8 Cylinder Torpedo Engine - Restoration

[SimonBrown]

21 minutes ago, attleej said:

The special tool for the cam plug is in the post to you.  We all cannot wait to see what is revealed next!

Thank you John - its much appreciated.

I have a rough idea what is coming next, but I suspect when that cam is pulled off its still going to be a 'Wow' moment.

Hopefully progress it this week.

[SimonBrown]

On 3/24/2019 at 4:02 PM, SimonBrown said:

In the meantime another visit to the National Archives is planned. One of the documents is entitled "Torpedo engine operation without water cooling" which will no doubt simply tell me how long it can run before seizing.

In typical torpedo fashion the document was a surprise. The tests were carried out on 18" engines and the limiting factor was not seizing up, but something else.

The tests were done using alcohol - methylated sprit diluted with water - as a fuel, and the engine could run steadily at 190~200deg C with the limit being set as anything higher would start to melt the solder used in making the sweated joints found on this type of engine. Even at low temps 80~90 bhp was produced and the conclusion was that if higher melting point solder was used in construction then higher operating temperatures could be achieved.

Later runs on a 21" engines saw 240 bhp and temperatures up to 600deg C. The conclusion was a 21" engine with a liberal oil supply could run at 400 deg C with reasonable mechanical durability.

Fascinating document that must have cost a fortune to produce, but I won't be adopting its findings anytime soon. The Mk VIII engine they used was 4 cylinders and had a cast bronze crankcase and barrels - not really comparable to the 8-cylinder with its aluminium crankcase and steel cylinders.

Edited March 26, 2019 by SimonBrown

[andym]

Still fascinating, though!

Andy

[SimonBrown]

Look what arrived in the post this morning:

The tool worked a treat. Fitted snugly into the castellated threaded fastener and with a swift tap it unscrewed.

A very, very big thank you to John for his generosity making up the tool. The idea of welding an old socket into the end was perfect for the breaker bar.

And so the big reveal:

Yup, not much I'm afraid. The cam refused to budge. Both castellated nuts were removed and the cam remained fixed and firm on the crankshaft. No amount of gentle persuasion would move it. Bit of a head scratching moment that yielded precisely zero progress I'm afraid, apart from knowing what does not work.

So I think its time to pull the drive side casing off and have a look-see from that end. Its possible everything assembles into the engine from the other side, so thats where I'm heading next.

[SimonBrown]

With a borrowed engine hoist the drive side of the engine was now ready for stripping:

First off, the centre cover, revealing a thrust bearing. Note the threaded securing ring:

When originally tightened someone had used a drift and hammer to tighten it up. I was about to start knocking it loose with an alloy drift when I noticed this:

A tiny hex socket grub screw used to lock the ring tight and pretty much guarantee it was not coming undone in a hurry.

With the grub screw out of the way the locking ring came undone and the thrust bearing removed. The casing could then be slid off, revealing a second and larger diameter thrust bearing:

And the internals of the engine, pretty much a mirror of the aux drive side:

The two brass split pins were removed from the castellated nuts. One came undone no problem (its a captive head bolt I think) and the second...well that started to turn then the bolt itself started turning. From investigations on the other side, this bolt is a special - low profile round head with a small machined locking pip. It feels like the pip itself has sheared and nut and bolt rotate together. This is a right PITA. 

Rather than dwell on it I spent the rest of the morning making sure all of the 80 pan head bolts that hold the cylinders down were undone and ready for cylinder removal and removing the four odd numbered tappet rollers and inlet valves.

The cams are proving to be a pain. I think its time to pull a few cylinders off and have a deeper look inside the bowls of the engine, to try and figure out how it went together, and comes apart.

I must say its a frustrating beast to work on a times. But thats part of the joy, figuring out how such a compact engine can be stripped and reassembled without so much of a hint of workshop manual. That would be far too easy.

[SimonBrown]

Today was one step forward and one back. Here goes...

First up, pot No 1 was pulled and I was greeted with this:

On the face of it, a pile of rust. But a quick wipe of a rag and the piston came up looking like brand new. The rings were gummed up but will free off after a soak and a clean. The cylinder had some very light corrosion  in the combustion chamber, but the bore was as good as the day it was made.

Inside, we get a peek at the complexity and compact design. Int this shot we can see the inlet cam (bane of my life) at top and   not one but two conrods meeting at the same big end. There are another two conrods joined to the opposite side of the big end. A single big end with four conrods...

