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Elvis
Chief Master Sergeant
Boring a removable liner is usually a cost cutting measure (no pun intended). Otherwise, its kind of a foolish proposition.
High altitude Wright R-1820
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GregP
Major
Most of the liners were designed to have 3 or 4 bore sizes: nominal, and two or three overbores.
Again, on the Allison, they made pistons and rings for nominal bore (5.500"); 0.010" over; and 0.020" over. Once the liners got to 0.020" over they were scrap when they needed to be honed again. Anything under 0.020" over, and they were serviceable. You could always hone them to get rid of ring ridges and make the bores round again, as long as the final bore was not more than 5.020".
In the field, I'm sure they'd replace the cylinders if needed or swap out an entire engine. Quick Engine Change (QEC) modules were always welcome. At maintenance depots, they had equipment to make whatever repairs they thought best. A freshly-overhauled engine was always welcome to any crew chief or pilot. The reason most engines were swapped out before wearing out is that they wanted most engines to be overhaulable, and not be candidates for scrap. That's why TBO in WWII was short; it saved engines in such a condition that they were most likely reusable after overhaul as well as maintaining aircraft performance and reliability at the expected levels.
Again, on the Allison, they made pistons and rings for nominal bore (5.500"); 0.010" over; and 0.020" over. Once the liners got to 0.020" over they were scrap when they needed to be honed again. Anything under 0.020" over, and they were serviceable. You could always hone them to get rid of ring ridges and make the bores round again, as long as the final bore was not more than 5.020".
In the field, I'm sure they'd replace the cylinders if needed or swap out an entire engine. Quick Engine Change (QEC) modules were always welcome. At maintenance depots, they had equipment to make whatever repairs they thought best. A freshly-overhauled engine was always welcome to any crew chief or pilot. The reason most engines were swapped out before wearing out is that they wanted most engines to be overhaulable, and not be candidates for scrap. That's why TBO in WWII was short; it saved engines in such a condition that they were most likely reusable after overhaul as well as maintaining aircraft performance and reliability at the expected levels.
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davparlr
Senior Master Sergeant
Is this correct or am I missing something, or crazy? If the outer diameter of the steel liner, which goes on the inside, I think, is smaller than the inside diameter of the muff, which I think goes on the outside, the two would slide together rather easily. Cooling the liner, shrinking it, and heating the muff, expanding it, would just make the clearance larger. I think you meant to say the OD of the steel liner was larger than the inner diameter of the muff, which would require cooling the liner and heating the muff to get them to fit and when they were at normal temperatures they would be very tight. Like I said, I may be missing something. I do not have the engine expertise that you guys have.
Elvis said
. I believe the Chevy Vega's block was made of some alchemy of aluminum compound that when etched by acid in the cylinders, left a harden surface. I don't think it worked well, kinda liked the rest of the Vega, and many had steel liners put in. Info only.
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Just a couple of quick points.
The two stage R-1820 was the -48 not the 46.
According to White's book on the R-2800 all R-2800 had fordged aluminum cooling muffs shrunk on to steel cylinder barrels. The C series muffs were just a little bit larger to match the greatly improved cylinder head. Just looking at a good pictuer of a B series you tell that they're not steel fins by their depth and shape. Steel barrels tend to have more uniform and shallower depth to the fins. Steel after all is harder to cut than aluminum. Even more so for steel used in high ware applications like a cylinder barrel.
The two stage R-1820 was the -48 not the 46.
According to White's book on the R-2800 all R-2800 had fordged aluminum cooling muffs shrunk on to steel cylinder barrels. The C series muffs were just a little bit larger to match the greatly improved cylinder head. Just looking at a good pictuer of a B series you tell that they're not steel fins by their depth and shape. Steel barrels tend to have more uniform and shallower depth to the fins. Steel after all is harder to cut than aluminum. Even more so for steel used in high ware applications like a cylinder barrel.
