Oil Stuff

[Slick Goodlin]

As I mentioned on another thread, I’m trialling CamGuard in the old Cub this year on a largely unscientific basis to see if I explode the engine by introducing a new variable. I’m hoping to slow the pace of internal corrosion in an engine that spends a lot of time sitting.

Speaking of sitting, I’m getting some blow by on that A40 and one cylinder is blowing white smoke. I’m hoping it’s just a stuck ring and I can get it freed up without going all surgical on the little thing and to help it along I was thinking of resorting to my old friend Marvel Mystery Oil.

Think MMO plays nice with CamGuard?

[Colonel]

Can you spend a minute and diagnose it?

Put the cylinder at TDC and put 80 psi of air in it (leak test) and have a buddy hold the prop - it won't move at TDC, but -
and climb around the airplane. Where is the hissing?

If it's blowing out the breather tube, yup it's going past the rings.

If you can hear it out the air filter, the intake valve is sticking open or the mating faces are dirty or warped. Try the cheap fix first and whack the valve with a piece of wood and a hammer. This is called staking the valve and if there's crud in the guide/stem this can free it up. If your mechanic doesn't know how to do this, get an older mechanic who does.

Could be the exhaust valve - do you hear hissing out the exhaust pipe? Stake the exhaust valve as above and see if the problem goes away - you can see the pressure immediately jump on the leak test gauges. If the exhaust valve is the leak - common - it's either the valve guide/stem which is dirty (AvBlend in the oil helps with that, and of course staking) or the face needs lapping to clean up the valve and seat mating surfaces. See Mike Busch's video for lapping in place. Cheap and fast. If lapping doesn't fix it, the exhaust valve could be warped or broken which requires removal of the cylinder to replace. A borescope really helps with this. If you do NOT see a circular color pattern on the exhaust valve, you need to lap.

Back to the rings. If the air is getting past the rings, they might be dirty or broken. If they are just dirty, you can do a wash with solvent of the rings in the cylinder which dissolves the carbon around the rings, and of course requires an oil change afterwards. This can work very well at getting rid of carbon deposits. If the rings are broken the cylinder needs to come off. I know it's a pain but if you can borescope the cylinder through a spark plug hole, you can look for scratches and corrosion on the cylinder wall indicating damage requiring removal. It should have a nice cross-hatch. Shiny is actually not good. He knows this. He told me that he doesn't want to go to Heaven when he dies because none of this friends are there.

Anyways. First you need to diagnose, then you need to treat the problem. Hope this helps.

PS I've never figured out a use for MMO. Avblend, Camguard and Seafoam all have their place.

[Colonel]

Remember there are two scenarios:

1) keeping a good engine good
2) fixing a broken engine

for (1) Camguard is an excellent additives package that I use with straight "W" ashless dispersant oil
to create a super-oil that oil company executives thought no one would pay for. It reduces internal
corrosion and valve sticking when an engine sits too long. I wish I didn't know this.

for (2) you are looking for solvents to remove deposits, which you hope is your problem, and you hope
that nothing is broken requiring removal and replacement. You need to think about what solvents you
want to put in your oil, and what solvents you want to put in your gas. Obviously you don't want to
damage anything. AvBlend is the most expensive ether (a solvent - smell the can) that the FAA has
ever approved to add to your oil and works wonders at removing carbon deposits from inside an engine.
However it will not remove lead deposits. I have never found a solvent that will, and I've tried them all.
You have to mechanically remove lead deposits. I have had very good results with flex-hones.
Lycoming says to use reamers which is insane.

Note that there is no paper for this fuel solvent:
https://www.aircraftspruce.com/catalog/ ... key=166877

Obviously one way to remove deposits is to disassemble the engine, clean it all up, put it together
with new gaskets and a paint job. A varsol overhaul! If the engine is not badly worn or broken this
actually can be really helpful and reduces oil leaks. I think the kids these days call it a Craiglist
overhaul, if you just squirt some paint on it.

