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Member postings for Craig Booth 1

Here is a list of all the postings Craig Booth 1 has made in our forums. Click on a thread name to jump to the thread.

Thread: V-Twin 100cc Design & Build
12/07/2019 21:38:56
Posted by JasonB on 12/07/2019 12:33:50:

Craig, unless you particularly want chromed exhaust stubs you could solder them up from stainless steel and polish to your desired finish.

Jason, have never tried silver soldering stainless, but could be a better idea than having to rely on external chrome plating. Also like to try something new.

12/07/2019 10:28:40

To give a rough idea how the engine will fit in the cowl. The exhaust manifold will wrap around the outside of the cowl curved to the rear.

Ignore the outlet on the other side, I now need to mirror both the cylinder head and cylinder for that side.


11/07/2019 21:08:04

Some more work on the head to change the inlet/exhaust connection. I now have a plate connection which will allow me to easily make the manifolds that will be need to be bent to shape to suit the cowl. Manifold will be copper, silver soldered to flange. The lot can then be chromed.




11/07/2019 16:47:10
Posted by Niels Abildgaard on 10/07/2019 08:29:57:

I think You need to reserve more space in crankcase for crank,counterweigth and conrod big-ends.

The crank shown from a leaf-blower engine balances all rotating and half reciprocatory forces.

To achive primary perfect massbalance i a 90 degree V-twin You shall balance all rotary and one reciprocatory totaly.

This means that Your crank will be two times as voluminous relative to piston as shown on picture.

Hi Niels, yes balance will be via all rotary and 2 times half reciprocating mass.I'm pretty sure I have enough space to do this as there will also be the rear crank web. Of course it will not be based on volume as you note above but mass, with the steel of the crank web having a greater mass per volume than the lighter mass of the piston.

Another good think about Autodesk Inventor is that it calculates mass and centre of gravity of all parts based on material, so I will be able to use this rather than trial and error balancing.


11/07/2019 13:03:12

Cylinder head altered a little, increased height by 2mm which allows better sleeve support and also slightly larger fins.


10/07/2019 11:56:26
Posted by Dave Halford on 10/07/2019 11:43:50:
Posted by Emgee on 10/07/2019 10:01:57:


Isn't the greater weight of the counter balance shown in your pic a result of the heavy fan unit, on the model engine it will only be a much lighter prop driver.


prop driver plus prop.

I still think the valve guide is not supported firmly enough in the head.

The spring plate, being separate will have to be a clearance fit would it not?

That gives approx. 3mm of guide supported by the head, I would have thought that there would be a high chance of a crack forming at the base given the rotary movement of the rocker 'working' the top of the stem sideways over time.

But then I could be wrong

Hi Emgee, yes I see your point, will look to address this.


10/07/2019 11:53:57
Posted by John MC on 10/07/2019 11:41:51:
Posted by Craig Booth 1 on 09/07/2019 22:21:06:


You need to sort out the crankshaft bearing arrangement, I assume they are ball races.


Hi John, can you please expand more on the crankshaft arrangement. Yes, they are deep groove ball bearings. Main bearing open, nose bearing sealed only one side, what is not shown yet is the rear bearing and second crank web.

cheers Craig

10/07/2019 07:56:47

a few more details:

Main body and head: Aluminium HE30

Piston and conrod: Aluminium HE15

Piston Sleeve: Cast Iron

Piston Rings: Cast Iron

Crank: EN16

Crank support: roller bearings: nose/main/rear

Conrod: needle bearings big end/colphos bushing small end

Valves: Stainless

The camshaft will be mounted within the main crankshaft body on needle bearings, driven by a toothed belt and pulleys at the rear. This is the main area I am still working on in terms of how I achieve the connection to the crankshaft.

Cheers Craig

10/07/2019 07:46:08
Posted by Tim Stevens on 09/07/2019 23:09:27:

Might the valve guides be on the short side? - resulting in valves not seating firmly, perhaps.
And is the plate through which the valves work a separate part as drawn (but not illustrated in colour) - (increasing the problem, perhaps)?

Regards, Tim

Hi Tim, thanks for the comments. I've shown a closer cut away below. The valve guide in contact with the valve is 13mm in relation to a 4mm diameter valve. The sleeve (colphos) also passes through the rocker arm bracket (aluminium), but the valve does no come into contact with it.

Let me know what you think. In my head 13mm feels about right to keep the valve aligned, but I don't have any reference to go by so happy to listen to experience.

While we are on valves, I am going to use a split collet/collar to retain the spring. My last engine used a circlip which makes me nervous about failing.

Cheers Craig


09/07/2019 22:24:34
Posted by Emgee on 09/07/2019 22:19:50:

Did you consider less than 90 deg Vee to keep width less ?


