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SimonBrown

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.

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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.

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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?

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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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