[Slick Goodlin]

My low level diagnosis is that I have one cylinder smoking when adding power (it has individual pipes so that one’s easy to spot) and the breather is breathing out pretty hard in flight (it’s on top, right behind the prop and sticks through a hole in the cowling).

One of the fun(?) things about the A40 is it’s a flathead with no way to oil the valve guides while it’s running so no way to get oil into the combustion chamber that way. I should really check compression no matter what, though.

As for the MMO, it’s mostly white spirit or some other solvent IIRC and has worked wonders in the past for me in freeing intermittently sticking valves. It has a janky snake oil name and seems sus that it works in gas and oil but was developed by a big company that made an awful lot of trusted stuff. Do you have a Marvel carb on any of your planes? Same guys.

[Colonel]

the breather is breathing out pretty hard

Yeah, your rings are probably not sealing. That's going to heat up your oil with blowby gases and contaminate
your oil pretty quickly, requiring more frequent oil changes.

Hopefully it's just carbon deposits around the piston rings/lands. I would do a ring wash which consists of
filling up the cylinder with solvent and gently forcing it by hand past the rings (to dissolve the deposits) into
the crankcase, after which you change the oil to get rid of the mixture of oil and solvent in the crankcase.

That's a very effective and well-known procedure for high time engines - search it.

This is Mike's version:
https://www.savvyaviation.com/wp-conten ... -flush.pdf

This is Ed's version
https://vansairforce.net/attachments/oi ... pdf.24816/

That's going to work a LOT faster at freeing up the rings, than putting a solvent like Avblend into the oil.

Note that modern car engines, with their low-tension rings - to reduce friction and increase gas mileage -
badly suffer from ring carbon deposits, requiring similar treatment to reduce the carbon on the rings. Also
with direct injection, the carbon deposits on the intake valves can be horrible. A different story for another
time.


Back to aircraft engines. They have three major problems:
1) valve sticking due to guide/stem deposits
2) valve / seat deposits (non circular heat pattern on exhaust valve)
3) deposits on rings (excessive oil consumption, poor compression)

If you can learn to clean 1/2/3 above, you can really improve the performance and longevity of your
aircraft engine.

Of course, it helps to operate it to reduce deposits, but that's another story. One of the biggest things
you can do to help your engine is to operate it frequently. You let it sit 6 months, deposits are going
to cause you problems. And internal corrosion will take it's toll.

Maybe I'm kidding myself, but after a flight I like to open up the oil cap/dipstick on the top of the engine
and let the convective heat carry out the airborne moisture in the engine that didn't get burned out the
crankcase breather. Get the moisture out of the engine!

Funny. With my data logging engine monitor, I can see that my oil temps are actually highest after I
touch down after a flight, and the air stops moving through the engine as I roll out on the runway and
taxi in. I like that high temp - it aggressively boils off moisture in the engine.

I hate seeing an emulsification - or even straight water - coming out my crankcase breather tube. I
feel like a bad parent.

[Slick Goodlin]

I’ll have to give those flushes a good think. Trouble with the flathead is there’s some combustion chamber under the cylinder bore so clearing afterwards is going to be tricky without pulling the head. If I’m going that far I may as well make up a replacement cylinder block assembly from spares and re-ring the thing while I’m in there. Might even be faster than dicking around with mixes and flushes and it will keep me from accidentally backfilling the csrb with solvents because, well, it’s me.

[Colonel]

Ok. Let me know how it turns out. It might be easiest to just run a strong concentration
of Avblend in your oil and maybe it will dissolve the carbon.

[David MacRay]

You guys are inspirational in oddly opposite ways.

I enjoy reading the colonel’s stuff with his sometimes nearly, “Change that axe handle then later the head.” approach.

On the other hand I really appreciate Slick running original stuff that most young guys would be afraid to fly.

[Slick Goodlin]

You guys are inspirational in oddly opposite ways.

Aw shucks, I’m just out here trying to make good use of the only truly finite resource: time.

On the other hand I really appreciate Slick running original stuff that most young guys would be afraid to fly.

You should have seen my daily driver a couple summers back…