Roger B

I am not sure if it is better to ream the bores before or after drilling the ports?  For the sleeve bore I tried running the reamer through again after the ports had been drilled. The rotor bore was reamed after the ports were drilled as I had done for the diesel injection pumps.

The rotor and the sleeve were then lapped with 5 micron  diamond paste. The rotor was finished to 5.98 mm along the length as well as I could measure with a micrometre. The sleeve was lapped out until the 5.97 mm pin gauge would pass through and then step by step until the rotor would just slide in.

Next lap the rotor bore to fit the shuttle parts.

Picking this one up again. I had some problems with tapered bores on the nominal 5.95 bore. Unusually the entry was on size and the exit was 0.03 – 0.04 mm oversize. I wanted to make a longer brass lap to finish the outside of the rotor but found that the bore was tapered  After a number of experiments I am still not sure of the root cause. I thought that I had a fairly good understanding of reaming from my diesel injection work. Another 5.95 mm reamer from a different source and adjusting the spring loading on the floating reamer holder seemed to help.

Having, hopefully, solved the reaming problems I started on a new 6mm external lap, rotor and sleeve.

The parts were made much as before.

Running nicely and a good save on the crank web     

Glad to see you back on this build  The valves and cam followers look good   

Welcome to the Forum   

Welcome to the Forum   

Welcome to the Forum   

The parting marks were faced off and 1.5 mm air hole was drilled in the centre.

Next up were a fixing bracket from 25 mm black angle iron and an outlet fitting. It is difficult to get a good bend close to a union but I think that this arrangement will work. If not I can make a ‘banjo’ type fitting.

The final check was that it fitted in the transport box so I could stack another engine on top.

A bushing for the outlet was turned from some 11 mm brass rod and was tapped M5 x 0.5.

I first soldered the coupling in place and then turned it the other way up and soldered the end cap and the bushing.

Next I needed a cover. This was turned from 35 mm aluminium bar, reduced to 34 mm for the knurled part and 28 mm to fit into the coupling.  I cut a groove for a 1.6 mm section O ring which will, hopefully, act as a seal and retainer. The cover was then knurled and parted off.

I needed to make a fuel tank for the four stroke diesel rather than using the one from my injection pump test fixture. This would avoid having to prime the fuel system every time I wanted to carry out some trials. I guessed around 30mm diameter and 50mm tall would be sufficient and had a look for suitable materials.

Copper pipe in this size range was only available in 2.5 or 5 m lengths and was not cheap. I saw that there were some 28 mm end feed fitting available singly and purchased a coupling and an end cap.

There was a suitable piece of 40 mm wide, 5 mm thick brass in my bits box to make the joining and support piece. I cut off a 35 mm long strip and centred it in the 4 jaw independent chuck to give an additional 5 mm for the two M3 fixings. The bulk of the material was cut out with a hole saw, leaving a potentially useful disc. This was then bored out to 28 mm. To make the two recesses for the pipe fittings I used a small boring tool so I could cut the rear one to the same depth as the front one.

This all seemed to fit together so I changed back to the 3 jaw chuck to make the 8 mm outlet hole in the end cap. I had concerns about a normal drill snatching so I used an endmill which worked without problems.

I now needed to look at the nominal 6mm bore between the rotor and the sleeve. I took a trial length of 12 mm silver steel and drilled it 3 mm then 5.9 mm. My dial calliper registered between 5.90 and 5.94 mm so as expected the hole was oversize and oval.

I then reamed it to 5.95 mm using the floating reamer holder. The 5.96 mm pin gauge would not enter but the 6 mm barrel lap would pass through.

I then started lapping, using 5 micron paste, and the 5.96 mm would quickly enter. On with the lapping 

Although I had a cranking compression pressure above 30 bar this dropped at low speeds and it was still possible to slowly ease the engine over compression. A check using a length of plastic tube as a stethoscope suggested a small leak past the inlet valve.

I removed the cylinder head again and took out the valves. The inlet valve looked OK but there were some markings on the valve seat. I gave the valve seats a clean up with the original cutter and lapped the valves with 5 micron diamond paste. After a wash in the ultrasonic bath I put it back together. There was no detectable leakage from the valves.

The compression is better at low speeds, however the inlet valve timing starts to have an effect as well. In the previous test it would reach 30 bar at around 1000 rpm, after lapping the valve 30 bar was reached at around 800 rpm. There is also still a small leak via the compression tester, either through the ball valve or one of the several joints.

https://youtu.be/GpMDgod9S0M?si=Zw0PC0jN3LD-2q6h

Bolt on ER chucks exist in various shapes and sizes. I don't know if this will fit your chuck mounting. There were a few variations in register diameter and PCD on the smaller minilathes. As ShopShoe says this will allow you to pass longer pieces through the headstock

https://www.rcm-machines.com/en/rcm-production/chuck-er/1-er25-collet-chuck--80-mm/rcszf2580t

RCM offer other sizes as I expect do other suppliers.

Thank you for putting that together     

I remember reading LTC Rolt's 'Tools for the Job' many years ago that covered some similar themes.

Excellent   

You do rescue some very elegant and nicely running engines