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8 Cylinder Torpedo Engine - Restoration


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4 hours ago, watercart said:

I took a measurement of the internal diameter of the air line from the Mk.VII torpedo air reservoir. It is 3/4 inch, so capable of discharging a lot of air quickly.


12 hours ago, watercart said:

So far so good, but the system essentially runs off both high pressure and massive volume throughput of the air.  The torpedo air pipes direct from the air flask are quite large compared with dive cylinders.  I will have a look at the sectioned Mk.VIII and confirm what air pipe diameter it has.  Getting ahead of ourselves a bit, but knowing the cubic inch displacement of the 8 cyl engine compared with the Mk.VIII's BBC 4 cylinder would give some idea of what increase in volume flow rate would be needed.  If a Mk.VIII engine rates at 550HP and the 8 cyl rates at 800HP, then roughly 50% more air flow for the 8 cyl?

Thanks for the measurement. The manifold inlet on the 8-cylinder is approx 1" dia, so its a useful comparison and it triggered a read of the archive docs.

From the records I found performance specs from two 8-cylinder engines, with swept volumes of 406 cu in (6.65l) and 460 cu in (7.53l) respectively. The former was listed as built, the latter listed 'design delayed'. When Britain entered the war effort shifted from R&D to production, such that by 1943 we had more torpedoes than we needed, but it was acknowledged any R&D would not be in service until the war ended. Air consumption for the 8-cylinder that had run is listed at 269lbs of air - which converts to approx 94,374l of air for a 60 knot run for 148 seconds/5000 yards! . By comparison the standard 4-cylinder Mk. VIII & IX 21 inch engines consumed 141lbs (49,467l) of air for a 45 knot run  for 197 seconds/5000 yards.

A typical 15l dive cylinder at 232bar will hold 3480l of air...so if my maths is right we won't be running the motor for too long. Which considering its age and rarity is perhaps no bad thing?

On the other hand, divers like myself use enriched air - breathing gas mix with anything between 21%~100% O2 - for reducing risks with decompression sickness...and the Japanese did indeed put enriched air torpedoes into service...given the risks dealing with high pressure O2 this idea will need to go through the "Can I? Should I?" filter more than a few times I think. I digress.


Given that it is an historic artifact, keeping a bit of patina on the steel and brass would be standard museum practice.

I really am in two minds with what to do? Preserve the patina or restore to look new? Only get one bite at this cherry and once done there is no going back.


If you want to go down that path (as opposed to attempting to make it look brand new), you can get products now that apply over the steel components' patina that makes them look good and protects against further rusting.

Preserve is now under consideration. Could you share a link to such products?


From the photos, it is not clear whether there is much brass as the earlier engines, but it would be the crank case material and some pipework if anything.

The main body is aluminium.. There is a brass component on the aux end, its purpose currently unknown but is (I think) either a lubrication pump or an incomplete fuel pump. It does have a nice patina...I have created some highly detailed images (called orthophotos - 1mm per pixel is a typical scale, great for recording stuff under water) that act as a permanent record of the motor before I touch it. The aux view of the engine can be seen near the bottom of this link: Orthophotos of torpedo engine.

So...keep the patina? Or return to the as-manufactured look?


Edited by SimonBrown
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Simon,  the standard approach for conservators in most situations is to only do what is reversible, so your comment about bites of the cherry is prescient.  Overall, the objective is to get the motor looking decent, rather than being a frosty looking ball of corrosion, so I would go with the steel wool and oil approach to begin with.  At least that will have the least risk of doing irreversible damage.  If it still looks a bit rubbish, you can ponder the alternatives then. 

Some of my professional work deals with the effects of salt water corrosion, so that may be another avenue of consideration if the motor is a combination of steel, aluminium and brass that has been sitting in salt water for a long while.  The bad news is that chloride ions penetrate deep into metals such as steel over a period of time and can play havoc with the metal once it is out of the water, eg, anchors that have been sitting on the bottom of the bay for 200 years OK, and explode into giant puff balls of rust when within months of being landed.  Lots of work has been done in this area with Mary Rose and USS Monitor, etc.  Bottom line is that regardless of your treatment, chloride contamination may make life interesting.  You will know you have it if you get aggressive rust forming under paint / preservative on what you thought was a clean and well prepared surface.  For steel tanks and ship hulls that have not had long term seawater exposure onto bare steel, ultra high pressure water blasting (approx 30,000psi) can be effective, as it can remove salt embedded in the surface of the object.  However, this can be very harsh on aluminium, and is not too effective on a long term salt water immersion.

I do not have the specific info on the preservation products, but I saw a can of it at a local automotive paint supplier. It is a silicone based product used by the oily rag / barn find restorers where original paint and patina are the priority.

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52 minutes ago, watercart said:

Simon,  the standard approach for conservators in most situations is to only do what is reversible...

This policy shall be the guide I think.