At the bottom of the image above is the lower skirt of one of the pistons.

Here's another view looking down past the piston skirt, down the conrod and directly at the big end:

This engine is like nothing else I have ever seen. There is no big end cap and four conrods connect to the same big end.

Thinking about it, the fact its a 2-stroke - with a power stroke on each downward stroke of the piston  - there is no requirement to really suck hard on the way down like its 4-stroke cousin. Its all pure power every time the piston descends...and when going up the bore the piston is always being forced by the big end to compress. The forces trying to hold the piston in the barrel as the crank pulls it downwards are minimal, so why have a big end cap?

There is a very neat design that holds the conrod in place, but its too buried to photograph...

So I turned my thoughts to the special bolt that had decided to shear its locking pin and not undo. The tub of cunning and guile was smeared over the problem and thus a solution found:

The bit you can't see is jamming the special bolt in place. Which undone after a bit of fettling of the tool:

And at that point the cam still refused to even budge a thou. It sat there looking at me...and I looked at it, wondering what to do next?

I do not want to do any harm to this beast. Its too rare. So do I press on and find a way? If I remove the pistons can the conrods and crankshaft be removed as an assembly from the casing? Or should I realise its all smothered in oil, clean and looking just fine and not go any further?

Something to ponder for a few days I think. The principle of do no harm applies to all patients, including torpedo motors.

Edited March 29, 2019 by SimonBrown

[terryb]

it looks like two four cylinder engine combined back to back. As the exhaust ports in the cylinder open into the crankcase-is the exhaust vented out through a hollow driveshaft?

[attleej]

Simon,

 

My counsel is that you are approaching the task in a very methodical manner.  You are using special tools when necessary.  You are consulting others including the Explosion Museum and, whilst rare, it is not the Lost Ark.  You are not going to negligently muller anything or apply disproportionate force. If you did accidentally damage anything, there is very little that cannot be remanufactured, repaired, drilled and tapped oversize etc.

My understanding is that, whilst a fully armed torpedo obviously makes only one run, the practice torpedoes would be used several times and therefore would be overhaulable.

As for running it, for the reasons that Richard described, there might be problems using it with a vehicle or without a constant load.  Since it has very limited rotating mass and is very powerful, it would over-rev and blow up due to centrifugal force (I know, there is no such thing!).  However, given your maritime experience, you could mount it underwater (either at sea or some other suitable place) with a suitably sized propeller to absorb the power.   You might need to have a slightly different fuel and / control system but that need only be temporary.

In concept, I wonder if it is more a motor driven by compressed air and by letting some fuel into it then gets even more power as a two stroke diesel.

I would carry on giving it a 'base overhaul' with a view to running once or twice and then putting it into deep preservation along with records of all that you have learnt.

John

[radiomike7]

Simon, a radial engine commonly uses a master con rod with the remaing rods pinned to it in order that the cylinders can be in the same plane and the engine depth kept to a minimum.

John, the term that describes the force exerted by a rotating object is centripetal force.😊

[SimonBrown]

23 hours ago, terryb said:

it looks like two four cylinder engine combined back to back. As the exhaust ports in the cylinder open into the crankcase-is the exhaust vented out through a hollow driveshaft?

Yes and yes. All the exhaust gases vent through the driveshaft. Will take a photo later.

23 hours ago, attleej said:

My counsel is that you are approaching the task in a very methodical manner.  You are using special tools when necessary.  You are consulting others including the Explosion Museum and, whilst rare, it is not the Lost Ark.  You are not going to negligently muller anything or apply disproportionate force. If you did accidentally damage anything, there is very little that cannot be remanufactured, repaired, drilled and tapped oversize etc.

Thanks John. Those special tools are invaluable and very appreciated indeed. 

Everything can indeed be remanufactured, but prefer not to. It just offends the soul to mangle something without purpose. I did wince when the brass split pins snapped...

Quote

My understanding is that, whilst a fully armed torpedo obviously makes only one run, the practice torpedoes would be used several times and therefore would be overhaulable.

The Whitehead factory in Wyke used to test fire the torpedoes off the line 3 or 4 times before being fitted with a live warhead and delivery to the end customer apparently, and there is a torpedo range marked on old charts. Dummy warhead was fitted with lead substituting the bang. We have found several of those lost in Weymouth Bay. As to a full strip of the engine every time, I think this unlikely but not impossible.

