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Thermal Barrier Coatings

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Flow

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Joined
Apr 27, 2016
Messages
86
Location
Auckland
Hi folks.


We are running a Limbach L2400 and looking improve top end reliability by reducing valve/seat and cylinder head temperatures.


We are exploring many angles but this has been suggested and the side effects are some what unknown.


Coatings:
Piston Top
Exhaust Port
Valve Heads
Combustion Chamber


The benefits are understood but what are the potential pitfalls:
Raised Exhaust Gas Temps causing more back pressure and potentially causing a fire in the hot air pick ups for the cabin and carb heat??
Cooking our Nikasil bores??
Welding our top ring to the piston??


Do we need to coat down to the top ring?
If we do this is there enough clearance there to prevent contact with bore at max piston rock?
How much should we expect the EGT to go up?
How much should we expect the head temps to go down? (Currently 400F)
Should we coat before or after machining the cylinder lands on the heads flat? ie. Do we want to be conducting heat between the cylinder and the heads?


If any one has experience with this any guidance would be kindly appreciated.
 

mcrae0104

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Oct 27, 2009
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3,647
Why jump to fancy coatings? You might do better to pick the low hanging fruit of cooling air inlet/exit design, baffle design, etc.
 

Wayne

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Welcome to HBA, Flow! You will get a ton of advice here from some very talented ladies and gents!

You remind me of where I used to live in 1970 and 1971 when I was 6 and 7. I can still remember how beautiful Auckland and NZ in general were with the black sand beaches, and the deep forests we used to camp in. **** those were the days.

I'm pretty much the least technical guy on the forum but I see that you are referencing the Limbach engines http://limflug.de/downloads/datasheets/L2400-EB-datasheet-en.pdf
and quite powerful ones at that. We have tons of threads on the forum about the impact of heat rejection for VW engines, which I think the Limbach engines are derived from so a search will be your friend - unless I'm wrong about the core of the engine and it's not a VW.

Since Limbach are factory manufactured engine don't they have operating recommendations and so forth to guide you about heat management? Has the engine failed at this point or are you making sure it doesn't? Some of the experts will show up soonish - it's past midnight here in the Central US.
 

TFF

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Apr 28, 2010
Messages
14,177
Location
Memphis, TN
Well if you coat one part coat them all or you might create the weak link. Coatings themselves are not going to be that big of deal with stock timing and jetting. What you do once coated is try to run more timing and run the engine leaner to get more power. That is where you might burn up the engine. If you dont change those parameters, it should help longevity and friction.
 

Flow

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Joined
Apr 27, 2016
Messages
86
Location
Auckland
Obviously the likes of mixture timing and baffles are a known quantity. We have little gains left to make there.

HTCs are an interesting option but we need to understand the side effects. Would very much like to hear from folks that have done it and with measured results. Are thermal barriers on internal components dangerous in an air-cooled application?

Thermal Barrier Coatings:
Piston Top
Exhaust Port (Plasma application hard coating)
Valve Heads
Combustion Chamber


The benefits are understood but what are the potential pitfalls:
Raised Exhaust Gas Temps causing more back pressure and potentially causing a fire in the hot air pick ups for the cabin and carb heat??
Cooking our Nikasil bores??
Welding our top ring to the piston??
Cooler piston and hotter cylinder causing greater clearances, more blow by, oil consumption, wear etc??


Do we need to coat down to the top ring?
If we do this is there enough clearance there to prevent contact with bore at max piston rock?
How much should we expect the EGT to go up?
How much should we expect the head temps to go down? (Currently 400F)
Should we coat before or after machining the cylinder lands on the heads flat? ie. Do we want to be conducting heat between the cylinder and the heads?
 

nucleus

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Joined
Mar 21, 2016
Messages
65
Location
Atlanta, Georgia
Exhaust tubing ceramic coating is great stuff, should improve power slightly and reduces under cowl radiant heating dramatically.
 

Victor Bravo

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Jul 30, 2014
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KWHP, Los Angeles CA, USA
Although not a high tech coating, first, put about 6 or 8 ounces of Marvel Mystery Oil into every 12 or 14 gallons of fuel. This will assist the top end of the cylinders, help keep the rings and valve guides from sticking, and provide a cushion on the valve face/guide impact area. You should be able to see some heat reduction, but more importantly I believe you will see a small decrease in wear.

