Smokehouse69

Here are a couple of pictures I took a couple of weeks ago while I was pulling intake and heads. As I lifted off the manifold I noticed a couple "chunks" of crud laying in the lifter valley. As I flipped the manifold over I saw the source of the crud, the bottom of the intake was covered with about a quarter inch of carbon.
The second picture is what I found while looking at the manifold. I found that one of the front water passages in the manifold and the corresponding port on the head was plugged solid with mud.
I am really surprised that the car was running as good as it was. I was running a little rough, but I new that was caused by a seriously burned valve. All the carbon and the plugged water port were a real surprise to me.
When I got the car it ran horribly, it was so overjetted that the exhaust fumes would gag you. I pulled off the horrible parts store Q-jet and put a Holley on it. That cured my overly rich condition. The car doesn't burn any oil and only smokes for a few seconds on a cold startup.
Anyone have any ideas where all the carbon could have come from? This is a 69 350-300 without and EGR, so I can't blame that for the Carbon.





[Modified by Smokehouse69, 8:32 PM 12/28/2001]

Rocket Ron

carbon under the intake is normal.A good quality oil and frequent oil cahnges will less the buildup. The newer cylinder heads have the rear water passages blocked off. Is that the passage you are talking about?

BLT-71

Looks like a Quaker State job. That stuff gums up bad.

Techno

The carbon is there from two related causes. The exhaust pipe has a valve in it that closes off the exhaust on one side of the engine and forces it through the intake casting for improved cold running. So your intake has hot exhaust gases running through it.
No heat shield under the intake. I don't think chevys use them. Although I've seen it on this shield too.

These two items allow oil to splash directly onto the hot intake casting.
A few extended oil changes and you have fungus.

LT1driver

Infrequent oil changes and possibly short drives with no warm up of engine. Hey I don't agree with the Quaker State statement. Been using it since 66 and never had a problem. Use it and change oil every 3-5000 miles on my driver (83 Supra) and it has 292,000 and no problems, no sludge etc. :D :D

Chris@VetteFinders

Check this out. The carbon was so thick in mine, near the center valves in the block, that the pushrods were actually touching the carp. Mine definately had bad valve seals and cracked heads. Not sure if that was THE cause though.

Tom454

Chevy uses the heat shields- even the BB TriPower has them. The 5.0 EFI roller Ford has two of them. My original cast iron square port intake from my 66 327 has a heat shield on it. These shields keep the oil from hitting the hot passage where the exhaust passes over (crossover passage) to heat up the carb when cold. Although the EGR uses the same passage, it pre-dates EGR systems and its primary purpose is to heat up the carb quickly when cold. Since I sandblast intakes, I always have to remove the pins and tap the holes for screws to re-install the shield(s). Otherwise, enormous amounts of sand gets trapped under the shield. It is possible for a manifold not to have the shield, but they are "normal". If yours does not have the shield, look for 4 small holes (about 1/8") where there may have been pins for a shield. If the holes are there, and the shield is missing, bubba has been there.

Over time, even with the shield, carbon (burnt oil) still builds up under the shield. This is normal, but the carbon should be removed because as it gets extremely thick, chunks fall off and drop into the oil pan where they plug up the oil pump intake screen.

john's '81 mouse

What you found is not surprising to me. I found the same thing on my 97,000 mile 350, when I did my re-build a year ago, and I had the factory aluminum intake with the heat shield installed. Clean up took a lot of time, chipping away crud, and using vacuum cleaner to suke all the chunks out of the lifter valley. I plugged the oil return holes, and left the old lifters in the bores, during the clean up to minimize the chance of the chunks falling to the bottom of the engine, but ended up pulling the pan anyway, so no big deal.

The carbon build up was so bad, that the center pushrod holes in the head were completely plugged except for the hole in the space occupied by the pushrod.

Lt1er

Years ago I would just cut out the exhaust heat riser and put block off intake gaskets. Now I install manifolds without the cross over. Or better yet you buy heads without it even being there.

Rockn-Roll

Carbon deposits will come from only one place...the combustion chamber. There will also be some blow-by and your oil will get dark in color because it's collecting it as it should to keep your engine clean. If you let your oil get too dirty then it won't absorb the blow-by so it begins to collect elsewhere like under the intake manifold...probably cause it's the coolest place in the motor so it condenses there.

It is possible to have too much blow-by like with cracked or missing piston rings and still get deposits even though you change the oil regularly.

With an engine that bad I suggest pulling the bottom end apart and checking the cylinder walls for gouging and out-of-round, and check the rings. I think you will also find that the main and rod bearings are badly worn and rod journals are beyond tolerance. It's always a good idea to spend the $500 to rebuild the bottom end when you find a lot of carbon deposits instead of waiting until something breaks and raises the price to $1500 for a new block and stuff.

Tom454

Playing the devils advocate....


How does the carbon build up on the back of the intake valve? Blow-by doesn't go "out" an "in"take valve....

It comes from oil that seeps past the valve stem seals.

Eh?

Smokehouse69

I have to agree with you Tom, the stem seals on the valves were crumbled and cracked and I had no blowby with the engine. The cylinders were in great shape, crosshatching from honing is still visible in the the bores.

