Installed M&K Premuffler : questions about engine health

[kyngfish]

Hola. So I just installed the premuffler and one of the things people called out is that if you were burning any oil - you’d see it.

I recently did a ton of work on my car and did a leakdown. I was under 6% on all cylinders on a SUPER cold engine.

I also know leakdown doesn’t see valve guide wear.

When I start up with the premuffler I get very little smoke. But I do see a reasonable amount of oil burning at cold idle after a little running. It goes away once the engine is hot. I don’t get any smoke on decel that I can see.

I consume around a quart every 600-700 miles give or take.

I thought idle smoke was piston rings and decel smoke was valve guides. But everything I’ve tested seems to suggest my rings and cylinders are fine. What gives? Or is that normal with the premuffler.


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[ClickClickBoom]

For the 93rd time, leak down on anything other than an operating temp engine means less than nothing. It’s a trend monitoring tool, exactly, nothing more, great you have 6% on a super cold engine, so how often do you drive a a super cold engine all day? I have done more than a thousand on aircraft and cars. The majority of problems on these cars is they flat out don’t get used enough for the oil additives to activate, rings get gummy and stick, crud on valve stems and seals. Oil consumption is related to 3 or more factors, 1-valve guides, 2-piston rings, 3-start up, the contents of the oil tank is in the bottom of the engine, splashing and getting whipped into a froth until the scavenge pump clears it back to the tank. The oil sticks to the cool surfaces and lollygags it’s way back to the sump and scavenge pump until the engine is up to temp. I saw more than a few aircraft engines corroding internally, scrap after sitting for most of their life. Drive a thousand miles a month for 6 months, you won’t believe how good it will be running.

[kyngfish]

Originally Posted by ClickClickBoom

For the 93rd time, leak down on anything other than an operating temp engine means less than nothing. It’s a trend monitoring tool, exactly, nothing more, great you have 6% on a super cold engine, so how often do you drive a a super cold engine all day?.

I’m not really sure what you’re saying. The only reason the engine was cold was because I was doing the leak down as part of a 5 month full suspension refresh + a bunch of seals, sensors, bushings and etc. I drive the hell out of this car. Is the takeaway here that a cold leak down test is invalid? So what do you mean by “overall trend”? All I’m looking for here is whether or not cold oil burning is normal when going with a premuffler or indicative of worn valve guides.


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[ClickClickBoom]

A single leak down test is useless. You do one, log the results and sometime in the future do another, compare, then do it over and over and over. Commercial piston aircraft do them every 100 hrs and record the results. Your oil consumption could be related to cold starts, more cold starts per 100 miles could burn a lot of oil. If you want to inspect the exhaust guides, pull the exhaust, if they are leaking it will be obvious, same with intake. If your plugs are caked with carbon it could be rings or lots of cold starts. I have posted the Continental Aircraft Differential Pressure bulletin multiple times, read it, it is interesting.

https://www.lycoming.com/sites/default/files/Cylinder%20Compression.pdf

Or:

https://www.aircraftspruce.com/catalog/pdf/servicebulletin.pdf

652 Oliver Street
Williamsport, PA 717/3236181
DATE:
SUBJECT:
17701
U.S.A.
INSTRUCTION
Service Instruction No. 1191A (Supersedes Service Instruction No. 1191) Engineering Aspects are
MODELS AFFECTED:
TIME OF COMPLIANCE:
Cylinder Compression
All Textron Lycoming aircraft engines.
As required to determine cylinder compression.
TELyXcToRmOiNng
SERVICE
September 28, 1998
The condition of the working parts in the combustion chamber of a cylinder can be determined by measuring the static leak rate of the cylinder as compared to the leak rate through an orifice of specified size. This is accom- plished by attaching a differential compression measuring device, which incorporates the orifice, to one spark plug hole of the cylinder while the piston is at top center of the compression stroke.
CAUTION
TAKE ALL NECESSARY PRECAUTIONS AGAINST ACCIDENTAL FIRING OR ROTA- TION OF THE ENGINE.
The piston is held at top dead center by firmly holding the propeller to prevent the engine from turning when air pressure is applied through the differential compression device to the combustion chamber.
CAUTION
USE GLOVES OR RAGS TO PROTECT THE HANDS WHILE HOLDING THE PROPEL- LER BLADE. ALSO, BEFORE ATTACHINGTHE COMPRESSION TESTER, CHECK THE AIR SUPPLY REGULATOR TO MAKE SURE THE AIR PRESSURE TO THE CYLINDER IS NOT EXCESSIVE. AIR PRESSURE IN THE CYLINDER CAN CAUSE THE PROPEL-
LER TO TURN; KEEP CLEAR OF THE PATHOF THE BLADES.
To assure that the piston rings are seated, the propeller is moved slightly back and forth with a rocking motion while air pressure is applied; thus providing a more accurate reading. Meanwhile, a second person adjusts the air supply pressure to 80 psi, indicated on the supply pressure gage of the differential compression device. Then, observation of the engine cylinder pressure gage will give an indication of the condition of the parts in the com-
bustion chamber of the cylinder.
NOTE
The orifice size of the differential compression measuring device is critical if consistent and meaningful cylinder analysis are to be obtained; the larger the orifice the less chance of detecting potential problems. Therefore, a specific orifice size that provides an acceptable leak rate has been selected for all Textron Lycoming engines; the instructions described herein are based on thisorificewhichis.040in.dia.(No.60drill)x.250inlo ng,withentranceangleof59/60 °.
At any time loss of power, increasing oil consumption, hard starting or other evidence of unexplained abnor- mal operation is encountered, a compression check of the cylinders is recommended with equipment and in the manner described above by personnel experienced with the equipment and with the type of engine to be checked. In practice the procedure is as follows:
GeneraAlviation ManufactureArsssociation
Page 1 of 2
FAA Approved

