Author Topic: 30cc Flat Four (Puma)  (Read 2355 times)

Offline doubletop

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30cc Flat Four (Puma)
« on: June 27, 2019, 11:10:53 AM »

I built the Malcom Stride Bobcat something like six years ago







When I was building it t occurred to me that the crank could easily accommodate another pair of cylinders in a flat four configuration.
 


It was put on the “to do” list. I did build the Lynx and then locomotives got in the way.
 
Jason and Brian beat me to doing a flat configuration but they both did a twin based on Malcolm’s Bobcat or Jaguar parts.

Jason’s Ocelot



Brian’s Opposed Twin



A year or so ago I needed to teach myself CAD and used Malcolm’s drawings as the basis for my learning. That didn’t get much further than the parts for the original Bobcat design and a bit of a lash up in the assembly package.

Fast forward to a few weeks ago an I picked it up again and did the drawings for the parts to make the flat four.





All Malcolm’s engines have drawing numbers -
 
Lynx - NE15S – Nemet 15cc single
Bobat – NE15IT - Nemet 15cc Twin
Jaguar - NE7.5S   - Nemet 7.5cc Single

Jason has followed the convention with

Ocelot - NE15FT Nemet 15cc Flat Twin

Its been a while but here we go and unless there is a reason or not using the name ‘Puma’ this is going to be
 
Puma - NE30FF Nemet 30cc Flat Four

Pete
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Online Jo

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Re: 30cc Flat Four (Puma)
« Reply #1 on: June 27, 2019, 11:14:16 AM »
 8) I'll be following along

Jo
Usus est optimum magister

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #2 on: June 27, 2019, 11:38:31 AM »
….. and its not vapourware, I’ve made a start









I’m not promising rapid progress and there may be a few stumbles on the way. I’ve had to make drawing changes already. But I guess that’s to be expected.

Pete
« Last Edit: June 27, 2019, 11:41:59 AM by doubletop »
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline Jasonb

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Re: 30cc Flat Four (Puma)
« Reply #3 on: June 27, 2019, 12:29:00 PM »
You have made good progress since we exchanged e-mails the other week, Puma sounds good to me.

looking forward to see the belt driven twin cams turn out rather than the gear drive option, almost seems a shame to cover it up.

Offline b.lindsey

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Re: 30cc Flat Four (Puma)
« Reply #4 on: June 27, 2019, 02:57:08 PM »
Looks like a fine project Pete. Watching along here as well.

Bill

Offline Ye-Ole Steam Dude

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Re: 30cc Flat Four (Puma)
« Reply #5 on: June 27, 2019, 03:03:04 PM »
Hello Pete,

I will be following along on this build, looks like a great start already.

Have a great day,
Thomas

Offline Laurentic

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Re: 30cc Flat Four (Puma)
« Reply #6 on: June 27, 2019, 06:21:25 PM »
Looks an interesting engine already Pete, nice looking start, I'll be following this one along too.

Chris

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #7 on: June 27, 2019, 09:43:36 PM »
Thanks for your good wishes everybody.

I had to make a start before I posted anything. It would have been too easy to fiddle about in the CAD package tweaking this and that and then getting distracted by something else. Cutting metal makes a commitment to carry on. 

My emails with Jason the other week were around any problems he had experienced with his flat twin and whether I should continue with the flat four or consider doing it as a V4. I was concerned about oil in the cylinders, I have some thoughts and Jason has some suggestions so we'll get to that at some point.

Jason has asked about covering up the belt drive, I have considered that. The parts have arrived from Belting Direct and although I have allowed for the extra size adding a belt tensioner may be a problem. We'll cross that bridge when we get to it. Making a round bearing holder would certainly be easier and help with the setting up. I may well do that for now.

I don't like doing repetative work so making four or eight of everyting will be a challenge so posts here will be infrequent, I'll just show differences to Malcolms original design and sub assemblies as they are made. It won't be a blow by blow 'how to' guide. Malcolms original aricles did a better job than me on that and 90% of the parts are to his original design.

I'm waiting for the bearings to arrive so I'm on the cams at the moment. They need a bit of concentration.

regards

Pete
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline Brian Rupnow

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Re: 30cc Flat Four (Puma)
« Reply #8 on: June 27, 2019, 10:18:48 PM »
Doubletop--Very nice cad work. I wish you great success with the build and will follow along. I anticipated trouble with an oil base, just as Jason experienced with his twin. The revolving crankshaft picks up the oil and throws it into the cylinder on one side of the engine. I solved that issue by having a removeable cover-plate which let me give the crankshaft and rods a good squirt of oil from a can before I ran the engine.---Brian

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #9 on: June 27, 2019, 11:23:36 PM »
Brian

I'm planning a deeper sump so the oil has somewere to return to and I have discussed baffles with Jason. Simple plates with slots in for the conrods. They could well be integral with the sump.

Pete
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline Art K

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Re: 30cc Flat Four (Puma)
« Reply #10 on: June 27, 2019, 11:46:36 PM »
Pete,
This looks like a great project and I will be following along. I totally understand taking your time, we will be here.
Art
"The beautiful thing about learning is that no one can take it away from you" B.B. King

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #11 on: June 28, 2019, 11:44:10 AM »
A chilly Friday night here in NZ so I tinkered with the CAD

Feasibility of adding the oil baffles and an alternative simpler exhaust pipe on the right hand side



And timing belts



More by luck than design, apparently the pulleys and standard belts I ordered will fit without the need for a tensioner. We'll see.

Magnet disks for the ignition should be easy to install and as Jason suggested the cover can be dispensed with.

Getting a bit ahead of myself though.

Pete
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline Jasonb

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Re: 30cc Flat Four (Puma)
« Reply #12 on: June 28, 2019, 12:26:31 PM »
Exposed belts look good, a bit of tarting up of the plain pulleys may add a bit wow factor.

For the sump I was thinking of a trough, similar to what Graham has on these two engines and Jo's Seal & Seal major will have the same sort of arrangement. Once the oil in the trough has been flung out as the engine is started it can only flow back slowly through a small hole or two which limits what gets thrown about. Alternative with your deeper sump would be to have some oil flingers and keep the oil level below that of the crank and big ends so only a small amount of oil gets picked up.

http://www.modelenginemaker.com/index.php/topic,4680.0.html

Offline cnr6400

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Re: 30cc Flat Four (Puma)
« Reply #13 on: June 28, 2019, 03:34:21 PM »
Great looking engine CAD work!  :ThumbsUp: :ThumbsUp: :ThumbsUp:

One suggestion - Looks to me like the crankshaft pulley has about 90 degrees of "wrap" of the belt. I would suggest adding an idler pulley in the non-tension side span between crank and cam to get closer to 120-180 degrees of "wrap". This will reduce stress in the belt and lower the chance of skipped teeth as the belt warms up at high rpm. Just food for thought, I've designed some timing belt systems for a few companies, and had the hoo-ha's with low wrap / high load situations.

Offline Allen Smithee

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Re: 30cc Flat Four (Puma)
« Reply #14 on: June 28, 2019, 08:07:02 PM »
Slightly surprised you went for two camshafts - surely with a two-throw crank (so the left and right cylinders are alternate-firing) you only need one camshaft?

AS
Quidquid latine dictum sit altum sonatur