52 minutes ago, watercart said:

Some of my professional work deals with the effects of salt water corrosion, so that may be another avenue of consideration if the motor is a combination of steel, aluminium and brass that has been sitting in salt water for a long while. 

Thankfully this engine has not been in salt water for a long time - if ever. Its only light surface corrosion so far.

I lifted a cannon ball from a wreck site we found on Chesil Beach after winter storms uncovered the pile of cannon and shot. That was about 5 years ago and as far as I know its still in a fresh water bath, encouraging the 300 years of salts out of the iron and back into solution. Had the engine been raised from the seabed I think it would be in a far worse shape.

52 minutes ago, watercart said:

I do not have the specific info on the preservation products, but I saw a can of it at a local automotive paint supplier. It is a silicone based product used by the oily rag / barn find restorers where original paint and patina are the priority

That sounds just the ticket. I will have a hunt around - cheers!

Edited by SimonBrown
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The hydraulic platform warranty repair arrived this morning. Lots of excitement, with all hopes dashed when the load bed refused to lower when anything of any mass was placed on it. Back to square one with a refund now heading my way.

Disappointment did not last when the postman arrived with a package containing a set of Britool BSW sockets. Shiny, quality  tools are always a joy to work with.

The 'C' spanner arrived too, so it was time to start work on stripping the engine.

The inlet manifold is made up of several sections and the 'C' spanner managed to undo the first 3 couplings no bother. The joins are sealed with some very fancy copper washers. The rest of the unions are stuck fast and refused to budge, even with a little percussive maintenance...so they are soaking in penetrating oil now while I acquire a decent blowtorch and get a bit of heat into them


The sockets went to work on the aux drive end of things - the bronze yet-to-be-identified parts at the rear. What I thought was an oil pump may well not prove to be so after stripping. Its a geared, two speed affair with a set of unidirectional dog clutches. Its purpose remains unknown...however, sitting under this body was a gear pump.


The galleries leading from this pump lead deeper into the engine body, so at this stage I'm guessing its for engine lube. I'm not sure there is a sump and it reminds me of a JAP speedway engine fitted with a pilgrim pump, so called as the oil goes just one way so my dad told me. The design of the gear pump does now tell me rotational direction of the engine, if nothing else at this stage.


Next up, the bronze end cover/oil pump housing came off to reveal the outer end of the crank main bearing. From what I can see its looking near-brand new inside, which means we are not dealing with a seawater flooded pile of internal rust.


Overall, the engineering is pretty impressive for a motor designed to function just a few times before its terminal destruction.


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With an hour spare, more progress.

The bronze lump on the aux drive end is almost certainly for fuel distributor/injection timing. With a bit of penetrating oil, lateral thinking and gentle pressure the large cylindrical barrel slid out of the housing.


The barrel has a series of ports, each of which have a sliding block (the copper-looking rectangular bits in the image above) that marry up to an array of ports that have been drilled into the bronze liner thats been pressed into the casting. You can just see the bronze liner above.

From what I can tell - and I need to stick some fluid through it to prove it - the four ports at the bottom (you can see three above) are feeding pairs of cylinders. The exact timing is unknown.

The rest of the gear assembly came apart a treat, with just one rusted split pin refusing to budge. That will need careful drilling next.



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A little progress this weekend. The rusted split pin was drilled out and the last set of fuel timing gears were freed from their bronze casting :


Two 'C' spanners were welded together to fit the exhaust coupling slots better - but I'm not sharing photos of that. Its been 30 years since I last used an arc welder and lets just say it shows. The welding is good enough to hold them together and work as a pair, but not quite display material.

Friday the engine stand I ordered turned up. Whoever designed it had never envisaged it being used to support an 8-cylinder radial 2-stroke diesel engine, so some lateral thinking/cutting/welding will be needed to hang the engine off it and not cause damage to the aluminium crankcase in the process. But if I'm being honest, its solving problems like this that makes it all the more rewarding.

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10 hours ago, robin craig said:


was the " lateral thinking and gentle pressure the large cylindrical barrel slid out of the housing" to use air pressure to push it out?


At the point I was pulling this bit apart I wasn't really sure a) what it was and b) how it came apart.

With no manual it became a bit of trial and error until I realised the distributor barrel was machined to very fine tolerances and it was 50~70 year old gummy fuel residue putting up resistance... but until that point the last thing I wanted to do was force something and inflict damage what may be the last of its kind.

In the end, it took a gentle but persistent push with some penetrating fluid down the bore and ports and it slid out with nothing more than finger pressure.

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16 hours ago, robin craig said:


I envisage seeing a video one day of it scooting across the local boating pond, hopefully.

I can see the newspapers making the most of it, with a headlines like this:-

1.   War Breaks Out On Boating Lake.

2.   Boaters Terrorised By WW2 Torpedo.

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A few hours spare over the last couple of weeks has got the adaptor sorted for the engine stand. 

