Skip to content

276. The Scores on the Bores

12/10/2016

Today we had a look at the dismantled engine, and went through the alternatives with Shuttleworth Chief Engineer Jean-Michel Munn and engine expert Phil. It was sobering stuff…

Jean-Michel showing us the main crankshaft bearing, and Theo and David thinking 'So much for my pension.'

Jean-Michel showing us the main crankshaft bearing, and Theo and David thinking ‘So much for my pension.’

Thankfully the bearings all seem to be okay, but elsewhere things didn’t look so rosy.

Phil on the left is describing the

Phil on the left is describing the gunge that almost filled the inside of the engine that presumably was caused by our use of castor oil.

I’ll give you a more detailed run down on the individual bits of the engine so you can see more or less how it all goes together.

The starting point is the crankshaft, which is stationary. The bit at the back of the picture is mounted in the airframe. The crank is normally at the top, with the oil gallery next to it. the main bearing is on the outside, that's what the crankcase is mounted on.

The starting point is the crankshaft, which is stationary. The bit at the back of the picture is mounted in the airframe. The crank is normally at the top, with the oil gallery next to it. the main bearing is on the outside, that’s what the crankcase is mounted on.

This is the crankcase into which all the cylinders are screwed.

This is the crankcase into which all the cylinders are screwed.

Here is a cylinder, and in front of it is an old cast iron cylinder liner that's been removed by breaking it out. You can see that it's incredibly thin - no more than about 1.5mm by my reckoning and it's a press fit into the cylinder. So it has to be made much thicker and bored out in situ before it's honed. The cylinder itself has been machined from a solid forging...

Here is a cylinder, and in front of it is an old cast iron cylinder liner that’s been removed by breaking it out. You can see that it’s incredibly thin – no more than about 1.5mm by my reckoning and it’s a press fit into the cylinder. So it has to be made much thicker and bored out in situ before it’s honed. The cylinder itself has been machined from a solid forging…

Here's the connecting rod, together with the block that fits on the crank. The block has grooves in it into which the strangely-shaped big ends fit and interleave with each other. there's no master con rod, as on most radial engines. They just move slightly in the grooves as  the engine rotates.

Here’s the connecting rod, together with the block that fits on the crank. The block has grooves in it into which the strangely-shaped big ends fit and interleave with each other. there’s no master con rod, as on most radial engines. They just move slightly in the grooves as the engine rotates.

This is the commutator ring that fits on the back of the crankcase. The HT lead from the magneto connects to a carbon brush which presses onto the face of the commutator ring you can see here. the brass inserts are connected to the brass eyebolts you can see sticking out and each one is connected by a piece of piano wire to its spark plug.

This is the commutator ring that fits on the back of the crankcase. The HT lead from the magneto connects to a carbon brush which presses onto the face of the commutator ring you can see here. the brass inserts are connected to the brass eyebolts you can see sticking out and each one is connected by a piece of piano wire to its spark plug.

This is the back of the front plate to which the propeller is attached. The gear ring is for the cam rings, which we won't go into on this page!

This is the back of the front plate to which the propeller is attached. The gear ring is for the cam rings, which we won’t go into on this page!

We were quite surprised at the rough quality of the machining on the inside of the front plate, but were told this was pretty common practice on the American engines, most of which were manufactured after the war, and it shouldn't cause any problems.

We were quite surprised at the rough quality of the machining on the inside of the front plate, but were told this was pretty common practice on the American engines, most of which were manufactured after the war, and it shouldn’t cause any problems.

And now for the problems.  A number of the cylinder bores are scored. You can see an example here. The scoring is too deep to be honed out - particularly since the liners are already so thin - and so they'll need to be replaced.

And now for the problems. A number of the cylinder bores are scored. You can see an example here. The scoring is too deep to be honed out – particularly since the liners are already so thin – and so they’ll need to be replaced.

Here's what the original steel piston skirt should look like; the marks on the skirt are machined in deliberately to aid lubrication.

Here’s what the original steel piston skirt should look like; the marks on the skirt are machined in deliberately to aid lubrication.

And here's a bad piston, with the machining marks worn away and some scoring evident as well. The plan is to replace all the pistons with new, aluminium ones (and yes, later le rhones were fitted with aluminium pistons). All the rings will be replaced as well, since the current ones seem to curve inwards at the cut, which means they've never sealed very well.