The ceramic heat reflective coatings are reported to work well, but if you do the piston tops with it you should also do the inside of the combustion chamber. If the piston tops reflect the heat away from the piston, this will try to send the heat right off to the "roof" of the chamber, which is already too hot. So you have to protect the metal on both sides of the fire, and force that heat out through the exhaust.

Remove any "choke" in the cylinder bore, this often causes friction between the piston and cylinder at higher temps.

The oil provides a very significant part of the cooling in these style of engines. Make sure you have plenty of oil pressure, but more importantly plenty of oil flow. Cooling the oil is critical, make sure you have a good, working, effective system. You could have a giant oil cooler and still not be cooling the oil enough... make sure the air flow through the cooler in flight is doing what it is supposed to do.

The exhaust coatings work well for reducing the temperature in the engine compartment, but probably doesn't do much for the cylinder heads themselves.

Try the "Dykes" style piston ring, which uses combustion pressure to expand the ring against the cylinder wall. The rest of the time the rings are "Relaxed" with far less pressure (friction) against the cylinder.

You can buy "temp-a-dot" stickers which you place in various locations around the cylinder heads, and they will record the maximum temperature by changing color. At very little cost you can perform a survey that identifies exactly where the hot spots are on your engine. This will quickly allow you to determine whether this is an internal temperature problem, a cooling baffle/cowling issue, etc. This eliminates all the guesswork, and gives you an excellent/relevant data source, at a low cost.

I cannot speak for the VW derivatives, but on the Continental 4 cylinder engines using air flow to cool the lower part of the ma in eng ine crankcase makes a truly surprising improvement in oil temp AND therefore cylinder head temp. I would bet money that this will reduce some or all of your heat/reliability/longevity issues on the Limbach too.... even if it is solving them from a direction unrelated to the actual problem.

Engine oil with Molybdenum ("Moly Oil") makes a significant reduction in friction, at the cost of more frequent oil changes and agitation to keep the Moly particles in solution. If you are not willing to do extra maintenance, up to and including draining the oil out and mixing it, then putting it back in, you will have problems with the particles settling into a sludge at the bottom.
 

Flow

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Joined
Apr 27, 2016
Messages
86
Location
Auckland
Thanks Victor,

Yes all understood on the oil front as well. We have little left to gain in that department as well.
The potential benefits of HTCs are well expounded and we have had extensive conversations with various HTC vendors.

What we need to know is what are the dangers of dramatically reducing the absorption of the combustion chamber, valves/seats, exhaust ports and piston tops without protecting the cylinder walls or top rings.

Are we to believe that we will only see an increase in EGT with no increase in cylinder temps and top ring temps? Would the increased burnt charge temp not have an exaggerated impact on any uncoated surfaces?

I see it said here that coating the exhaust may increase power. This is hard to understand how increased exhaust velocities/back pressure in a non tuned exhaust system could help.

Do we know anyone here that I could reach out to that has coated the flame side internals and can comment on before / after temps and any negative side effects seen.

Thermal Barrier Coatings:
  • Piston Top
  • Exhaust Port (Plasma application hard coating)
  • Valve Heads
  • Combustion Chamber

The benefits are understood but what are the potential pitfalls, for instance:
  • Raised Exhaust Gas Temps causing more back pressure, less power/efficiency and potentially causing a fire in the hot air pick ups for the cabin and carb heat??
  • Cooking our Nikasil bores??
  • Welding our top rings to the pistons??
  • Cooler pistons and hotter cylinder walls creating greater clearances, more blow by, oil consumption, slap, wear etc??

Application considerations:
  • Do we need to coat down to the top ring?
  • If we do this is there enough clearance there to prevent contact with bore at max piston rock?
  • Should we coat before or after machining the cylinder lands on the heads flat? ie. Do we want to be conducting heat between the cylinder and the heads and in which direction?

Real world experiences:
  • How much should we expect the EGT to go up?
  • How much should we expect the head temps to go down? (Currently 400F)
 
Last edited:

Flow

Well-Known Member
Joined
Apr 27, 2016
Messages
86
Location
Auckland
Thanks, I have already had a good chat with Nicolai and David Gouk. Keen to hear if anyone has EGT and CHT before and after measurements and if they have seen any of the above side effects? Very much interested in any horror stories as you can't pull over and tow trucks have trouble parking under clouds...
 

