I am getting blue smoke and oily plugs. Compression is 51, 55, 47 and 48 front to back.
Is it coming from the valves
That would not be too common, or easy to do, in a flat head engine, where the oil has leak upwards through the valve stem clearance. Yes, oil mist can get sucked up though the intake valve clearance, but I can't imagine any great volume of oil gets moved in that way.
That is what I was thinking Jerry.
I did a vacuum check, at idle 15 inches steady at higher rpm 13 inches steady.
When I say steady the needle moves about a 8th to a 1/4 inch in each direction.
In a post from March from Charlie B he said
"The engine ran so a vacuum gauge could have told him the condition of the intake valve guides. A vibrating needle at idle shows that their worn and you'll smoke like hell if they’re really shot"
What is considered vibrating? How much movement?
Oil control rings. KGB
I would do another dry compression check, then a wet one. If the compression improves significantly on the wet test, the problem is rings.
At idle it can run with very little smoke if I increase rpm still very little smoke. Then suddenly the smoke increase for a while then stops.
So it's intermittent, what can change to cause this
Peter, I rebuilt my 26 last winter. I had good compression but when I got into the motor the oil rings were worn smooth! They almost looked like compression rings. Oil consumption was also intermittent. PK
On September 14, you posted that you changed the oil.
Maybe you over-filled the crankcase?
It could be the oil rings, or it could be excessive valve guide clearance. Neither one would effect your compression readings, but would allow oil into the combustion chamber. When I rebuilt my coupe engine, I let the valve guides go with about .006" clearance and now wish I would have reamed them to the next size. It smokes a little, not all the time, but doesn't foul the plugs. I'm sure sucking oil up past the valve stems.
I though about too much oil and checked it, it seem ok
Pete: what you're describing sounds like an oil build up . Smokes then quits then smokes again. The only spot that comes to mind that would do that is the valve gallery with partially blocked drain holes. An abundance of oil here just might get pulled up by the valves then drains a bit at lower speeds. I remember doing the intake valve seals on a number of crudded up Ford V-8's back in the 60's for exactly the same symptoms you're describing. By the way that vacuum gauge reading for bad valve guides would be a very quickly vibrating needle. Almost a blur. I don't think your rings are the culprit for 2 reasons: your comp. is very good and that smoking is intermittent. Would be constant with bad rings.
There is no pressure in the valve chamber so oil burning through valve stems would be minor, however, leaky rings could cause blowby into the valve chamber which could cause air pressure on the valve stems causing oil to be directed upward. Check around the oil filler cap when the engine is running to see if smoke comes out. If it does, you have blowby. Worn rings will suck oil into the cylinders to be burned and also cause blowby into the crankcase.
Yes there is smoke coming out of the oil filler
In fact I made up my own PVC valve setup to see if it would help, It didn't help but it doesn't hurt either but a least I don't have smoke coming out from the hood
One of my long ago T mentors had a theory about this. He had one that smoked intermittently. Due to the fact that the top ring goes clear to the top of the bore, there is a wear band more or less in the middle of the cylinder. Oil would build up in there between the piston and the cylinder walls. Maybe only one hole was doing this. When that film of oil got built up to a certain point, it would come out, causing it to smoke. Varying degrees depending on which cylinder or cylinders were puking it out at any one time. Ran great otherwise. His solution was to rotate cleaned plugs every so often. I know where that car is and I might ask him if it stilldoes it.
Compression: 47 to 51 PSI. It is not blow by. If it was every T with less compression, I'm betting most, would be smoking like crazy. Smoke will come out of the oil fill cap. It's a vent besides being a filler cap. That's what it does. Besides if it was blow by it would puff as each cyl. charges the crankcase with pressure. It smokes then it stops then starts again as described in the original posting. Oil is pooling, being used up then pools again. It's being sucked up thru worn intake valve guides as the cam followers splash it around then it gets low enough and it quits smoking for a while until partially clogged return holes in the oil gallery allow it to pool again.
Yep. Kieth said it all.
This evening, I spoke with the old fellow that ended up with my friends T that was an intermittent smoker,see above. It still does it, never gotten any worse.It also still does it with the valve covers off.This is not a high-use car. His grandkids and great-grandkids run it around the farm at every family gathering,and,as he says, they 'really give 'er hell'.They time themselves how long it takes them to get around the trails in the woods and the lane to the back pasture. Grandma disapproves. He says the occasional big puffs of smoke gives it character. I couldn't agree more.