Hi Emgee, yes I did, but was struggling to get the cam shaft housing to work, plus the 90deg actually works well with the plane I am designing. The cylinder heads will intentionally project out of the cowling as I want them on show to suit the style of plane. (I will try to get a drawing of the plane uploaded soon)

09/07/2019 22:21:06

next step was to draw everything in Autodesk Inventor. I am learner to this software but it is proving relatively easy to use and extremely useful in checking clearances, parts fit, and also checking the moving parts. Each part right down to the bolts are drawn as individual components and then "assembled" using physical contraints. Any subsequent changes to the components is automatically reflected in the assembled model. A big plus also is the it is extremely easy to output working drawings (and again these automatically update if any changes are made in the model).

Below is rendered version from the assembled model, plus a series of screen grabs.





09/07/2019 22:11:10

Hi all,

and so on to my next project. This is going to be a big challenge but have always wanted to design my own engine, so have made a start using some spare time this summer holiday.

The engine type and size is based around a new RC plane I am also designing. The engine specs so far are:

Type: V-Twin gas

Capacity: 100cc (2 x 50cc)

Stroke: 3.9cm

Bore: 4.0cm

Compression Ratio: 8.5

Ignition: Spark

My starting point was to draw the basic geometry in Autocad to check the key dimensions. Hopefully the time spent on this will reduce the problems I have later.





Thread: WT2527 15cc Glow Engine
09/07/2019 21:36:03

Hi all,

Just to wrap this thread up, below is a link to successful maiden of the Spacewalker with the WT2527 engine. Just gave it a short flight and landed (sucessfully) so I could check everything. Happy with results. Hope to get her out again soon.

20/06/2019 21:21:09

thanks guys. The engine is now running solidly up to 8000rpm on a 14x8 prop and has had another 6 or so tanks of fuel through it. Reckon she is ready to spread her wings this weekend weather permitting.

A double maiden of the plane and the engine.


08/06/2019 20:30:13

Hi all, a bit of an update.

So I had decided to try making a new piston with 2 rings rather than 1 as the plans have. There was not enough room to fit 2 on the original due to the cut out used to fix to the gudgeon pin with c-clips plus the diameter of the gudgeon pin. I used Autodesk Inventor to design a new one, Obviously had to keep the distance from the centre line of the gudgeon pin to the top of piston the same to retain the same compression ratio, so reduced the gudgeon pin diameter and also did away with the c-clip fastening, instead using bronze plugs at each end of the pin to keep centre.

I had a few problems cutting perfectly perpendicular ring slots in the piston, but eventually suceeded (thanks to all suggestions from my post for help on the other page).

Happy to report after a few tanks of fuel through it today, and a bit of fiddling with carb settings I have managed to get it running fairly smooth and reliable. The range is now 2600-7600rpm, with the top end getting a bit higher with each run.

Very happy and starting to think that I will actually be able to put it in the plane that I've built especially for it.

A short video of one of the engine runs below:

Thread: Piston Ring slot
02/06/2019 07:39:18

thanks clogs, this is for the WT2527 15cc glow engine, detail over on the work in progress thread.

01/06/2019 20:47:34

Hi all,

Success, thanks for the suggestions. I reground the tool, and reduced the overhang. Not sure if it was one or both of those factors, but I have 2 nice ring grooves now with nice parallel sides.

Have tested the piston in the sleeve with one ring fitted and certainly feels like a good seal.




31/05/2019 07:12:44

thanks all for comments and thoughts, that's the great thing about this site.

I'm practicing on a blank so have the piece firmly clamped, pretty sure it is not slipping.

I will be able to reduce the tool overhang by quite a bit, so will try that.

I'll double check squareness.

I don't currently have a 1.5mm parting tool and I already have the rings cut so that would be a last resort.

Jason, yes the tapered edge is wider, sorry can get close enough to get a photo in focus. Guess that could mean flexing.

I'll try again tonight and report progress.



30/05/2019 21:32:41

possible. I'm using a 6mm tool bit and i've kept the cutting edge as short as possible. Tool bit is about 15mm out from the tool post.

30/05/2019 21:24:15

Hi all,

Looking for some suggestions please as to what I'm doing wrong. I'm trying to cut piston ring grooves in a piston and I keep getting a small taper on the right side of the groove.The left side is always good and perpendicular. The groove width is 1.3mm, and i'd guess the taper is around 0.1-0.2mm, certainly visible under the magnifying glass.

I have ground the tool bit and have relief on all sides. I thought it might be one of the feeds creeping, but even holding all feeds steady it still happens.

Any suggestions?

Thanks Craig

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