Continental Cylinders

[geoffb]

So, dropped 2VF off for annual.  I've had the plane since Christmas and put ~80 hours on it by the time I dropped it off for annual end of June.  Seems to perform OK.  Oil tight.  Compressions were good, 70+, when I did my prebuy.  In the shop now, #3 is about zero, broken exhaust stud on #6.  I probably missed the stud during my cursory prebuy, no biggie, exh flange is fine.

Oh, yeah, TSIO360-MB1B, ~308 since factory reman installed as part of the 262 conversion in 1998.  Yes, I know, low utilization.  Last 10 years it pretty much sat.

So, I decide to just get a new cylinder for #3, send old out for freshening up and keep on the shelf.  Airpower ships new from stock, all good and now I just need to get the stud out of 6.  This I am learning is a real treat, even with access to a machine shop, tools and a little knowhow.

While waiting on other parts, like a new intake tube, intake tube modification coupling kits and on and on, I decide to investigate cyl #3.  I find the TCM overhaul manual, the generic maintenance manual and am fully armed with documentation, spring compressors, micrometers, hole gauges, home made check sheets and ziploc bags.  Following TCM guidance, I whack the top of the exh valve stem a couple times with a soft rubber mallet, sorry TCM I only had vegan mallets, no rawhide.  Then flip the cylinder over and fill it up with flammable solvent (not sure what the non-flammable solvent TCM recommends is) and enjoy watching it run out around the exh valve seat.  No noticeable leakage at head to cylinder joint or around the intake.  OK, all as expected.  With the help of my beautiful assistant, I remove the spring assy and drop the valve out.  Again, as expected from the heat signature, the valve and seat got into some sort of a tiff and decided to stop mating.  Grabbed a little lapping compound and my tool, popped the valve back in the guide and said, "hey should the valve be that loose in the guide?"  Couple quick twists of the lapping tool and pop the valve back out and it's apparent we won't be restoring that seal so easily.  Now, about that valve to guide fit......

Bust out the measuring tools.  Since I had trouble trying to stuff the 2-6 inch bore gauge in the valve guide, I had to resort to hole gauges and some trusty Starrett mics.  Not being quite as sharp as the kids that work for me, I'd say I'm no better than +/- 0.001, maybe 0.0015 with a T-gauge.  But the results are close enough for an air cooled tractor engine.  My trusty TCM Form X30596A (overhaul manual in 'Murican) tells me the spec for valve to guide clearance is 0.003-0.008 diametric if I read this silly chart correctly.  New valve guide ID should be 0.376-0.377.  So armed with specs and tools, I can see what we're dealing with.  Stem measures something reasonable, don't have the numbers handy, but would make tight end of the spec clearance with a spec guide.  Something like 0.375 OD, but with a tiny bit of taper as you move down the stem.  Maybe a thou, not much, but there.  Hmmmm.  Now the guide.  top of the guide, about 1/4 in from the top, 0 and 90 degrees to the rocker axis, let's call it 0.378.  Not exactly new spec, but close and as far as we can tell, round.  All good.  What's funny though, is it's about the same in the middle of the guide, but push the tool a little deeper and it will just about drop through, uh-oh.  So, what about the bottom of the guide you ask?  It's not super easy to measure that with a snappy T-gauge.  Ideally you'd come in from the bottom.  But you'd need cute little squirrel hands, squirrels crack my wife up, to get in the there with the tool and actually operate it.  This left me with going in from the top, trying to get enough tilt on the arm so I could get some expansion of the gauge, try to get some feel, lock it and drop it out the bottom.  Did this several times to see if I could get repeatable measurements, or at least repeatable enough to come to some conclusions.  And, looks like that valve guide bore tapers about 12 thou from top to bottom!  I assume that will keep you valve from seating well, allow it to heat locally and just get crappy.

So now I thought, maybe it would be prudent to check on #6 before I get too froggy with the drills, stud non-extractors and other medieval implements.

