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Sticky valve on a Thunderbolt IO390

As an opposing data point my 390 thunderbolt oil does not get black and goes aboit 20 hours plus on a quart maybe more. My hours are a lot of cruise and joyride. I don’t do a lot of aggressive flying or much pattern work. Perhaps the use of the engine is a key factor.
 
My worst one (#3) had a build-up of very hard material on the valve stem. The guide had only a small amount of softer, black "tar" inside - very different looking from what was on the stem. Makes me wonder if this is a problem with the stems, the guides, or a combination of both.

The stems get hotter than the guides. The heat from the exhaust valves is transferred from the stem to the guide and then out through the head fins. Typically the stems don't collect a lot of coke, as it tends to scrape off as it passes the edge of the guide 20 times per second, though it will often form below the motion contact area of the stem. It is possible that you guides may be a bit on the loose side.
 
Sticky valve at 160 hrs

Hei Guys

Just one more data point. With the great help of Dan 57 we just reamed the exhaust valve guide for cylinder nr2. After only 160 hours we experienced some morning sickness, clearly visible in the data with a dropping EGT2 for half a minute or so…

Cheers
Fabian
 

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Intake Valves

Anyone having issues with intake valves. I have several that are concerning to me.
150 hrs. on a 390 Thunderbolt non-exp engine. Always LOP operations at 65% power.

Exhaust valves look great.
 

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Another update with a problematic IO390 (Thunderbolt). Brief recap, I experienced my first sticking valve around 270 hours, combination of inflight symptoms and morning sickness. Reamed the culprit (cyl #2). Second incidence was around 395 hours (delta 125 - bad trend), again on cyl #2. I reamed all exhaust guides including performing wobble measurements. Found coking on 2 cylinders, but only #2 was below wobble specs (before reaming - within spec after). As preventative treatment (gotta try something), I added Camguard to my oil, installed the tunnel cooling flap to increase operating temps, and began cruising at higher power settings.

This month was my annual, about 50 hours since last valve treatment. I decided to proactively ream the guide on cyl #2 even though I had no symptoms, hoping that I might get to an annual preventative treatment rather than reacting to a sticking valve. I was disappointed to find the same amount of coking on cyl#2 valve guide after only 50 hours - well, not quite the same amount since symptoms hadn’t started yet.

My next reaming will occur at the earliest of 1) next annual at 120-150 more hours or 2) reoccurrence of sticking valve symptoms. Total time on the engine is now about 450 hours.

Engine update: I now have 505 hours - 55 since last reaming. No symptoms, but I had cyl #2 rocker cover off (chasing a minor oil leak) and decided to check the exhaust valve. I removed the rocker, spring, cap, etc. and was pleasantly surprised the exhaust valve moved smoothly. Running the reamer in the guide produced absolutely no coking - a clean guide.

So what changed? I had started using Camguard, but after 2 oil change intervals, discontinued it after Lycoming indicated they didn’t think it mattered. I have continued running at higher power settings (no aggressive LOP operation) and have the tunnel cooling flap installed, but this has all been true for over 200 hours. So … I don’t know, but I’ll take it.
 
I would add the breakthrough for me was an extendible magnet (a collapsible pencil sized extender) with a diameter less than 1/2 inch. Insert through the valve guide, raise the valve stem to the magnet, lift the valve to approximately aligned and coax it into the guide by withdrawing the magnet.

OOOH! That is a really good idea!!

Thanks
 
This seems like a really good idea! I may do this on my angle-valve 360, since I also do not want to tear my baffles apart. My baffles on the back of #3 have a narrow chute to bypass the zero-height cooling fins, but I did not do the same thing on the front of #2 - wish I had. But this series of tiny holes may just help a lot.

Dennis,

By-passing air on the front of #2 around that casting flash and zero fin depth is the best, but not the only way to effect some improvement. I made the chute on my 7, but my 10 friend was already flying and did not want to tear into the baffles. A sticker for data, he drilled 5 holes aligned with the fin channels in the cross angle that holds the baffles. I think they were #30 drill size. He found a 10-15 deg reduction in the CHT as a result. The holes were located in the root radius and opened into the gap below. At about 30 deg off vertical. He now has over 600 hrs and no adverse structural effects from the holes.

You would be surprised how much air will go through a #30 hole at 12-15" of air pressure. When I was doing pressure testing of my plenum and swapping hoses, The flow through a 3mm tube was enough to cool my face in the cabin. And that was 4 ft of tubing with associated vicious losses.
 
