Author Topic: 30cc Flat Four (Puma)  (Read 7148 times)

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #15 on: June 28, 2019, 11:31:31 PM »
Thanks for the feedback, thatís why we are here.

Jason - Now I understand what you meant by the curved baffle; I was planning to ask you. I've been away from here for too long and have missed following what others have been up to. It certainly looks like the solution. As well as limiting the amount of oil thrown into the bores it will direct it at the cams. In fact, when I was boring the crank case I had considered leaving the curves in place at the sides and leaving the camshafts in their own separate bore. There would have then been a lubrication problem to solve for the camshafts. I thought that was a step to far at this point and went with Malcolm's approach of a fully opened out crankcase.

cnt6400 - Thanks for the advice. The belt I'm using is a standard 145mm I had expected a bit of slack that needed tensioning but the CAD package tells me not. If I went to the next size of 165mm I could add a tensioner. We'll see when I've got the crank and camshafts in. I've yet to make them and can't dummy them up as the bearings haven't arrived yet.

Allen - Yes; that was my first thought and started out on that route. With a single centralised camshaft the tappet guides would have been quite long, but not really a problem. However, I think the crank would have fouled the camshaft. I could have moved it up a bit and had the pushrods at a slight angle. Not wanting to make too many changes went for twin cam to keep it as close as I could to using Malcolmís original components.  Given a cylinder configuration of 1. front left, 2. rear left, 3 rear right 4 front right.  A single camshaft would give a firing order 1,4,2,3 with 2 camshafts you have the opportunity to do 1,3,4,2 which may be a bit more balanced. Whatsmore a 30cc Flat Four Twin Cam is a bit more sexy.

Pete

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

Online Art K

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Re: 30cc Flat Four (Puma)
« Reply #16 on: June 29, 2019, 02:14:48 AM »
Pete,
The only thing that I would throw in the mix, not to muddy the water though. Is that most full sized flat fours have a crank much like a inline 4 the end throws up and the center two down. I did see another flat 4 build that had the same crank configuration as you're planning so I know that it works.
Art
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Offline Jasonb

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Re: 30cc Flat Four (Puma)
« Reply #17 on: June 29, 2019, 07:22:09 AM »
. Whats more a 30cc Flat Four Twin Cam is a bit more sexy.

I think that sums it up well, when designing an engine that won't really be put to work so weight, performance, etc are not such an issue the designer can just go with what they fancy. If I remember rightly I had to move my single cam slightly further away from the crank and had to alter the gear teeth to suit.

The Jung's flat 4 model has a similar crankshaft arrangement so you should be OK. Malcom did do several articles about crank designs and balance as a build up to the Bobcat series and goes into detail why he opted for a flat crank.

Offline bruedney

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Re: 30cc Flat Four (Puma)
« Reply #18 on: June 29, 2019, 08:00:09 AM »
Following along Pete.

Look forward to seeing it in the flesh sometime.

Where are you getting your bearings from? I source bearings from NZ Miniature Bearings if I am not wanting to wait for them to come from Aliexpress sellers

Cheers
Bruce
ĎResults! Why man, I have gotten a lot of results. I know several thousand things that wonít work.í ó Thomas Alva Edison

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #19 on: June 30, 2019, 10:48:01 AM »
I'm happy that the crank, as proposed, will be OK it will allow a cylinder to fire every half rev so that would balance everything out without needing any balance weights. Again, we'll see.

Bruce - the bearings are coming from Bearings Direct in the UK. Unfortunately, NZ suppliers seem to be overly expensive and although Aliexpress are cheap their delivery timing can be a bit hit and miss.  I may be taking it to the club night on Wednesday.

This weekend has been a bit of a mission in making the cams. After a failed attempt I ended up with two good blanks. Then I struggled to get the rotary table line up accurately on the mill. Leaving it until the next day I had it done in 30 mins. I then made a start on machining the cam profiles but realised, after about 30 steps, I was going the wrong way! That required another blank making.

Malcolmís cam table only shows the 120steps between 300->0>60 degrees. The base circle is another 240 steps so with two blanks 720 steps plus the wasted so about 750. (No need for suggestions of CNC thanks, I get it. This isnít the first job Iíve done that Iíve been winding handles for hours mentally adding CNC to the to do list.)

Malcolm suggests cutting the profiles using the Z axis of the mill. I did that the first time round but as you are cranking the weight of whole mill head up and down, at times only 0.01mm, I found it less than satisfactory. This time I used the Y axis and had far better control. However, it does require the rotary table and fixed centre to be set up accurately along the X axis. If you use the Z axis you just need to ensure the height of the centre is accurately set. Alignment along the X axis isnít that important. Maybe thatís why Malcolm suggested doing it his way?







So Iíve now got 8 cams ready to be separated the bosses trimmed to length and the holes drilled and reamed, then thatís another of bigger jobs done.

Pete


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

Offline MJM460

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Re: 30cc Flat Four (Puma)
« Reply #20 on: June 30, 2019, 12:34:46 PM »
Hi double top, a great thread, I am enjoying following along. 

Donít worry too much about rotating the wrong way when you were making that cam.  In my working life, I was in an office of a very large company who were making steam turbines.  In the foyer was an example of their work, a turbine rotor, about five meters long, with the smaller parts of the shaft over 300 mm dia, and the blades ranging from around four cm long, not very long as it was obviously a very high pressure turbine rotor, as an example of the work they do.  All machined in one piece from a single forging.

I asked how it came to be available to put on display.  Apparently it was machined to rotate in the wrong direction!  It happens to the very best of us.  You can put yours on display beside the engine at a show.