Davparl that's correct the od of the steel barrel was slighty greater than the aluminum muff. This ensures really good contact between the two. You really don't want any warping between the two parts. That was a major problem in the early days of radials befor the technique was developed.
Shortround6
Major General
You are correct, the error is mine.
I believe on the aircooled engines it was common to replace a cylinder (or "jug") rather than repair (bore out or hone to larger size).
This could vary (?) depending on both the availability of spare cylinders and the level of the maintenance facility. The equipment needed to resurface or reline a single cylinder might be more than the equipment needed to replace an air cooled cylinder.
Sometimes one or more cylinders were replaced before an aircooled engine was sent for complete overhaul.
In the liquid cooled V-12 throwing away an aluminum block holding 6 cylinder liners and the work needed to fit the pistons/rings to 6 new liners because a single cylinder is out of spec is much more wasteful. Replacing the cylinder liners on an individual basis makes more sense but was probably done at an overhaul facility rather than at squadron/group level.
As engines got better overhaul procedures changed. IN the 1930s it was not uncommon to perform "top end" overhauls in which the valves, valve seats, springs and other valve gear was inspected and replaced/repaired in between complete overhauls. In the "top end" overhaul the crankcase was left intact so the crankshaft bearings (both main and rod) weren't even looked at.
On all the Pre-WWII radials the cylinder barrels were steel alloy with machined in fins so there was no question of replacing a cylinder liner. It was all one piece.
GregP
Major
Most cylinders did NOT need to be bored, just honed. The OD of the liner is larger than the aluminum cylinder ID by a small amount. You heat the cylinder and freeze the liner, insert quickly (less then 20 seconds), and it in is there until removed (interference fit by .002" - .004"), also with heat and cold (we use crushed ice inside the liner and a propane burner on the block). You didn't really need to hone unless there was a ring ridge or the cylinder was slightly out of round. Out of round was easy to tell. Lotsa' oil on the cowling; greater oil consumption, and / or loss of compression with no other symptoms. A ring ridge would be discovered only at overhaul.
The only real reasons to BORE might be if 1) the electrode of the spark plug cracked off and bounced around in the cylinder until expelled by exhaust, or 2) if the wear was near the 0.010" or 0.020" limit, AND if the dents / scratches in the cylinder were less than 5.010" / 5.020" to remove. Otherwise, hone and go. For instance, if the cylinder was at 5.006 with smooth sides and some scratches, hone it. If it was near 5.008, bore to 5.010 and proceed with 0.010" over pistons and rings. No problem.
They generally collected the "bore" cylinders / liners and sent them to a repair depot, and changed cylinders, or sometimes liners, otherwise. It depended on the equipment available or fabricated. Most crew chiefs were pretty resourceful about fabricating tools. They almost HAD to be. Most came from mid-America farms and had worked on tractors at home, and were quite mechanically-inclined. I knew one former WW2 crew chief who fixed his Ford 9N tractor with JB Weld when the block cracked. He was still using it 10 years later! Just not usually at full power.
It wasn't rocket science. It was piston engines. Ain't all THAT tough to figure out, once you've done it a few times, assuming you learn as you go.
The only real reasons to BORE might be if 1) the electrode of the spark plug cracked off and bounced around in the cylinder until expelled by exhaust, or 2) if the wear was near the 0.010" or 0.020" limit, AND if the dents / scratches in the cylinder were less than 5.010" / 5.020" to remove. Otherwise, hone and go. For instance, if the cylinder was at 5.006 with smooth sides and some scratches, hone it. If it was near 5.008, bore to 5.010 and proceed with 0.010" over pistons and rings. No problem.
They generally collected the "bore" cylinders / liners and sent them to a repair depot, and changed cylinders, or sometimes liners, otherwise. It depended on the equipment available or fabricated. Most crew chiefs were pretty resourceful about fabricating tools. They almost HAD to be. Most came from mid-America farms and had worked on tractors at home, and were quite mechanically-inclined. I knew one former WW2 crew chief who fixed his Ford 9N tractor with JB Weld when the block cracked. He was still using it 10 years later! Just not usually at full power.
