Random smoking from front exhaust

[upperchris]

This is my first posting Have to say I have learned a lot from just browsing I have not been able to find anything close to the problem I am having. Bike is a 62 Panhead with 76 Shovel top end. Motor was done about 10,000 miles ago. Has Mallory electronic ignition. HD CV carb found in swap meet milk crate! Andrews B grind and solid lifters. If you have not gone the electronic ignition and CV carb route I highly recommend it.
Also am trying an AGM battery. Kind of pricey but can be justified if it lasts as long as think it should.
Now.... my problem is the bike will run fine (it always does despite this problem) but sitting at a light it will start smoking from the front exhaust. Compression test was good. Did not check with oil to seal rings. Plugs fine. Somtimes it will not do it at all. The bike did sit for a season, but it did this before that. Running 20-50 HD oil. Next will try 50 weight. I am leaning towards dirty or clogged crankcase breather. Next step is to pull gearcase cove and check.
Also have a belt drive. Instead of venrting through the inner tin cover, I soldered a plate in the tin and left the oiler form the motor open. I can hear if puffing when I kick it over so I know that part is breathing. It is a small gap there. Does this need a larger area to vent to?
The reason I am leaning towards a breather problem is the oil tank becomes pressurized. If I crack the oil cap to release pressure the smoking will die down.
My question is what would cause the pressure in the oil tank and then the smoking?

[FlatHeadSix]

the smoke is probably a combination of valve guide wear and return flow restriction somewhere.

the pressure could be breather timing.

when you start mixing and matching parts from different generations its a can of worms with a loose lid.

jmho

mike

[scumbagel]

yes, another pan shovel. i apprciate this site, good info. but sorta pure pan head orientated. i have my breather set up like yours, little gap between end of breather an back of primary. it sounds strange but i had a bad oil filter pressurize my oil tank once. i tightened the oil filter on with some giant channel locks and it got a bit dented. i changed it out and my pressure in oil tank stopped bein a problem. not sure about the smoking part.

[Cotten]

A very common aluminum head disease develops when valve guides have been poorly cleaned before removal. Hard carbon will score the bore in the head when the guide is pressed out, forming an avenue of leakage from the top of the head to the port.

Add the fact that many modern shops ignore the gasket beneath the guide, and many mysterious smoking habits can come and go without any rhyme or reason, as riding conditions change.

....Cotten