[Crowbar44]

So I've been using a TON of oil (2 quarts in 500 miles!) on my newly acquired '81 S2. I'm running Mobil 1 20W-50 V-Twin oil, I switched from Mobil 1 10W-30 which the PO had been running. I live in Texas, and felt the heavier oil would do better in the heat.

I did a compression test today, long rod was disconnected from the bellcrank, wire from coil to the dizzy disconnected, engine was hot ~180 degrees, I pulled each plug when I tested each cylinder, but the others were in place - here are the results:


Cylinder 1 - 92 lbs DRY - 160 lbs WET
Cylinder 2 - 90 lbs DRY - 150 lbs WET
Cylinder 3 - 90 lbs DRY - 150 lbs WET
Cylinder 4 - 92 lbs DRY - 140 lbs WET

Looks like the rings are the culprit - can I really be losing that much oil with cracked rings? The car does not smoke, it is running a bit rich (plugs electrodes are black after about 1500 miles) What's the next step in zeroing in on the problem? Any other ideas?

Many thanks, as always,

GC

 

[alfaparticle]

Do a leakdown test to identify the sources of the compression leaks.

 

[spiderserie4]

I did a compression test today, long rod was disconnected from the bellcrank....

so you did not do the test WOT? (wide open throttle)
I'd do it again.

 

[Crowbar44]

I didn't do it WOT...assumed the fuel rushing into the cylinder would corrupt the results...

 

[65Sprint]

so you did not do the test WOT? (wide open throttle)
I'd do it again.

+1

 

[alfaparticle]

It does not need to be at WOT but the throttle should be at least partly open.

 

[Chas H]

Compression tests are of little value in cases of oil consumption. Compression ring have little to do with oil control and oil rings have little to do with compression. But if you are going to do a compression test, do it right. All spark plugs out during the test and WOT. WOT may not be absolutely necessary, but it is consistent.
What is it you hope to know from the compression test? You already know the engine uses oil and a compression test tells you nothing about the condition of the valve guides and stem seals or of the oil control rings.

 

[alfaparticle]

A throttle opening of 10% will supply sufficient air for the engine to rev at 6000 rpm. That is about 200 times higher than the engine is spinning during a compression test. The WOT requirement is an old wives tale.

 

[Chas H]

A throttle opening of 10% will supply sufficient air for the engine to rev at 6000 rpm. That is about 200 times higher than the engine is spinning during a compression test. The WOT requirement is an old wives tale.

Just how does one be certain the throttle is sufficiently open? There's no need to guess if the throttle is wide open. It's not a matter of old wives, just of convention, convenience and common sense.

 

[spiderserie4]

to me it is just better to stick to a simple procedure
WOT, hot engine, all plugs out.

for instance, injection will go into 'clear flood mode' with WOT whilst cranking (say <600 rpm)....meaning the injectors will not spray.

 

[Chas H]

to me it is just better to stick to a simple procedure
WOT, hot engine, all plugs out.

for instance, injection will go into 'clear flood mode' with WOT whilst cranking (say <600 rpm)....meaning the injectors will not spray.

Yup, KISS.

 

[alfaparticle]

Yup, KISS.

:x

Did a compression test on an Alfa race car in the paddock at Road Atlanta this weekend. I can assure you that it is a darn site simpler just to crack the throttle than get it wide open when you have Webers and double return springs.

 

[ARwrench]

for instance, injection will go into 'clear flood mode' with WOT whilst cranking (say <600 rpm)....meaning the injectors will not spray.

I'm not sure about that on a Spica car :001_unsure:

 

[Crowbar44]

I'm running Webers, should I clamp the fuel line during the redone compression test with WOT?

 

[PSk]

to me it is just better to stick to a simple procedure
WOT, hot engine, all plugs out.

for instance, injection will go into 'clear flood mode' with WOT whilst cranking (say <600 rpm)....meaning the injectors will not spray.

Amen. I takes seconds to get a reading per cylinder (you only want a max of 3-4 revolutions of the engine per compression check, otherwise you will kill the battery) ... heck I've never worried about fuel.

Just do it as it is supposed to be done. Don't worry about fuel and get your numbers
Pete

 

[ARwrench]

All this is nonsense...Chas H said it all in post #7 :wink2:

 

[PSk]

All this is nonsense...Chas H said it all in post #7 <img src="http://www.alfabb.com/bb/forums/images/AlfaBB_2015/smilies/tango_face_wink.png" border="0" alt="" title="Wink" class="inlineimg" />

Heck good point!
Pete

 

[bruce1976spider]

Closed throttle DOES make the resulting reading lower!!

Frankly, even-ish reading between cylinders is more saying "general wear" than a cracked ring (then one cylinder is dramatically different). Or head gasket failure - that's typically uneven pressures.

Looking at the original question: Oil lost.

1) Is there OIL in the ANTIFREEZE??
2) Cardboard under the car - Oil puddle anywhere??

 

[papajam]

Closed throttle DOES make the resulting reading lower!!

Well, of course it does. And the reason is quite simple. An internal combustion engine is a pump. An air pump to be more precise. The output is therefore dependent upon, among other things, it's input. The lower the input, the lower the output. This is why closed throttle compression readings are ALWAYS lower then WOT readings.

The dry/wet compression numbers do tell a bit of a story. The reported symptom is 250 miles/quart of oil. If all of this oil was coming up past the oil control rings, the cylinders walls would be oil coated. This could give false high compression readings as the dry test is effectively a wet test. However, the delta between the dry and wet test readings is too high. Therefore, the oil rings are NOT the major source for the oil consumption.
Moot point really as the dry/wet readings indicate compression problems anyway.

 

[ossodiseppia]

A throttle opening of 10% will supply sufficient air for the engine to rev at 6000 rpm. That is about 200 times higher than the engine is spinning during a compression test. The WOT requirement is an old wives tale.

Ed, I'd like to challenge you on this. Running the test with the throttle wide open makes for consistency across each of the cylinders. Rhetorically, how can anyone know that they are consistently holding the throttle in the exact same position if it's not wide open. As Jim stated, it's all about moving air through the cylinders. More air equals more horsepower.