Farm Boy

I have just ordered one Steve but thank you for the offer

No problem.

Steve.

P.S. The build looks great so far. Nice work.

Very little done today just the valve spring keepers, made from stainless steel the measure 0.400" X 0.125" with a 0.125" hole for the valve stem, and also sized a small piece of brass for the rocker arm ready to be drilled and machined.

Finally got around to the rocker arm and a small steel bearing which will push on the exhaust valve. As can be seen it is just a fraction over 1 1/2" long.

Next job the rocker arm support

Jason, They say you can learn something new every day- Your referance to the sparking plug thread being UNEFis the first time I have seen that advised. All the Drawings and notes of engines I have made have just said I/4 X 32,so ME hasbeen the one used with no problems. Perhaps I have not read the right paper?

Keith

Maybe Rimfire's site has the right paper, and a plan with the form specified.

Jason, once again you have the answer, but that is an engine I have not tackled, yet!

Keith

Made the rocker arm pivot pin but I feel that it needs shortening as when it is put through the support for the rocker the split pin is about 1/8" away from it. The pin was made to the measurements on the plan

Rocker support in place I need to make a small flat on the bottom so that a grub screw has somewhere to grip as well as keep the support at the correct angle for the exhaust valve

Made a couple of pins for the rocker arm.

Then onto the conrod which after three failed attempts I have now managed to get further. I made up a set of filling buttons to do the small end. As well as that I need to shorten the the big end cap to remove the centre hole when the outer edge was turned

Then managed to get most of it complete except for some machining to lighten the rod which means making a fixture to machine those. They are the two cut outs along the side of the rod.

Is the ball race in the rocker arm a good idea ? The radius is very small on the valve stem. Noel.

This is what shows on the plans but will not know until it is assembled with the springs in place. I have seen one running with no problems.Check from 4:22

Should be fine on a slow runing Hit and Miss engine, I've smaller bearings on the Bobcat based opposed twin and not heard of anyone building the Bobcat or jaguar having issues and they run a lot faster nor the several 100 Farmboys out there.

6mm dia bearings on 3mm valve stems

I should really complete the con rod but as I was away the weekend I thought something small before resuming on that. So I found the oilers for the crank shaft bearings and started on the first of the two, made from brass. I still need to drill out the larger hole in the top but that will wait until I have got the second one to this stage before I drill and tap a piece of metal on the lathe to screw these into to do that operation.

They do not show any caps for these but I may make a couple of them later on.

I did have a go at grinding my first form tool for the outside shape and pleased the way that and the oiler looks.

I agree with Noel that bearings are not recommended for rocking motions where the balls/rollersdo not overlap each other in their motion, clock makers use them on most arbors but not on escapement arbors for reasons of rubbish collecting at either end of the movement which can effect the motion of the escapement. this sort of thing would not effect a ic engine but would still give uneven wear pockets in the bearing tracks. Bushed rocker arms would also share the load over a greater area with the accompanying larger oil film.

What sort of run times would you expect to see wear after?

The average model engine may run for an hour or so a year once the initial playing with it once complete has worn off, bit more if in the US as they tend to run their engines at shows rather than the statick exhibits we tend to have. So will the bearings wear with this amount of use remembering that a hit and miss engine will only be fully opereting the exhaust valve once every 8-12 cylcles and even then they ar every slow reving.

There are many popular hit and miss engines that just run a cast bronze or GM rocker arm straight onto the top of the valve, others fabricated from mild steel that is not hardened. If a bearing is going to show wear then why do I not see reports of these softer rocker arms wearing and needing replacement or is it just theory over practice?

Edited By JasonB on 12/09/2023 18:39:32

sorry Jason I did not mention rocker arm tip wear but pivot bushing!

I thought you were agreeing with Noels comment about the bearing which is at the tip of the rocker arm not the pivot.

Though looking closely it is actually a plain steel roller not a Ball Race as Noel commented on.

Edited By JasonB on 12/09/2023 19:48:15

Sorry Jason my mistake but if you zoom in on the far roller I think there is a bearing cage visible

I think you are confusing the two between my head assembly and that of Jasons.

Got around to getting the con rod complete first part was to mount it on the platter that I made and set it up to mill out the recess I had to do this 4 times total because of the taper.

The next up was to slim down the big end cap as it was too large. The screw that you can see in the big end is not a mistake but designed to be like that when I make the big end bearing I have to make a cut out on both sides to allow for them. Also seen is the little end bearing which is a tight fit. Final job was to make the cut out for the little end bearing oil way which can be seen in the second photo along with the oil hole for the big end.