Model Engine Maker

Engines => Your Own Design => Topic started by: Steve Crow on November 22, 2020, 06:11:42 PM

Title: Cosworth V8 1:12 scale
Post by: Steve Crow on November 22, 2020, 06:11:42 PM
A few months ago, I decided to have a go at making a 1:12 scale Cosworth V8 DFV Formula 1 engine.

It will be a 2-stroke running on air (or CO2?) with a bore of 7.2mm and a stroke of 5mm.

I want to share my progress so far as I’m sure I will need some advice.

After making the drawings, the first thing I did was make card models of the main components.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879842.jpg)

 

This helps me visualise things and see if any screws interfere with each other etc.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879845.jpg)

 

The block started life as 1” square mild steel bar.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879843.jpg)

 

I sawed of a piece about 3” long and this was clocked in the 4 jaw and eccentric bosses, on the crank centre line, were turned at both ends. This gave me an accurate way of holding it while boring out the cylinders and milling the block to shape. In the picture below, the milling is part done.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879844.jpg)

 

The block, milled to shape. The bores are a bit rough but true. They will have brass liners anyway.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879846.jpg)

 

The block was drilled and tapped and the sump blank bolted to it.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879848.jpg)

 

The whole assembly was then drilled and bored out as one piece and the bosses removed.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879849.jpg)

 

More to follow….

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on November 22, 2020, 06:16:25 PM
The next job was to remove some metal from the inside of the sump and the block to provide clearance for the con rods.

Here is the block, ready to be milled. Note the miniature brass V-blocks – very handy things. You can see they are numbered. This is to ensure repeatability when using them with a 4-jaw.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879850.jpg)

And here they are completed. The block now weighs 60g. The initial square blank weighed 370g. That might not sound a lot of swarf to you guys with big-boy’s lathes, but it made a mess of the kitchen table with my Sherline.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879851.jpg)

More soon.
Title: Re: Cosworth V8 1:12 scale
Post by: Vixen on November 22, 2020, 06:19:28 PM
 :ThumbsUp: :ThumbsUp: :ThumbsUp: :ThumbsUp:
Title: Re: Cosworth V8 1:12 scale
Post by: gerritv on November 22, 2020, 06:23:11 PM
Wow, this makes it real.

Gerrit
Title: Re: Cosworth V8 1:12 scale
Post by: steamer on November 22, 2020, 07:08:45 PM
Wow!  nicely done!    following along!   

 :popcorn:

Dave
Title: Re: Cosworth V8 1:12 scale
Post by: crueby on November 22, 2020, 07:44:44 PM
Beautiful work - I like the little v-blocks too, have to remember that one.

 :popcorn: :popcorn: :popcorn:
Title: Re: Cosworth V8 1:12 scale
Post by: Roger B on November 22, 2020, 08:00:35 PM
Splendid  :ThumbsUp:  :ThumbsUp:  :)  :wine1:

I am also a user of CAD (cardboard aided design)
Title: Re: Cosworth V8 1:12 scale
Post by: Art K on November 22, 2020, 11:13:34 PM
Looks like a fun project, great work. Clever use of the brass V blocks to hold the block for machining.
Art
Title: Re: Cosworth V8 1:12 scale
Post by: Dave Otto on November 23, 2020, 01:02:01 AM
That is some nice table top machining there!
Your parts look very nice!

Dave
Title: Re: Cosworth V8 1:12 scale
Post by: Ramon Wilson on November 23, 2020, 08:31:36 AM
Very nice workmanship Steve - just shows what can be done on small kit when the desire is there  :ThumbsUp: :ThumbsUp:

I look forwards to seeing this progress further in coming weeks

Regards - Tug
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on November 23, 2020, 09:28:08 AM
Regarding the little brass v-blocks - I use them along with this gadget for holding small square sections in the 4-jaw chuck.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/844996.jpg)

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/844997.jpg)

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/845042.jpg)