AIRSUPPLYPRESSURE
AIRTOENGINECYLINDER
ENGINECYLINDERPRESSURE
AIRSUPPLYPRESSURREEGULATOR
AIRSUPPLY
Typical Differential Compression Measuring Device
1.Operate the engine until normal cylinder head and oil temperatures are attained; then shut down the engine making sure that magneto switches and fuel supply valves are shut off. Proceed with the test as soon as pos- sible after shut down.
2. Conduct the test in accordance with the test equipment manufacturer's recommendations.
3. Interpretation of the results of the test is highly dependent on the skill and judicious opinion of the tester; however, the following observations cover the principle factors to be noted:
a. Pressure readings for all cylinders should be nearly equal; a difference of 5 psi is satisfactory; a difference of 10 to 15 psi indicates an investigation should be made.
NOTE
Unless the pressure difference exceeds 15 psi the investigation should not necessarily mean re- moval of the cylinder; often a valve will reseat itself and result in acceptable compression during a later check which should be made within the next 10 hours of operation.
b. If the pressure reading for all cylinders is equal and above 70 psi; the engine is satisfactory; less then 65 psi indicates wear has occurred and subsequent compression checks should be made at 100 hour intervals to determine rate and amount of wear. If the pressure reading is below 60 psi or if the wear rate increases rapidly, as indicated by appreciable decrease in cylinder pressure, removal and overhaul of the cylinders should be considered.
c. Low pressure in a single cylinder is indicative of air passing by the piston or by the valve.
d. Air discharged from the breather or oil filler tube indicates leakage in the area of the piston and rings. e. Air discharged through the intake system indicates leakage at the intake valve.
f. Air discharged from the exhaust system indicates leakage at the exhaust valve.
Page 2 of 2
Service Instruction No. 1191A

[kyngfish]

Got it. Good info. Thanks.


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[dfhtrhjn]

Maybe I'm exposing my ignorance here, but isn't a quart every 6-700 miles high? My engines are fairly fresh I guess, but even after 2k miles I haven't quite lost a quart...

[ClickClickBoom]

2000 miles on engine? Barely, if, broken in. Aircraft engines are considered broken in when oil consumption stabilizes. Between 5-10 hours at 75% rated power at lower altitudes for best cooling. Cars could be considerably longer since it’s hard to keep 75% power.
I will reiterate, most of the people on these boards simply don’t drive their cars enough to keep them healthy. Bearings sit metal to metal, oil oxidizes, heating and cooling cycles cause moisture condensation/collection. Add washing repeatedly, then waxing traps water in crevices and low areas. The simple act of driving mixes all the stuff up, airflow dries things out and redistributes the lubes and oils.
I have pulled cylinders off of aircraft engines that had the rings corroded to the cylinders, rusticles hanging from the cam, dripping into the sump.
The main byproducts of internal combustion are CO2 and H2O along with a few other compounds. Every single engine that has run has water in some amount inside.

http://forums.pelicanparts.com/porsche-911-technical-forum/1035411-3-2-oil-catch-can.html

My car isn’t “happy” until it’s temp is up and 20-30 miles are under the tires. Everything smooths out and settles in. But I average 1000 miles a month, rain or shine.
If you are worried about date codes on your tires, wear them out, problem solved. The simple fact that there is so much concern for date codes prove they aren’t driving enough.
Drive it, like the good Dr says.

[darrin]

clickclickboom -- believe Steve's indicating that it takes over 2k miles before his engine requires a quart of oil, not that he's only 2k miles past a rebuild.

I agree wholeheartedly with your "drive it" comment -- had to get the top end rebuilt on my '86 when, at 80k miles, I was barely getting 500 miles per quart. Post-rebuild, I put around 10k miles on it per year and was still seeing over 2k miles per quart when, with over 100k miles on the top end, I decided to bump it to a 3.4.

Do wonder, however, whether the OP's engine may well have also been cursed with premature valve guide wear that affects some '86 engines (like mine) and whether the damage has already been done (and can not be rectified) -- On mine, the valves' lateral play made it pretty clear that the guides were SHOT

[ClickClickBoom]

Originally Posted by darrin

clickclickboom -- believe Steve's indicating that it takes over 2k miles before his engine requires a quart of oil, not that he's only 2k miles past a rebuild.

I agree wholeheartedly with your "drive it" comment -- had to get the top end rebuilt on my '86 when, at 80k miles, I was barely getting 500 miles per quart. Post-rebuild, I put around 10k miles on it per year and was still seeing over 2k miles per quart when, with over 100k miles on the top end, I decided to bump it to a 3.4.

Do wonder, however, whether the OP's engine may well have also been cursed with premature valve guide wear that affects some '86 engines (like mine) and whether the damage has already been done (and can not be rectified) -- On mine, the valves' lateral play made it pretty clear that the guides were SHOT

Proof that these engines and chassis aren’t that fragile:
Almost 1000 hp from 1980s technology, 930/82 3.2l , pissed off:

https://youtu.be/wPfK_BispVo

[dfhtrhjn]

I apologize, my wording was not clear. I'm seeing over 2k miles of driving before I require adding a quart. I'm glad to see Darrin experienced the same.

To address Darrin's point, 6-700 miles per quart does make one suspicious of the value guides...

[ClickClickBoom]

Originally Posted by dfhtrhjn

I apologize, my wording was not clear. I'm seeing over 2k miles of driving before I require adding a quart. I'm glad to see Darrin experienced the same.

To address Darrin's point, 6-700 miles per quart does make one suspicious of the value guides...

The point is it 2000 miles nonstop or 1 mile a day? Cold starts can consume a lot of oil.