As a complete aside, my Weymouth friend will be disposing of some of the torpedo parts acquired over the years soon, to make space in the garage for classic 70's 2-stroke motorbike restoration. First up will be a 21" Mk 23 torpedo practice warhead - if anyone is interested, please drop me a PM.

Quote

As for running it, for the reasons that Richard described, there might be problems using it with a vehicle or without a constant load.  Since it has very limited rotating mass and is very powerful, it would over-rev and blow up due to centrifugal force (I know, there is no such thing!).  However, given your maritime experience, you could mount it underwater (either at sea or some other suitable place) with a suitably sized propeller to absorb the power.   You might need to have a slightly different fuel and / control system but that need only be temporary.

Running it remains the end goal and aspiration. There are a few technical issues to overcome - somehow - but everything remains possible.

Quote

I would carry on giving it a 'base overhaul' with a view to running once or twice and then putting it into deep preservation along with records of all that you have learnt.

Agreed. Best policy and practice I think. I have certainly learned loads just by tinkering with it and that knowledge needs recording somewhere, to travel with the motor in future.

18 hours ago, radiomike7 said:

Simon, a radial engine commonly uses a master con rod with the remaing rods pinned to it in order that the cylinders can be in the same plane and the engine depth kept to a minimum.

John, the term that describes the force exerted by a rotating object is centripetal force.😊

Yes, in most "normal" radial engines there is master con rod. However, as we are finding out, nothing much is normal with this beast and there is no master con rod. All con rods are equal, of the same shape & design and sit on a common big end. 

I have been pondering what the next project should be - getting ahead of myself - but a petrol radial engine needing some TLC would be right up there in the "yes please" list. That or another 2-stoke diesel like a K60 perhaps? I did see an unusual V12 Rolls Royce 'barn find' appear on Ebay a few weeks ago - not a Merlin I think and possibly a civvy variant of a Meteor (did they do such a thing?)  - but the listing has gone. That would be right up there on a list of things worthy of overhaul...I digress.

You cannot imagine the memories that phrase triggered radiomike. "Centripetal force" took me right back to college!

Edited March 31, 2019 by SimonBrown

[watercart]

Simon, looking back at the stats quoted earlier, I am thinking about the power you will have to dissipate when running it up, if you decide to go for full power that is.  If the 8 cyl vs. 4 cyl Mk.VIII / IX engine stats apply to this engine, you are consuming almost twice the air in about 3/4 of the time that a Mk.VIII engine would.  On a dynamometer, we were getting about 550HP out of a Mk.VIII engine, which is significantly higher than the handbook minimum.  Are we therefore contemplating in the ballpark of 1200 HP for this engine?

Much as I would like to see this thing go full power, I am not sure how you would set this up for a run without the risk of things getting out of hand!  We have been concentrating on the engine somewhat, but the actual torpedo that contained this 8 cylinder beast would need to be somewhat different to a Mk.VIII / IX.  For a start, doubling the air capacity would need to double the reservoir length or the storage pressure.  I had a quick look through the previous 5 pages buy did not see reference to the diameter of the engine / torpedo (sorry if I missed it).  As a 21 inch torpedo is a more or less standard length to fit in in-service launching tubes, this would require the same size reservoir and doubling of the reservoir pressure.  Otherwise, to keep pressures under 250bar, are we looking at a 24inch diameter weapon?

Getting ignition would also be interesting, as I cannot tell whether there is a pre-combustion igniter on the engine. In Mk.VIIIs, this as a device with three hammers that are cocked and released to fire three blank cartridges as the first blast of compressed air and fuel go to the engine.  I assume that the fuel admitted to the cylinders ignites by the usual diesel principle, as the pre-ignited mix is now warm as opposed to actually burning (??).

If I were in your situation, I may be thinking about finding a tame racing engine workshop with a dyno that could take 1200HP and a fairly sizable test rig containing fuel and compressed air. And a method of directing the exhaust outside...

Maybe just sticking to turning it over with compressed air for a few seconds would prove functionality as well as avoiding accumulation of corrosive combustion products internally, which may cause seizure in future. After all, Mk.VIIIs where fuel ignition failed were still capable of about 22 knots over a few hundred yards.  Cheers,  Damien

[radiomike7]

3 hours ago, SimonBrown said:

 

Yes, in most "normal" radial engines there is master con rod. However, as we are finding out, nothing much is normal with this beast and there is no master con rod. All con rods are equal, of the same shape & design and sit on a common big end. 