TFF

Well-Known Member
Joined
Apr 28, 2010
Messages
14,177
Location
Memphis, TN
Race car guys are really the best place to look. That last 1% is very important to them as a group. Only a very small percentage of homebuilders would care an probably most who do it is about buying the "best" not the performance part.
 

Bill-Higdon

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Joined
Feb 6, 2011
Messages
1,002
Location
Salem, Oregon, USA
The late Bob Hoover (The other one) did a lot of work on reliable VW aircraft engines, at the time of his passing he did a lot of research on coatings & what they could do. You should search through his blog Bob Hoover's Blog for his findings. Also some of the Type 4 racers are using them check out Aircooled Volkswagen Forum - Internal engine coatings Jake Raby is a believer in them.

Bill Higdon

Hi folks.


We are running a Limbach L2400 and looking improve top end reliability by reducing valve/seat and cylinder head temperatures.


We are exploring many angles but this has been suggested and the side effects are some what unknown.


Coatings:
Piston Top
Exhaust Port
Valve Heads
Combustion Chamber


The benefits are understood but what are the potential pitfalls:
Raised Exhaust Gas Temps causing more back pressure and potentially causing a fire in the hot air pick ups for the cabin and carb heat??
Cooking our Nikasil bores??
Welding our top ring to the piston??


Do we need to coat down to the top ring?
If we do this is there enough clearance there to prevent contact with bore at max piston rock?
How much should we expect the EGT to go up?
How much should we expect the head temps to go down? (Currently 400F)
Should we coat before or after machining the cylinder lands on the heads flat? ie. Do we want to be conducting heat between the cylinder and the heads?


If any one has experience with this any guidance would be kindly appreciated.
 

Armilite

Well-Known Member
Joined
Sep 5, 2011
Messages
3,416
Location
AMES, IA USA
Hi folks.
We are running a Limbach L2400 and looking improve top end reliability by reducing valve/seat and cylinder head temperatures.
We are exploring many angles but this has been suggested and the side effects are some what unknown.

Coatings:
Piston Top
Exhaust Port
Valve Heads
Combustion Chamber

ADD for Ceramic:
Exhaust Header, Inside & Outside

ADD for Heat Dispercent Coating on outside of:
Heads & Cylinders


YOU can do most of these COATING in your shop in a Free Electric House Stove!

The benefits are understood but what are the potential pitfalls: It COST MONEY!
Raised Exhaust Gas Temps causing more back pressure and potentially causing a fire in the hot air pick ups for the cabin and carb heat??
Cooking our Nikasil bores??
Welding our top ring to the piston??


Do we need to coat down to the top ring? ====> I would Coat only the Top, that is what NASCAR guys do. On a 2 Stroke that use's tapered Pistons I would.
If we do this is there enough clearance there to prevent contact with bore at max piston rock?
How much should we expect the EGT to go up? =====> None your just protecting the other parts.
How much should we expect the head temps to go down? (Currently 400F) ====> 20% on Average if you do all the Coatings!
Should we coat before or after machining the cylinder lands on the heads flat? ie. Do we want to be conducting heat between the cylinder and the heads?
====> You do the COATINGS after any Machining.


If any one has experience with this any guidance would be kindly appreciated.
NASCAR PISTONS. One Step better, also Diamon Dyze the Pistons then do the Coatings. You would probably have to send the Pistons out for the Diamon Dyze.
 

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Spinnetti

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Joined
Dec 24, 2005
Messages
95
Location
Dallas TX, USA
I wonder the same thing... I race and it definitely helps get that last bit of power out of car engines, and I would think it would be even more beneficial here. I'd do moly skirts, and ceramic on the piston crowns, combustion chamber and valve faces. The more heat goes out the exhaust (more power at a given load) that also then doesn't have to get shed via air & oil... seems like a very good idea to me but not seeing any discuss in aviation circles...
 

pictsidhe

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Joined
Jul 15, 2014
Messages
8,812
Location
North Carolina
As a heat barrier, these coatings have limited use in a spark combustion chamber. The better they insulate, the hotter the surface temp. Hot surfaces promote knocking and preignition. They can make a small difference, but need to be done right. In an exhaust port, they can be applied much thicker to cut the cooling load.
 

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