Member postings for Steve Crow

Here's how the valve parts fit together, open and closed.

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.

Steve

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.

Here's 16 of them on a penny.

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

At this magnification, you can see bits of paste from when I ground them into their seats.

Edited By Steve Crow on 28/05/2022 17:17:15

A quick update.

I've had a go with Ramon's mandrel and wet & dry method and it works very well.

As expected, as the liners are a tight friction/force fit in the block, the bores had "shrunk" slightly when fitted. This was soon fixed.

I started with 800 grit and worked up to 2000. I did it on the watchmakers lathe under power at about 200-300 rpm. It does remove metal quite quickly like this (the paper loaded up in no time) but it is very controllable. I was able to get all 8 bores to have the same "feel" with the plug gauge.

I'm half way through making the pistons now.

Thank you to Ramon and everybody else for the help and suggestions.

Steve

Yes, posts overlapped.

Useful thread, thanks.

Maybe I should have explained a bit more.

What I am asking is which design of dovetail cutter would work best?

I am looking to make a dovetail cutter using a 55 degree insert (DCMT?).

Would I be best using the insert "square" for a 55 degree dovetail like in the first drawing or leaving some clearance on the bottom for a 60 angle like in the second one?

Incidentally, the dovetails used on my Sherline machines are 55.5 degrees.

Cheers

Steve

Thank you Ramon, I'm going to try your wet and dry method.

A couple of questions- How wide should the paper be in relation to the bore length and should there be some axial motion as well as radial when polishing? Also, would WD40 be a suitable medium (I have no paraffin)?

I've got to thinking about making hones for future projects though. Do you think this would work?

The idea is that the lap is superglued to the d-bit and then drilled and tapped through both materials. The grub screw combined with the glue should secure the ali lap enough during operation. The screw is fine pitched for small adjustments.

Cheers

Steve

Edited By Steve Crow on 03/01/2022 15:44:21

Thanks to you all for some very interesting suggestions.

Ramon, your lapping thread looks really informative, I will look closely at it now I have time.

I actually don't mind if the bores are increased slightly (I haven't made the pistons yet) as long as they are all consistently enlarged. I sort of took for granted that any polishing/smoothing/lapping would involve some sort of metal removal.

The reason for the go/no go gauges was to ensure that all 8 liners had a consistent starting ID.

If I go down the split lap route I assume that it will have to be made from something softer than brass, ie. ali?

I am liking the idea of Ramon's mandrel and wet and dry method. I don't mind a bit of low tech if it works!

I made a couple of liners with slightly under sized OD's which are now in the scrap tin. I suppose I could practice on these.

Thanks again and any other advice is welcome.

Steve

I've just made the cylinder liners for my model V8.

They are bored out to 7.2mm and the OD is just over 8mm for a nice friction fit in the block. I made go-no go gauges to keep the bores consistent to 0.01mm.

I am not happy with the finish of the bores. I am looking for someway of smoothing/polishing them while maintaining the "roundness" and "parallelness" of the bores.

I am considering turning down a bar to a whisker under bore diameter, charging with an abrasive paste and polishing it that way.

Is that a good idea? And if so, what material for the polisher? A softer metal like ali. or harder like silver steel?

Also, would an axial or radial motion be the way to go?

I was thinking of Eucryl mixed with light oil (a toothpaste powder, I've used it before) followed by Autosol.

Any advice, suggestions or guidance would be much appreciated.

Cheers,

Steve

Edited By Steve Crow on 02/01/2022 16:54:16

Thanks Nigel, I did initially consider pre-parting them and I now wish I did for a few of them.

My problem is, apart from half a dozen gears, I don't know how thick I might want any other pinions to be.

I hate parting off gears. The teeth act like a musical box with a loud high pitched whine.

Thanks Brian, I will be using some for a 1/12 scale V8 for the cam gear train and some more for a tumbler reverse gear in the matching gearbox.

Also I may use some for motion work in a clock project and to make a spur gear differential.

Steve

I spent the weekend cutting gears.

There are 3X12, a 14, 15, 16, 18 and a 20 tooth, all Mod 0.3.

More sizes than I really need but setting up for pinion cutting is a bit of a pain so I thought I would "future proof" my parts box. You never know when you might feel a five-speed gearbox coming on.

Steve

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.

Here are some sat in their final position.

Steve

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.

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.

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

Steve

I usually put something in my photos for scale - I forgot this time.

To give you an idea, the total length of the assembled engine and gearbox is 85mm, 5mm longer than a cigarette.

Next time I take some photos, I'll include a coin or something.

Steve

Hello,

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

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-

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

Indian pale ale?

After taking on board your advice, I have come up with this design -

Can anyone see any potential problems or means of improvement with this?

Also, I would be interested in any methods for introducing oil to the air supply.

In the intake manifold (plennum?) I have made, I've left space for bleeding off some air in case I need to inject some oil any where but mixing with the air supply sounds a lot simpler.

Cheers

Steve

Thank you Jason, you answered pretty much all of my questions there!

I intend to introduce a bit of oil so I'll go for the aluminium.

Steve

Hello, I'm 16 months into building a 1/12 scale V8, powered by compressed air/gas. The bore is 7.2mm and the stroke is 5mm. I will not be using rings. There is thread on here about it but I haven't updated it in ages.

I've made nearly all the parts but I haven't even started designing the pistons yet. I made the con rods and the crank nearly a year ago!

I haven't been able to find any help on the net as regards proportions of the pistons. I'm sure somebody here can help.

Here's a diagram to help me explain:-

My questions are-

Is there a rule of thumb for the proportion of D to x? I realise that having a bigger x will help keep the piston parallel.

Is it more advantageous to have the centre of the gudgeon pin (p) between a and b as in the first diagram or is it ok below as in the second?

Grooves as shown on the left. Are they a good thing?

Finally, materials. I haven't made the bore liners yet and have been thinking of using brass. For the pistons, I have no idea. I would like to keep the weight down, how about ali with a steel sleeve for bore contact?

Any ideas, advice or experience would be very welcome.

Cheers

Steve