# 1/5 scale Bristol Centaurus



## EthanHopper (Mar 20, 2017)

Hello I'm pretty new here and this is my first thread so pardon me if i did this wrong. But I've embarked on a new project recently and thought I'd share it and gain wisdom from some others more experienced in the hobby. 

I've drawn in cad the plans for a model of an 18 cylinder double row, sleeve valve bristol centaurus radial, quite a daunting one I'm aware. The engine will not be an exact replica and is quite simplified but will have the same overall characteristics and mechanical workings. It was an engine primarily used in  the british hawker sea fury fighter of WWII and is a really interesting engine. It is a standard 18 cylinder double row configuration but uses sleeve valves used in other engines like the napier sabre instead of poppet type valves.

I'm a high school student and I'm doing this as a senior double credit project that i was able to decide. I know at first thought you may think it is way out of my range and your probably right, but i do know what I'm getting into and I'm not that bothered with the nay sayers and the project is going quite well, I have a decent knowledge of engine mechanics and machining, and the fact that i made the drawings and took on the project in the first place i think shows that. I welcome your thoughts, questions or concerns. I've attached a picture of the plane, engine, the progress on the crankcase so far and rough cylinder blanks


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## Herbiev (Mar 20, 2017)

Wow. That's some project. I'll be following with great interest


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## Cogsy (Mar 20, 2017)

I'll be following too. Lots of work but it can be done. Good luck!


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## Charles Lamont (Mar 21, 2017)

This may be of interest:

http://www.enginehistory.org/ModelEngines/bristol_hydra.shtml


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## EthanHopper (Mar 22, 2017)

My 72 head bolts came in today and at a good time with all the cylinder blanks bored and turned (no cooling fins yet, i wanted to machine my ports first). Because of the sleeve valve design the engine is a 4 stroke but has a 2 stroke style head with no valves and only the ignition i n it, therefore it allows for very simple head fastening with 4 bolts running through the head and cylinder into the crankcase. I apologize for the sideways pictures if anyone has a fix please let me know. Thanks


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## IceFyre13th (Mar 22, 2017)

This is going to be cool!!!!!


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## wirralcnc (Mar 22, 2017)

www.agelessengines.com/sleeve.htm

Check this one out.


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## EthanHopper (Mar 22, 2017)

Thats a beautiful looking engine. It looks like a model of a bristol hercules, same company, same design, just 4 less cylinders than the centaurus. He's doing a much more exact replica to the full scale one and it looks perfect.


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## Cogsy (Mar 22, 2017)

Firstly, your engine is looking great. I'll be following along for sure.




EthanHopper said:


> I apologize for the sideways pictures if anyone has a fix please let me know.


 

 As for your pictures, it's likely that you're using an iPhone or iPad to take them. If so, make sure the 'home' button on the device is at the bottom when you take 'portrait' pictures, or the right side when you take 'landscape' pictures. Apple products are very stubborn about the "right" way up for images they take.


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## EthanHopper (Mar 23, 2017)

Thanks! I did wonder if anyone had any suggestions on parting tools for cutting cooling fins? the size of the fins were not an issue for design and won't affect any other part of the engine so they can be decided upon later. The smallest parting tools we have here at the school shop are 1/8" carbide which makes for a fairly rough and toyish look with the fin grooves being so wide, i can use a HSS tool bit ground to be a small parting tool and will likely do this for the piston ring grooves, but they tend to gum up with a long deep cut and don't handle it as well as the carbide. I'd still like for the fins to be fairly small and close to give it a closer look to full size engines but beggers can't always be choosers


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## deverett (Mar 23, 2017)

You obviously have access to some good tooling at school.  School must have plenty of spare funds (!) so why not persuade them to invest in something like
http://www.thinbit.com/
There are other companies that have similar tooling but you'll get the idea.

Great progress you are making, by the way.

Dave
The Emerald Isle


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## EthanHopper (Mar 28, 2017)

Back at it again, had a few days off school last week but full steam ahead this week. I've started on my cylinder heads now as I'm waiting on tooling to finish up the cylinders, you can see the rough blanks have been cut and faced. They're a very simple design because of the valveless head. You can see here in the drawing (head is in purple) it's basically just a large step turned with the glow or spark plug thread in the center, and the 4 head bolt holes. There is a small groove at the bottom you can see and this is actually for a piston ring, because of the moving sleeve valve which is also the combustion chamber the sleeve needs to seal both on the piston and the head; Therefore it has rings on the piston and on the head that protrudes into the cylinder. I said earlier glow or spark plug because I've allowed room for either but haven't quite decided yet. It has an 8:1 compression ratio so i think should work good with gas or glow and there is a place and optional drive for distributors on the back I'm just still working out if spark is worth the extra time i don't really have


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## deeferdog (Mar 28, 2017)

I think your work extremely good, as for the fins, have you thought of using a hacksaw blade. Grind the end to shape. I don't imagine you would be going in to any great depth and would give a nice thin groove.
Cheers.


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## EthanHopper (Jun 12, 2019)

It's been a couple years, not sure if anyone's still out there, but intending to get back to this engine. The crankcase has been a cool display on my dresser for some time, I graduated and it got shelved like lots of things. But I think it's time to continue it. I would also like to endeavor into some aluminum casting for fun and reduce some of the large billet otherwise needed that's difficult to buy in small lengths. I've also decided that if I'm going to finish it im doing it right and going with spark ignition, any articles and pointers on that are appreciated. Also since I need 18 spark plugs the $30 miniature ones will get a little expensive, if anyone knows another option for more commercially available small ones I'm all ears.


