Farm Boy

[DalboyParticipant @dalboy]

Now down to some serious assembly on the engine. Slowly putting it back together and checking everything as I go.

This is as far as I have got. The fuel tank still need fixing to the base

[DiogenesParticipant @diogenes]

Lookin’ good, not far to go now..

[Diogenes]

On Diogenes Said:

Lookin’ good, not far to go now..

Thank you.

Main engine assembled and timing and valve clearance set, need to find a spring for the governor balls. Will search through my spring box. As it is, I found a spring for another part and ping it went off on it’s travels never to return, luckily I found another to replace it with.

Working on a Fuel ordered while waiting for that I can work on the wiring and getting the fuel tank fitted, and a top made as well as an exhaust that will look the part all set up ready to machine that.

[DalboyParticipant @dalboy]

Another little job today, please give your thoughts on this will it work or is it a try it and see.

As the plans don’t show an exhaust, just a threaded hole in the head, I thought of making one based on something I have seen around the rally fields.

There will be a short pipe joining them. As can be seen a little on the small size but any bigger I felt would be out of place.

 

The two part before fixing together

 

Assembled and cleaned up. £1 coin for scale

 

 

[DiogenesParticipant @diogenes]

Probably be okay as long as the slot area is bigger than the valve open area.

..it’s quite hard to tell without seeing it up next to the engine, but if you think it looks ‘right’ it probably will be.

I might do the engine ‘setting-up’ without it at first and once you have a stable runner, see how it sounds and whether it affects the running.

 

[Diogenes]

On Diogenes Said:

Probably be okay as long as the slot area is bigger than the valve open area.

..it’s quite hard to tell without seeing it up next to the engine, but if you think it looks ‘right’ it probably will be.

I might do the engine ‘setting-up’ without it at first and once you have a stable runner, see how it sounds and whether it affects the running.

 

Thank you yes I agree get the engine working first. The area of the slot is about the same as the valve opening

[DalboyParticipant @dalboy]

Back onto the Farm Boy engine, this time the wiring for the ignition. I am going to add a switch to the outer surface of the base for easy access.

Having to keep the sensor wire away from the spark plug wires, I made some small pieces of brass tube and glued these in place around one edge. The main plug wire and earth will go into the hole near the stud

The battery box and ignition box just placed in position. The switch for the battery box is underneath and the access for the batteries on top in this photo, so I will add a switch through a hole yet to be drilled in the open space.

[DalboyParticipant @dalboy]

Last of the wiring in place except for the switch which I had to reorder as I messed it up.

 

 

The switch I messed up. I drilled the hole with a flat drill bit after doing a test on another piece of Oak end grain. I placed it on one end so it does not matter which way around I display this, it can be easily reached.

All the studs and fixings that go into the oak base are brass except the nuts, but even then I made brass washers to keep them from direct contact with the base wood.

[DalboyParticipant @dalboy]

All the machine work completed, the only thing left is to run it when the fuel pipe arrives.

I managed to find a display case and now it has a home, the wife thought it would be better so it does not collect dust.

The display case comes flat packed along with some cotton gloves to assemble it as well as a cloth for cleaning it with when needed. There is also a string of coloured LED lights but I have not put these in.

 

[Roderick JenkinsParticipant @roderickjenkins93242]

That’s very smart, nice work.

Do you have a link for the display case?

Rod

[Roderick Jenkins]

On Roderick Jenkins Said:

That’s very smart, nice work.

Do you have a link for the display case?

Rod

Thank you

 

I got this one from Amazon 

 

[Roderick JenkinsParticipant @roderickjenkins93242]

That’s great.

Cheers,

Rod

[Speedy Builder5Participant @speedybuilder5]

Has anyone got a dimension between the piston crown at TDC and inside face of the cylinder head please.  I am making to plan, but may be a few thousandths of an inch out here and there.  Is it critical ??

Bob

[Howard LewisParticipant @howardlewis46836]

The bump height will affect the compression ratio, which will probably be of the orderof 5 or 6:1, at most.

The build instructions should quote the clearance at tdc. This will be affected by the build up of dimensions, so should be measured before fitting the cylinder head. The ignotion timing may well be specified as a dimension btdc

The compression ratio will also affect the ignition timing, and mixture, so may need to be fine tuned, once the engine is up and running.

Nice work so far!  It will be a thrill once you see and hear it actually running, before putting under the cover.

Howard

[JasonBModerator @jasonb]

It really won’t matter, I don’t know the dimension on any of the hit and miss engines that I have made but they all run. I don’t recall seeing it given on any of the engines built or the other sets of drawings I have. lets face it if one person used a paper gasket that could be 1/64″ Okenfold and another uses liquid gasket which will be les sthan a thou that is going to be more than any accumulation of small deviations.

4:1 compression ratio is more likely

Timing tends to be given as angular relative to TDC so easy to set by looking at the side of a crankshaft web. Again if given treat that as a starting point you can advance and retard the timing quite a lot which helps if just running the engine for display where you want it nice and slow with a long coast between Hits rather than having it work and be firing on every cycle.

[Speedy Builder5Participant @speedybuilder5]

How do you measure compression ratio.  Distance between TDC of piston crown and bottom of cylinder head – easy, but where does the compression stroke start ?  Is it at the time both valves are shut/ position of piston in cylinder.

Bob

[JasonBModerator @jasonb]

Cylinder volume at BDC divided by Cylinder volume at TDC will generally get you close enough without having to work out any voids around spark plugs etc.

As an example I just had a look at my ball hopper engine drawings.

Crankshaft ctr line to top of cylinder head is 8.00″, less 0.375″ spigot on head = 7.625″

Crank throw 1″  plus conrod length 4.625″ plus gudgeon pin to piston crown 1.25″  = 6.875″

 

7.625 – 6.875 = 0.75″ theoretical gap between head and piston crown at TDC.

You don’t really need to use volume both lengths will be getting multiplied by pi so just us elengths

Length at BCD = 2″ stroke plus teh 0.75″  = 2.75″ / 0.75″ head gap = 3.66:1 comp ratio

It is actually more like 3.3:1 as there is a valve box on the side of the head but whose counting!

[Speedy Builder5Participant @speedybuilder5]

Thanks for that Jason, Some serious measurement tomorrow in the workshop and compare with the drawings.

Bob

[DalboyParticipant @dalboy]

When I built this one I did not check the compression ratio. I still not run it yet even though everything is in place and I have the fuel. NOTE to self must get and run this engine I think I was having too much fun just building it

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