I have been pondering what the next project should be - getting ahead of myself - but a petrol radial engine needing some TLC would be right up there in the "yes please" list. That or another 2-stoke diesel like a K60 perhaps? I did see an unusual V12 Rolls Royce 'barn find' appear on Ebay a few weeks ago - not a Merlin I think and possibly a civvy variant of a Meteor (did they do such a thing?)  - but the listing has gone. That would be right up there on a list of things worthy of overhaul...I digress.

You cannot imagine the memories that phrase triggered radiomike. "Centripetal force" took me right back to college!

Out of interest what stops the big end flapping around if not restrained by a master rod?

Don't think Meteor ever found a civilian use but the 8 cylinder Meteorite was used in civilian Thornycroft Antars and for marine use as both a petrol and diesel.  Did you know the Meteorite blocks were machined on the Meteor lines for economy and retained the 60 degree V angle rather than the correct 90 degree which gave uneven firing intervals?

[SimonBrown]

27 minutes ago, radiomike7 said:

Out of interest what stops the big end flapping around if not restrained by a master rod?

Thats part of the unusual design. Here's the best photo I can get showing the arrangement:

Above are two con rods connecting (in the loose sense) to a common big end. From the opposite side, two more con rods meet on the same big end. There is running around each end the big end two circular pieces of metal that form an undercut, and the con rods extend into this undercut. This undercut is what holds the con rod onto the big end.

Does all that make sense? Thanks to its compact nature its difficult to photograph but I hope you get the idea...

As promised, a view down the drive shaft:

You can see right into the crankcase, with one of the con rods and one of those retaining metal disks visible. Beyond is - I think - the other bank's big end. There is no centre main bearing, everything runs on the two bearings that are in each end case.

If none of this makes sense, just ask! 

Ah yes, the Meteorite...now that needs to go on the list of 'Next?' I think.

Edited March 31, 2019 by SimonBrown

[SimonBrown]

3 hours ago, watercart said:

Simon, looking back at the stats quoted earlier, I am thinking about the power you will have to dissipate when running it up, if you decide to go for full power that is.  If the 8 cyl vs. 4 cyl Mk.VIII / IX engine stats apply to this engine, you are consuming almost twice the air in about 3/4 of the time that a Mk.VIII engine would.  On a dynamometer, we were getting about 550HP out of a Mk.VIII engine, which is significantly higher than the handbook minimum.  Are we therefore contemplating in the ballpark of 1200 HP for this engine?

From the archives, the closest but not exact match I have found so far is a similar 8-cylinder engine that kicked out somewhere between 750~800hp. 

It may well prove to be more powerful, but there's going to be quite a few factors affecting that. As we don't know what the manifold pressure was, or the exact fuel used, then its going to be somewhere between "a fair bit" to "did not expect that much" right now. 

Quote

Much as I would like to see this thing go full power, I am not sure how you would set this up for a run without the risk of things getting out of hand!  We have been concentrating on the engine somewhat, but the actual torpedo that contained this 8 cylinder beast would need to be somewhat different to a Mk.VIII / IX.  For a start, doubling the air capacity would need to double the reservoir length or the storage pressure.  I had a quick look through the previous 5 pages buy did not see reference to the diameter of the engine / torpedo (sorry if I missed it).  As a 21 inch torpedo is a more or less standard length to fit in in-service launching tubes, this would require the same size reservoir and doubling of the reservoir pressure.  Otherwise, to keep pressures under 250bar, are we looking at a 24inch diameter weapon?

Right now its believed to be an engine destined for a 21" torpedo. The working assumption is there was so much geared around the size and length of this weapon it had to fit right in. Two ways to increase efficiency of the air cylinders would be to a) use a higher pressure rating and b) used enriched gas or pure O2. Both would give you more bang for your buck (volume) and there are some papers that are dealing with the increased pressure route as quality and strength of steel for the cylinders improved.

Right now, no hard data to support any theory. Its all just that - theory.

And yes, things could get out of hand and run away before we get a chance to stop it. Not the first time I will have seen a diesel run away with itself, and having seen the somewhat destructive nature of the laws of physics applied am keen to avoid at all costs.

Quote

Getting ignition would also be interesting, as I cannot tell whether there is a pre-combustion igniter on the engine. In Mk.VIIIs, this as a device with three hammers that are cocked and released to fire three blank cartridges as the first blast of compressed air and fuel go to the engine.  I assume that the fuel admitted to the cylinders ignites by the usual diesel principle, as the pre-ignited mix is now warm as opposed to actually burning (??).

