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Old 04-29-2017, 09:07 PM   #31
deverett
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I'm back on the case again - at least for a little while.

Before putting holes in the cylinder liner for the ports, I made a start on the cylinder head. This is basically an inverted top hat that sits in and on the liner.

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The central hole on top is for the cylinder priming cup in full size. With the basic turning done, it was put in the vice and the six holes for the head studs were drilled.

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The engine body was put in the vice next and the holes for the studs were drilled and tapped. I wanted to put the holes as far from the outside edge as I dared so that the cylinder head nuts didn't overlap the edge. 7 BA nuts are too large across the flats, so I'll have to drill out and tap some 8 BA ones. I was mightily relieved that the holes were tapped without any problems after my experiences with the crankcase holes.

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The casual observer will notice some filler on the casting. When I slipped the head into the cylinder liner, it was flush in places and proud in a lot of others. The cross section of the casting resembled the moon 3 days before full. The only way I could think of making it round and to the correct size was to apply some (plenty) filler. It was over 20 thou thick in places at the top to get it circular.

The reason I made a start on the cylinder head now was that I can temporarily bolt it in place to clamp the liner for drilling the exhaust port and glow plug hole. The drill tip will mark the head so that I can be sure the recess will be put in the correct place.

Dave
The Emerald Isle


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Old 05-28-2017, 08:27 PM   #32
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I know it's been a while but other things have been distracting me from the job in hand.

Now it is time to put in the exhaust and transfer ports. The liner was slipped into the cylinder and clamped by the cylinder head; the exhaust manifold was secured to the casting to use as a drilling guide. After putting the casting in the vice, a piece of 8mm bar was used to line up the exhaust hole.

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Once lined up the exhaust port was drilled through. The liner was then removed to get ready for the inlet port. The transfer passage is a good 13mm wide, but the inlet port is only 11mm wide - plenty of leeway. Just to be sure there was no cock-up, I used a handy narrow 6 inch ruler that happened to fit nicely in the transfer passage and the limits of the passage were marked on the top of the cylinder casting.

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The liner was then replaced and the piece of 8mm bar was put through the exhaust again as a lock so that the position of the inlet port could be marked on the liner - hopefully in the correct orientation. Then it was out with the liner and off to the vice where it was lined up and the inlet port was machined with a 3mm slot drill.

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There were some burrs where the holes had been put in the liner, so I needed to put the lap through the bore again to remove them. In hindsight I should have waited until this point before starting the lapping process in entirety.

Slipping the liner back in the casting I was pleased to note that with the exhaust lined up, and testing the inlet port with a bent scriber, the inlet port came midway between the transfer passage walls as closely as could be judged.

The reason why I didn't just put the transfer port directly opposite the exhaust port is that the cast in passage and the exhaust were not exactly 180 degrees apart - about 8 degrees out as far as I could tell. It won't make any difference to the running of the engine, but if I had just gone ahead and machined without checking, the transfer port would have been partly obscured.

Dave
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Old 06-02-2017, 08:15 PM   #33
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The last hole to go in the cylinder was for the glow plug. Back near the beginning I said I had modified the design to get closer to the original. Before putting the glow plug hole in the casting I used the stub from the bottom of the main casting which I fortuitously saved. This was a test to check that I could safely tap the cast aluminium and to check the recess depth for the copper washer. With the modification, the washer sits below the diamond shaped plate and the circular part of the plug has to compress it while out of sight.

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Fortunately the threads came out satisfactorily and the washer recess was a good depth. With that test done, a bar was put through the exhaust port to lock the liner and the head was refitted. The engine casting was then set up on the milling machine table to put in the real hole.
Using a sticky pin, the centre of the glow plug boss, previously centre popped, was picked up. The actual hole is 50 thou below centre to take into account the modification.

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Before drilling, I added another hold down for added security. Don't want to let anything move unexpectedly!
The glow plug tapping drill went through the liner and into the head but the thread was only in the casting. A quick test with the plug screwed in place showed it will seal OK.

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The head was removed and set up at a 45 degree angle to mill out the combustion chamber recess. The bottom of the head sits well down in the liner and without the recess, the fuel could not be ignited.