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## ddmckee54 (Jun 12, 2019)

Ethan:

I didn't have much luck on this site searching for threads on building your own spark plugs, apparently the search function is smarter than I am.

I did however find several threads over on MEM, here's one on how to build your own.   There's more, this is just an example.  http://www.modelenginemaker.com/index.php/topic,3172.0.html

After all, how long could it take to make 18-ish spark plugs?  Because you know your going to need spares.

Don


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## stevehuckss396 (Jun 12, 2019)

Www.miniaturesparkplugs.com


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## EthanHopper (Jun 12, 2019)

I have heard of people making them but I don't know if I'm that motivated lol. Was thinking something as small as is easily available, weed wackers or something along those lines, the heads have lots of room since the lack of valves. As far as info though anything about distributors or hal effects sensors would be cool, i'd to keep it simple and fairly reliable which is ironic I know for making an 18 cylinder radial but all the more reason so as to ease troubleshooting.


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## EthanHopper (Jun 12, 2019)

ddmckee54 said:


> Ethan:
> 
> I didn't have much luck on this site searching for threads on building your own spark plugs, apparently the search function is smarter than I am.
> 
> ...



I dont know if im motivated enough to make 18 spark plugs lol, but would be cool. Lots of room in the heads due to the lack if valves so was thinking as small as you can buy from commercial manufacturers for small weed wackers etc. But I'll consider anything. As far as info and articles distributors, hal effects and ignition systems would be cool, not much of an electrical guy but always interested in learning


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## ddmckee54 (Jun 12, 2019)

Not motivated enough, I don't see why not, it's not like you're making 18 copies of just about everything else.  Wait a minute, you are - ummmm...  Well, what's one more measly little part?  You could even make them in different colors.  Then instead of "Joseph and his multi-colored dream-coat", it'd be "Ethan and his multi-colored Centaurus."

Good luck with the build, whatever you decide.

Don


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## lohring (Jun 13, 2019)

This is a sleeve valve engine and cutting the sleeve ports is not trivial.  Below is a diagram that gives an idea of the layout and timing for this and similar engines.  The basics of the sleeve drive can be seen in this single cylinder engine.  An engine like yours can be seen here.

Lohring Miller


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## Ivan Winters (Jun 13, 2019)

If you are actually planning to fire up this engine then I would be worried about your previous comments re cutting cooling fins  with a very fine passage between them (your post of Mar 23 2017 refers to this - to remind you over two years later !). With a small passageway between the fins airflow will be restricted and hence heat dissipation. Heat dissipation is important because the piston and cylinder bores must heat at a similar rate. Otherwise if the piston heats a lot faster than the bore it will jam on the inside of the bore. If the bore heats a lot faster than the piston then the sealing around the sleeve valve as the piston moves up and down will be lost !!


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## JimDobson (Jun 14, 2019)

What a great thread.


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## Motorman1946 (Jun 14, 2019)

I'm going to be following this thread along because partly it's an interesting engine being a radial sleeve valve engine, partly because undoubtably I will learn a lot (already found how to make spark plugs!) and partly because it's really quite an ambitious project build, so there will be some interesting techniques to witness and admire!  So I wish you the best of success and very much hope it comes to fruition and runs well.

Now, I know this maybe will seem like teaching granny to suck eggs, but beware of excessive clearances especially sleeve to liner.  I have built a small bore (0.7875") single cylinder sleeve valve engine which hasn't run yet.  Part of the problem is acute lack of compression.  The cylinder has an aluminium barrel, with a cast iron liner, a hard steel sleeve and an aluminium piston with cast iron rings, and a junk head with a 'piston' ring type seal.  The head seals to the liner top well.no leaks.  The liner is a tight sliding fit in the barrel.  The sleeve bore was honed so as the piston was a fairly neat sliding fit too, plus the piston has two rings to correct clearances.  But I neglected the sleeve to liner clearance.  Must have got sloppy in the measuring or just had a senior moment.  Or both probably.  Measured them after getting no compression and found sleeve to liner had a clearance of about 0.005", not much but enough to loose all compression straight back out the ports.  Currently remaking a liner which will be a lapped fit with the sleeve - I hope that will do the trick!

Chris


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## ragnarok (Jun 14, 2019)

What an amazing first project. I will be watching this.

Here is a thread of another 18 cylinder radial build, by mayhugh1.  It's a very different model of engine, but mayhugh1's posts are long and detailed, with many explanations of his thought processes, techniques, and results, and many pictures. So maybe it can help(if you have time to sift through over 400 posts).

https://www.homemodelenginemachinist.com/threads/another-radial-this-time-18-cylinders.21601/


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## Gary Sweetland (Nov 15, 2019)

Anyone know where I can get a clear copy of the port timings earlier in this thread. I'm thinking of having a go at a sleeve valve engine, maybe a single to prove it works ok at first. And if that works, maybe a radial..


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## Precision Transmission (Nov 22, 2020)

Have you checked out this video?





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						Ageless Engines
					





					www.agelessengines.com


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