The Stovebolt Site Forums The Shop Area Engine Shop 283 ring seating issue

I have a 1960 283, stock, 10,000 miles since total rebuild. Smokes when starting out, and blowing oil out road draft tube. I pulled the motor, and I have only gotten the 2 worst pistons out so far(by looking at spark plugs). The top compression ring is shiny all the way around, and the full width (aprox. .100) of the ring. The bottom compression ring is shiny all the way around, but where it is split it is shiny the full thickness, but the rest of the way around, it is only shiny for about .03 up, on the side next to the oil ring. The upper 2/3 is dark brown. The dot is up on both compression rings. What would cause this type of seating? It supposedly has .0025 piston clearence, but I have not checked it yet. They are cast iron rings, and seem to be loose and free turning
Thank you for your help.

Did they check closely for the cylinders being out of round? Did you use the chrome moly rings? They can be a bear to seat sometimes.

Are you sure they are cast iron? I would check the cylinder for taper as well as out of round. Did you do a good job of honing the cylinders to break the glaze?

These engines did not have positive valve guide seals and the guide top must be machined to accept the good ones.They are a MUST for oil control on the SBC.You can almost never get over 1200 miles per quart without the seals. Blowing oil out the draft tube: does it have the oil separator installed under the manifold? Is the crankcase vented up top near like original? It is important to allow air in here instead of the draft tube. Observation: PCV really was better when done right, even though we thought differently when it first showed up (1963 in Tennessee).Look at the piston tops, if the rings are passing oil we usually see the carbon on the crown washed away around the edges.If the guides are at fault look for excessive oil in the inlet and exhaust passages or on the valve stem/head.Yes the exhaust needs the seals also, just not as bad as the inlet.

Enginenut, The engine does have the breather canister under the intake, and also has a breather on the oil fill tube. I can't remember if the pistons edges were washed, but I do remember that the chambers in the heads, on the side of the intake, all had a goldish brown clean area, while the rest of the chamber had buildup on it, not massive, but a brownish layer. It does not smoke at start up or when I'm driving, only when I start out from a stop, or after coming down a long hill on compression. I probably won't get to doing some dimensional checks until this weekend.
Thank you for your help.

Did you have the block bored and put in oversize pistons? Did you check the rings to make sure they were the correct size?

I had a similar problem
I made the mistake of installing chrome-moly rings in a 283 years ago...
They never did seat very well and always a wisp of smoke .....
Ever since I use quality cast iron rings in stock rebuilds. No problems.

Some old mechanic types used to tell me ... " put a teaspoon of Bon-Ami down
the spark plug holes & get on it hard ... that'll seat 'em right up ..."

I never had the guts to try that one!!
mike

Sd66,
The symptoms you are describing, in my opinion, exactly point to the valve guides as the smoking problems on deceleration, idling, and any other high vacuum conditions.Not only SBC but, other engines with copious oil supply overhead, will smoke and foul plugs and "use oil" from valve guide leakage even with perfect cylinder and ring conditions. But, that being said, I can't reason that as a source for excess venting from the crankcase. I have never had a problem with long break in of chrome or moly-chrome rings when the cylinder size, finish, and shape was NEAR correct--even with re-ring of cylinders that should have been resized. The OEM has used chrome or Chrome+ rings as an industry standard exclusively since the mid 50's.The ring makers/designers stated years ago cylinder wear(cast iron) is reduced at least by 75% when chrome top and oil ring is used.I will(and have) pay extra to get top quality plated or filled rings. Our choice of guide seals were the Perfect Circle VS2 for the small block but as of recent times they are hard to find here and the Fel-Pro and equivilent for modern engines made of viton are easier to find--the catch with both is that the top of the guide is not machined to fit like the factory did about after 1965 (Hell, we aint got no problem)--finally they saw the light.The machining is done with a tool in a hand held 3/8 or 1/2 drill with the valve REMOVED.Takes about 10 seconds per guide and most head shops have what it takes.If you have trouble finding the tool, contact me and I'll loan you one.