Closer inspection of the crankcase housing reveals its an aluminium machined block, not a casting. It will be interesting to get the aux end cover off and peek inside.

I got some steel blanks plasma cut. Ordered online to the exact size I wanted, including the flange:


Holes needed marking and drilling but the steel blanks were perfect and burr free.


Quick loose fit of the flange confirmed the marking out was close enough.


And the main mounting plate lined up too.


After tack welding the spacers in-situ I took it off the engine to put a bit more weld around each. With my welding I was not planning to rely on the strength of the fillets, but by weld No 28 of 32 quality was improving:


And final fitting, ready for a lift onto the stand:


Next few days should see the engine off the floor and onto the engine stand. Then its back to stripping the motor down.

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It took longer to assemble the borrowed hoist than it did to get the engine onto its stand:


The inlet manifold threaded connectors are proving to be a PITA. Three of them have come undone no bother, but the rest are tight AF and are refusing to budge even with an extension bar on the C spanner and applying loads of heat. Its as if they were welded up but there's not sign of that.

I'm heating them with a blowtorch and allowing oil to run into the threads as they cool, but if anyone has any other ideas then feel free to chip in:


I couldn't resist a peek into the engine internals so I pulled the auxiliary drive cover off...Wow was the first reaction:


Everything is numbered to its relevant pot, which will make reassembly easier. Plus, it looks like we have an engine number of sorts: 113 is stamped on every component I can see so far. I had seen this stamped on one of the poppet valve covers and wondered its significance, but with everything carrying the same number + cylinder number its a logical conclusion:


Degrees stamped on the cam presumably relate to valve timing, but will verify at some point.

After drooling over the engineering I slipped the cover back into place and carried on heating and soaking the inlet manifold glands.


Edited by SimonBrown
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It was time to stop fussing around and get the manifold off. Plenty of heat, aided by youngest daughter directing the blow torch onto the coupling, and a long extension tube on the C spanner did the trick.


Finally shifted them and (crucially) with no damage. Wrestling one of the sections off the motor was fiddly, and it going to be fun trying to get that one back on. The complexity may well have been the killer of this idea. There is plenty of power in a very compact space, but the manufacturing and assembly plus any in-service work would have been expensive.


Glad I took the manifold off. Found my first bit of rusty crud in one of the inlet ports:


With the manifold out of the way the rest of the fuel pipes came off. Some route to/from what I thought was the fuel distributor, but I am wondering if they are not spill/return pipes? More investigation needed.

A bonus was finding inspection stamps on each of the cylinder castings, just next to the integral fuel injectors:


The only other time I have seen stamps akin to this are on aircraft components. Presumably stamped at the Whitehead works in Weymouth, they need following up at some point.

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Tool appeal:

Does anyone have a 5/16 BSW or 3/8 BSF crows foot spanner lurking in their toolbox they would be willing to sell? 1/4" or 3/8" drive would be perfect.

The cylinder bolts are difficult to access and whilst a ring spanner is about to go under the grinder, a crows foot spanner would be a great help. Even the internet agrees they are a rare thing - couldn't find one - but folks here might just have one not required and lurking in the depths of the toolbox?

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3 hours ago, attleej said:

If you could draw or sketch what you need, I am sure that I could make one from what tools I have got.in stock. I love making special tools!


A Whitworth crows foot spanner should be (or was...30+ years ago maybe) an off the shelf item, something like this:

Bacho crows foot spanner

If push comes to shove it looks like 15mm AF metric crows feet spanners are widely available, and with a little bit of fettling (5/16W spanner = 15.25mm across the flats) it could be a solution.

Now...if you fancy a challenge then I will need a tool to get the inlet valve covers out of the cylinder head.

When it comes to blanking plugs I have never seen anything like this bad boy before. Shown here in the lower left, the 8 pointed star shaped recess:


Knowing I will need something come what may, and someone on here might just recognise it as an X plug from a YYY type of vehicle and the tool is off the shelf (I know, zero chance...but you never know) here's a dimensioned drawing of what is needed:


Not being a toolmaker, I have not made any allowances for fit - the above measurements are of the recess itself and all dims in metric.

There is a lot* of work in making up such a tool...if its a challenge needed...


*thats a conservative estimation.


Edited by SimonBrown
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The thread gauge arrived today. Its needed because some of the inlet manifold coupling threads suffered galling when removing them.


Have a look at the image above - the first couple of threads have been damaged at some point in the past or during disassembly and need a bit of TLC before reassembly.


Rather appropriately the thread gauge is dated 1952 and comes with the crows foot...nice to have a contemporary tool complete with its original cardboard box.

Now the thread appears to be 1-5/8" (1.6250"), a rather fine 20 tpi and Whitworth form. The usual searches (Ebay and Google) reveal this thread exists, but tools are as rare as the proverbial rocking horse dung.

Anyone have a die or die nut lurking in the tool box? Long shot I know...


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