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: Mosey on November 23, 2020, 02:07:15 PM
Spiders, I think they're called
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on November 23, 2020, 02:21:15 PM
I made some endplates from 1/8” mild steel flat bar. These hold flanged bearings for the crankshaft, 4mm at the gearbox end and 3mm at the cam-drive end. There is raised boss on the back of both which are a snug fit into the crankshaft bore to keep thing nice and true.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879852.jpg)

The one on the left will house the flywheel and the one on the right, the cam gear train.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879853.jpg)

The sump and block were drilled and tapped 12BA to secure the endplates and everything was assembled.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879863.jpg)

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879854.jpg)

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879856.jpg)

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: Admiral_dk on November 23, 2020, 07:44:53 PM
Nice parts and progress  :ThumbsUp:

Getting the  :cheers: and  :popcorn: ready.
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on November 24, 2020, 11:33:17 AM
I then fly-cut some steel to size for the cylinder head blanks and drilled and counterbored to suit the block. All in all, I had to tap 30 blind holes to M1.6 in the block. A bit scary.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879864.jpg)

I also cut to size blanks for the cam carriers. They can just be seen in the background.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879865.jpg)

Another shot.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879866.jpg)

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on November 24, 2020, 11:36:47 AM
The flat-plane crank is assembled from EN1A webs and 3mm silver steel journals.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879873.jpg)

 

The assembly was a tight friction fit then drilled, countersunk, pinned and riveted. 1mm mild steel pins were peened into the countersink then filed and polished over to render invisible.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879874.jpg)

 
The unwanted journals were then sawn out and the gaps between webs cleaned up on the mill.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879872.jpg)

This still needs a bit of cosmetic fettling.

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on November 24, 2020, 11:39:35 AM
Here is some of the crank in situ.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879875.jpg)

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879876.jpg)

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879879.jpg)

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879880.jpg)

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: nj111 on November 24, 2020, 12:44:54 PM
Great little project! Well executed!
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on November 25, 2020, 04:10:46 PM
Here is a drawing of a cross-section through the cylinders. It is sort of colour coded. Grey is EN3B, light blue EN1A, dark blue are screws and silver steel and orange or brown are brass except for the exhaust headers which are copper tube.

 

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879942.jpg)

 

The air is fed from the two brass vessels (plenums?) in the vee.

This a hypothetical cross-section as there are 4 valves per cylinder and the banks are staggered.
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on November 25, 2020, 04:12:15 PM
Here is another cross-section, this time between the cylinders.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879943.jpg)

When designing this, I had a bit of a headache making sure the screws didn't clash with anything or each other. The problem is, even using the smallest economically available, the screws are grossly over scale.

I'm using M1.6 allen screws with the head turned down to 2.35mm to hold the sump, block, heads and cam carriers together.

12 BA cheesehead screws with the head turned down to 1.95mm for the con rods, exhaust and inlet manifolds and also the cam covers.

I will use either M1.0 or 14 BA cheesehead to secure the cam shaft. I want to find a good quality supply of steel screws first(non-stainless, I'll be blueing them). When I find them, I'll buy the appropriate taps. If anyone has any advice on this, I would be grateful.

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on November 25, 2020, 04:13:43 PM
This is the gear train for the cams. The camshafts rotate counter to the crank. The blue gears (EN1A) are driven or drive and the orange/yellow (brass/nickel silver) ones idle.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879944.jpg)

This is quite a bit simpler than the full-size engine, which has compound gears, but it does resemble it.

The gears are Mod 0.3 as I have a set of involute cutters. It would work in Mod 0.4 or 0.5 as well.

This is part of the build I'm looking forward to most.

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: Roger B on November 25, 2020, 04:55:50 PM
I use two European sources for small fastenings:

https://www.mikromodellbau.de/artikelauswahl.php?kid=173&sprache=2

https://micro-model.ch/de/1483-din84-m1

Hopefully someone will suggest a more local source for you.

I'm enjoying someone else working with very small things  :ThumbsUp:  :ThumbsUp:  :wine1:
Title: Re: Cosworth V8 1:12 scale
Post by: ddmckee54 on November 25, 2020, 04:58:54 PM
I love the fact that you're building this with a Sherline.  (I've got both a Sherline and a Unimat.)