MJM460

The more I learn, the more I find that I still have to learn!

Offline Allen Smithee

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Re: 30cc Flat Four (Puma)
« Reply #21 on: June 30, 2019, 08:31:52 PM »
Great stuff - really appreciate you sharing. Can I ask a question (I want to understand so I can copy ideas for my own projects!)?

Do I understand correctly that these blanks will each be cut up into four individual cams, each of which will then be bored and mounted on a shaft? If so how will they be fixed to the shaft - press fit, bonding, pinning, silver soldering or something else?

And would each resulting camshaft than be carried in two ballraces, one at each end?

Thanks,

AS
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Offline Brian Rupnow

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Re: 30cc Flat Four (Puma)
« Reply #22 on: June 30, 2019, 09:00:00 PM »
Allen--They are attached to the shaft with Loctite. It holds fine, and an added benefit is that if you install the cam segments ass backwards as I did, a little heat from a torch frees them up very easily and lets you turn them around.---Brian

Offline bruedney

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Re: 30cc Flat Four (Puma)
« Reply #23 on: June 30, 2019, 09:35:45 PM »
Bruce - the bearings are coming from Bearings Direct in the UK. Unfortunately, NZ suppliers seem to be overly expensive and although Aliexpress are cheap their delivery timing can be a bit hit and miss.  I may be taking it to the club night on Wednesday.

Hi Pete
I find NZ Miniature Bearing very reasonable https://nzminiaturebearings.com depends on size and what quality you want. I have also found and Aliexpress supplier that is quite consistant in their shipping https://fushi.aliexpress.com/store/511615?spm=a2g0s.9042311.0.0.27424c4dZsZPaM
I hope to be there on Wednesday but depends on how things go today and the next couple of days. Lee's mum passed away last week and the funeral is today.

Regards
Bruce
ĎResults! Why man, I have gotten a lot of results. I know several thousand things that wonít work.í ó Thomas Alva Edison

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #24 on: June 30, 2019, 10:01:09 PM »
Bruce - Sorry to hear about Lee's mum, hopefully I'll see you on Wednesday. On the bearings I'll admit to a bit of laziness. The bearing specs in the ME article for the Bobcat have an error so I went back to Bearings Direct to check what I had ordered last time. As I was there it was too easy to just re-order.

MJM460 - In my case if I had been on the turbine rotor job the 4cm blades would have been 2cm. I moved the Y axis in rather than out from the initial cut for the base circle. I was going well and went in for lunch and when I came back to the job I realised what I had done.

Alan - Yes ball races each end you can see them in the CAD pictures. Brian has answered you on the fixing of the cams. As he says the benefit being if you stuff it up you can go again. Given I'm doing two shafts with different firing order there's plenty of opportunity to do that. Fixing the cams to the shaft will be some time off yet and be done when I confirm the firing order and ignition so the whole thought process is done in one session. I did the cams now just to get a tedious job out of the way.

Pete
« Last Edit: June 30, 2019, 10:06:48 PM by doubletop »
?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 #25 on: July 01, 2019, 07:24:52 AM »
On the bearings I'll admit to a bit of laziness. The bearing specs in the ME article for the Bobcat have an error so I went back to Bearings Direct to check what I had ordered last time. As I was there it was too easy to just re-order.

I see what you mean Pete  :thinking: , the article starts by saying they should be 68000 bearings they clearly added one too many zeros at the end  :Doh: Maybe they got confused that it needed an extra numeral as the next bearing they quote is the 61800  :headscratch:

I can't see why you would choose the 61800 over the 6800, they are both open deep ball bearings of the same dimensions  :noidea:

Jo
Usus est optimum magister

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #26 on: July 01, 2019, 08:26:39 AM »
On the bearings I'll admit to a bit of laziness. The bearing specs in the ME article for the Bobcat have an error so I went back to Bearings Direct to check what I had ordered last time. As I was there it was too easy to just re-order.

I see what you mean Pete  :thinking: , the article starts by saying they should be 68000 bearings they clearly added one too many zeros at the end  :Doh: Maybe they got confused that it needed an extra numeral as the next bearing they quote is the 61800  :headscratch:

I can't see why you would choose the 61800 over the 6800, they are both open deep ball bearings of the same dimensions  :noidea:

Jo

 Jo

Worse than that the  bearing should be a 6801 12x21x5 not 61800 10x19x5  as stated in the ME article

.... and now looking at the invioce I didn't get them from Bearings Direct I've ordered them from Simply Bearings.

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 #27 on: July 01, 2019, 09:29:49 AM »
 :facepalm: See what you mean Pete. Looks to be two bearings of 19mm O/D and one of 21mm O/D. I did wonder why in the parts list they had broken the bearings out over two lines and then quoted the same numbers rather than just having one line.

At least they are not too expensive if you get caught by their mistake and have to buy another set  ::)

Jo

Usus est optimum magister

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #28 on: July 02, 2019, 10:33:10 AM »
Following along Pete.

Look forward to seeing it in the flesh sometime.

Where are you getting your bearings from? I source bearings from NZ Miniature Bearings if I am not wanting to wait for them to come from Aliexpress sellers

Cheers
Bruce

Bruce

Thanks for the heads up. NZ Miniature Bearings are certainly cheaper and I could well have them by now had I gone to them.

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

Offline Ian S C

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Re: 30cc Flat Four (Puma)
« Reply #29 on: July 02, 2019, 12:53:47 PM »
When I buy bearings I use SMP bearings in Carlyle st Christchurch, their prices seem ok.
Ian S C