Are you planning to make a compression tester? There is quite a difference between what feels like a lot of compression and enough to reach ignition temperature ~30 bar plus.
Model Diesel: 32mm bore, 38mm stroke, indirect injection
- Thread starter Nerd1000
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I have a small engine compression tester, but I would need to make some kind of funky adaptor to allow it to connect up to the injector hole.
I think my next mission is the rockers and pushrods. I've been a bit indecisive on this matter, and actually designed two options
Which option do people like more? I see pros and cons to each. The second option might also be altered to omit the side supports and just use the pillar in the middle.
I would remove the centre pillar from the second option and just support from the sides. This would give you more space if you have to modify the injector design (which my experience suggests will be the case).
I favour the former... as the rockers area straight line of thrust.
K2
K2
EDM I'm looking into this myself
I don't often have time to do machine work during the week, but the 3d printer is at my apartment so I can sometimes print a part. I just did the rear gear cover, from carbon fiber filled nylon 6.
I think this is the best part I've ever printed from this material, must have finally got the settings just right. The cover is also the housing for the centrifugal governor which accounts for the funky shape.
I think this is the best part I've ever printed from this material, must have finally got the settings just right. The cover is also the housing for the centrifugal governor which accounts for the funky shape.
After some trials, tribulations and a redesign, here are the rockers fitted along with the pushrods.
I like this system of rocker pedestals and trunnions, it turned out very nicely and I'd certainly use it again. I would however beef up the middle of the rocker a bit, I managed to squash one in the vise and had to remake it.
It's not so obvious in the photo, but I also made the copper head gasket. It seals well, and at present the only obvious leak is the valves. I'll have to re-lap them. Even with a substantial leak from the valves the compression pressure is considerable, the engine is very difficult to turn past TDC by hand. This of course raises the question of how I'm going to start it, as it is also a struggle for my electric drill.
In terms of major assemblies I only have the injection pump and governor left to go. Plus a few odds and ends. Very exciting and I can't wait for the next time I've got some free time for machining
I like this system of rocker pedestals and trunnions, it turned out very nicely and I'd certainly use it again. I would however beef up the middle of the rocker a bit, I managed to squash one in the vise and had to remake it.
It's not so obvious in the photo, but I also made the copper head gasket. It seals well, and at present the only obvious leak is the valves. I'll have to re-lap them. Even with a substantial leak from the valves the compression pressure is considerable, the engine is very difficult to turn past TDC by hand. This of course raises the question of how I'm going to start it, as it is also a struggle for my electric drill.
In terms of major assemblies I only have the injection pump and governor left to go. Plus a few odds and ends. Very exciting and I can't wait for the next time I've got some free time for machining
Buy a bigger drill?After some trials, tribulations and a redesign, here are the rockers fitted along with the pushrods.View attachment 156112
I like this system of rocker pedestals and trunnions, it turned out very nicely and I'd certainly use it again. I would however beef up the middle of the rocker a bit, I managed to squash one in the vise and had to remake it.
It's not so obvious in the photo, but I also made the copper head gasket. It seals well, and at present the only obvious leak is the valves. I'll have to re-lap them. Even with a substantial leak from the valves the compression pressure is considerable, the engine is very difficult to turn past TDC by hand. This of course raises the question of how I'm going to start it, as it is also a struggle for my electric drill.
In terms of major assemblies I only have the injection pump and governor left to go. Plus a few odds and ends. Very exciting and I can't wait for the next time I've got some free time for machining
But seriously:
Can you set up a movable shim on your exaust valve to be a decompression set up. Then once the flywheel has some speed you could drop the valve?
Buy a bigger drill?After some trials, tribulations and a redesign, here are the rockers fitted along with the pushrods.View attachment 156112
I like this system of rocker pedestals and trunnions, it turned out very nicely and I'd certainly use it again. I would however beef up the middle of the rocker a bit, I managed to squash one in the vise and had to remake it.
It's not so obvious in the photo, but I also made the copper head gasket. It seals well, and at present the only obvious leak is the valves. I'll have to re-lap them. Even with a substantial leak from the valves the compression pressure is considerable, the engine is very difficult to turn past TDC by hand. This of course raises the question of how I'm going to start it, as it is also a struggle for my electric drill.
In terms of major assemblies I only have the injection pump and governor left to go. Plus a few odds and ends. Very exciting and I can't wait for the next time I've got some free time for machining
Can you set up a movable shim on your exaust valve to be a decompression valve to let you spool it up freely?
"the engine is very difficult to turn past TDC by hand"
Only when you build will you know how it is
I spent today doing some odds and ends parts of the engine project. The crankcase has been drilled and tapped for mounting brackets so I can bolt it to a base, I made a new washer for the timing gears, put the nylon cap on the front end of the cam, and made a starter dog and driver. After re-lapping the valves yet again, they are finally sealing well enough that the rings are now the main leak. An aside here, they still leaked despite the lapping compound having made a dull ring all round the seat. I ended up checking by putting a thin coat of prussian blue on the valves and turning them in their seats. I also sealed the two crankcase halves together with RTV.
