Ron's Jowitt Popett Valve Engine

The order of my projects/builds has changed somewhat, my club have cancelled all track meeting dates until further notice. We can still use the track (minimum 2 people) at our discretion but I can see days when there would still be a number of people turning up and I dont fancy that. I can also see that this season at the track is lost or at best very late in the year before back to normal so the need to finish the class 22 loco does not have any real urgency about it.

So having enjoyed the little oscillator and enjoying the Jowitt even more when I have finished the Jowitt I am going to fit in a 3rd stationary build. I havnt decided on which engine yet but I do fancy having a go at a hit and miss which leads me to a question for Jason.

Jason, is there a basic hit and miss design that you can think of that size wise would fit my lathe and mill or one that maybe could be scaled to fit, also one that could be produced from bar stock would be good as I do enjoy making quite shapely parts from bar, the Jowitt cylinder for example.

Thanks

Ron

Your engine parts are looking great Ron. Can't wait to see it as a runner!

Hi Ron

You have a few choices in the way of small barstock Hit & Miss engines. The most common is probably the Kerzel at 3/4" bore, quite a few have been made so plenty of build threads and images to be found on the net. This is also the one that you see on the likes of e-bay ready made as the far eastern makers have based theirs on that design. Julius has also done a doubled up 38mm bore version which is in your preferred metric. If doing the original size then you may want to think about using an off the shelf sparkplug so tap the head 1/4-32UNEF.

There is also a design about for a 16cc hit and miss which looks similar to the Kerzel and is a little larger at 1" bore

Model Engine Builder published the "zero-six" design which is a good size and could use Stuart or the cheaper RDG 7" flywheels, digital back issues are available quite reasonably. I made a visually modified version of this as my first IC engine.

Thanks for the links and drawings Jason, I will have a good read through them.

Having had a quick look the doubled up 38mm Kerzel grabbed my attention as a good size but on first glance the drawings look a bit daunting though all the information is there of course.

I think the amount crammed onto each sheet can make it look a bit of a challenge but if yo look at the original drawings all the parts are basically teh same just a different size.

The other option is the Kerzel scaled up a bit, if you work to 1/32" on the original = 1mm on your model you will get a 24mm bore engine in metric sizes with very little effort that would come out at about the same size as the Jowitt.

Jason,

I have read through the Kerzel drawings and build notes and I think I am quite happy with them, though I did note that Kerzel does not recommend the engine as a first time IC, I say I,m happy but I could be missing something of course.

I did a search this site but couldnt find anything on the forum here and wondered if any of the forum members have built one..?

If I go with the Kerzel I think I would go with the Julius doubled up 38mm version, its quite a good size (7 inch flywheels) but all possible on my lathe and mill. I just thought that I may as well be building the larger version as the smaller one or am I being a bit over ambitious.

Ron

Ron, you will find more on "Home Model Engine Machinist" and "Model Engine Maker" forums.

Thanks Jason

I am almost there parts wise, finished the oil cups and the flywheels have arrived so once machined parts are complete.

Should it be of interest I just phoned M-machine metals and they are still open for business at the moment and are hoping to stay open which is good news, I would assume if they are open other stockists may well be open to.

Edited By Ron Laden on 25/03/2020 13:40:46

Hi Jason, there is a thread running at the moment on HMEM of a Kerzel build but the guy is making changes and doing his version, there was a post from someone building a double size version but sounds as if he has just doubled the sizes on the original and not using the Julius drawings.

The guy doing his own thing has led me to a question (sorry) the original has a liner, piston and rings all in C/I but he was going with iron liner bronze piston and steel rings. Later in the thread he says he is now going with Viton X O rings which surprised me in an IC engine.

Anyway it led me to thinking is an aluminium un-lined cylinder possible in a IC hit and miss engine and if so what material for the piston and rings or is it best to stay with the C/I for all three.

Ron

That guy's combination sounds a bit off an odd one to me, can't see the need for a bronze piston and steel rings are very rare.

The tried and tested all iron combination works and I have several open crank engines that use the same. An aluminium piston is an alternative to iron provided it is made say 1thou smaller than an iron one to allow for any expansion when hot.

The last four IC engines that I have made plus one other use a single Viton ring in a honed iron liner or iron cylinder with either CI or Aluminium piston and all seem to make good compression

I've not tried an aluminium cylinder so can't really comment except to say I probably would not.

Thanks Jason, understood.

Thanks for the pointer Jason, I had some 2.5, 3 and 4mm nuts arrive today from Polly models and as you say smaller and taller hex and excellent quality they really look the part, miles better than the every day off the shelf type.

The flywheels complete the parts list, now the fun begins or at least I hope it does..

A bit of an experiment that I hope will work, I have made a lap for honing the cylinder. I used a piece of wooden dowel on the little Muncaster cylinder which worked fine and I was going to do the same on the Jowitt but I have no suitable sized dowel or anything close other than metals.

So I have turned up a piece of 66 nylon to size and hope it will do the job, will let you know.

Well it worked fine, couldnt see why it wouldnt got a nice fit between the cylinder and piston I finished with 1200 grit so have a nice surface for the O rings to run on. I think I may well use nylon for any future cylinders.

Morning Jason

I have hit a problem or at least I think I have, yesterday I honed the cylinder and managed a good finish from end to end. This morning I thought I would try the piston with the two O rings fitted to see how it was looking but it was way too tight. I checked the dimensions, the cylinder is 24mm at the crank end and 23.99 at the other, the piston is 23.95. The O ring grooves were spot on as per the drawing 19.4 dia and 2.6 wide and the O rings are to the size recommended.

I removed the lower ring just leaving the top one and it was a bit easier but still too tight. I bit the bullet and reduced the ring groove from 19.4 to 19.3 and it was a bit easier but still too tight so took the grove down to 19.2 and easier still and thats where I am now. Having no experience of this I dont quite know what fit I should be looking for with O rings. I can slide the piston back and forth but there is some resistance which I would expect but is it too much..?

I watched your video a while back where you showed a piston slowly creeping down the cylinder under its own weight, cant remember if that was an O ring piston but if it was mine will not do that.

Can you advise what I should be looking for fit wise.

Ron

I would not go any deeper at the moment Ron, you will get a certain amount of initial bedding in of teh o ring which may well be enough to loosen things up.

Just took mine off the shelf and it will free wheel for about six turns with a flick of the flywheels that's with teh cam followers pulled back off teh cams. Then took the big end cap off and pulled the piston & rod out and there was quite a bit of resistance (one ring in the top groove) so I would say assembly and try it out.

A trial assembly without any rings would be a good idea just to check for tight spots as you can't feel them as easily with any ring resistance.

That video was just the turned piston with no grooves or oil so minimum drag

Thanks Jason, I will carry on just hope I havnt gone too deep at 19.2mm, I see yours is ok at 19.44.

One thing I meant to ask, is there any danger of the bottom of the piston touching the cylinder wall when fitted with just the top ring. It crossed my mind as if it did mine would be alu to alu but looking at your picture yours doesnt appear to have done that.

I doubt it would pick up unless run dry for a long time.