Trouble shooting oil consumption

[Cardinal767]

I've only had my 231 for 10 months now, putting 170 hours (more than it's flown in the last 8 years combined) and have been working out the years of poor maintance on the aircraft. Thankfully she only has 1600 total hours on her. Today I finally nailed down the 1/3 to 1/2 quart per hour oil consumption issue I've had from day one. I checked the usual suspects; Compressions, turbo, oil seperator, all good. Not until I replaced a cylinder intake gasket that I saw a possible cause. Oil pooled in the intake port and a coked up intake valve. I checked two other cylinder, same story, but no oil in the induction system, bone dry. After checking the TCM IPC, easy fix I thought, change the seals on the intake valve guides and let's see if we can make TBO. Cylinder after cylinder I found that no seals were installed. I called TCM to see if they were required on -GB engines as listed in the IPC . Yep, required per the Tech Support guy. After getting a seasoned Tech Guy on the phone I found out that they started installing the seals in the mid-80's. My cylinders are factory installed in January 1981, and have never been replaced. 1600 hours, wow, never heard that about a TCM ENGINE. The previous owner must have really babied the engine for the 25 years he owned it.

Seals are installed now, can't wait to see the results. I'll see if I can get 200 more hours then upgrade the engine to an -LB. 

Any thought on cleaning the coked up valves? TCM says to disassemble the cylinders. Really?

[ArtVandelay]

Isn't Marvel Mystery oil suppose help with dirty valves, etc?

[ltdoyle]

I had a C-175 that used to coke the valves frequently.  I got pretty good with the "rope trick".   I would ream the valve guides and clean off the valve stems with the cylinders still attached to the engine.

You can insert cotton rope through the spark plug hole, then gently pull the prop until the rope is against the valves.  You can then take the valve springs off.  After that, remove the rope and take the piston down to the bottom.  You can then tie a piece of floss on the end of the valve and push it into the cylinder (string and all).  After than you can run a reamer through the valve guide to clean it out. Pull the string out the spark plug hole with a claw grabber, exposing the valve stem where you can inspect it and clean any gunk off of it.   Use the claw grabber to go through the valve guide, and grab the string and pull it back through the valve guide.  You can then take a long screw driver through the spark plug hole to help you guide the valve back into the valve guide, while pulling on the string.  After that, put the rope back in and install the springs.  (I have also used compressed air instead of rope).  Takes about 30 minutes start to finish to do a cylinder.

Edited June 14, 2016 by ltdoyle
added text

[RLCarter]

The rope works well, used it several times on my buddies 0-300 Conti for a stuck valve

 

[Guitarmaster]

Okay. You've piqued my curiosity. What is the rope trick?

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[RLCarter]

Use a Colton rope threaded through the spark plug hole, then slowly rotate the prop to smash the rope in the cylinder up against the valves to hold them in place to remove the valve springs or to push the valve closed if it's stuck , it's done on the compression stroke

[Guitarmaster]

Cool. If I ever run into this problem, I will have to try this!

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[RLCarter]

I use to work on Sea-Doo watercraft back in the late 80's and it was in the service manual to use a rope to lock up the motor to toque the prop or the flywheel, the stuck valve is a little tricky do to the fact you can bend the valve if your not really careful 

[philiplane]

if you have Champion spark plugs manufactured prior to February 2014, high internal resistance produces a weak spark, which in turn contributes to high oil consumption. And to excess magneto wear, which compounds the problem. Especially if your engine has Slick magnetos. 

[helitim]

philliplane,

The issue you mention with the weak plugs.  Is that the reason one should always check the ohm resistance when cleaning and gapping a plug to make sure it stays below 5K?  

Tim

[philiplane]

Excess resistance in plugs weakens the spark, and eventually will crossfire inside the magneto. Neither is good. The best ignition system is Bendix magnetos with Tempest fine wire plugs. The worst is Champion plugs made prior to February 2014, with Slick (now Champion) magnetos made after 2001.

[takair]

On June 14, 2016 at 1:09 PM, philiplane said:

if you have Champion spark plugs manufactured prior to February 2014, high internal resistance produces a weak spark, which in turn contributes to high oil consumption. And to excess magneto wear, which compounds the problem. Especially if your engine has Slick magnetos. 

I am trying to understand the link to high oil consumption?

[philiplane]

low cylinder firing pressure due to weak ignition systems produces excessive ring blow by, and poor oil control. Oil control rings depend not only on ring tension but on cylinder pressure to force the ring against the wall. Anytime you have low compression, whether due to worn parts or low firing pressure, you will have high oil consumption. 

[takair]

I would think you would have numerous other symptoms like high EGT and reduced power if it was spark related, do you agree?

[philiplane]

not unless the piston rings are stuck to the piston. Which will happen after a few hundred hours of poor combustion.

Edited July 12, 2016 by philiplane