Cold Running? Engine mayonnaise

[Bill Scholfield]

Hi, I am in the middle of a tune up on my 356C.

I have noticed for some time a lot of condensation under the oil filler cap - went on a 250 mile run and it was still there.
I am now checking and adjusting the valves and found that whilst the left hand side (drivers side LHD car) rocker cover was nice and clean, the right hand side was thick with oil and condensation (mayo).

Is this normal or usual for one side only to be affected?

Second issue is re compression comparison between cylinders: no1 95, no2 101, no3 84 and no4 105. So 3 is down a bit compared to the others. I also notice that the engine doesn't feel exactly smooth, just a little extra vibration, which again may be normal, but isnt present on my other aircooled vw cars.

Regarding the valve adjustment I found 3 out of 4 exhaust valves were a little tight.

Is the compression of 1/2/4 ok or should that be higher?

Any thoughts appreciated.

Thanks, Bill

[Neil Bardsley]

"I am now checking and adjusting the valves and found that whilst the left hand side (drivers side LHD car) rocker cover was nice and clean, the right hand side was thick with oil and condensation (mayo)."

I'm interested to hear the experts opinion on this as I've never heard of mayo by the heads. I have some in my 912 in the filler canister but the head generally get pretty hot?

[Cliff Hanson]

I believe that most all of the engines will show condensation on the oil filler cap and at the top of the filler can. On my car (356SC) there is always condensation of water and oil mixture (mayonnaise) on the inside of the corrugated breather hose that goes to RH air cleaner. Unless the ambient temperature is high and the car is driven hard I don't think the oil gets hot enough to really get rid of the water vapor that is formed as a combustion byproduct, and the engine breather system possibly leaves a little to be desired. But from my experience with air cooled aircraft engines this is pretty common. I don't recall ever seeing the mayo inside the valve cover area however.

Cranking compression numbers are somewhat dependent on cranking speed but mostly on the compression ratio and how well the rings are sealing. With your "tight" exhaust valve clearance could you still rotate the pushrods? If so the valves would have been seated and not affected the compression numbers. I think that a variation of 10% from high to low is pretty much the accepted amount. Yours is more like 20% and probably to low on the one cylinder. Overall your numbers seem a bit to low to me. Others will have a better feel for a stock C engine than I do. A large variation in compression will cause a power unbalance between cylinders an rough running. My modified SC engine with 9.7:1 CR has about 145 psi cranking pressure.

I'd suggest you also do a differential compression test to seee where your cylinder leakage is and how much is leaking past the rings or possibly the valves.

[Ron LaDow]

Bill,
Is the right side rocker box cover vented?

[Bill Scholfield]

Ron, not that I can see, should it be?

Thanks, Bill

[Bill Scholfield]

The left hand side does not appear to be vented either

[jay abrams]

Call me anal, (I've been called worse), but I pop open my oil filler cap after every drive just to let the steam out. Don't know how much difference it makes, but it does make ME feel better to see all that vapor blow off.
Jay

[Cliff Hanson]

Call me anal, (I've been called worse), but I pop open my oil filler cap after every drive just to let the steam out. Don't know how much difference it makes, but it does make ME feel better to see all that vapor blow off.
Jay

I do that too. And I put a paper towel under the cap and over the filler neck and it absorbs lots of moisture. Seems like a good idea to get as much out of the engine as possible, rather than letting it condense inside the filler tank and get back inside the engine.

[Ron LaDow]

Ron, not that I can see, should it be?
Thanks, Bill

Cs had non-vented covers; it was all supposed to go in the right hand carb. But if someone swapped to a vented on sometime in the past, that could be where the 'leak to atmosphere' is.
Try swapping and see if the mayo follows the cover.

[John Brooks]

I think it is combustion moisture bypassing the rings. This is water vapor is condensing in the breather. Gets worse in the winter. Remove the oil filler cap at idle and see if there are excessive pressure pulses. Put your hand over the top and feel for puffing.

If so, run a leak down test on the cylinders and listen for leaking air at the oil filler. Your compression is a little low, you may need rings. Removing the cap and letting the moisture out will reduce the residue in the breather, but is not the cure.

My 912 does the same thing and the leak down is 79-84 with air leaking heard at the oil filler, and dip stick tube. Starts and runs fine but the compression is also little low.

[Bill Scholfield]

Have a leakdown tester on order - however, took the car for a road test this morning and, as a result of adjusting the 3 tight exhaust valves the car is smoother, so good result. My next worry is - are the exhaust valves burned

[Vic Skirmants]

Bill; unless your exhaust valves were at negative clearance, they will not get burned from being merely slightly tight. All the valve clearances increase as the engine warms up.

[Cliff Hanson]

I think it is combustion moisture bypassing the rings. This is water vapor is condensing in the breather. Gets worse in the winter. Remove the oil filler cap at idle and see if there are excessive pressure pulses. Put your hand over the top and feel for puffing.

If so, run a leak down test on the cylinders and listen for leaking air at the oil filler. Your compression is a little low, you may need rings. Removing the cap and letting the moisture out will reduce the residue in the breather, but is not the cure.

My 912 does the same thing and the leak down is 79-84 with air leaking heard at the oil filler, and dip stick tube. Starts and runs fine but the compression is also little low.

John is right on but you cannot drive with the filler cap off so the moisture will form and create the mayo where it condenses on the colder parts and high areas.

John, what are you using as the inlet pressure on your compression tester when you get 79-84 psi? I assume it is 100 psi and you are using an aircraft compression tester, as the size of the orfice across which you are measuring the pressure drop affects the numbers. On aircraft engines we use 80 psi as the inlet and get concerned when the cylinder pressure falls below 60 psi on Lycoming engines.

[Dick Weiss]

Bill,

Testing the compression should be done after the engine is warmed up or hot after a drive, the throttle blocked wide open,
coil lead removed, and engine turned w/starter for around 4-or-5 'hits'.
Check the vertical screws on both sides of the intake manifolds holding the vertical and horizontal side plates to the heads & cover gasket.
Any background of work done since the last time the valves were adjusted &/or the last tuneup or age of rebuild; etc.?
What oil are you using?

Dick

[Bill Scholfield]

Bill,

Testing the compression should be done after the engine is warmed up or hot after a drive, the throttle blocked wide open,
coil lead removed, and engine turned w/starter for around 4-or-5 'hits'.
Check the vertical screws on both sides of the intake manifolds holding the vertical and horizontal side plates to the heads & cover gasket.
Any background of work done since the last time the valves were adjusted &/or the last tuneup or age of rebuild; etc.?
What oil are you using?

Dick

Thanks Dick, last tune up that is recorded was at 95050 miles in 2011, the mileage now is 3500. In the 12 years I have known the car (I have only owned it since last August) no work has been completed on the engine.

Regarding oil, I use Valvoline 20/50