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The engine, liner and head ready for assembly.

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Dave
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Old 06-06-2017, 03:36 AM   #34
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Dave, glad to see you're well along and doing a fantastic job! I've not started on mine and watching your build is very encouraging and makes me want to get back on it. Hopefully soon. Best wishes......

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Old 06-18-2017, 12:55 PM   #35
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The piston was a piece of cast iron bar, not overly generous on length. To ensure adequate holding in the chuck I first turned the top part where the baffle would later be milled so that I could work on the main part. The design of the piston has a piece of brass tube silver soldered across the bore to take the gudgeon pin but I didn't like this idea. I have read that brass can be silver soldered to cast iron, but it's not something I have done so I made my piston in more conventional style, keeping the wall thickness a suitable dimension to support the pin and slotting the piston to allow the con rod to swing. It will be a heavier construction, but I don't envisage it creating any problems on this low performance engine.

When the diameter was to size, the piston was put in the vice to put in the con rod hole which was drilled and reamed. I will put a bushing on the small end of the con rod and allow it to swing on the gudgeon pin.
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The piston was now upended in the vice ready for the central hole to be made into a slot. To ensure the slot was perpendicular to the hole, a piece of gudgeon pin diameter bar was passed through the hole and using a DTI running along the bar the piston was adjusted to give no deflection.
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It was now easy to mill the slot for the con rod.
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Back to the lathe and the top end needed a slight taper where the baffle would come and put in the oil retention grooves.
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Then back to the milling machine to create the baffle. The same process as before was used to line up the gudgeon pin hole so that the baffle would be correctly orientated.
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It was then just a matter of milling away the top of the piston to leave the baffle and another part done.
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Old 06-18-2017, 01:16 PM   #36
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The con rod was supplied as a piece of aluminium section. This was drilled and reamed for the two holes. The bottom end had a bronze bush pressed in. The drawing showed the little end as just a bare hole in the ally. As there were oil holes in both ends, I guess the con rod swings on the gudgeon pin but the design of having a brass tube to support the gudgeon pin seems strange if it not to be a bearing. Anyway, I didn't like that idea, so decided to bush the top end as well and use that as the bearing.
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To shape the rod, I got a scrap piece of steel and drilled it for two pegs the correct distance apart so that the con rod could slip onto them. It was now an easy matter to cut away the waste on each side.
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The rod was now mounted on the rounding over jig and swung back and forward (always cutting against rotation) to round over the big end. I had previously used filing buttons to round the small end.
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As mentioned earlier, I don't like the idea of the gudgeon pin bearing on plain aluminium so as I had to make a bush for the big end, I made another for the small end. There may be many instances of aluminium running on steel shafts, but I think bronze to steel is a better combination. Last job then was to drill the oil holes in each end.
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The gudgeon pin was simply a piece of steel drilled through and a rounded over brass plug fitted in each end.



I now had a trial assembly of the working parts. I was pleasantly surprised that there was no binding of the piston in the bore. It felt reasonably tight so there is hope yet for acceptable compression.

But unfortunately there is a potential problem: When I rotate to crankshaft, the piston uncovers the inlet port completely but only comes down just over half way on the exhaust port. I checked all my measurements and I don't see any discrepancy from the drawings, so an email to Heinz to ask if my situation is correct. He said my con rod must be too long. Recheck and it is the correct length. Hmm.

I can think of two possible work-arounds: 1. to machine the exhaust side of the piston down so that the exhaust port will be completely open at BDC but by doing this the compression ratio will be lowered considerably, probably unacceptable without other modifications to restore the compression ratio

or 2. to machine a small half-round cutout in the side of the piston to achieve the desired result of getting the exhaust port completely open. This is my preferred option at the moment. Whichever way, the piston at present is about 100 thou too high.

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Old 06-18-2017, 01:18 PM   #37
Brian Rupnow
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Dave--I am following this thread. I will really be interested in what rpm your engine will run at. The clone I built of this engine runs well but the lowest speed I can run it at is about 900 rpm. I know that it is supposed to run at 300 to 400 rpm, but I think that is pretty optimistic.---Brian


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