Right now, we have nothing upstream of the inlet manifold. Starting and running are unknown, so pre-heating is possible - maybe even necessary thanks to the chilling effect as the incoming gas expands - but we have nothing to go on. The ignition is, I believe, just compression ignition and nothing special...but that remains a best guess based on no evidence to the contrary. Given that everything else has proved 'special' then nothing would surprise me to find it had glow plugs...or some such method.

Quote

If I were in your situation, I may be thinking about finding a tame racing engine workshop with a dyno that could take 1200HP and a fairly sizable test rig containing fuel and compressed air. And a method of directing the exhaust outside...

A tame racing engine workshop was not something I had thought of...but do have a contact in just that...good idea!

Quote

Maybe just sticking to turning it over with compressed air for a few seconds would prove functionality as well as avoiding accumulation of corrosive combustion products internally, which may cause seizure in future. After all, Mk.VIIIs where fuel ignition failed were still capable of about 22 knots over a few hundred yards.

Compressed air only is the first, tentative step planned. We can prove out the lubrication system at the same time.

But I think we are some way off that.

Edited March 31, 2019 by SimonBrown

[attleej]

Simon,

 

I have a 250 cfm diesel compressor which would easily make it turn over but not too fast..

 

John

[watercart]

Simon,  the best indicator of the torpedo diameter is measuring the maximum diameter of the engine.  If it just squeezes inside a 21inch circle, then it will certainly be a 21inch weapon.  If the weapon was 24 inches, the designers would have used up every bit of that additional diameter in their quest for maximum power. If 21 inches, then your observation that higher pressure (400 bar) or higher percentage O2 was used will be the only alternatives. The 8 cylinder stats quoted with respect to a similar range and double the air volume tend to make me think it was not high purity O2, but you never know. In general reading, I was under the impression that several countries including UK experimented with varying percentages above 20% purity.  As we know, the Japanese seem to have been the only ones to get higher purity O2 wrangled properly for their various torpedoes, which gave an old Whitehead long stroke 2 cylinder design a new lease on life.  D

[SimonBrown]

On 3/31/2019 at 4:31 PM, attleej said:

I have a 250 cfm diesel compressor which would easily make it turn over but not too fast..

Duly noted!

18 hours ago, watercart said:

Simon,  the best indicator of the torpedo diameter is measuring the maximum diameter of the engine.  If it just squeezes inside a 21inch circle, then it will certainly be a 21inch weapon.  If the weapon was 24 inches, the designers would have used up every bit of that additional diameter in their quest for maximum power. If 21 inches, then your observation that higher pressure (400 bar) or higher percentage O2 was used will be the only alternatives. The 8 cylinder stats quoted with respect to a similar range and double the air volume tend to make me think it was not high purity O2, but you never know. In general reading, I was under the impression that several countries including UK experimented with varying percentages above 20% purity.  As we know, the Japanese seem to have been the only ones to get higher purity O2 wrangled properly for their various torpedoes, which gave an old Whitehead long stroke 2 cylinder design a new lease on life. 

Measured over the top of the cylinders, we have a max diameter of 20". Leaving a 1/2" inch for outer casing...tight but not impossible and there would be no need for any space to work around it, once fitted.

The UK did experiment with HTP - High Test Peroxide - but this ended when a torpedo loaded onto HMS SIDON blew up and sunk the submarine in Portland Harbour, killing 13 of her crew. Its thought the similar issue caused the loss of the Kursk, I believe. No evidence to suggest this engine was using that, so far at least.

Not found any evidence of higher % 02 mixes being used in the UK archives, but there are still some documents to view, so it remains a possibility.

[SimonBrown]

The cam removal can now be ticked off the list. But more of that later.

The rest of the barrels were pulled today:

Which gives us a much clearer view of the slightly insane yet compact design of the big end and its four con rods:

The bronze big end bearing can be seen with the con rod running under the retaining lip.

With the pots pulled it was time to sit the engine vertically on the bench. A 100mm hole saw put a hole in the bench for the drive shaft. With the cam castellated retaining nuts removed an alloy drift knocked said cams off. A snug fit but not a press fit, that one:

A few more the pan head "studs" that hold the barrels on came loose and after cleaning up a small pip can be seen under the head of the screw:

Which looks like nothing more than a blob of solder. This was intended to stop the pan head screws from turning in the crankcase as the nuts were tightened, but 70 years of crud meant they were not coming undone. The debate I am running in my mind now is do I revert to solder and keep it original? Or do I reach for the Loctite?