The fact that you're mostly building it out of steel is even more impressive.  Why did you chose to use steel for the block and heads over something easier to machine like aluminum or brass?

Don
Title: Re: Cosworth V8 1:12 scale
Post by: sco on November 25, 2020, 05:12:22 PM
I recently used this site for some small screws: http://www.modern-screws.co.uk/ (http://www.modern-screws.co.uk/).  They seem good quality but were expensive but then the small sizes all seem expensive for what you get by weight!

Looking at your block cross-section between the cylinders - is there definitely room for those head fasteners - the walls must be getting very thin?

Simon.
Title: Re: Cosworth V8 1:12 scale
Post by: Jo on November 25, 2020, 05:39:48 PM
The Swiss screws are very nice I normally buy mine in the UK from Everett Model Engineering Supplies. I am also a masochist and make my own small screws, so far nothing under 16BA  :paranoia: 

What sizes are spectacle and watch screws? I notice that Fleabay has a lots of small metric screw suppliers (they are not very pretty)

Jo
Title: Re: Cosworth V8 1:12 scale
Post by: Jasonb on November 25, 2020, 05:47:51 PM
GHW do some neat slotted and cap head screws down to M1. I tend to use them for small hex metric fixings

https://ghw-modellbau.de/index.php?cPath=4_108&MODsid=02c5200eaa0f2b2c7410f27ba5f3cda5
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on November 25, 2020, 06:51:57 PM
Thank you for all the suggestions regarding small screws. I will look through them all before making the M1/14BA decision.

Then there are the taps to consider - all a bit spendy. I want good ones.

I would prefer steel over stainless because I want to blue them but I can live with SS if they are good quality. I've found that the British made 12BA steel screws I've been using are far better quality than any stainless I've seen.

The ebay spectacle and watch screws are particularly shabby.

I have made my own screws, one at M1 x 0.25 but it took me all day and it was just to see if I could.  I need over 50 at that size so that's out of the question.

I need 50 modified M1.6 allen screws but I've done all those and tapped the holes. Also just over 50 12BA cheeseheads. I've modified about half of them so far, I'm doing it as I need them.

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on November 25, 2020, 06:59:11 PM
Looking at your block cross-section between the cylinders - is there definitely room for those head fasteners - the walls must be getting very thin?

Simon.

I had a bit of a measure and the thinnest wall is 0.4mm - plenty of meat!

Steve




Title: Re: Cosworth V8 1:12 scale
Post by: Jo on November 25, 2020, 08:49:37 PM
I need 50 modified M1.6 allen screws but I've done all those and tapped the holes. Also just over 50 12BA cheeseheads. I've modified about half of them so far, I'm doing it as I need them.

Be careful about mixing threads  :paranoia: I normally try to keep to one type i.e BA & ME, or Metric, or UNC/UNF. If you loose  :facepalm2: a screw you have a better chance of replacing it without getting it wrong and crossing the threads.

Jo
Title: Re: Cosworth V8 1:12 scale
Post by: gbritnell on November 26, 2020, 12:05:26 AM
I tried to figure out your crank to cam gear ratio but it didn't seem to come out to 2:1
gbritnell
Title: Re: Cosworth V8 1:12 scale
Post by: Roger B on November 26, 2020, 07:30:27 AM
George, I think it is intended to be compressed air powered so the ratio is 1-1.

I use Volkel taps and dies via their online shop:

https://voelkel.com/en/produkt/hand-tap-set-of-3-pieces-din-352-hss-g-m-1-m-100/
Title: Re: Cosworth V8 1:12 scale
Post by: Jasonb on November 26, 2020, 08:29:44 AM
Yes it's a 2-stroke see first post, all the gears are idlers except ones on crank and cams.

I also use the Volkel ones in the smaller sizes, Rotagrip do them via website or  as "fordeight" on e-bay
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on November 26, 2020, 09:03:52 AM
I used Volkel taps for the M1.6 holes. As soon as I got them out of the packet, they seemed superior to all my other small ones. They don't seem to do 14BA though.