It wasn't rocket science. It was piston engines. Ain't all THAT tough to figure out, once you've done it a few times, assuming you learn as you go.
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- #28
Elvis
Chief Master Sergeant
A small favour to ask everyone who participates in this thread....
It's getting a little confusing (at least to me), as to which style of cylinder liner you guys are referring to, since the conversation swaps between air-cooled and water cooled engines.
When we refer to the shrunk-in liners on the air-cooled engines, could we please start referring to those as "Sleeves" (or a "sleeve"). That way, any use of the actual word "liner" can more easily and quickly be defined as the removable type, like one might find on a V-block engine.
It just makes it a little easier to understand what the poster is getting at in any particular post.
Thank you to all who participate in this thread.
Elvis
It's getting a little confusing (at least to me), as to which style of cylinder liner you guys are referring to, since the conversation swaps between air-cooled and water cooled engines.
When we refer to the shrunk-in liners on the air-cooled engines, could we please start referring to those as "Sleeves" (or a "sleeve"). That way, any use of the actual word "liner" can more easily and quickly be defined as the removable type, like one might find on a V-block engine.
It just makes it a little easier to understand what the poster is getting at in any particular post.
Thank you to all who participate in this thread.
Elvis
Shortround6
Major General
For the Americans only the late R-2800s (the "C" series ) a small number of late R-1830s and the R-4360 used the "Sleeved" cylinders.
Wright did not and neither did most other American manufacturers of major engines.
P&W just to confuse things
called the steel part the "cylinder barrel" not "liner" and called the aluminium part (the cooling fins) the "cooling muff".
The rusty part is the "Barrel" which sticks down into the crankcase and also has the mounting flange for all the bolts that hold the cylinder to the crankcase. The lower set of fins is the "cooling muff" and while it may contribute something to the strength of the cylinder it probably isn't much. The cylinder head is shrunk and screwed to the top of the "barrel" and is the upper/wider set of horizontal fins blending to the vertical fins.
Franklin used steel "sleeves" and aluminum fins on their "flat" engines while Continental and Lycoming did not ( talking WW II here).
Wright did not and neither did most other American manufacturers of major engines.
P&W just to confuse things
called the steel part the "cylinder barrel" not "liner" and called the aluminium part (the cooling fins) the "cooling muff". The rusty part is the "Barrel" which sticks down into the crankcase and also has the mounting flange for all the bolts that hold the cylinder to the crankcase. The lower set of fins is the "cooling muff" and while it may contribute something to the strength of the cylinder it probably isn't much. The cylinder head is shrunk and screwed to the top of the "barrel" and is the upper/wider set of horizontal fins blending to the vertical fins.
Franklin used steel "sleeves" and aluminum fins on their "flat" engines while Continental and Lycoming did not ( talking WW II here).
Shortround6
Major General
Getting back on subject a bit there is a difference between a turbo-charged engine and a mechanical two stage supercharged engine from a cooling point of view.
The turbo makes 200 or more horsepower from the exhaust gases and uses it ti drive the auxiliary stage compressor to deliver sea level pressure air to to the carb.
An engine that uses an engine driven two stage supercharger has to make 200-300hp more power inside the cylinders to drive the auxiliary stage compressor to get the same power to the crankshaft.
This can be seen with the P&W R-2800 engines that get 1650hp to the prop at high altitudes while using the same manifold pressure and rpm that gives 2000hp at sea level. Granted the air in the intake is hotter and less dense even at the same pressure but that aux stage needs well over 200hp to drive it.
The Wright R-1820 may have worked fine as a turboed engine in the B-17 but may have offered several hundred HP less at 20,000ft and above using a mechanical two stage supercharger. You also have to fit in the intercooler.
The late model R-1820s (the 1300hp and up versions) had much better cooling fins compared to the 1200hp versions and might have been a better candidate for such a supercharger?
