machine the heads to accept a positive seal, but that requires stripping the heads down anyway.

Or, if it's the rings, that means pulling the engine to check.

 

Pulled the intake again. Got it off with the valley pan left behind and still stuck to the heads. Found oil puddled on top of 4 closed intake valves. the ports also have an oil film on them. I don't know how to post pictures but it is a lot of oil on the valves. Carefully pried the valley pan loose from the top down, did not seem to be "stuck" to the bottom of the intake ports. I would guess this has to be where the oil is coming from. I can drop the manifold on naked and check it as Oddball suggested. If it all checks good is there a better gasket set up than the stock valley pan?

 

There's no way you would get that much oil through a valve stem unless it was *completely* wasted. If so then your builder should be ashamed.

Right, place the intake with no gaskets. I bet it'll be tight all along the top and you'll have 5thou+ at the bottom corners.

As with anything on the internet, this is controversial. There are plenty of threads on here talking about intake gaskets.
The main thing I've found is that if the block or heads are decked - at all - at least the same amount if not a bit more also needs to be cut off of the intake to head surface.
There's a wide assortment of 2-peice gaskets available. Search for "455" intake gaskets to see all the options - the 425 uses the "big port" as compared to the 330/350/403 heads, and the pattern is the same other than the height of the ports for all 65+ v8's.
The 2 piece gaskets crush differently. In the past I've used spray copper on the intake ports and silicone on the water ports, this last build I tried gasgacinch on the intake ports and silicone on the water ports.
I had a lot of trouble with this last build, mainly because I started with a 350 D block that spent time at the bottom of a lake and had a lot of work done to it by, well, decent but certainly not exceptional machinists. I experimented with literally every available aftermarket gasket except the Cometic - they didn't get delivered in time. They all showed similar crush, so as of this moment (subject to change without notice) I'm recommending the SCE Pro (has the silicone rings) with gasgacinch. Every gasket crushed less than 4 thou or so, which surprised me. I thought they had a lot more compliance than that.

Is your exhaust crossover still open in the heads? My very first 350 was built that way and when I pulled the intake after a year there were two handfulls of burn oil sitting in the valley. It's easy for oil to splash up to the intake, hit the bottom of the intake where the hot crossover is the lowest part of the intake, and burn. I went through several years of pain trying to address that. There are various splash shields (note they are for flat tappet lifters only!). Turns out those are only worried about the *oil* heating the *intake* and don't do protect the intake sufficiently to stop burning on the bottom. I tried using different shim stock to block the ports but they would always burn through - I was probably running pretty lean back then too which doesn't help, and I still had manifolds. The only thing that worked for me was to take a stock intake gasket and cut out all the ports just barely below the bottom of the heads and keeping all 4 locator tabs. Install the new "valley pan" then the intake gaskets. The locator tabs keep it in place and don't seem to affect the intake gasket, but you can trim away the intake gasket where the tabs sit.
If the crossovers are sealed in the head then you don't need anything.


The *other* option is the very old school shadetree fix - stock metal intake gasket and use a whole lot of gorilla snot (aka weatherstrip cement) around all the intake ports, both sides.

YMMV.

 

I've found that many people do not know how to properly install the stock metal gasket. First, it is not reusable, so are you using a new one every time? Second, there are four formed bosses in the corners of the gasket that have to fit into holes in the heads. Dry fit this first. FelPro had a batch a while back with these improperly located. Once it fits correctly, use a sealer like Permatex Ultra Black. I ASSUME the mating surfaces are flat, correct?

 

Cleaned everything up and checked the heads and intake. Heads are flat but intake has a noticeable "bow" particularly on the right side. Dry fit the intake and saw the same thing. Pulled intake from my spare 425 and checked it, both sides are flat. I have used a new valley pan every time and always dry fit. When i pulled the intake this last time the pan stayed behind. I carefully pried it loose from the top down and it didn't seem to be stuck at the bottom of the intake ports. To me these all point to it leaking. Strange how it held 18" of steady vacuum. Do you use the ultra black around all ports or the GM sealer around the intakes?

 

I use a very thin bead of Ultra Black around all the ports, not just the water ports. This is where I like the "squeeze cheeze" tube with the spout that can be cut to a small opening. That's been working fine for me. Obviously take care not to use too much around the intake ports to avoid RTV oozing into the ports.

 

Thanks Joe. I'm getting ready to start putting it back together. Will post how it turns out. Have a lot more confidence with this intake manifold and the information gathered from everyone that responded.

 

nope, the factory metal valley gasket can be used multiple times. I’ve got Stocker engines that have been through multiple tear downs reusing the same metal valley gaskets and head gaskets.

if you’re a clutz and destroy it, then ya, it’s not reusable. I’ve got factory steel shim head gaskets that have been reused many many times over decades.