blowby issue when under load - smokey!

[CamaroMan]

Hi all - have a a4.. just replaced the head gasket (it blew) - was an old asbestos one.. head wasnt warped.. just did a nice block sand and its holding well.

Now when under throttle, after a while there is quite a bit of smoke coming from the filler cap making it quite unpleasant below.

The card was rebuilt, the vent hose is in good shape.. seems either the valve guides are real bad (oil being pulled in when hot) and a certain amount of blowby-

Usually blowby is mostly air, but the smoke seems to indicate oil. Fyi new oil 5 hours ago and still very clean.

Any ideas? iirc weight was a 10w30-

Is there an option to put a cap on with a hose to the air intake or maybe block it off and force the vapors thru the carb via the intake?

[Dave Neptune]

CamaroMan, Indigo makes a PCV kit for just what you are talking about. Frankly I would not run an A-4 without one!!! These engines were designed before the PCV valve was invented. The designers did engineer a slash tube to try for the same thing, the valve just works better and is far more efficient at reducing blowby fumes from the engine.

Do you use your blower full time or just to start. Gasoline engines should have a full time blower no exceptions for safety! IMHO

The other cause/remedy is to much lead in the timing. IE your timing needs to be set and probably is to advanced. Try backing the timing up a bit ab=nd be sure the c-advance is functioning.

Dave Neptune

[CamaroMan]

thanks dave - will try the timing and look into the pcv kit! I kinda did set the timing by ear - motor warmed well, in gear at dock and around 2500-3k rpms.. rotate to when rpms just start to increase near max under load- I have no access to the flywheel.. starts and ticks over quite easy-


fyi how would timing cause blow by? pushing back past rings while piston still moving up?

Guess ill have to go and remove #1 plug, use a straw, find the center of the dwell and paint on a dab on water pump body and pulley

[Dave Neptune]

CaamaroMan, it is the "timing" of the fuel burn that makes pressure against the piston creating your power. If the burn starts to soon the pressure increases faster than the piston can react causing an excessive load on the rings to seal and thus "blowing" by a bit. When the burn is right the cylinder pressure is more constant and the "leverage angles" of the rod against the crank increase as the cylinder pressure increases creating a happy "torque" making engine.

The A-4 has very low compression and requires a very low pressure fuel to make smooth reliable power. Regular grade gas of today is designed for far higher compression. For this reason using Premium grades is a waste and if we could find a lower octane fuel it would work better in the A-4. The fuels of long ago would barely run in todays engines.

Setting the timing by ear is fine if you are careful. Do it at a good hard cruising speed on the water if possible or even against the dock lines. Be sure she is all warmed up and the distributor is loose enough to rotate but stay in place when released. Slowly rotate until a max RPM is reached then "retard the timing just a tiny bit which will smooth it out and loose very few RPM. This will make a good smooth running engine.

Dave Neptune

Dave Neptune

[JOHN COOKSON]

How long has it been since you serviced the advance?
If the flyweights are sticking or moving with friction the timing will never be correct.


ex TRUE GRIT

[Al Schober]

Based on your replacing a copper/asbestos head gasket, it's been a LONG time since someone's been into that engine (perhaps never). IMHO, it's very likely that it needs rings. Good news is that's likely ALL it needs. I'd recommend you plan on pulling the engine (at your convenience, good therapeutic winter job) and going through it.
Bearings may be fine - do some diagnostics on your oil pressure. How is your oil pressure currently? What pressures do you get if you tighten/loosen the oil pressure adjustment?
Dave's tuning suggestions may reduce the blowby to the point where you can live with it until you do the rings. Running the blower (sucker?) will certainly help.
Engine in the shop/basement is a good time to clean it out and convert to glycol cooling (heat exchanger) if you don't already have it.

[CamaroMan]

hi chaps - thanks once again. I did check the distributor springs, they were loose and snapped back-

I wet down there today and she wouldnt start!! I have almost no access to the flywheel for a tdc mark so i rotated till t#1 was on comp and just stopped blowing- used a screw driver and rotated backwards and got a good snap of a spark..

still really struggled - i suspect the new oil switch is perhaps not functioning (AC delco) - the pump did not seem to prime unless i jumped the wires, possibly indicating a low oil pressure situation (dip stick reads 2/3rds to full mark).

just went thru everything basically - only thing is the coil primary resistance is perhaps a little low at 2 ohms - so once with 3 is on the way 2moro but a lower pri resistance coil should deliver a hotter spark -

either way going back in the morning early before work to see what I can do.

Thanks for the input! i did do a comp test when gasket was blown and she was around 55-60 on all and all four were pushing bubbles out between block and head-

fyi is the idle mixture rich or lean when turning out? i suspect lean?

[Dave Neptune]

The idle mix adjustment is air control so out is lean & in is rich.

Dave Neptune

[CamaroMan]

well went down, found tdc using a flashlight and watching the piston dwell, marked the pump pulley for zero and a few leading dots- cleaned plugs, backed mixture out 1/2 a turn and she fired up - ran her at 2500 for about 5 minutes and shut her down- all 4 plugs were now tan in color so will see ow she does under load 2moro..

[Dave Neptune]

Curious

CamaroMan, looking back I would like to know if your tach is accurate. Is your engine a "direct drive" or have a reduction unit? Very few A-4's with reduction units see 2500 let alone 3000. Most with reduction units top our around 2500 some a bit higher and direct drives around 2000. Some direct drives with the special Indigo prop will see 2500.

Dave Neptune

[ndutton]

To support Dave's comments, my direct drive with precise timing (set with a light to factory spec) and a smallish 10x8 two blade prop maxes out at 2600 RPM (calibrated tach) in forward gear.

[edwardc]

... Very few A-4's with reduction units see 2500 let alone 3000. Most with reduction units top our around 2500 some a bit higher and direct drives around 2000. Some direct drives with the special Indigo prop will see 2500.

Dave Neptune

I guess I’m one of the few.
My A4 with a 2:1 v-drive reduction, and a 3-blade 15x8 prop, gets to 3100 rpm at WOT in a flat calm. (With a clean bottom)