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on November 26, 2020, 02:08:56 PM
I love the fact that you're building this with a Sherline.  (I've got both a Sherline and a Unimat.)

The fact that you're mostly building it out of steel is even more impressive.  Why did you chose to use steel for the block and heads over something easier to machine like aluminum or brass?

Don

Hi Don,

Aluminium was my first choice, (after all the original is aluminium) but I just don't get on with the stuff. Swarf ends up all over my kitchen, it sticks to coated cutting tools and I thought it might be a bit soft for the more intricate parts of the cylinder heads.

I did consider brass but felt it didn't look right so I went for steel.

The block was really on the limit of what my Sherline lathe could handle. The billet I machined it from would only just swing over the table when in the 4-jaw. Even then, I had to file a few mil off one corner to give clearance. When I was turning the eccentric bosses, I had to keep the revs down real low to stop the lathe from rocking about.

If I was to make this again, I would use a different method.

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on November 26, 2020, 05:43:54 PM
Now for the conrods.

These were cut from 2mm clockmakers brass in strips of 4.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/880970.jpg)

They were then tapped 12BA.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/880971.jpg)

I forgot to take photos of the clamping half but they were made the same way.

They were then separated with a jewellers saw.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/880972.jpg)

I then screwed the two parts together, blended in the curves and tidied them up a bit. They were then drilled and reamed to 3mm.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/880973.jpg)

These still need surface finishing.

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on November 26, 2020, 05:48:06 PM
Before I went any further, I thought I'd test fit them on the crank.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/880974.jpg)

A fiddly job attaching these but everything fits and moves nicely with minimum play. The middle one at the front looks like it isn't straight but that's the camera angle.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/880975.jpg)

I then tried the whole assembly in its bearings in the block.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/880976.jpg)

The conrods do foul the block in parts but this is because they are no liners or pistons in yet so the rods are rotating more than intended.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/880977.jpg)

I've got to say that it doesn't look like the bottom end of a racing engine - more like some late Victorian marine engine. The thickness of the conrods is massively overscale. This is a consequence of using the smallest screws I had.

Even then, I had to turn down the heads to 1.8mm and dome them for clearance.

This is also the reason why there is only two bearings. There just wasn't space for other journals.

I'm happy to answer any questions or receive any criticism.

Anyway, will update as I make more parts.

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: crueby on November 26, 2020, 07:00:25 PM
Very well done, watching along!
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on November 27, 2020, 03:42:14 PM
I made this gadget (mandrel?) to hold the cylinder heads while I milled it and drilled and counterbored the inclined valve holes.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/882104.jpg)

It is basically a 18mm diameter brass bar with 4mm removed on the flat. The silver steel rod is 8mm so I can hold it in various tool holders and collets.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/882105.jpg)

The idea behind this is that the 16 degree inclined valves converge at a point 5mm below deck height, the bottom of the cylinder head. If I axially centre a cutting tool, I can do all the operations just by rotating 16 degs. either way.

The above photo were taken after I'd used it, hence the square pattern of shallow holes where the drill (intentionally) broke through.

Here it is set up and the flats being milled.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/882106.jpg)

It took me a long time to set this up. I had to clock it axially and make sure it was centred both ends. It seemed like hours with a little rubber hammer tapping things true before I was happy. This was done before I attached the workpiece.

After that it was drilled 1.6mm through, c/bored 2mm for the valve guides and c/bored 2.7mm for the springs.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/882107.jpg)

This worked a treat. My Y-axis remained locked for the whole process.

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on November 28, 2020, 01:11:16 PM
I made 3 cylinder heads, a left, a right and a universal.

The universal is going to be used as a test-bed for cutting the valve seats and a couple of other things. After that it will go back on the mandrel and will be a sacrificial holder for the cam carrier blanks when it comes to machining them.

