Help / Brain Cells Request Continental O-300 Problem

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Pops

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I had my own farm fuel tank at the county airport for many years. Filled up with the auto fuel at home airport and with 100LL on trips , I was burning about 50/50 and the Cont-0-300 liked that. No lead problems.
 

speedracer

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An engine like that should use the UREM37BY plugs, and I think they're approved for the O-300. They have extended electrodes that are really resistant to fouling.

View attachment 116489

Champion REM37BY at the top. UREM37BY is Tempest's version, and a better plug. I used those Tempests in all our engines that were approved for them, with great success, especially in the O-235 in the Citabria 7ECA. Those engines are famous for running cool and fouling sparkplugs. No lost flights due to fouling with the UREM37BYs, though.

Besides that, the O-200 and O-300 have cylinder heads that have the bottom plugs really low in the head so that oil in the cylinder runs into the bottom plugs. Idling when cold will let plenty of oil past the rings in those engines, sometimes even when hot. It's ridiculous. Such leaky rings. It's the low manifold pressure that sucks the oil past the rings at idle.

And yes, a stuck valve is a possibility.
DT is right! When I ran one mag and one EI in my 360 Long EZ I would get an occasionally fouled mag plug. After going to the REM37BY's I never fouled a plug.... never. I finally installed a second EI and now run eight $6.00 car spark plugs instead of four.
 

proppastie

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how can I do all my startup, "idle", taxi, etc. at 1500 RPM without burning out my brake pads
lean till it wants to die....if you increase rpm it will die....should get about a 100 rpm drop at what ever setting you happen to be at.
 

proppastie

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had friends would scrub the alcohol out by putting the mogas in a tank with 10% water shake it up and decant the gas so you do not get the water/alcohol or drain the water alcohol/water first. somewhat a PTA.
 

TFF

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With helicopters we came up with lean shut downs. We have to cool the engines, because they are generally run hotter than airplanes. At idle without belt engaged, we lean to the rise and wait for our target temp. It’s under no load and we are in a lean of peak type situation only burning minimum fuel. There is an initial temp rise then it falls out as it cools. My friends well worn O-235 had to have the REM 37s or it would be a solid blob on the insulator. Low compression and lots of lead.
 

wsimpso1

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Do the plugs happen to be older Champions? They are known junk. Champion finally admitted same and redesigned the internal resistor. Check resistance value for all the plugs. I forget what value range is acceptable but I think anything over 5K ohms is no good.
you probably should just pull that engine and use the jugs to make 3 O-100 engines ;)
The issue was interesting too.:
  • Champion had a long history of building the aviation spark plugs in one factory. The resister was connected by simple contact. Not the best scheme, but they made it work and had a long history of high quality long lived spark plugs that way;
  • Champion moved production to a Mexican plant (IIRC), and apparently the institutional knowledge and/or trade secrets to make them work was lost/disregarded/etc. Plugs made at the new plant corrode a little at the connections, resistance goes high, airplanes run badly, no one at Champion caught it for years, and their reputation is trashed, giving Tempest a huge break in the market;
  • Champion has since redesigned aviation plugs with welded connections so that a modest amount of internal corrosion means nothing. Last I had heard, Champion never recalled plugs from the pipeline nor attempted to replace plugs from the bad era with the fixed product. Story is there are still lousy plugs finding their way into airplanes...
I buy and use Tempest plugs and oil filters, so does my FBO.

Billski
 

Victor Bravo

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I have seen shiny round lead balls in spark plugs, but I never saw the elongated tan colored mouse turds. Is this a different problem, or a different material, than the round balls? Is this the Marvel Oil burned into a turd, or is this some other issue?
 

karmarepair

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had friends would scrub the alcohol out by putting the mogas in a tank with 10% water shake it up and decant the gas so you do not get the water/alcohol or drain the water alcohol/water first. somewhat a PTA.
Put a little food coloring in the water so you can detect the interface. You'll end up with lower octane gasoline though, as ethanol boosts octane. There are YouTube videos on how to do this.
 

addicted2climbing

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I have seen shiny round lead balls in spark plugs, but I never saw the elongated tan colored mouse turds. Is this a different problem, or a different material, than the round balls? Is this the Marvel Oil burned into a turd, or is this some other issue?
VB there is a shop near KVNY that will clean the lead off the plugs for a cheap price. Mine came back looking brand new and same day turnaround if I dropped off in the morning
 

Victor Bravo

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I know about the shop, she is known far and wide as "Spark Plug Jeannie" (Jeannie Fenimore), she's a long time 99, and runs a very good shop. Her brother overhauls mags and vacuum pumps and what not, his shop is called "Aircraft Accessories".