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Mikes logic here is that lead is found with carbon in the build up, therefore it must be coming from the fuel. Unfounded supposition IMHO. Your oil has disspersnts that hold debris in suspension. Much of that debris is lead particles, along with carbon. Therefore the oili is filled with lead particles and is then pumped into the rocker box and coats the valve stems and guides. When oil gets too hot, it oxidizes and becomes a hard substance called Coke, with the lead particles that were held in suspension now encapsulated in the Coke. This is an equally reasonable theory for the presence of lead in the guide build up, but Mike chooses to ignore it and go with a different theory. That's his perogotive, but doesn't mean everyone should accept it at face value. If mike were correct that it is lead that is the problem, how does he explain the presence of carbon in the build up?

Unfortunately no one really knows why it is such a problem with Lyc compared to all other engines. At least my theory has a variable that is unique to Lyc engines. Not sure we will ever know the true reason. Clearly lyc thinks it is too much heat, which is why they now use exotic filled valves to keep the valve stem heat down.

Larry

I am in complete agreement with Larry here. I once in a while (not often) find myself disagreeing with Mike Busch. In addition to the arguments Larry makes, here are two pieces of evidence to support that excessive valve deposits are related to high temps, not low temps, and probably not related to the lead content in the fuel.

1) years and years of experience with water-cooled car engines running leaded fuels. The 94 (R+M)/2 octane Premium motor fuel of the early 1970's had about the same amount of lead as today's 100LL. Note that the spec for 100LL allows for up to twice as much lead as those old premium fuels, but today's 100LL is made with better base fuel and only uses about the same amount of lead as the old Premium.
Did ANYONE ever have sticky valve problems on car engines? Note that cylinder heads on liquid cooled car engines run at MUCH lower temperatures. Water temp of 185F. Head temp? Maybe 200F? If Mike Busch's hypothesis was correct, car engines would have all kinds of trouble with sticky valves.

2) My angle-valve IO-360 runs at cruise with CHTs of 260F to 290F. For 750 hrs now with zero troubles. Knock on wood. Point is, if low CHT was the problem, I would be having serious problems. I think if I told Mike Busch that my engine lives happily with such low CHTs he would spill his coffee.

It seems clear to me that higher temps aggravate oil coking on hot components. Higher CHT would seem to be the problem.

BUT....

Most parallel-valve engines run with CHTs in the 360-390F range a lot of the time, and they don't seem to have the problem either, at least not chronically.

It must be something about the combination of the poor top-end oiling, the fit and design of the lifters, and the high temps at cylinder #2, that in combination are making this an issue.

Step 1 - improve cooling on cylinder #2. If not by creating a baffle bypass for the zero-height cooling fins, then maybe the bleed holes that BillL described.

Step 2 - adjust your oil pressure to be higher. I have mine so that at full operating temp (oil 190F) I have 75 psi oil pressure. This should at least help with the poor design (or lack of design) of the top-end oiling.
 
I am in complete agreement with Larry here. I once in a while (not often) find myself disagreeing with Mike Busch. In addition to the arguments Larry makes, here are two pieces of evidence to support that excessive valve deposits are related to high temps, not low temps, and probably not related to the lead content in the fuel.

1) years and years of experience with water-cooled car engines running leaded fuels. The 94 (R+M)/2 octane Premium motor fuel of the early 1970's had about the same amount of lead as today's 100LL. Note that the spec for 100LL allows for up to twice as much lead as those old premium fuels, but today's 100LL is made with better base fuel and only uses about the same amount of lead as the old Premium.
Did ANYONE ever have sticky valve problems on car engines? Note that cylinder heads on liquid cooled car engines run at MUCH lower temperatures. Water temp of 185F. Head temp? Maybe 200F? If Mike Busch's hypothesis was correct, car engines would have all kinds of trouble with sticky valves.

2) My angle-valve IO-360 runs at cruise with CHTs of 260F to 290F. For 750 hrs now with zero troubles. Knock on wood. Point is, if low CHT was the problem, I would be having serious problems. I think if I told Mike Busch that my engine lives happily with such low CHTs he would spill his coffee.

It seems clear to me that higher temps aggravate oil coking on hot components. Higher CHT would seem to be the problem.

BUT....

Most parallel-valve engines run with CHTs in the 360-390F range a lot of the time, and they don't seem to have the problem either, at least not chronically.

It must be something about the combination of the poor top-end oiling, the fit and design of the lifters, and the high temps at cylinder #2, that in combination are making this an issue.

