piston mills diesel 1.3cc model engineering mikes models

Session 1 31st July 2008.

Before a start can be made on the piston the con rod and little end pin have to be finished.
Having made the pin it was then time to start machining what I consider to be the worst
material to work with. Cast Iron. It is dirty and so abrasive if left around it can soon damage
any lathe or milling machine. So I protect my lathe bed as best I can so the bulk of the metal
swarf is collected. Even so it is very important to keep any fine dust at bay.

Firstly the bar was faced off the centre drilled before drilling and boring out to size. The next
stage was to turn the outside diameter to fit the cylinder liner plus 1 thousandth of an inch (to
allow for honing piston later). Ron says the correct diameter is if the piston just starts into the
cylinder liner. As the liner was honed with a taper towards the top of the liner then the piston
should not be able to enter the top of the cylinder, but just enter the base. I was pleased to
see this was achieved.

Withoout taking the piston out of the three jaw chuck, it was transfered to the milling machine
and set to be truly horizontal to the milling table (ensures the holes for the small end pin is at
right angles to the piston , a critical issue).

Using the led edge finder, the centre line of the piston and the bottom edge was found.
Remembering to take half the diameter of the edge finder off, the gudgeon pin hole was first
centre drilled, then drilled out to size. It was then a simple task to move further up the piston
to cut the slot which deflects the fuel (if I can find any!!) into the cylinder.

Then it was back to the lathe to part off the piston leaving around 100 thou surplus. Since it
was now parted off but needed to be finished to size, the ER25 collet chuck was mounted on
the lathe and the piston held securely in the collet.

The final stage of making the piston is to hone it to size. To do this two fixtures need to be
made. One, a false con rod to hold the piston when honing, and two, a the piston hone itself.
This is where the story will continue next session...........getting near the end now.

One last job was to clean up the ML10 and I decided to remove the topslide completeley
and clean off the underside and the top of tha lathe, adjusting when refitting.

Time spent so far 3 hours 40 minutes.

Session 2 1st August 2008.

Today I made both the piston holder and the piston hone itself. I will be putting a page on
dealing in detail with honeing and it will be based on my experience gained from the article by
Ken Delong in issue 2 of the American magazine, Model Engine Builder.

Back to the Mills hone. A bar of aluminum was turned to size and then cross drilled 3/16th
the 1/8th. Next a nylon gudgeon pin was made to fit. This is a safety device so if the piston
snatches when being honed, the pin will go instead of possible damage to the piston.

The next part to make was the piston hone. Again a scrap piece of aluminum was turned to a
reasonable outside diameter. The bar was then centre drilled and faced off. Next it was
drilled through using two drills, the second close to the finished size of 0.410". Using a small
boring bar the bore was finely finished.

The chuck was then removed with the bar still in place and taken to the milling machine. Here
ir was secured to the rotary table by the adaptor made previously (see home made tools -
click here )) The six holes were then drilled after centering the piece at 60 deg positions. A
slot was then milled through to enable the fixture to be closed up as the lapping takes place.
Just before I finished the slot I realised that I had not cut the recommended 20 thou deep
spiral inside the bore. So it was back to the lathe and change the gears to enable an 8 tpi cut.
The lead screw certainly moves fast! Not having a variable speed motor as with my larger
lathe is a distinct disadvantage! I may well consider a new variable speed motor now for the
Myford ML7 refurbishment.

Having cut the spiral it was back to the milling machine and finish off the slot. It was then just
the insets to make for the closing bolt. Because the distance from the ER25 collet to the work
piece was longer than the small drill required I decided to remove the hone from the chuck
and use the Proxxon mini drill in its stand. It was just a case of drillin a clearance hole then
tap the bottom hole 6BA for the socket screw. And that completed the fixture and piston
holder so the next session would be honing the piston. That is until I looked at the photo's
and saw I hadn't cut the slots in the 5 holes to the centre! So the next session will be over to
the small bandsaw and make the slots.

Another slight oversight which dampened my excitement at finishing was the fact that I have
yet to make the contra piston! so that will be the last piece of the jigsaw and the next session.

Time spent so far 6 hours 20 minutes.

Session 3 7th August 2008.

The contra piston was a joy to make! It was a part where, unusually for me, nothing went
wrong! The description of how to make it was taken from the article from Ken Croft in
issue two of Model Engine Builder. So perhaps it is Ken I should thank!

Today I whent to hone the piston. I followed Ken and Ron's instructiona and got a nice
finish on the piston, but forgot to keep checking the fit in the cylinder liner. I know, I know,
dumbo. Yup the piston went smoothly and where it should stick it just by passed that area
and only started to go tighter at the top of the liner. The good news is the taper seems fine
in the cylinder liner....the bad news was I hade taken too much off the piston. So it was
now required to make another piston. Drat. However the second piston went by quite
quickly and was honed but this time it was checked against the cylinder liner frequently.

I must admit that I would have liked to have the finish I got on the first piston, but this time
my finish point was linked to where the piston should start to stick and when achieved I
stopped.

Next I made two cutters to make a gasket for the rear crankcase and took the opportunity
to make a spare.

All that was left to do was to clean all the parts prior to assembly of the completed engine.
I'll just say that again...completed.......sound nice. However I best be carefull because it has
yet to start and there may be some remedial work to be carried out...time will tell.

Time spent this session 3 hours 10 minutes. Total time on these parts 9 hours 30 minutes.