Author Topic: Cosworth V8 1:12 scale  (Read 3548 times)

Offline Kim

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Re: Cosworth V8 1:12 scale
« Reply #45 on: November 30, 2020, 05:26:02 AM »
Nice work Steve  :ThumbsUp:

Kim - as your question was a bit of two questions in one (one about this particular and one general) ->
Generally all V-engines have a mirrored parts, though the placement is usually a con-rod offset between the halves (there are exceptions, with 'Fork 'n' Knife Rods').
Inlets and Exhausts have different pressure and temperature -> bigger diameter on the Inlet ducts and valves and smaller diameter on the exhaust side -> optimum power, etc.
Interesting... that makes a lot of sense.
Thanks, for the additional explanation, Per.
Kim

Offline Steve Crow

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Re: Cosworth V8 1:12 scale
« Reply #46 on: January 04, 2021, 04:02:35 PM »
I still have not finalised the design for the pistons for this engine.

I am hoping to use brass liners in the cylinders.

Any suggestions or help with piston design?

Specifically:-

Which material?

What sort of fit and finish?

Does it need any grooves?

Many thanks in advance,

Steve

Online Jo

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Re: Cosworth V8 1:12 scale
« Reply #47 on: January 04, 2021, 04:28:09 PM »
I am hoping to use brass liners in the cylinders.

 :headscratch: On small Aero engines we use steel with Cast Iron or Ali pistons (CI pistons do not need rings, Ali ones will). Never heard of using Brass  for liners. I'll go and see what my books say

Edit: Yes book says hard brass liner chrome plated in the bore was used on commercial engines. They would use ringless aluminium pistons. This means you need to need to use a low-expansion aluminium piston and a plated brass or aluminium cylinder, this requires that the piston fit when cold be tighter than it will be at operating temperatures  :paranoia:

The expansion rates of brass and aluminium alloys which are suitable for cylinders need to be around the same. This limits the designer's scope to choosing between different piston alloys, with a higher silicon content  which have lower thermal expansion coefficients. With commercial ABC engines the pistons are cast, this allows for them to be made of an alloy of up to 18% Silicon. With competition engines the pistons are made of an alloy formed by fusing a mixture of powders under heat & pressure, this allows Silicon contents up to 30% to be achieved.

Jo
« Last Edit: January 04, 2021, 04:50:37 PM by Jo »
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Offline Steve Crow

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Re: Cosworth V8 1:12 scale
« Reply #48 on: January 04, 2021, 04:35:50 PM »
"On small Aero engines we use steel with Cast Iron or Ali pistons (CI pistons do not need rings, Ali ones will). Never heard of using Brass  for liners. I'll go and see what my books say"

Please bear in mind that this engine will run with compressed air. I should imagine that this has very different requirements to IC engines.

Steve


Offline steamer

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Re: Cosworth V8 1:12 scale
« Reply #49 on: January 04, 2021, 07:14:20 PM »
For compressed air service, and well lubricated, brass should be fine...

I probably wouldnt enter it at Lemans...but I suspect it will make all the right noises when run
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Offline stevehuckss396

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Re: Cosworth V8 1:12 scale
« Reply #50 on: January 04, 2021, 09:43:46 PM »
When I built mine I used Delrin (plastic) for my pistons and made them about .002 smaller than the bore. No rings are used.
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Offline Steve Crow

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Re: Cosworth V8 1:12 scale
« Reply #51 on: January 05, 2021, 10:49:06 AM »
Lovely engine Steve!

Is there a build log or more photos on this site?

I understand its advantages but I am reluctant to use delrin for the totally baseless reason that it's not metal. I know it doesn't make sense, just being a traditionalist.

Offline Steve Crow

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Re: Cosworth V8 1:12 scale
« Reply #52 on: February 08, 2021, 09:04:27 AM »
Hello, I haven't updated this thread for a while so here we go.

I have been cutting the gears for the cam gear train, and lots of spares.



There are 11 gears in the train in 4 different sizes.


 

They all came out ok apart from the 20 tooth wheels which I didn't give enough depth of cut. Only a couple of thou but it's made a difference at Mod 0.3. This is unfortunate as 7 of the 11 gears are 20 tooth! I'm just going to have another go.

To hold the wheels for facing, drilling etc. I made pot chucks for each size.



These just screw into a 8mm collet thingy.



They give a nice friction grip that doesn't do any damage. You don't need glue or shellac.



I made a spare of course.



I centre drilled one of each size as "test" gears. I'll fix an arbor to each and put them in my depthing tool and see how they mesh.



More soon.

 

Steve

Offline Steve Crow

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Re: Cosworth V8 1:12 scale
« Reply #53 on: February 08, 2021, 10:17:16 AM »
These are the cam carriers. I think that's the term. If someone has a better name for them, let me know.



They are about 80% finished. I just need to cut a groove for the cam bushes and drill and tap a few holes for end plates.



Made from 1/4 x 3/4 mild steel bar. Quite tricky milling operation with all the angles.



A total of 48 M1.2 holes to tap - I have done around half.



Steve

Offline Steve Crow

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Re: Cosworth V8 1:12 scale
« Reply #54 on: February 08, 2021, 10:20:07 AM »
Cam carriers and cylinder heads.





Steve

Offline Steve Crow

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Re: Cosworth V8 1:12 scale
« Reply #55 on: March 01, 2021, 01:34:19 PM »
I made a start on the camshafts. First of all I turned the blanks and a couple of spares from 1/8" silver steel.



 

The brass gadget on the end is to support and provide a female centre for the shaft and also, when I move it in the collet chuck when milling, I can use the flat part for indexing and make sure all the lobes are of correct orientation.



Here they are sat on the cam carriers.



Here they are with the lobes milled.


 

Each lobe has 36 facets which I will have to file and polish out.




This is the cam profile I've tried to achieve. There is no science behind me using this shape - it's just easy to draw and "looks right".




It was difficult to get a photo of the profile but you can get a good idea from this one.



More soon,

Steve

Offline Admiral_dk

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Re: Cosworth V8 1:12 scale
« Reply #56 on: March 01, 2021, 06:57:55 PM »
You have been busy with some very small parts and they look good.  :cheers:

Per

Offline Steve Crow

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Re: Cosworth V8 1:12 scale
« Reply #57 on: March 08, 2021, 02:25:16 PM »
I made some temporary arbors for the cam train gears and checked them with a depthing tool.



They meshed very nice and smoothly and the centre distance seemed bang-on as well.

But, they just didn't look right in brass, it made everything look a bit "clockwork", so I remade them all in steel.



Here are the steel test gears with temporary arbors and a brass one for comparison.



Steve