Step 1 - improve cooling on cylinder #2. If not by creating a baffle bypass for the zero-height cooling fins, then maybe the bleed holes that BillL described.

Step 2 - adjust your oil pressure to be higher. I have mine so that at full operating temp (oil 190F) I have 75 psi oil pressure. This should at least help with the poor design (or lack of design) of the top-end oiling.

I am convinced this problem stems from poor oil flow flow to the rockers. Most every lifter made since the flat head engines have bypass channels to pass oil up the pushrod. For some unexplained reason, Lyc chose not to do this. The only flow that gets to the pushrod is that which bleeds past the clerance between the two parts of the plunger assy. These are tight clearance and hand lapped at the factory. If yours are a bit tight, you get less oil bleed, if loose, you get more. Any engine designer knows that you use oil to cool the valves. Good flow to the rocker box = good cooling and poor flow = limited cooling. I believe that tolerances in the plunger assy's explain why some have issues and some don't. Also, those running multi vis oil will likely have fewer issues, as the bleed rate is heavily influenced by the oil's viscosity, as the clearance in the plunger is around around a thou.

Larry
 
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Just to poke a hole into Larry's theory, my angle-valve 360 only ever gets a sticky exh valve on cyl 4, which is always the coldest one on my engine by 15 degF (typically around 330F in cruise in winter).
 
MMO Test still ongoing…

I started this thread and was interested in learning more and sharing what works. In Post #14 of this thread, I promised to report back. I was not heating or cooling the cylinder but doing the old school MMO fuel treatment.

To recap - My first sticky valve indication occurred 6/29/2022 T:157,H:181. It was very obvious in Savvy graphical display. It locked up solid about 10 hours later (in flight - also very obvious). I performed SI1425a on just the impacted cylinder.

Since that point, I continued to run W100Plus in the warm months and Phillips 20/50 with Camguard in the winter months. Operationally, I have not changed any pre-sticky valve event practices. I run LOP most of the time.

The one change I made was to add MMO (4oz / 10Gal) and thus far (T:288, H:330), there has been no data indicating any stickyness.

Adding MMO at fillups is a bother (although the scent is delightful). No data of impact is not proof that this works. I’ll keep collecting data until there is something to report.
 
Oil Color ??

I started this thread and was interested in learning more and sharing what works. In Post #14 of this thread, I promised to report back. I was not heating or cooling the cylinder but doing the old school MMO fuel treatment.

To recap - My first sticky valve indication occurred 6/29/2022 T:157,H:181. It was very obvious in Savvy graphical display. It locked up solid about 10 hours later (in flight - also very obvious). I performed SI1425a on just the impacted cylinder.

Since that point, I continued to run W100Plus in the warm months and Phillips 20/50 with Camguard in the winter months. Operationally, I have not changed any pre-sticky valve event practices. I run LOP most of the time.

The one change I made was to add MMO (4oz / 10Gal) and thus far (T:288, H:330), there has been no data indicating any stickyness.

Adding MMO at fillups is a bother (although the scent is delightful). No data of impact is not proof that this works. I’ll keep collecting data until there is something to report.

Previous thread mentioned that his coldest cyl was the one that would stick. That seems to be an outlier as every or almost every sticky valve on a 390 is the hottest cylinder (#2). I completely removed the air dam in front of 2 and that has helped lower the CHT ~ 10 F of cyl #2.

Since the OP runs Phillips 20-50 with Camguard winter and W100 plus summer do you or anyone else notice a color difference at the same number of hours? I always run 100LL but with W100 plus at 30 hours the oil looked very dark. I was taught to change the oil when it gets fairly dark and have done so since new. At ~400 hrs I switched to Phillips 20-50 (Victory) and at 30 hrs the oil was noticeable not near as dark. (Amber) I ran that for 60 hrs (2 oil changes) and next oil change went to Aeroshell 15-50 and ran for 60 hrs (2 oil changes) Same result. Nice amber color. Oil analysis has gone from ~3,000 ppm lead to ~ 2,400 ppm lead. Not sure that is significant, but something seems to have definitely changed using a multi-weight. I believe Larry brought up the multi-weight theory and maybe it has more to do with oil viscosities than CHT temps?? I'd love to test the theory and go back to W100 plus but why push it?
 
Just to poke a hole into Larry's theory, my angle-valve 360 only ever gets a sticky exh valve on cyl 4, which is always the coldest one on my engine by 15 degF (typically around 330F in cruise in winter).