There are 48 inclined holes here, that's 144 separate operations.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/882108.jpg)

Here is the under side of the heads. The central holes were drilled at the same time as the holding down bolt holes.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/882109.jpg)

Here is a close up. The web between the two valve holes is 0.1mm thick which I was a bit worried about as even the slightest variation from this between cylinders would be visible but everything came out alright.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/882110.jpg)

A close up of the underside. The central hole is not for a miniature spark plug but a guide for the tool I'm going to make for cutting a recess.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/882111.jpg)

All in all, I'm quite pleased with these. I can't find any errors so all the careful clocking and indexing paid off. Saying that, I'm glad it's over. It took me a whole day of dial-counting and double checking before drilling.

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: Kim on November 28, 2020, 05:18:17 PM
Really nice work, Steve!

I don't have a lot of experience with IC engines. So can you help me understand the difference between the Left, Right and Universal heads?  All three look the same to me.

Thanks,
Kim
Title: Re: Cosworth V8 1:12 scale
Post by: Twizseven on November 28, 2020, 07:27:30 PM
Looking forward to seeing the valves, cams and gearing. You must have damn good eyesight.

Colin
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on November 28, 2020, 10:05:09 PM
Really nice work, Steve!

I don't have a lot of experience with IC engines. So can you help me understand the difference between the Left, Right and Universal heads?  All three look the same to me.

Thanks,
Kim

Hi Kim

There is no real difference between left and right - the holes are effectively symmetrical. I've just given an extra mil of metal at the front end of each to accommodate cam gears. The universal has an extra mil at both ends.

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: Kim on November 29, 2020, 05:54:43 AM
I don't have a lot of experience with IC engines. So can you help me understand the difference between the Left, Right and Universal heads?  All three look the same to me.

There is no real difference between left and right - the holes are effectively symmetrical. I've just given an extra mil of metal at the front end of each to accommodate cam gears. The universal has an extra mil at both ends.

Yes, subtle indeed!  Thanks for the explanation :)
Kim
Title: Re: Cosworth V8 1:12 scale
Post by: Daggers on November 29, 2020, 03:30:41 PM
Nice work Steve, following every step with interest.  :ThumbsUp:
Title: Re: Cosworth V8 1:12 scale
Post by: Admiral_dk on November 29, 2020, 08:33:29 PM
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.
Title: Re: Cosworth V8 1:12 scale
Post by: Kim 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
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow 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
Title: Re: Cosworth V8 1:12 scale
Post by: Jo 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
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow 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

Title: Re: Cosworth V8 1:12 scale
Post by: steamer 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
Title: Re: Cosworth V8 1:12 scale
Post by: stevehuckss396 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.
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow 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.
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow 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.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/888679.jpg)

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

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/879995.jpg)
 

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.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/888687.jpg)

These just screw into a 8mm collet thingy.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/888686.jpg)

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

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/888689.jpg)

I made a spare of course.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/888688.jpg)

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.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/888685.jpg)

More soon.

 

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow 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.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/888675.jpg)

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.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/888674.jpg)

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

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/888673.jpg)

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

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/888676.jpg)

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on February 08, 2021, 10:20:07 AM
Cam carriers and cylinder heads.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/888682.jpg)

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/888678.jpg)

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow 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.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/888670.jpg)

 

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.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/888671.jpg)

Here they are sat on the cam carriers.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/888672.jpg)

Here they are with the lobes milled.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/889811.jpg)
 

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

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/889813.jpg)


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".

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/889897.jpg)


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

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/889812.jpg)

More soon,

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: Admiral_dk on March 01, 2021, 06:57:55 PM
You have been busy with some very small parts and they look good.  :cheers:

Per
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow 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.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/889875.jpg)

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.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/889814.jpg)

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

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/889815.jpg)

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on December 03, 2021, 03:34:13 PM
Hello,

I haven't updated this in ages so here are a few images of where I am with the engine and gearbox.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/901743.jpg)

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/901744.jpg)

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/901745.jpg)

I still have the pistons, valve springs and and a few minor things to make for the engine.

For the gearbox, I have to make the forward/reverse gears. I also need to design a clutch that will fit in here-

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/901746.jpg)

The crossed-out side plates on the gearbox are tempory. I wanted to be able to see the diff but I've cut a "viewing window" in the top of the gearbox instead. The plates will be replaced with scale looking ones.