Having done all this, temptation took over and i put the head on and cranked the engine with a more powerful drill in low gear. There was a noticeable smell of burnt oil, and so, optimistic, I sprayed some 'start ya bastard' into the intake port and tried again... a large cloud of white smoke shot out of the exhaust as the valve opened. We've achieved compression ignition! After a few more tries the engine stopped firing after getting a squirt, so I put a bit of oil down the intake and it fired on the next attempt. Seems like we just need the rings to bed in (or to crank faster than 550 rpm). I pulled the head, and here's what I saw on top of the piston:
As you can see, there's a burn mark, where the oil on the piston crown got scorched. It's right under the pre-chamber passage, which would be consistent with ignition happening in the pre-chamber and shooting hot gases out towards the piston.
This is all very promising, I'm pretty confident that if we can fire from cold on starter fluid we can probably get it running on diesel. However, the starter dog is a problem.
The setscrew securing it to the crankshaft chewed up the flat on the shaft pretty badly. I need a better solution, currently thinking of changing to a clamp style design that grips the shaft by closing up. And of course, we need the injection pump so it can run for more than one revolution.
Having done all this, temptation took over and i put the head on and cranked the engine with a more powerful drill in low gear. There was a noticeable smell of burnt oil, and so, optimistic, I sprayed some 'start ya bastard' into the intake port and tried again... a large cloud of white smoke shot out of the exhaust as the valve opened. We've achieved compression ignition! After a few more tries the engine stopped firing after getting a squirt, so I put a bit of oil down the intake and it fired on the next attempt. Seems like we just need the rings to bed in (or to crank faster than 550 rpm). I pulled the head, and here's what I saw on top of the piston:
As you can see, there's a burn mark, where the oil on the piston crown got scorched. It's right under the pre-chamber passage, which would be consistent with ignition happening in the pre-chamber and shooting hot gases out towards the piston.
This is all very promising, I'm pretty confident that if we can fire from cold on starter fluid we can probably get it running on diesel. However, the starter dog is a problem.
The setscrew securing it to the crankshaft chewed up the flat on the shaft pretty badly. I need a better solution, currently thinking of changing to a clamp style design that grips the shaft by closing up. And of course, we need the injection pump so it can run for more than one revolution.
I use a split clamp for my starting dog. I doesn't damage the crankshaft so much and will act as a mechanical fuse if something jams whilst you are cranking with a drill.
Congratulations on the first puffs of smoke
Congratulations on the first puffs of smoke
I'm making some progress on the injection pump. The body of the pump and the barrel are done and the barrel has been lapped, though I may give it one more go with finer abrasive. I also made a plunger. Both plunger and barrel are of silver steel and hardened by quenching in oil. Worked well for the barrel, but it backfired with the plunger! I tried lapping it today and discovered that it warped from the quench, so I couldn't get it to clean up all the way around before it went undersized.
I'm part way through making a replacement. I think I will forego the heat treatment this time.
I'm part way through making a replacement. I think I will forego the heat treatment this time.
ruben
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ruben
Well-Known Member
- Joined
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- Messages
- 122
- Reaction score
- 14
I think it would be better to harden the plunger while it is round and then grind the helix otherwise the unequal sections will distort when hardening. I moved from hardened and lapped silver steel to commercial pin gauges for my plungers.
Nerd, I missed the engine firing party, but want to add my congratulations!
I brought an apple pie, too.Your tenacity is admirable and contagious. Well Done !!
Lloyd
My understanding of helix plungers is that they need to be rotated(or the pump body) to align the helix for a given discharge volume.
What are you guys, who use helix plungers, using to rotate the plungers?
What are you guys, who use helix plungers, using to rotate the plungers?
My plunger passes through the middle of a control collar that has a slot cut in it. The plunger is cross drilled for a pin that rides in the slot.
@The Ignoble Troll
The GM plungers had a flat ground along the outboard end to make it D shaped. Then a small gear with a matching D hole thru it allowed the plunger to move up and down thru the gear. A rack went cross-axis, and off the center axis, thru the injector body and engaged the gear. Pulling the rack in and out rotated the plunger.
One problem with all of the helix arrangements is that they are easy to twist when not under load. But when they are pumping and under load for the down-stroke, it is like shifting a trans with dogs but no synchronizers: it will only rotate when the load is off for that half cycle. The Detroit Diesels had a hydraulic assist in their governors to move the racks in and out in unison even when in that loaded half of the pump cycle. The ramp angle of the helix can really affect its sensitivity where (in a worst case) any slop in the linkages can cause different amounts of hysteresis and thus inconsistent injection amounts. I find it amazing that they work at all, LOL.
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