Tom454

Yeh... I was just havin' some fun.

I have been building engines long enough to know where the crud comes from.
The exhaust crossover passage is one of the hottest places on the engine when the heat riser valve is closed. That is exactly why there is a heat shield on it. I just finished a 305 +.030 for my own truck and here is what I did:

Degreased the intake, removed the heat shield, sandblasted the intake, tapped the four shield retaining pin holes, re-installed the heat shield with machine screws, painted the exterior of the manifold with 500 deg. primer, painted it with 500 deg Chevy Orange, installed the engine in my truck. Within a few days, all of the 500 degree paint had already been burnt off the top of the manifold ONLY where the crossover passage is. The rest of the manifold retained its paint. In fact, this is a good test to see if your crossover/heat-riser system is working (not plugged). And... if it is plugged, it can cause your car to fail emissions testing.

Blow-by may be a source of carbon deposits, but it is certainly not the only source.

A friend of mine just built a 350 for his 72 and had several problems sealing the intake ports to the cylinder heads. When I went over to assess the situation, there was already substantial deposits on the back side of the intake valves. The engine was bored, new pistons, new heads, new valves, perfect circle type valve seals (Edelbrock heads) new pistons, total seal (gapless) rings... and no blowby. The carbon buildup on the back of the valves was from the intake gaskets not sealing... oil getting sucked from the pushrod valley into the combustion chamber.

The carbon buildup under the heat shield is from oil and oil vapors burning on the extremely hot surface of the exhaust crossover passage. It's as simple as that. The rest of the "gooey" buildup in the pushrod valley and on the bottom of the intake is from a combination of blow-by, oil, and oil vapors. The lifters and pushrods generate a lot of the mist all by themselves.

I hate to sound like a "broken record", but I have been in the engine building business for over 30 years... so I'm not just guessing at all this stuff. No flames intended.

Vetterodder

I've seen many cases where otherwise perfect engines have had substantial carbon buildup on the backs of their intake valves. The source of the carbon was gasoline that hadn't been atomized and, as a result, wets the back of the valve and gets cooked (rather than being burned inside the combustion chamber as intended). Though the intake valve doesn't get as hot as the exhaust valve, it gets hot enough to "bake on" deposits. Once a layer of carbon is established, due to it's porosity, it will soak up more fuel and accelerate the buildup. In some cases the problem was caused by over rich idle mixtures and in many others it was the result of the owner over pumping the carb at startup. This can happen despite the detergents that are used in the best gasolines.

ED DINAPOLI

What Additive will clean the carbon on the back of the valves ? Is there anything you can add to your fuel to break this stuff up?
Ed

Tom454

I am not aware of any additive that can break up the stuff. If it is very thick, you don't want it to break up anyways because it gets caught between the face of the exhaust valve and its seat on the way out and this can cause a burnt/pitted exhaust vlave. Manual cleaning is the only sure cure. Additives that claim to clean valves are most likely referring to the combustion side, not the underside of the head. When I clean valves for re-use, I tape off the stem and sandblast the crud off. Sometimes it is so thick & gooey that I have to pre-clean them by chipping off the big chunks with a 1/4" chisel. Chemical cleaners such as carb cleaner (in a bucket) does not touch the stuff, and a course wire wheel is marginally effective.

Budman68

Smokehouse,
You are going to be spending alot of time behind a drill with a wire brush my friend. I've seen old truck motors look that bad, but never that bad. It's amazing that crude didn't lock up a bearing.
Good luck

Smokehouse69

Budman,
The inside of the engine was amazingly clean, very little carbon on top of the pistons, no carbon buildup around the top of the cylinders. 90% of the gunk and carbon that was there wiped off with lacquer thinner and a rag. The little that was left, came off with a fiber scouring pad and solvent. The lifter valley was completely clean (with the exception of what fell from the bottom of the intake manifold when I lifted it off.) I am really pretty amazed.
The bottom end is is good shape too, I dropped the pan so I could replace the oil pump and clean and repaint the pan. While under there I pulled the main bearing caps one at a time and they were in beautiful shape, no appreciable wear at all.
The engine has about 60K miles on it since it was rebuilt back in the 80's. There is no visible sludge or varnish, the lifters were free and easily removed with my fingers.
Was resigned to a complete rebuild or a crate engine replacement, but I don't think it is necessary. The inside of the engine looks good and the since I don't plan on any heavy duty racing, I think I'll just put on the new heads, cam, lifters, oil pump, timing set and intake and call it good for another few years.
I do have a packet of receipts for every oil change since the rebuild. There are 28 different receipts, 12 of them show Pennzoil, 7 Quaker State and several unidentified types of oil, just listed as 10w-30.
I'll post some pictures as soon as I get my digital camera back, I left it at a relatives over the holidays.
I'm going back with Vortec heads, a Edelbrock Performer (Vortec.) The Vortecs don't have an exhaust crossover so I shouldn't see a carbon problem in the future.

Chris@VetteFinders

Just curious... Why would anyone risk a wire brush on a drill?? I know mine throws off a bunch of metal wires when I use it. Those in the engine would be terrible.