No reason for this photo. Its just engineering and engine porn and I make no excuse for sharing it:

The pistons do not have a traditional gudgeon pin and I will turn my attention to these next. All of the pistons are numbered and some have what appears to be size/tolerance numbers stamped. Its a neat design and will get some more photos of how the pistons are held in place without a gudgeon pin. Its clearly an expensive way to make an engine, but driven by demands of a 21" tube and a buyer willing to pay for it then who can blame them?

In the meantime, the engine sits on the bench and looks rather fine indeed.:

[terryb]

the big end bearing is sheer genius-that is definitely thinking outside the box! On the crakcase to barrel surface, is that an oil jet orifice? and why the 2 offset slots in the piston? 

[SimonBrown]

12 hours ago, terryb said:

On the crankcase to barrel surface, is that an oil jet orifice? And why the 2 offset slots in the piston? 

Well spotted. All the external pipes (that have now been removed) were oil feed. Each inlet valve had a direct feed, and each cylinder is lubricated in the bore via the hole you spotted. As of now I have yet to find any way a pressurised oil feed fed the big ends, but there are four nozzles on the rear crankcase cover that would blow an oil mist over them.

The offset slots on the piston crown? Purpose and reason unknown, but they may line up with the blanking plugs - I will check. Either way, purpose unknown.

[BRDM Driver]

Those conrods look really beefy! Clever how the valves are driven direct off the crank, I guess all radials work like that?

Would like to see the arrangment of how the conrods attach to the crank.

Great photos. Keep em coming!

[SimonBrown]

30 minutes ago, BRDM Driver said:

 Clever how the valves are driven direct off the crank, I guess all radials work like that?

Direct acting cams - basically turning at same speed as the crankshaft - will only work (I think) with a two-stroke engine.

A four-stroke radial engine would still need a 2:1 reduction on the camshaft, so it rotates at half crankshaft speed and makes sure the inlet and exhaust valves open once every four strokes. If that makes sense?

Quote

Great photos. Keep em coming!

Thank you! More to follow as and when. 

[andym]

This thing is truly a work of art.  It deserves to be sat in a museum somewhere with perspex replacements for the end covers, being slowly turned so that people can observe the genius behind the design!

Andy

[SimonBrown]

1 hour ago, andym said:

This thing is truly a work of art. 

Isn't it just? Its going to get better...read on...

Quote

It deserves to be sat in a museum somewhere with perspex replacements for the end covers, being slowly turned so that people can observe the genius behind the design!

Been thinking about what to do with it once the job is done? Inclined to mount it under a thick piece of glass  and turn it into a coffee table...or just leave it on its stand in the living room and marvel at it every day...chances are that idea will be vetoed quickly by SWMBI.

Starting to clean things up and No 1 cylinder & parts have been degreased. The good news is the gummy preserving oil holding the piston rings in cleared up and the rings are now free:

Still not turned my full attention to removing the pistons - One of the bronze bushes was pressed/tapped to see if it would move and the short answer is "Not without more force than available right now" so they have remained in-situ. The thread, in case anyone is wondering, is another Admiralty pattern (The thread chart here has been used many times - thanks MatchFuzee) 5/8" with a 20 TPI pitch. I am now thinking the bronze bushes are pressed into place as a one way trip and may prove difficult to press out again, as its likely there would never be a requirement to strip and service.

The degreaser has worked its wonders. The barrel was left to soak while all the nuts and pan head screws went into the ultrasonic cleaner with a 30% degreaser/water solution:

Now its cleaned off its pretty clear the barrels are plated on the outside, and its probably a nickel finish. I suspected this as when the inlet manifold unions unscrewed some of what looked like plating peeled off and galled in the threads. The plating is peeling as 70 or so years have taken its toll:

Now, a nickel plated set of barrels is going to look simply jaw droopingly beautiful, 8 of them gleaming like new.

But should they be replated? Or do we leave the patina? For now, an issue to set aside as there is still plenty to do elsewhere.

[MatchFuzee]

5 minutes ago, SimonBrown said:

But should they be replated? Or do we leave the patina? 

If you put it to a readers' vote, mine would be "leave the patina".