Intake Valve Carbon.. - Chevelle Tech
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post #1 of 32 (permalink) Old Apr 18th, 17, 2:17 AM Thread Starter
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Intake Valve Carbon..

I know carbon build up here is very typical, but is the carbon crud on the rear of intake valves from fuel or from oil?
If fuel, then there's not much I can do about it aside from maybe adding a bottle of fuel system cleaner which I'm skeptical about it's effectiveness anyway..

The engine consumes about a quart of oil (5W30 syn) every 500 miles (BBC always revving with 4.56s and 5K converter), but it's a little more than I expect to be normal, albeit a slight leak from a valve cover that I am about to fix. A quart every 1000 miles I'd think would be more on the money..

I know it's easy to simply replace the intake valve stem seals and I have a set handy to go right now, but it's only been ~3000-4000 miles since I last replaced them, and when I do, I use a sheath that protects them from the stem's keeper grooves, so I know their lips are not damaged during installation.
They are Viton seals and the ones I have are Comp. I expect to get plenty of miles out of a set, especially on new heads with good guides, which these are.
They've always come out dry previously, but there is oil on the plug threads too.


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post #2 of 32 (permalink) Old Apr 18th, 17, 7:45 AM
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jeff
 
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Re: Intake Valve Carbon..

It is the oil causing that. The fuel will actually clean it off to some degree.

I have ran combustion chamber cleaner through some newer cars and removed carbon on piston tops and chambers.. not so much cleaning on the back side of the valves.

I have noticed some oils have a low vapor point and this shows up as what you describe an engine that uses oil.

My son's Mazda miata MX5 never used any oil in the 3000 mile change intervals.
He got a coupon from the Mazda dealer for an oil change.. about 10 bucks cheaper than he could change the oil.

After 1000 miles he calls me and asked what will make an engine all of the sudden start using oil.
I said is it leaking? NO
Is there a vacuum hose off ? NO
Did you change brands of oil?......Yes.

He told me about the coupon.
I said top it off and see if it continues. 1 quart for 1000 miles was used.

It continued and he drained it all and stuck his brand oil back in and never used a drop.

I had the same thing happen when I went with conventional Rotella in my 302.
It sucked that stuff up.. I switched back to T6 Rotella and eliminated the oil usage.

Maybe try a different oil.

I will assume the PCV valve is well baffled and not over a spraying rocker arm.
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post #3 of 32 (permalink) Old Apr 18th, 17, 12:29 PM
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Geoff Swanson
 
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Re: Intake Valve Carbon..

Quote:
Originally Posted by BlackoutSteve View Post
I know carbon build up here is very typical, but is the carbon crud on the rear of intake valves from fuel or from oil?
If fuel, then there's not much I can do about it aside from maybe adding a bottle of fuel system cleaner which I'm skeptical about it's effectiveness anyway..

The engine consumes about a quart of oil (5W30 syn) every 500 miles (BBC always revving with 4.56s and 5K converter), but it's a little more than I expect to be normal, albeit a slight leak from a valve cover that I am about to fix. A quart every 1000 miles I'd think would be more on the money..

I know it's easy to simply replace the intake valve stem seals and I have a set handy to go right now, but it's only been ~3000-4000 miles since I last replaced them, and when I do, I use a sheath that protects them from the stem's keeper grooves, so I know their lips are not damaged during installation.
They are Viton seals and the ones I have are Comp. I expect to get plenty of miles out of a set, especially on new heads with good guides, which these are.
They've always come out dry previously, but there is oil on the plug threads too.