...No sticky valve, but what's the deal with #4 on the IO-360-A1xx? I've had two now that run 15°F - 30°F colder than their cohorts...
 
Forgot to mention…

I did make one other change - shortened the oil change cycle to 20 to 25 hours or on condition. I only recollect one time that I changed oil based on my perception of darker than ordinary. So yeah, I made two changes - MMO and oil change interval. Not very well controlled experiment.

I change out filters every other oil change.

I will track and report back.
 
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Just to poke a hole into Larry's theory, my angle-valve 360 only ever gets a sticky exh valve on cyl 4, which is always the coldest one on my engine by 15 degF (typically around 330F in cruise in winter).

Unfortunately the cyl head is a pretty large chunk of metal and the sensor is kind of in the middle of it. We really don't know what temps our individual exh valve stem and guide are seeing during operation. I suspect that there are several variables that can influence differences in temps at the guide vs the head at sensor. While I have no real data, I strongly believe that CHT is not a good representative indicator for what those guide temps are. For example, if one cyl had twice as much oil flow to the rocker box as another, this would likely reduce the localized temps of the areas receiving that oil (splash oil has a known temp reducing effect). However, the overall head temp would likely be unchanged.
 
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Add another #2 sticking exhaust valve on an IO-390. There are several sizes listed in the SI, what size reamer should be used?
 
Hi ShortSnorter,

Specs for the reamer can be found on post #14.

How many hours, oil type, oil condition and any other details you care to share?

Thanks
 
Hi ShortSnorter,

Specs for the reamer can be found on post #14.

How many hours, oil type, oil condition and any other details you care to share?

Thanks
290 hours
oil changed every 50 or 4 months
XC 20w-50

On climb out #2 dropped out completely which produced heavy shaking/vibration. After ~3-4 seconds it resolved and engine ran fine. At altitude (25/25 Peak EGT) I tested the mags which performed flawlessly as they had done during the run up. Looking back I had a similar instance a few months back during a run up that I wrote off to a fouled plug because it "cleared" after I leaned heavily with power that was probably the same stuck valve.
 
Oil Color ??



Previous thread mentioned that his coldest cyl was the one that would stick. That seems to be an outlier as every or almost every sticky valve on a 390 is the hottest cylinder (#2). I completely removed the air dam in front of 2 and that has helped lower the CHT ~ 10 F of cyl #2.

Since the OP runs Phillips 20-50 with Camguard winter and W100 plus summer do you or anyone else notice a color difference at the same number of hours? I always run 100LL but with W100 plus at 30 hours the oil looked very dark. I was taught to change the oil when it gets fairly dark and have done so since new. At ~400 hrs I switched to Phillips 20-50 (Victory) and at 30 hrs the oil was noticeable not near as dark. (Amber) I ran that for 60 hrs (2 oil changes) and next oil change went to Aeroshell 15-50 and ran for 60 hrs (2 oil changes) Same result. Nice amber color. Oil analysis has gone from ~3,000 ppm lead to ~ 2,400 ppm lead. Not sure that is significant, but something seems to have definitely changed using a multi-weight. I believe Larry brought up the multi-weight theory and maybe it has more to do with oil viscosities than CHT temps?? I'd love to test the theory and go back to W100 plus but why push it?
Busch says that the single weight oils have more capacity to keep contaminates in suspension. Viscosity improvers in multi-weight oils take the place of more detergents. Makes sense that W100 would get dark sooner and absorb more lead.
 
Anecdotal, but none the less....

Now about 1200 hours. No sign of sticking. It's past the 1000 hour point for a wobble test as specified in SI 1485A, applicable to almost every 390 ever built, but I have not done it yet. Need to get busy and build a dial indicator fixture.

15W-50 Aeroshell semi-synthetic. Cruise at peak EGT, or very lean if loafing. 50 hour changes, no additives. Typical cruise CHT between 325 and 360F. Never been over 380.

I don't know what Lycoming wants to see on a Thunderbolt cylinder, but these were uniform at a fuzz over 0.001 clearance on the intake stems, and 0.004 on the exhausts. That's near minimums.

Does Lycoming list clearances on a build sheet for the customer?
 
Anecdotal, but none the less....

Now about 1200 hours. No sign of sticking. It's past the 1000 hour point for a wobble test as specified in SI 1485A, applicable to almost every 390 ever built, but I have not done it yet. Need to get busy and build a dial indicator fixture.