There is till a lot of work in finishing and polishing not to mention blueing about 130 screws.

More pictures soon.

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: Admiral_dk on December 03, 2021, 08:54:04 PM
You have been busy - and with a lot of fine and very small parts  :o   :ThumbsUp:
Title: Re: Cosworth V8 1:12 scale
Post by: Art K on December 04, 2021, 02:57:05 AM
Steve,
It looks like you've been up to some very intricate work, twice. Looks very good.
Art
Title: Re: Cosworth V8 1:12 scale
Post by: steamer on December 04, 2021, 10:24:33 PM
That's coming along beautifully Steve!!!

Dave
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on December 06, 2021, 03:13:13 PM
One of the most fiddly things on this build was hand fettling the bearing blocks so the camshaft turns freely with a minimum of play.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/901747.jpg)

The cam shafts are supported by a sort of shell bearing. These were made by turning down brass bar to 2mm and boring out to 1.6mm.

These were then trimmed down to a semi circular C-section and burnished/work-hardened into place using a polished steel 1.6mm rod.

They are now held firmly in place by there own springiness.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/901750.jpg)

I'm making all this up as I go along but it seems to be working fine.

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: crueby on December 06, 2021, 05:02:19 PM
Quite impressive!!
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on December 07, 2021, 11:02:01 PM
My next challenge is to finish the cam gear train. The principal gears are in place and running smoothly, I just need to sort out the idler gears.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/901751.jpg)

Here are some sat in their final position.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/901752.jpg)

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: Admiral_dk on December 08, 2021, 11:22:49 AM
Very nice progress  :ThumbsUp:

You are not doing things the easy way ...!

Since you have very small tollerances on the placement of these gears - are you placing the axels on excentrics so you can adjust them ?
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on May 28, 2022, 05:23:10 PM
It's time I resurrected this thread. I've had a couple of months off metalwork but I'm back into it now.

Yesterday, two years to the day from the first idea and drawing, I finally finished making all the major components.

I've completed the task I dreaded most. The valves, guides, tappets and springs - 32 of each.

The valves took the most time as they are rather small with quite tight tolerances. Each one needs 8 machining processes.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/908495.jpg)

Here's 16 of them on a penny.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/908497.jpg)

And a close up of one so you can see the slot.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/908499.jpg)

At this magnification, you can see bits of paste from when I ground them into their seats.
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on May 28, 2022, 06:37:43 PM
Here's how the valve parts fit together, open and closed.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/908496.jpg)

The valve guides are brass and reamed with a 1.026mm carbide reamer (Jurassic Tools - great price). They are a friction fit in the cylinder head and the springs keep them seated.

The tappets are adjustable using the 3 holes and the slot in the valve using a tool that I have not finished yet.

Here is a tappet and an untrimmed spring. And a penny.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/908501.jpg)

Steve
Title: Re: Cosworth V8 1:12 scale
Post by: A7er on May 28, 2022, 08:16:23 PM
A great piece of work! I haven't read through the whole process to see if you have already covered this question, but why 1/12th scale?
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on May 29, 2022, 10:37:59 AM
A great piece of work! I haven't read through the whole process to see if you have already covered this question, but why 1/12th scale?

It's the smallest I could get away with! Also, it's easy to scale from the imperial measurements of the original. The block fits nicely into a 1 inch square bar, look at my earliest pictures.
Title: Re: Cosworth V8 1:12 scale
Post by: Steve Crow on May 29, 2022, 10:44:41 AM
Here is one cylinder head with valve gear installed and a cam carrier behind it.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/908500.jpg)

Valves, tappets and springs (and spares) for the other head.

(https://www.model-engineer.co.uk/sites/7/images/member_albums/163849/908498.jpg)
Title: Re: Cosworth V8 1:12 scale
Post by: Admiral_dk on May 29, 2022, 10:14:34 PM
Very impressive work and scale  :praise2:

I can't remember, but you are getting close to first run, aren't you ?

Per