And here’s a bad piston, with the machining marks worn away and some scoring evident as well. The plan is to replace all the pistons with new, aluminium ones (and yes, later le Rhones were fitted with aluminium pistons). All the rings will be replaced as well, since the current ones seem to curve inwards at the cut, which means they’ve never sealed very well.

We’re waiting for Jean-Michel to come back to us with a more detailed cost breakdown…

Advertisements

From → Uncategorized

10 Comments
  1. I hope the quote isn’t too eyewatering. If it is, I’m sure crowdfunding could be an option, there will be plenty of people willing to contribute to get this wonderful machine fixed.

    The engineering on the rotary is amazing. Astonishing to think this technology is over 100 years old, from a time when ic tech was young. Thanks for the pics and commentary

    • Amazing, isn’t it? When you think how quickly metallurgy had moved along. I still can’t imagine how they manufactured ball bearings in those days.

  2. Kenneth J Stevenson permalink

    Fascinating, I always wondered what this type of engine looked like when stripped down. I’d love to see it while it’s in pieces as there is still quite a lot I don’t understand. good luck with the refurb., I hope everything goes well, and I just wonder if the aluminium pistons were the same diameter or possibly slightly smaller.
    Regards Ken Stevenson

    • So would I. I hope I can get over when Phil starts to rebuild it. I am particularly fascinated by the valve mechanism, and even Phil couldn’t describe how it worked! Apparently the aluminium pistons had slightly larger clearances. There appear to be major differences in piston design. The current ones are the original American ones – steel, with a domed crown. The aluminium ones they currently have – and which we can probably use – are likely modelled on the ones made by Thulin in Sweden and have a flat top. The ones made by Allens in the UK had a dip in the top. You pays yer money…

  3. Doesn’t seem that calamitous: I’ve seen many worse pistons and liners, but I guess they weren’t keeping me from the ground a thousand feet or more below. Are new pistons readily available? It all seems like consumable components, but I’m very glad I don’t have to pick up the bill, especially when they come in nines.

    It seemed amazing to me at first that you could just replace steel pistons with alloy, but I suppose with the rotary engine the pistons are balancing each other. I’m just trying to get my head round exactly what and where out of balance reciprocating forces are and struggling. I get that the cylinders are simply rotating in a circle round one centre, and the pistons rotating in a circle round a different centre, but is there some kind of force with a period 9 times rpm? Between the situation where there’s a piston at TDC and 1/18th of a revolution later no piston at TDC but one at BDC? I don’t think I’ve got the maths to model it.

    I suppose thinking about it alloy pistons must have a greater static clearance because of different expansion rates. Do the different piston tops also go with different compression ratios? I suppose with a low rpm engine the flame path is less critical than on modern engines, but one combustion chamber shape must be better than another.

    • I’m not sure about the finer points of balance, and presumably the con rods don’t describe a perfectly even circle, but with speeds no more than 1000 – 1200 rpm, I don’t think it’s too much of an issue. I asked about compression ratio, and apparently all the different shapes work out the same. And I’m sure you’re right about the flame front; ignition is about 20 degrees before TDC and the exhaust valve opens about 45 degrees before BDC, so at 100rpm that leaves around 10 milliseconds for the flame. I’ve no idea, but I assume that’s an order of magnitude more than anything ‘normal’.

  4. Dave Clement permalink

    Interesting to see that the Le Rhône 9C’s cylinders had INTEGRAL cylinder heads, like the Offenhauser straight-four American race car engines so famous at the Indianapolis racing events…or like Saito Seisakusho’s model aircraft four-stroke engines of today!

    • They were all the same. It would have been for weight you get rid of all the weight of the joint faces and bolting arrangements. Apparently every part of the rotaries were forged steel. The cylinders were machined from a solid billet, and when you look at the machining involved, it makes your eyes water. Even with a modern 5-axis CADCAM machine, it would be a massive challenge.

  5. ivor davies permalink

    i have worked on tractor engines over the years but this is all new to me , I would like to know why has using castor oil done so much damage when it was used originally and is there an alternative, also how long did engines go for in WW1 before needing overhaul

    • We had two problems. Using pure castor oil caused deposition of masses of gunge inside the engine. If we’d used Castrol R the detergents would have kept it clean.
      The scoring was caused by LACK of castor oil – I’d accidentally turned the oil supply off to the engine before the last flight, and the Shuttleworth Collection has come across a NACA report from the 1920s which says that a rotary engine will run for about half an hour before causing problems, which is exactly what ours did…

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: