The Official 356Talk Forum

And we are all waiting anxiously for the results...

It sound that about everything has been checked, but have you inspected the
breather / oil filler unit? Perhaps even take the generator stand off to verify that
there isn't anything left there?

Generally, small carbs would reduce the volumetric efficiency which reduces the tendency toward detonation, maybe. On the highway you are not using much throttle so the throttle position makes the carbs effectively very small no matter what size they are.

Ron LaDow wrote:And if detonation was a problem, the result would not be intermittent.

Im not sure Ron wrote this correctly but he will let us know. Detonation is always intermittent. Most engines only detonate at WOT under load and if you drove at very small throttle openings on flat ground they would never detonate. Open to WOT under load and the detonation comes on and hammers the rings making them flutter, lose seal, and create substantial blow by. Intermittent.

I am grasping a bit for an answer. I am confused why the engine doesn't detonate when driven hard while not on a highway. Driving a 356 on the highway does elevate the temperature a little vs the back roads and that may be just enough to initiate detonation.

Really, detonation is a long shot but what other condition causes excess blow by only intermittently?

Your dyno operator MUST duplicate your highway use, 20 minutes of steady 70mph under modest (wind resistance) load. Just doing acceleration runs may pick up a problem but isn't going to mirror your big problem on the highway.

Could this be a case of crankshaft beating oil into a froth. Perhaps cam gear set is doing something odd with the oil. Is the oil level high or the dip stick short? Is the oil some wierd sort of synthetic that can be used to blow bubbles? Something boiling in the sump? Water or gas in the oil?

C J Murray wrote:

Ron LaDow wrote:And if detonation was a problem, the result would not be intermittent.

Im not sure Ron wrote this correctly but he will let us know. Detonation is always intermittent.

Agreed. But the if detonation yields blow-by, those *results* are not likely to be intermittent; a broken ring-land or a hole in a piston don't go away

So this morning we equipped the car with two water manometers, installed a 912 breather can with the extra tube for head vent and plumbed that to one of the water manometers, re bypassed the bypass filter and plumbed the other water gage to the crankcase drain back that the filter uses.
Took her for a run on the highway, at 60mph steady state we recorded 11" of H20 on the crankcase and held steady, upping the speed to 70 and holding that speed the water column stated rising gradually until it hit 15" just as we were to declutch smelled oil. The event occurred about 17". Returning to the shop at varying speeds, 40 to 80, about 4".
We're still scheduled for the Dyno on Friday and will as Cliff suggested repeat the event, then up the speed to 80 and pull it back to 70.
What I haven't been able to find is what is considered normal crankcase pressure for an engine that has been fully run in. I've pulled engines apart with broken rings that didn't have oil pumping out the breather. We also have a small amount of oil in the tube attached to the 912 breather can which negated the pressure reading at the can.

Rusty, your next post will be 356. Congrats. Aren't elusive problems fun?

Today is the day! All will be revealed! I hope. Good luck.

We await with moist (oiled) anticipation.

My 356th post, pretty cool. Yesterday we did the chassis dyno run Dyno was a Mustang MD 600.
We did several tests at 70mph/ 4th gear, required Hp around 25. We held it at that load with nothing being revealed regarding crankcase pressure, less than 4"H2O column. From there we loaded the dyno and full WOT holding the speed at 70, max load to hold 70 approximately 50hp.
Nothing remarkable regarding blow by. The lambda was reading around 0.7, somewhat rich.
The Zeniths were set up with 28 chokes, 210 air correction jets and 140 mains. the chokes were machined to 28. No crankcase issues at full load testing.
Drive back to the shop at 70 t0 80, approximately 4"max crankcase pressure.
Another run on the interstate, the crankcase started to build, it was caught by declutching and didn't burp the oil.
Today we are putting to Webers back on the car (to clean up the running). Still have to work on the excessive crankcase build up.

Just wanted to take a moment and thank all of you for your input. We'll kick it eventually.
Special thanks to Gregg, I know it's been hard on him since he sold a one owner 71 911 to buy this 65 C.
Thanks again,
Rusty

Do you ever hear even the slightest hint of pinging? Can you make it ping, even faintly, by going WOT from 2500 to 4000rpm in 2nd or 3rd?

CLiff, 40 to 80 in 4th, not a hint of an issue or ping. Timing is at 35 full advanced, it likes 37.

Gregs out in the shop reinstalling the Italian Webers, 40IDF, 28 choke. I think it's too rich to ping is that possible? If I can get it leaned out enough we'll see if she pings.

Webers on and seems to be a bit more crisp. Ran around 8 miles on the back roads to warm the engine properly before the steady state driving. Got on the highway and at 70 started building press after having a steady 4 inches of Water column. Got up close to 10 inches and I pull to the side of the road at idle, I didn't time it but pressure came down slowly to zero, got back out to the next exit and got to 3.5". Returned to the shop, pulled the oil can off the breather an had about two tablespoons of oil in it. It seems to me that the beather is flooding with oil and when I let it idle the breather emptied the oil back into the case and pressure came back to zero. When I first pulled over the blowby held at its highest point and went up slightly before coming down.
I'm heading to Florida in a couple of days to play in an old boys soccer tournament. Will think on it more, but when I get back will pull the engine again, remove the third piece and mount Greg's full flow oil filter. Look inside to see if anything is unusual. Any insight you can contribute much appreciated.
In a previous post the question was asked about checking for obstructions in the oil fill area, and yes we have had that apart checked with a borescope and bent wire, all good.
Damn, this is frustrating. Engine runs so good in all other respects and not a drop of oil anywhere. Go figure!