Help me quit smoking (engine, of course)

Need some theory and/or "the answer." Stock 1600, dual Kadron (adjusted by Mr. Kadron) motor will spew one big plume of smoke out the exhaust after a good freeway drive. Temp is good (170-200 degrees, doghouse), 1.5 qt. sump installed. After a drive, I stop at a light and idle a few, and when I take off, the guy behind me has to wait until the fog clears.

Is that rings or blow-by?

The smoke doesn't look blue but light gray. If it's rings, why only after a drive and sitting a few? And I really don't understand the whole blow-by concept but was told by the shop that stock 1600 shouldn't have a problem that requires breather box, and the stock oil filler/drain tube and "mini-breather filter" is okay for that size motor. Also, installed sand seal pulley which I hear reduces some breathing too. Thanks in advance.

Rings are added near the top of the piston to form a seal between the piston and cylinder wall.

Blow-by is when compressed gasses slip past the rings and into the crankcase. The result is a pressurized engine. Has nothing to do with smoke out the exhaust. You see blow-by by taking off the oil filler cap while the engine is running. If you have blow-by, you will see faint light colored smoke or feel air coming out, like a fan, or both. Blow-by is an indicator of how worn your piston rings are. The more blow-by, the more your rings are worn.

On the flip side, the bigger the engine displacement (on VW's) the more blow-by you have. A perfectly healthy 2180 will produce blow-by. Nature of the beast as the say. To relieve blow-by (which usually manifests as oil leaking from everywhere) you have to "vent" the case. Translation _ put a hole in your valve covers and oil fill tower for the gases to escape. You don't want a mess so put hoses on the holes and pipe the stuff to a breather box which traps any contaminants (smoke = oil).

Now blue or light gray out the exhaust is also an indicator of ring condition. With new rings (fresh rebuild) or worn rings oil slips past the rings the other direction and makes it into the combution chanber and is burned with the gas, producing light colored smoke.

There are several rings on the piston. One of them is dedicated to keeping the oil in its place. If one of these breaks, you get lots of smoke.

If you are getting a lot of smoke, enough to screen the car behind you, sounds like you may have a broken ring. At highway speed, compression is higher ad very little oil can get into the cylinder due to pressure, but when you idle at a sop light, low compression and oil gets in. When you take of it burns off the oil.

Thanks Ben for the "blow-by-blow" explanations there (oh that's bad - I kill myself sometimes! :-)
Sounds like I got a bad oil ring or two (or four). Now I'll have to do all the other engine stuff I've wanted to do once I've got the cylinders off - bigger cans, a little head work, ratio rockers and such. 1600 to what size new pistons? Hmmm... I'll have to read the old posts as this has been done before a couple times. But I'll still appreciate your opinions, one and all, on the sizing matter.

Before planning a rebuild you need to do the obvious checks. Do a compression check, check your oil (is there a gas smell on the dip stick?) etc...

Another thought: If you are producing that much smoke (ie: bad rings) you should be experincing a loss of power, fouling plugs (which will make it miss and run rough).

Mike makes a good point. Before doing a teardown, check for other possible causes. His comment spurred another memory of what might be wrong.

Check for over-full oil, do a compression check, Make sure the smoke is coming from your exhaust not dripping on your exhaust and burning off (as in oil leak).

I noticed in your post that you said you had a sand seal installed.
There are 2 ways to install a sand seal 1)an alum. collar pressed into the case onto the crank behind the bottom pully. this collar has a standard crank seal used by modern cars pressed into it. and 2) cut the case and press the seal directly into the case, forget the collar.

install 1 retains the flinger washer (stock bug engines keep the oil in by puting a washer on the crank that "flings" the oil back into the case). Install 2 does not (or at least the mechanic who did mine didn't think so).

This brings up a memory for me. I had a bug that had a bad seal. When I went up hill, or got on it, all the oil went to the back of the case and since the seal was bad and the flinger was gone, it leaked out at the crank (behind the pully) . Guess where that leaking oil went... right onto the exhaust! Produced a lot of smoke! You would swear I blew the motor when I went up hill. Never leaked much any other time. It was a difficult thing to track down because it didn't leak sitting in the driveway idling and most of the evedence went , ahem, up in smoke. ONe item of evidence is that my engine looked like someone sprayed the engine with a fine mist of oil after a incident. Fine little drops everywhere in the engine compartment. (Oil flung off the crank pully). Feel the back of the pully, is it wet with oil?

Sounds like this could be your problem as oil burning off the exhaust is typically lighter in color than smoke produced by bad rings.

Got a great tip from Gordon saying "What I would bet on, is that the intake valve guides are worn, allowing oil to get sucked past the intake valve stems when idling. What happens is, when you're running hard at turnpike speeds, the higher engine RPM is pumping more oil throughout the system, and relatively more (compared to an idling engine) finds its way into the valve covers (after lubricating the rocker arm assembly). Then you stop, and there is still a lot of oil inside the valve covers as it drains back down the pushrod tubes into the crankcase. While you're idling, a little of that excess oil gets sucked past the intake valve guide/valve stem and into the cylinders. You don't usually notice that the exhaust is slowly beginning to smoke a little, but when you step on the gas and accelerate, a big puff of gray-ish smoke pours out the back. Why gray and not Blue? Well, the oil in the cylinder is thinned out by the incoming fuel mixture, so it "leans out" a little in the cylinder and turns gray when it burns. Cracked or worn rings allow a LOT of oil to slip by, and that causes the exhaust smoke to be blue."

Jarco; if getting bigger pistons go with the 90.5's (preferably) or the 94's....

To confirm valve guides either drive dwon a long downhill grade or
bring your car to highway speeds, rapidly lift your foot off the pedal leaving your car in gear. This increases the internal vacuum
of your engine inlet. Normally a piston on it's downward path forms
a void(low pressure) which sucks air around the intake valve thru the intake/carb. By slamming the carb closed that extra vacuum is
stuck and will "suck" the oil around/thru the valve guides.
good luck.