I would put my money on an intake leak pulling oil from the lifter valley. It is very easy to verify as there will be oil between the gasket and head area leading to the port and maybe on the manifold, but in my case it was on the head. I had the EXACT same issues as you and it turns out it was a used manifold I purchased that had been re-cut. the manifold can be re-cut to the correct angle to match the head, but you need to determine the amount if this is indeed the issue as I would bet highly on it.
There is a test you can do with lead shot to determine if the surfaces are parallel to each other or how far off they are. If the gap is larger at the top of the manifold flange it is good as long as it is .007 or less. If it is at the bottom, It will leak and siphon oil. I had a lifter valley baffle so theoretically there should have been no oil on the bottom of the manifold and I still lost about a 1/2 quart per 1000 miles. If you think the valve is bad, your piston and chamber are just as bad.

Last edited by tucson67ss; Apr 18th, 17 at 4:57 PM.
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post #4 of 32 (permalink) Old Apr 18th, 17, 10:27 PM Thread Starter
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Re: Intake Valve Carbon..

A close inspection of the gaskets showed no signs of oil getting passed into the intake ports.

The oil I use (Mobil1 5W30) is the same oil I have used for a while now and the consumption has increased lately. If I had changed brands, grades or type, that would certainly be a clue and have me considering the oil as perhaps being the culprit.

I have the "Crane's Corvettes" OE style valve covers and the stock box-style baffles inside are very basic, so I am using Edelbrock's A&B epoxy putty to close up all the gaps with exception of a gap furthest and lowest from the PCV grommet for the PCV to inhale from.
When the epoxy has set, I will fill it with a course non-disintegrating steel wool in hope to baffle it further and offer plenty of surface area over the longest distance within the baffle that hopefully catches the oil mist particles.
At the lowest points when installed, I have also a couple of 1/8" holes for oil drain back off the steel wool.

If that fails, then perhaps I will consider an in-line oil separator along the PCV hose and see what is being caught. Some info on a Google search shows some new cars catching plenty of oil from the PCV hose, that would otherwise be ingested into the engine. Maybe that is what is happening here.

FWIW, I am going to swap the valve stem seals on just the intakes and along with my new valve cover gaskets, see how oil consumption goes from here.

Thanks for your responses and ideas guys.

Something like this stuff..

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post #5 of 32 (permalink) Old Apr 18th, 17, 10:31 PM
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Re: Intake Valve Carbon..

What sealant did you use on the rocker studs that protrude into the intake port? That's if they protrude into the port.

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post #6 of 32 (permalink) Old Apr 18th, 17, 10:32 PM
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Re: Intake Valve Carbon..

Quote:
Originally Posted by BlackoutSteve View Post
A close inspection of the gaskets showed no signs of oil getting passed into the intake ports.

The oil I use (Mobil1 5W30) is the same oil I have used for a while now and the consumption has increased lately. If I had changed brands, grades or type, that would certainly be a clue and have me considering the oil as perhaps being the culprit.

I have the "Crane's Corvettes" OE style valve covers and the stock box-style baffles inside are very basic, so I am using Edelbrock's A&B epoxy putty to close up all the gaps with exception of a gap furthest and lowest from the PCV grommet.
When the epoxy has set, I will fill it with a course non-disintegrating steel wool in hope to baffle it further and offer plenty of surface area within that hopefully catches the oil mist particles.
At the lowest points when installed, I have also a couple of 1/8" holes for oil drain back off the steel wool.

If that fails, then perhaps I will consider an in-line oil separator along the PCV hose and see what is being caught. Some info on a Google search shows some new cars catching plenty of oil from the PCV hose, that would otherwise be ingested into the engine. Maybe that is what is happening here.

FWIW, I am going to swap the valve stem seals on just the intakes and along with my new valve cover gaskets, see how oil consumption goes from here.

Thanks for your responses and ideas guys.

So you pulled the intake off ? I have never heard of that much oil going out the PCV. I would be looking for a blow by issue if that was the case.
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post #7 of 32 (permalink) Old Apr 18th, 17, 10:43 PM Thread Starter
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Re: Intake Valve Carbon..

Quote:
Originally Posted by 496blaze View Post
What sealant did you use on the rocker studs that protrude into the intake port? That's if they protrude into the port.
Yes they do. A lick of GM sealer.