I figured 12+ years is time to change the plugs, they might have been in there for 20 years before I got the airplane.
 

Victor Bravo

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OK, so here's the update, not particularly good news for me. One stuck exhaust valve in cylinder #4,, one mystery remaining in cylinder #6. Cylinders are not particularly attractive inside.

I ran the engine again in front of my hangar last night, and it sounded like it was running on 4 cylinders instead of 5 or 6. I got out and felt the exhaust pipes myself, and sure enough the front two left side exhausts were cold. All four others were hot. This test run was done with 12 brand new spark plugs.

After the short run, I removed the upper plugs from the 2 "cold" cylinders and there was no oil, soot, or goo on them.

Addicted2Climbing was kind enough to loan me a little probe camera to look inside the cylinders thru the upper plug holes..

The piston tops on Cyl's. #4 and #6 were largely covered in white chalky crusty crap. They had a little oil in them on the bottom. I was able to see the lower spark plugs, and they were clean too. No oily puddles in the plugs.

There was some crusty gunk in the sides of the combustion chambers (and above the TDC level of the pistons), different colors, definitely not "solid black soot" or burned oil.

the two front cylinders and pistons on the other side of the engine (#3 and #5) looked significantly better. Less oil in the bottom of the cylinder, less crusty white crap in the combustion chamber, less white crap on the pistons.

The borescope did not have a mirror on it, so I was unable to see the valves very well.

We put the probe camera up into the exhaust stubs and into the exhaust ports of the two cold cylinders. The inside of #6 exhaust stub and exhaust port were coated with white crap. I have no idea if this is burned engine oil, burned Marvel Mystery Oil, or burned avgas lead. But it did not appear to be normal exhaust residue or coating. The other "cold" cylinder exhaust stub #4 was a much more normal looking grayish brown.

But we noticed that the #4 cylinder had a "classic" stuck exhaust valve. Looking in through the port and the plug hole verified this, and I was able to swing the rocker arm back and forth 20 degrees by hand without the rocker touching the valve.

The #6 exhaust valve opens and closes normally, despite the white crap all over everything.

So the stuck valve is one issue that can be solved easily, either take off the cylinder and have it top overhauled, or try the old "rope trick" and see if it can be fixed in place.

The #6 cylinder with the excess white crap has SOME reasonable compression (thumb over the plug hole test), despite the white stuff, but this cylinder is not firing. So it may be an ignition-magneto problem. But, the amount of white junk in there tells me I really ought to find out what is causing it. This cylinder (#6) is also the one with the most engine oil sitting in the bottom, and the most oily residue. So it kinda ought to come out and be looked at, because the rings may be bad. even if it is making some compression.

Here are the photos of the exhaust stub and port on #4 and #6. The same white crap as I found inside the cylinders and on the pistons. Can anyone identify this stuff as engine oil, MMO, lead, or melted aluminum piston???

0-300-1.jpg
0-300-3.jpg
 

Aviacs

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So the stuck valve is one issue that can be solved easily, either take off the cylinder and have it top overhauled, or try the old "rope trick" and see if it can be fixed in place.
I want to relate one potential issue with the -300,-200 series engines once you go messing around with the pushrods:
It is possible for the cup in the tappet to "suck" onto the end of the rod and be pulled out of the tappet body.
Let's not go into how i learned that, the memory is still painful. Nonetheless, the evidence was reported in an article in Light Plane Maintenance about the rope trick, and my "Snagger Tool" a couple decades ago.

So don't pull a pushrod out unnecessarily, be aware if you do (twist, and pay attention), and don't keep running your engine without spring pressure between the parts and the pushrod. If you pull a pushrod and it won't go back in "naturally and easily" it may be necessary to atleast inspect with a borescope (these days) or pull the jug.

With the above caveat out of the way.....:)

It is possible to perform the rope trick on that type Continental cylinder without removing the manifolds. The valve can be "lassoed" through the bottom plug hole, pushed down into the cylinder, and the stem brought up through the top plug hole to inspect and clean.
At the same time, the guide can be inspected and cleaned in situ. I hate to say reamed. Reamers can be tricky devices. Mine is an adjustable, set undersize, that was proven in separate test holes. Mic the guide bore, read the shop manual specs for size and bell mouth, and observe them. It may be that you still have to pull the cylinder if the guide is out of tolerance. A too-sloppy guide will continue to "gunk up" because the heat transfer between stem-to-guide-to head gets evermore inefficient; combined with evermore loose oil finding its way down to burn in place.

