Bristol Mercury revisited

[zeeprogrammer]

I can't say much more than "Wow!".

Fascinating post.

[petertha]

Fantastic pictures and description, Mike.

[gbritnell]

Truly outstanding work Mike! It almost wants me to make another radial, this time 9 cylinders instead of 5.
I really enjoy your documentation and know how much work it is to stop and take pictures while you're making parts.
gbritnell

[Vixen]

Thank you all for calling in. 

It is only the positive response of our MEM forum members that makes it feel worthwhile to continue to write and post build progress.

With the number of model shows on the decline, I look at the MEM forum as our virtual, on-line, model show, somewhere were we can all showcase our work to a worldwide audience of like minded individuals.

And George, if you want to build a nine cylinder radial, you had better start soon. They take an enormous amount of time and effort to complete and none of us are getting any younger.

Mike

[Dave Otto]

Amazing work Mike!
Its always fun to see an update on your projects.

Dave

[Vixen]

Dave
Thanks for your kind comment. It's also fun to be at the receiving end.

Mike

[Vixen]

Some more small detail work underway for the two Mercury engines. This time I have been casting spark plug caps in polyurethane synthetic rubber.

This has required some mould making and more kitchen chemistry.

Each engine requires 18 spark plug caps, so I decided it would be reasonably efficient to make them in batches of 6 at a time, this obviously means 6 moulds and several repeat casting sessions. I started by making the moulds in perspex (I do like that material) with turned aluminium inserts to form the cavities for the cable and the spark plug. The pespex part was made from two 10mm thick blocks clamped together and drilled from all directions to form the mould cavity for two individual spark plug caps. Aluminium inserts were turned and used to 'core' the moulds. File lines were engraved in the perspex from the ends of the casting to the base of the mould. A vacuum is applied during the casting process to draw the PU rubber into and completely fill the mould. You can see the suction base on the right and the cardboard gasket used to seal the mould to the suction base.




The mould has been given a generous coating of furniture wax, inside and out, to act as a release agent. Here the first mould is clamped to the suction base, to which is attached the little hand vacuum pump I had previously used to test the valve seating on the Bristol Jupiter. Here we are all set-up and ready to go. We are either going to get some rubber spark plug caps or a lot of sticky goo. Fingers crossed




That's the engineering done, so here comes the kitchen chemistry. I bought a small two part PU casting kit; Mouldcraft PT-flex 85 PU casting rubber from a UK firm called Mouldcraft. Equal quantities of the two parts are required to be thoroughly mixed to make the PU rubber. I only need to mix a small quantity for each batch so I measured out equal quantities of the part A and part B in two small containers salvaged from some redundant fluorescent light starters. The two measures were mixed in a deep coffee powder spoon and mixed thoroughly.




A small quantity of the mixture was poured into the funnel on the top of the mould, a couple of strokes on the vacuum pump pulled the resin into the mould. The clear perspex made it easy to see when the mould was completely filled. The funnel was topped up, the first mould was removed and allowed to cure while the next mould was attended to.




The PU is supposed to cure in less than an hour but I left it overnight to be sure. Next morning, the mould was dismantled and the aluminium inserts removed with a twist and pull. The furniture wax released perfectly. The three moulds produced 6 plug caps, three were good and three had flaws. Not a bad yield for the first go round. The moulds were re-waxed and re-assembled ready for the next season. I hope to have learned a few lessons and the yield may be better next time round






The great thing about model engineering is the wide variety of challenges encountered. There is always something new to try.
And the great thing about the MEM forum are the members

Stay tuned

Mike

[Roger B]

Splendid  Can I put in an order?

[deltatango]

Thanks Mike, that post is an inspiration! One more to add to the long list of inspirations from your work. When I built Mastiff and the Wyvern I did think about how to make realistic, and useful, plug caps but dismissed the idea as impractical - I was clearly wrong.

David

[Vixen]

Hello David,

Thanks  , but there are a number of different ways to make nice looking plug caps. Have a look at Graham Meeks method. Starts about 1/4 the way down this page. https://modelengineeringwebsite.com/Miniature_spark_plugs_2.html

Cheers

Mike

[deltatango]

Hello Mike, Thanks, I hadn't seen Graham Meeks' work. His plugs and caps look entirely practical. If you need soft plug caps, e.g. to keep out water in a boat installation,  then molding from a soft(er) material may be better. Making, say, 18 plugs for a 9-cylinder rotary using GM's method looks more practical, and cheaper, than any other that I've seen.
David

[Vixen]

Hello David,

Quite so. I was impressed by Graham Meek's designs. I used his 'fish spine' spark plug design for the 1/3 scale Bristol Jupiter. I did a write up of the manufacture and test of these spark plugs in the 'By Jupiter' build log starting at reply #425 http://www.modelenginemaker.com/index.php/topic,7559.400.html.

And as you say, the soft PU plug caps are potentially (sic) more waterproof than GM's hard material caps. However most folk don't run their engines in the rain and wet.

Mike.

[deltatango]

Mike, I just followed that link and discovered (re-discovered) that I'd read it already  .

I can just about claim advanced age as an excuse but still!!

David

[Vixen]

David,

It's not the age but the mileage, which matters.

You going to the F1 this weekend?

Mike

[90LX_Notch]

Mike-

I'm still following along and I am blown away by the quality of this build.

-Bob