Same exercise minus the solvent fish tank test and the beautiful assistant who had better things to do.  Valve guide exhibits pretty significant taper of the bore.  Not as bad as #3, but at the bottom, guide to stem total clearance is probably 9-10 thou.  Compressions were good.  Valve heat signature looks ok.  But, with the guide looking like it's on the way out, and the broken stud, I've ordered another new cylinder assembly and this one can go out for valve job too and wait to be called into action when the next compression test fails.

Now the questions:

The E had a Lycoming of course with the fancy nitrided barrels and compressions never seemed to change, so we never had the occasion to look into them.  Sounds like if you're a Lycoming driver, you don't know what a cylinder is.  You're just acquainted with camshafts.  Oh, none of that was a question.

Are Continental cylinders really as bad as advertised?  This engine is pretty low time and it will now have had 3 replaced, the first at <150 hours.  It's always run cool in the time I've had it, never seen a 400 degree CHT and only cracked 380 a couple of times for < 1 minute.  The cylinders bores are in spec.  Interesting that they seem to wear the most right below the head to barrel junction.  

Is rapid valve guide wear like this common?

Are Superior guides any better?

If I have a good shop replace the guides, cut the seats concentric to the guides with good tools and verify valve seating, can I expect them to last longer?  

Other than a really diligent valve job, anything else to be done to make them last?

 

[N201MKTurbo]

I'm in the process of referbing a set of C-145 (O-300) cylinders. They have 1000 hours since overhaul. The valves and guides are like new after I cleaned all the crud off of them. So, Continental didn't always make crappy cylinders.

BTW,

I was just going to clean them and paint them. I took them off to replace all the seals. While I had them off, my hangar neighbor says You might as well bead blast them since you have them off. So I had to take them all apart to bead blast them and well, you can't put ugly valves back in, so I cleaned all the valve parts. Now I'm looking at those ugly pistons... Might as well do those too.

Now the engine only has the P leads and four motor mount bolts holding it on, I might as well put it on the engine stand to paint it.

It's like a disease....

[geoffb]

Mine are pretty clean and paint still looks nice.  Since they don't have many hours on them....

[philiplane]

yes, Continental guides are really that bad. And the rotocoils stop rotating the valves around 600-800 hours. And the bores rust easily. Add that all up, and that's why the cylinders are worn out at half life, where Lycomings will go 2000-2500 hours before an exhaust valve finally gives up due to guide wear. 

Part of the problem is that Continental guides don't get cooled as well as Lycomings. Remember how Continental fans rave about the cam being on the bottom, so it's always oiled? Well, the downside of that, is that the pushrods are also on the bottom, so the oil that comes through them, doesn't splash upward onto the valve springs and guides. You need anti-gravity oil to fix that...oh, wait, then the oil pump pick up would starve...never mind.

Edited August 4, 2021 by philiplane

[smwash02]

@philiplane I didn't realize this was such a common thing. Last year I replaced two with bad exhaust valves. Both had shot rotocoils. Had a 3rd cylinder with bad patterns starting, surprise bad rotocoil. ~500-600 STOH at the time.

Sounds like I should stock up on them before this year's annual and do the rest.

[A64Pilot]

Some of it has it do with Sodium filled exhaust valves. As Wright used them in their 1925 J5 whirlwind they aren’t exactly new technology. I’ve wondered without any research why all exhaust valves aren’t Sodium filled?

Edited August 4, 2021 by A64Pilot

[KSMooniac]

The really particular owners in the Beech world send new engines (or cylinders) directly to an expert (like Powermasters in Tulsa) to have all of the valves completely reworked before putting them into service. After that, they typically make a full TBO run without coming off.

Sent from my LM-V405 using Tapatalk

[aviatoreb]

Are continental cylinders still crummy even new ones even still now?

[philiplane]

23 minutes ago, aviatoreb said:

Are continental cylinders still crummy even new ones even still now?

Yes, but their nickel bore versions are better. I have a set on one IO-550N and they're at 1200 since new, with compressions like a Lycoming (all upper 70's).