If the guide and stem are cleaned up and mic within tolerance for size, bell-mouth in guide, and barrel shape on stem...
Then take the lassoed valve back down into the cylinder, and with some aluminum wire &/or clean wooden/bamboo spits through the now vacant top plug hole, guide and fish the valve stem back into the guide.

When you can grip the stem with your fingers, latch on tight, loosen the lasso, and carefully remove it. Feed in the rope, and bring the piston up to press the valve into the seat, so you can install the spring, cap and compress it to install the keepers.

Another finesse: once the rope is in the cylinder and raised so the valve cannot be lost, i have a small straight shank collet chuck that is sized to grip the end of the valve stem. With the stem firmly gripped in the collet, the valve can be pushed down a little, and twisted and tapped up against the seat, to bust up minor crud on the seat. A little MMO can be used. Or there may still be some light engine oil or MMO on the valve stem that trickled down from pre-lubing the guide before re-assembly. This is with the rope still in place, and just a little play by means of piston position, so the if the stem pulls out of the collet, the valve won't take the opportunity to dive down into the cylinder. Don't use a jaw chuck (drill chuck) - it won't hold the valve on the small area above the keeper land for tapping, & it will score that area.

On an engine with as much time in service as it sounds like yours has, the cylinder is probably going to have to come off due to out of tolerance parts. However, IF you decide to explore by means of the "Lycoming Rope Trick" it is possible to do the entire procedure including inspection (miking) the parts, and cleaning them, relatively rapidly with not other intrusion into the engine. I'm out of practice, but once could do it at a strange airport in maybe 20 minutes, not including cowl off/cowl on. I can still demonstrate it with a sectioned cylinder for audience view of what is going on in the bore (& a soup can for piston :) ) in about a 1/2 hr presentation.

It's also easy to use a platform made out of a scrap of flat steel, offset with holes to bolt over a couple/three pan/(valve cover) screw holes on the cylinder top, that a mag base (or clamp base) indicator can mount to, to do the wiggle test, if you want to do that for spec.

smt
 
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TFF

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If you can’t tap on the valve and have it reseat, it’s probably bent.

Running reams through guides, you are supposed to have one that backs debris out. There are three types. Forward, back, and straight. You want to stack the deck that stuff doesn’t go into the bore.

#6 is probably burning oil. Seeing some of the white stuff is normal, but not lots where it’s clogging. If you loose all the rings totally, it will usually blow the oil out the crankcase if the cylinder is firing. Borrow a spark plug lead tester and check them. You might have two unrelated problems in that cylinder.
 

Victor Bravo

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Thanks everyone so far for assisting with your experience and knowledge. Much obliged.

I am very interested in continuing to hear all educated/experienced opinions on what that white stuff is, and why it's in one of the cylinders/pistons/exhaust far more than the others. I understand airplane engines to some reasonable degree, but I do NOT have decades of experience rebuilding them like some people here probably have.

Second question... at what point do you just remove and repair just the bad or weak cylinder(s)... and at what point do you say "well, jeez, it's kinda worth it to just take them all off and top them... and at what point do you start thinking it's worth it to put six new replacement jugs on it???
 

Aviacs

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This is not fully educated - Do you use TCP?
Also, one form of lead oxide is white. Used to be the substance in lead paint, back when one major paint MFG advertised "guaranteed, 5 lbs in every pail"1633713264799.png
 
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proppastie

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Second question... at what point do you just remove and repair just the bad or weak cylinder(s)... and at what point do you say "well, jeez, it's kinda worth it to just take them all off and top them... and at what point do you start thinking it's worth it to put six new replacement jugs on it???
depends on how well you sleep at night..... as long as the engine will fulfill your mission it gets complicated.......all of your options have risks .... obviously if you can not taxi and take off without a fouled plug you will need to do something....probably starting with the least complicated fix and working up from there.
 

TFF

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My opinion is do it airline style. A little at a time. Do a jug every six month unless dire. Gives a little recovery time for pocketbook. Plenty of flying in between. Three years and all good. What is the time in the engine?
 

Pops

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In my experience 1200 hrs is about normal for the life of the average 0-200/0-300 cylinder before needing some work. Some more, some less.
 
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