The turbo makes 200 or more horsepower from the exhaust gases and uses it ti drive the auxiliary stage compressor to deliver sea level pressure air to to the carb.
An engine that uses an engine driven two stage supercharger has to make 200-300hp more power inside the cylinders to drive the auxiliary stage compressor to get the same power to the crankshaft.
This can be seen with the P&W R-2800 engines that get 1650hp to the prop at high altitudes while using the same manifold pressure and rpm that gives 2000hp at sea level. Granted the air in the intake is hotter and less dense even at the same pressure but that aux stage needs well over 200hp to drive it.
The Wright R-1820 may have worked fine as a turboed engine in the B-17 but may have offered several hundred HP less at 20,000ft and above using a mechanical two stage supercharger. You also have to fit in the intercooler.
The late model R-1820s (the 1300hp and up versions) had much better cooling fins compared to the 1200hp versions and might have been a better candidate for such a supercharger?
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Elvis
Chief Master Sergeant
...and this is why turbo's are more more prevalent these days, than mechanically driven superchargers.
The problem with turbo's, for many years, was reliability at the axle that connects the two impellers.
Finding a bearing type that would work over time was quite a challenge.
The enemy's here were heat and speed.
A mechanically driven supercharger turns at tens of thousands of rpm, but an exhaust driven supercharger turns at hundreds of thousands of rpm.
A mechanically driven supercharger only sees the intake side of the engine, but the turbocharger sees all that heat from the exhaust, constantly.
Big difference in bearing requirements.
Elvis
P.S. - We fell off subject a long time ago, but it's ok if you guys wanna talk about R-2800's instead. =)
The problem with turbo's, for many years, was reliability at the axle that connects the two impellers.
Finding a bearing type that would work over time was quite a challenge.
The enemy's here were heat and speed.
A mechanically driven supercharger turns at tens of thousands of rpm, but an exhaust driven supercharger turns at hundreds of thousands of rpm.
A mechanically driven supercharger only sees the intake side of the engine, but the turbocharger sees all that heat from the exhaust, constantly.
Big difference in bearing requirements.
Elvis
P.S. - We fell off subject a long time ago, but it's ok if you guys wanna talk about R-2800's instead. =)
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Shortround6
Major General
Modern turbos turn at Hundreds of thousands of RPM. GE aircraft turbos of WW II actually turned a bit slower than some mechanical superchargers. A wright supercharger in Hi gear (10 to 1) could turn 25,000rpm for a crankshaft speed of 2500rpm.
P-38J with improved turbos was limited to 26,400rpm on the turbos, older P-38s had a lower RPM limit
Just used the R-2800 as an illustration because some two stage R-1830s seem to have some limits. Like being allowed 2700rpm for take-off and low altitude but only 2550rpm at high altitude in hi gear on the auxiliary supercharger. Which makes drawing comparisons hard.
I don't know why the limit is there. Guessing either inadequate cooling of the engine or of the intake charge in the intercooler leading to detonation problems?
I don't know what the F4F pilots did in combat.
P-38J with improved turbos was limited to 26,400rpm on the turbos, older P-38s had a lower RPM limit
Just used the R-2800 as an illustration because some two stage R-1830s seem to have some limits. Like being allowed 2700rpm for take-off and low altitude but only 2550rpm at high altitude in hi gear on the auxiliary supercharger. Which makes drawing comparisons hard.
I don't know why the limit is there. Guessing either inadequate cooling of the engine or of the intake charge in the intercooler leading to detonation problems?
I don't know what the F4F pilots did in combat.
Again this is not correct. ALL R-2800 had aluminum cooling muffs. This can clearly be seen in these beautiful photos of a B-26 wreck.
Further more starting with the Cyclone HC series (The R-1820-56 being the most common example) Wright switched to stamped aluminum cooling fins sawged on to forged steel cylinder barrels. Basically the made a tiny radiator with one really big ass pipe (the cylinder barrel) running though it.
Edit: I should not that the R-3350 used these fins as well.