I vote for the valve seal problem too. The longer you idle at a light, the bigger the cloud when you take off, correct?

I'm with Bob and Fred, I would have blamed valve seals right off - been there

Bill

Well, here's a bit of the long story. The motor had never been apart. I took it to a shop, and they did a complete on it. I droped it in, and at 4,500 miles, I found a rocker problem. Wound up rebuilding everything again, had to grind the crank, it was a mess. The cylinders wound up getting bored out .040 over on the first job, who knows why, the bores were in good shape. When I tour it down, the cylinders were wavy vertically. about every 1/2" it was shiny from the rings riding on it, and recessed in between. I had another shop hone it out. Seemed to clean up everything, and rebuilt it with cast iron rings. I had the second shop put the bottom end together, and I finished it off. Now 10,000 miles later, I'm back again. So as far as the heads, I have had 2 different shops go thru them. I realize that does not mean they are still correct, but I have to assume something, until I check them. Thanks again.

Well, I did some checking. I have .004 - .0045 piston clearence, and .029 ring gap. The most wear in the cylinder is at the bottom where the skirt rides in and out of the bore. All of the pistons have the same poor ring seal on the lower compression ring. I would have to assume, that the pistons are rocking in the bore on the top ring, causing the bottom one to only hit around the bottom edge. As far as bad valve seals, how owuld that effect the seal on the bottom compression ring?
Thanks again for your help.

As I said, I don't think guide sealing will affect the blowby. As far as the uneven wear on the second ring, I believe that will be normal for a modern ring that has a taper face for quicker break in--in other words it is not fully worn in until the face has worn enough to be flat. Usually the top ring is ground with a barrel face which is higher in the middle.
Your ring gap is great and the piston clearance is just right to run without any danger of seizure.
You did measure the piston at the largest diameter of the skirt?
I assume they necessarily honed the slightly excessive clearance to correct the waviness you saw at the second teardown.
It sounds like the machinist would have caught this condition if he had used a positive expanding hone as a final finishing operation. The faster abrasive brush type tool will hide the irregular surface where a positive expanding hone will show it up and correct it.

Bad valve seals let oil in around the valve stem along with the fuel mixture. The oil is coming from under the valve covers which is splashed around by the rocker arms, springs, and push rods. During idle where the vacuum is highest, more oil is pulled in with the fuel which causes the smoke. When you take off from a long idle, engines really smoke heavy till the oil is burned off. You might not notice as much smoke while driving due to the vacuum variations and the amount of air going in. Also, long decelerations like down hills, or coming to a light pull high vacuums, which pulls more oil. With the carburetor throttle shut, the engine is trying to pull what ever air in it can get, this includes air inside the engine.

Its been my experience that bad rings cause more blow by then smoke. If yours is blowing oil out the valve covers, seals, and vents, then the rings are not seated or the cylinders are not round. They tend to use oil in this condition, but the true sign is lots of blow by.

You should check the cylinder walls and ring gap at the top of the bores, thats where all the wear is. The most pressure from combustion is right at the top so the rings and cylinders wear the most, by the time the piston reaches the bottom, most of the force is gone and the exhaust valve has already opened relieving the pressure.

If you look at the exhaust ports & manifolds and notice a black sticky goo, thats burnt oil. I have seen exhaust valve stems built up with so much crude they look like a solid slug the same diameter as the valve head!

You need to look between the valve spring coils and see if you can see a seal. If not, pull one spring on one intake and one exhaust valve to verify they are or are not there. If by chance it has white teflon seals, throw them away and go get a high temp Viton seal.

As mentioned above, most heads will need the top of the valve guide boss cut for a seal. It's a very common operation and can be done at home with a decent drill or drill press. Any shop should be able to do it also. I can't believe it wasn't already done.