Of course, they are hard to get. 

[aviatoreb]

15 minutes ago, philiplane said:

Yes, but their nickel bore versions are better. I have a set on one IO-550N and they're at 1200 since new, with compressions like a Lycoming (all upper 70's).

Of course, they are hard to get. 

I had my continental  steel cylinder valves guides reworked snd valves lapped by victor before I ever put them on.

[carusoam]

Take a moment to congratulate Geoff on his well written post!

That is worth today’s Creative Writing award!

Thus proving even on a bad day… it isn’t all doom and gloom… 

Like a well rounded athlete… he has two strong skills…. technical skill and the ability to write.

Lets see if @M20Doc is around for comment…

+1 for some Continental valve systems were not very good leaving the factory many years ago…

Go MS!

Best regards,

-a-

[geoffb]

On 8/4/2021 at 5:21 PM, aviatoreb said:

I had my continental  steel cylinder valves guides reworked snd valves lapped by victor before I ever put them on.

Eric,

 

What did they do with the guides?  Just verify the bore diameters?  With all the talk of poor adherence to specs at TCM, I can see taking the effort to verify valve to seat concentricity before even putting them on.   

I talked to J&J Airparts about a valve job on the two I've got off.  We've only got two guides to choose from, Superior and TCM.  Didn't get the impression from J&J that there was any real difference.  They prefer factory but have many customers who insist on Superior.  I don't know, but if forced to guess I'd assume both are a very traditional Al-Si bronze guide.  Maybe it is all just a matter of poor manufacturing quality control leading to the geometry of the rocker to valve guide to seat being all over the place.

I hope that the two new ones fare better than the originals.  At the rate she's going, all 6 will have been replaced here pretty quick.  Not going to pull the other three just to inspect.  I'm curious, but also have places to be and want the air car back.

[aviatoreb]

3 hours ago, geoffb said:

Eric,

 

What did they do with the guides?  Just verify the bore diameters?  With all the talk of poor adherence to specs at TCM, I can see taking the effort to verify valve to seat concentricity before even putting them on.   

I talked to J&J Airparts about a valve job on the two I've got off.  We've only got two guides to choose from, Superior and TCM.  Didn't get the impression from J&J that there was any real difference.  They prefer factory but have many customers who insist on Superior.  I don't know, but if forced to guess I'd assume both are a very traditional Al-Si bronze guide.  Maybe it is all just a matter of poor manufacturing quality control leading to the geometry of the rocker to valve guide to seat being all over the place.

I hope that the two new ones fare better than the originals.  At the rate she's going, all 6 will have been replaced here pretty quick.  Not going to pull the other three just to inspect.  I'm curious, but also have places to be and want the air car back.

I believe it is just what you said - verify - which means reject if not to spec so that I receive guides to spec.  And the valves are actually reshaped (lapped).  And also flow balancing.

[kmyfm20s]

I bought 6 new Continental NiC3 coated cylinder and had them dropped shipped straight to Lycon. Lycon ported, polished, flow balanced the cylinders and refaced all the valves and seats. Im hoping this will overcome some of the problems people have been experiencing. So far only 100 hours on them.

[N201MKTurbo]

27 minutes ago, aviatoreb said:

I believe it is just what you said - verify - which means reject if not to spec so that I receive guides to spec.  And the valves are actually reshaped (lapped).  And also flow balancing.

FWIW, lapping valves doesn't change the valve or seat shape. That would be grinding. Lapping just generates the final seal on the sealing surface by lapping the valve to the seat. I'm doing that right now (well last night and an a a couple of hours from now) on my Cessna cylinders.

[aviatoreb]

1 hour ago, N201MKTurbo said:

FWIW, lapping valves doesn't change the valve or seat shape. That would be grinding. Lapping just generates the final seal on the sealing surface by lapping the valve to the seat. I'm doing that right now (well last night and an a a couple of hours from now) on my Cessna cylinders.

Ok - I don’t know what I’m saying or what exactly they did / but they did some kind of pre conditioning and I’m happy with it.