Quote:
Originally Posted by tucson67ss View Post
So you pulled the intake off ? I have never heard of that much oil going out the PCV. I would be looking for a blow by issue if that was the case.
I haven't seen proof of it on my engine, but looking on Google for ideas has showed examples of this.

Admittedly the Google images here of PCV catch cans are out of context. I have no idea what engines, what engine condition, what oil and over what mileage.
They simply suggest to me the possibility of oil being ingested via the PCV and something to be curious about given my oil consumption.



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post #8 of 32 (permalink) Old Apr 18th, 17, 10:45 PM
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Re: Intake Valve Carbon..

Did you re valve job the heads when they were new?

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post #9 of 32 (permalink) Old Apr 18th, 17, 10:49 PM Thread Starter
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Re: Intake Valve Carbon..

Hey Mark.
You may remember a valve seat moved on these new AFR 300s after the first dyno run.
They went to the machine shop and all the seats were whacked to ensure they were "home" and valves reseated.
As far as the guides go, no. No work was done to them and they are as supplied from AFR.

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post #10 of 32 (permalink) Old Apr 18th, 17, 10:49 PM
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Re: Intake Valve Carbon..

Since you are in there, pull a intake rocker stud and look for signs of oil wicking its way down the threads. I have been using red loctite since thread sealer did not work well in my opinion.

1970 Chevelle SS 396 (491 now) 4spd
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post #11 of 32 (permalink) Old Apr 18th, 17, 10:52 PM Thread Starter
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Re: Intake Valve Carbon..

T&D shaft rockers.. Yeah, I'll pull a bolt and double check. Cheers.

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post #12 of 32 (permalink) Old Apr 18th, 17, 10:55 PM
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Re: Intake Valve Carbon..

Quote:
Originally Posted by BlackoutSteve View Post
Hey Mark.
You may remember a valve seat moved on these new AFR 300s after the first dyno run.
They went to the machine shop and all the seats were whacked to ensure they were "home" and valves reseated.
As far as the guides go, no. No work was done to them and they are as supplied from AFR.
What did the machine shop say about the runout?

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post #13 of 32 (permalink) Old Apr 18th, 17, 11:01 PM Thread Starter
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Re: Intake Valve Carbon..

Quote:
Originally Posted by 496blaze View Post
Since you are in there, pull a intake rocker stud and look for signs of oil wicking its way down the threads. I have been using red loctite since thread sealer did not work well in my opinion.
Todd, you are a champ.
I just stuck my finger in all 8 of the ports and 3 of the bolts were wet with a drop of oil.
Pretty sure I GM sealed them. Maybe I didn't...
Certainly an issue, but still not out of the woods. All valves have the carbon. Not just those 3.

Quote:
Originally Posted by VORTECPRO View Post
What did the machine shop say about the runout?
Gee, now you're asking.. I can't remember the details, but whatever it was, they said they had rectified any issues when reseating.

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post #14 of 32 (permalink) Old Apr 18th, 17, 11:18 PM
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Re: Intake Valve Carbon..

Quote:
Originally Posted by BlackoutSteve View Post
Todd, you are a champ.
I just stuck my finger in all 8 of the ports and 3 of the bolts were wet with a drop of oil.
Pretty sure I GM sealed them. Maybe I didn't...
Certainly an issue, but still not out of the woods. All valves have the carbon. Not just those 3.


Gee, now you're asking.. I can't remember the details, but whatever it was, they said they had rectified any issues when reseating.

Did you pull the intake ?
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post #15 of 32 (permalink) Old Apr 18th, 17, 11:42 PM Thread Starter
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Re: Intake Valve Carbon..

Quote:
Originally Posted by BlackoutSteve View Post
Todd, you are a champ.
I just stuck my finger in all 8 of the ports..
Quote:
Originally Posted by tucson67ss View Post
Did you pull the intake ?
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