Ron's Jowitt Popett Valve Engine

The cylinder block is to size apart from adding a spigot ring, I machined it all on the mill using the 25mm end mill and its turned out nice and square so thats good.

Its now set up in the 4 jaw ready for drilling and boring, I know a recent thread said the proper way is to go from the pilot drill straight to the largest drill size but there is no way my lathe will cope with that so am going with a set of drills and do it in stages. I am going to give a 6.0mm, 13mm, 16mm, 19.5mm and 22mm a try, then bore out to the finished size 24mm.

I must admit I am a bit nervous about it I think the largest hole I have drilled on the mill to date is 13mm so I will see how I get on. One area where I may have a problem is the boring, the largest boring bar I have is 12mm with a GT insert which is probably too small but we will see. From 22mm to 24mm I only have to bore out 1.0mm so hoping a series of light cuts will work, but I dont know.

Well I need not have worried the drilling couldnt have gone better, sailed through it, none of the drills grabbed at all and the lathe had no problem.

I turned up a spigot ring as the alu block was just too short to allow the spigot to be turned from the end face. The spigot is fitted into a recess with 638 retainer and I have left enough meat for it to be turned to size.

Next job is boring the cylinder to 24mm, currently drilled to 22mm.

That should work out OK Ron.

Thanks Jason,

Up early and turned the spigot to size and bored the cylinder using the 12mm bar (biggest I have) with a GT insert.

With a question mark over the size of bar I took it easy, 1.0mm to remove so went with 2 x 0.3mm passes, 1 x 0.2mm and 2 x 0.1mm all run at 650 rpm except for the last pass at 950 rpm. I may have just been lucky but as best I can measure using a Mitu Digimatic the bore is good to half a thou which over 60mm I am really pleased with.

Jason, thinking ahead a bit I see mention of the valve heads needing a good finish for seating, before I read that I imagined they would be lapped in but obviously there is no need.?

They should seat themselves but if you find they leak than a bit of lapping won't hurt. With the engine running on a couple of psi it is not as critical as say the valve son an IC engine where you need the compression to get the fuel/air mixture to ignite.

With the long guide hole you may find the valve binds a bit if the drill has wandered so may also need to lap the stems or even open up the 4mm hole a fraction at the valve end. Also don't use too heavy an oil as that can make the valve drag and not close under the light spring prssure.

Thanks for the tips Jason, I have added to my build notes.

Ron

A bit more done, drilling, tapping and reaming next then on to my favourite part the shaping.

Jason,

I am guessing you must have produced your own metric fastenings for the engine, they look different and much better than off the shelf types.

Ron

Well they were off the shelf but you need to be looking on the right one, though as there are not many you could make up your own.

They are a smaller and taller hex than the usual mass produced ones, Polly models in the UK sell them but I go direct to the people they buy them from in Germany GHW

Thanks for the links Jason.

Started the cylinder shaping using the exact same setup as Jason shows in his build thread, it works a treat.

One pass for each turn of the R/T handwheel (4 degrees) it certainly produces a good radiused finish, cant see it needing much work with the files to blend in.

Ron

The dividing head you have on the SX2p mill can you tell me what it is as I am looking to get one soon. I have a rotary table and find that the fixing bolts are a problem with the mill table lining up but I made adjustments to make it fit, that is why I have not got a dividing head at the moment. Sorry that this is not about your thread but looks a good set up.

Bob

Hi Bob,

Its not a dividing head its a Soba (Indian) 5 inch rotary table which I bought from Chronos, it comes as a set with tailstock, 80mm 4 jaw with mounting plate and a set of dividing plates.Its mid priced I guess at £324, I couldnt afford anything more at the time.

Its very good, in one or two places its a bit rough around the edges but overall good. The table has no play, backlash or float, the drive is very smooth and best of all it is accurate.

What really sold me on it was the size 5 inch which I think is a good match for my SX2P, 6 inch is too big and 4 inch a bit small.

Ron

Edited By Ron Laden on 28/02/2020 12:57:55

The most involved part just about there, things should speed up a bit now.

Looks good Ron and as you say the hardest part out of the way

Thanks Jason

I did enjoy making it and it is probably the most interesting part I have made to date and I am learning from parts like this all the time.

This morning I made the frame ends and feet which turned out well and the next job is the main bearings and caps.

Ron

Edited By Ron Laden on 02/03/2020 08:00:21

Edited By Ron Laden on 02/03/2020 08:01:04

Found a few screws just for a trial fit of the parts made so far, thought I had better check and all seems ok.

Well my first mistake, I turned up the piston today and bar one all dimensions are spot on to the drawing The diameter, the length, the wrist pin position, the ring groove width/depth are all good. Also the bottom ring groove position is good but the top one is 0.5mm too high, the groove top edge should be 2.0mm from the piston top but mine is only 1.5mm.how I managed that I,m not sure but thats what it is.

I am thinking it may be ok and not a problem in the operation of the engine, I,m sure Jason will be along to tell me yes or no. I can make another one if need be, not a problem but it seems a pity to bin it with all the main dimensions tight to the drawing.

That will be fine Ron so you can keep up the good progress.