[N201MKTurbo]

3 hours ago, aviatoreb said:

Ok - I don’t know what I’m saying or what exactly they did / but they did some kind of pre conditioning and I’m happy with it.

It’s cool, I read about it quite a bit, but it wasn’t until a few years ago when I had access to a 1951 army Jeep in bad condition that I brought back to life. I learned all about how to cut valves and valve seats. It is an art. Now I’m doing the same thing to my Cessna 172 (it’s like the Jeep). I just want to make it pretty and reliable, then I’ll give it back to the aviation community.

[jlunseth]

I don’t know what you guys are talking about. I had an emergency descent and landing that caused us to IRAN the engine at about 1200, and probably it had been run pretty hard before that. Since then I have several hundred hours at 71% HP cruise, LOP. My compressions are slowly going up at annual, except for my #2 that tends to run hot because of some baffling issues. That one is stable, not increasing. Compressions are in the 70s. And the engine is now nearly 300 over TBO with 900 hours on the cylinders since the IRAN. Knock on wood. OWT.

[N201MKTurbo]

11 minutes ago, jlunseth said:

I don’t know what you guys are talking about. I had an emergency descent and landing that caused us to IRAN the engine at about 1200, and probably it had been run pretty hard before that. Since then I have several hundred hours at 71% HP cruise, LOP. My compressions are slowly going up at annual, except for my #2 that tends to run hot because of some baffling issues. That one is stable, not increasing. Compressions are in the 70s. And the engine is now nearly 300 over TBO with 900 hours on the cylinders since the IRAN. Knock on wood. OWT.

All these engines benefit from frequent use. Keep up the good work!

[A64Pilot]

What was replaced during the IRAN? If it was bearings for example, you likely may have added a lot life to the motor.

People seem to often misunderstand what TBO means, it’s not an hour level at which time the engine is expected to wear out or to fail. It’s an hour level that an engine can be easily and often relatively inexpensively overhauled, because most often the expensive hard parts are still serviceable. Talking  to Pratt & Whitney Canada folks and GE, they seem to look at TBO as sort of a guaranteed time, not an hour level that a engine is worn out.

But anyway if you are capable of doing the work yourself and or rated to do so or can work under the supervision of a rated mechanic, following TBO can save you a lot of money in the long run, if you wait until there is metal in the oil then often a lot of expensive parts may need fo be replaced.

An overhaul doesn’t mean that you replace a bunch of expensive parts, you disassemble. clean and inspect and replace parts that are worn beyond limits, either new limits or serviceable limits whichever you choose. My IO-540 W1A5D for example once disassembled, everything measured out fine, it was a relatively inexpensive overhaul, as I didn’t have to pay any labor, but I reset the TBO clock, which added value to the aircraft.

This AC may help some https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_43-11_CHG-1.pdf

Edited August 7, 2021 by A64Pilot

[geoffb]

TCM’s mandatory replacement parts list for the TSIO is pretty long....

[geoffb]

On 8/6/2021 at 9:02 PM, jlunseth said:

I don’t know what you guys are talking about. I had an emergency descent and landing that caused us to IRAN the engine at about 1200, and probably it had been run pretty hard before that. Since then I have several hundred hours at 71% HP cruise, LOP. My compressions are slowly going up at annual, except for my #2 that tends to run hot because of some baffling issues. That one is stable, not increasing. Compressions are in the 70s. And the engine is now nearly 300 over TBO with 900 hours on the cylinders since the IRAN. Knock on wood. OWT.

I hope to get where you are.  There is interwebs chatter about particularly bad cylinders late ‘90s to early 2000s.  Mine are late ‘97 vintage.  I’m hoping that the new ones are better.  I’ll probably pop the valves out of the new ones and blue the seats before I hand them to the shop.

[geoffb]

How does one inspect a rotocoil?  

[PT20J]

6 hours ago, geoffb said:

How does one inspect a rotocoil?  

 

[geoffb]

Thank you, I guess it's pretty obvious now that you see it.