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Shortround6
Major General
You are correct on the R-2800 cylinders,
I think we are getting rather far afield on the "Sleeves" though. Compared to say a motorcycle engine like a Harley
Where you have a substantial aluminum fin structure and the studs go from the crankcase to the cylinder head and the "sleeve" is merely the surface the piston rides on (and helps hold the cylinder pressure).
The P&W and Wright engines used the Sleeve/barrel as a structural component to hold the cylinder and head to the crankcase and the fins did little but provide cooling surface.
The Wright (and Ranger) sheet aluminium fins in particular having rather low structural strength to contribute to the engine.
The V-12s didn't all use sleeves the same way either. I believe Daimler Benz threaded the lower end of the sleeves and used large nuts around the sleeves to hold the cylinder blocks to the crankcase instead of using bolts/studs.
The "BB" Series R-2600 (the 1900hp version/s) also used the Sheet metal fins.
R-3350 cylinder
I think we are getting rather far afield on the "Sleeves" though. Compared to say a motorcycle engine like a Harley
Where you have a substantial aluminum fin structure and the studs go from the crankcase to the cylinder head and the "sleeve" is merely the surface the piston rides on (and helps hold the cylinder pressure).
The P&W and Wright engines used the Sleeve/barrel as a structural component to hold the cylinder and head to the crankcase and the fins did little but provide cooling surface.
The Wright (and Ranger) sheet aluminium fins in particular having rather low structural strength to contribute to the engine.
The V-12s didn't all use sleeves the same way either. I believe Daimler Benz threaded the lower end of the sleeves and used large nuts around the sleeves to hold the cylinder blocks to the crankcase instead of using bolts/studs.
The "BB" Series R-2600 (the 1900hp version/s) also used the Sheet metal fins.
R-3350 cylinder
swampyankee
Chief Master Sergeant
- 4,022
- Jun 25, 2013
I believe that most big radials machined the cooling fins, as it was impossible to get the required fin area any other way. Pratt, I believed, used ganged saws. Those fins had to get read of a lot of heat in a small space.
Shortround6
Major General
This also evolved over time and depended on the particular engine. Low powered trainer engines could get away with casting, some medium powered engines used either casting or forgings with some (greater or lesser) machining. The High powered engines used forged heads and the ganged slitting saws controlled by cams. Please note that at times it is not question of designing the particular part but having the machinery needed to manufacture the design in quantity. You could have given the Japanese blue prints of the P&W "C" series engine in the fall of 1945 with an illustrated manual of manufacturing steps and about all they could have done was cried. They would have had the needed machine and foundry tools to build it in quantity even if they could have built a few hand built engines.
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- #37
Elvis
Chief Master Sergeant
Well, Honda was building its infamous "50" as early as '47 or '48, so it could happen.
They just would've needed some time to build the infrastructure back up.
They just would've needed some time to build the infrastructure back up.
Shortround6
Major General
Picture from a modern facility doing work on R-2800s.
During the war a "C" series cylinder head started as a 70lb billet and when through four forging steps, the first used a 2000 ton press and the next 3 steps used 4000 ton presses. Then the machining started. Finished head weighs 25lbs.
By the end of 1944 P&W Kansas City was making over 280 cylinder heads per day.
During the war a "C" series cylinder head started as a 70lb billet and when through four forging steps, the first used a 2000 ton press and the next 3 steps used 4000 ton presses. Then the machining started. Finished head weighs 25lbs.
By the end of 1944 P&W Kansas City was making over 280 cylinder heads per day.
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swampyankee
Chief Master Sergeant
- 4,022
- Jun 25, 2013
In the same vein, I have read that Japan could not produce anti-friction bearings of sufficient quality to build engines of adequate performance in sufficient quantity.
GregP
Major
Doesn't LOOK like a Wright R-1820 ... and that thing on the right is just Venus de Milo before they moved the nipples to the correct locations and turned her arms down. The head needed head bolts before it could fitted.
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