15W-50 Aeroshell semi-synthetic. Cruise at peak EGT, or very lean if loafing. 50 hour changes, no additives. Typical cruise CHT between 325 and 360F. Never been over 380.

I don't know what Lycoming wants to see on a Thunderbolt cylinder, but these were uniform at a fuzz over 0.001 clearance on the intake stems, and 0.004 on the exhausts. That's near minimums.
Dan - How old is your engine (calendar)? Probably speculation here, but it seems quite common on late model 390's as installed on the -14. I wonder if something has changed in the parts/mfg process. At ~150 hours my crankshaft seal began leaking. When I called Lycoming they explained its common on new engines since they were forced to change adhesives to a more environmentally friendly version. They did advise (with a wink) that if I was unable to source the environmentally "approved" adhesive was not available that I could use Pliobond.
 
Dan - How old is your engine (calendar)? Probably speculation here, but it seems quite common on late model 390's as installed on the -14. I wonder if something has changed in the parts/mfg process. At ~150 hours my crankshaft seal began leaking. When I called Lycoming they explained its common on new engines since they were forced to change adhesives to a more environmentally friendly version. They did advise (with a wink) that if I was unable to source the environmentally "approved" adhesive was not available that I could use Pliobond.
I had LyCon buid my custom (I)O-360 4 years ago, it incuded P-Mags, lightened flywheel, crankcase "O" ring seal, venturi ground valves and seats; 9:1 pistons; counterweighted crankshaft; and.....wait for it......a "performance" camshaft. I thought this was an after market cam, like the continentals with the "Ram" cams, but no, it was a used cam, reground to give the valves a bit higher lift for better breathing. If I knew it was a reground, I would have never agreed to it. So, now, 4 years and 527 hours later, (it has not been a "sitter") I had a sticking exhaust valve on #4. I found black substance in the guide (bromide / carbon) , along with shiny metal. This "performance" cam engine, treated with oil changes every 35 hours and cam guard, was spalling! Seems it wore through the hardened material and began to spall on the lifters. So, off to the engine shop, about $15K for an "IRAN" and about 4+ months, awaiting for parts (universal shortage); and better than new. I also found miro-metal embedded in the piston skirts and main / rod bearings. Used cams (reground) cannot be re-hardened, and the case hardening varies a bit, so my advice is spend the money on a new cam, and the new style "Diamond Hard Lifters". PS LyCon only warranties their experimental engines for 12 months!
Regards,
Gary
DAR-T DAR-F
 
Dan - How old is your engine (calendar)? Probably speculation here, but it seems quite common on late model 390's as installed on the -14. I wonder if something has changed in the parts/mfg process.
Early Lycoming 390 kit assembled at Barrett, production late 2006~early 2007. New cylinders, blueprinted for lack of a better term.
 
Need to get busy and build a dial indicator fixture
Not sure spending your time on this is being worth it. First point is that the kit being sold by ACS fits the bill pretty good. Second is that given a few practice runs, one doesn't need to measure anything at all, but once the springs are removed will feel the fluidity of the valve stem movement, and then check the lateral play by finger feel... that will be enough to ensure no sticky valve.

As a side note, I've had several valves sticking over the years, on different airplanes with different engines, and one of the reasons I stopped using the Phillips 66 XC oil...
 

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Still have not tested yet…

I found play in my pMag and am awaiting a discussion on what “excessive” means from EMagair before testing.

I can confirm that the VGR-LC4 reamer is correct - it is .5” with a .4995 pilot section. I chose this reamer specifically for the pilot concept.

Seems to me we have a group of RV14s whose CHT seem to be in the acceptable range with this problem. I would have more info on other cylinders if I had reamed all and vow to next time. That seems like a good idea.

Maybe there is nothing that can be done to avoid this issue. Depending on who you listen to, this happens because CHT is too hot or too cold.

We could
  • Cool with duct or blast tube
  • Cool by changing lifter
  • Change oil type
  • MMO?
  • Anything else?

Kiwipete is cooling by adding ducting
Keithb is increasing CHT

I am changing oil from Philips X/C 20/50 to Aeroshell W100 plus.
I will also take on playing roulette with the lifter at IR172’s suggestion - I can swap with another cylinder the next go round and see if the problem follows.

I have a crusty old timer mechanic who swears that adding MMO to the fuel is how he cures morning sickness. Anybody have experience with this?

I’ll report back on my results.
I know MMO is very controversial... But, it works for me. When I get the slightest hesitation under full power, I will add 6 oz to 16 gallons and run it for a few tank fulls.
 
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