Author Topic: Junkers CLM  (Read 39251 times)

Offline Roger B

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Re: Junkers CLM
« Reply #300 on: January 06, 2025, 04:54:29 PM »
Thank you all  :)  Kim unfortunately, in common with most IC engines, the moving parts will all be covered when it runs  :(

On with fixing some of the problems:

One of the big end journals has a slightly oversize ridge on it so the crankshaft will have to be set up in the lathe to skim the journal.

The conrod was turned down to 6mm (looks a bit thin) and the ends were radiused again. It still jams.

The piston skirt was shortened by 2mm and was bored out to 18mm. It can now be inserted without having to remove anything else but still contacts the piston skirt.

I can either reduce the rod diameter further or make the skirt thinner  :thinking:
Best regards

Roger

Offline Roger B

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Re: Junkers CLM
« Reply #301 on: January 06, 2025, 05:04:17 PM »
The next problem is that the piston is 4.5mm too high in the bore so that the injector port is blocked and the exhaust port is open at TDC  :facepalm: The problem is due to me measuring from the wrong part of the crankshaft drawing so it is referenced from the shorter stroke for the top piston.

Not a big problem to make a new conrod but the shorter rod will make the skirt clearance even more problematic.

The bottom conrod needs to be thin, like the prototype below, due to the very long stroke design, 20mm bore 37mm stroke. 8mm diameter aluminium is ok (it works on my other diesel), 6mm is probably borderline.

A composite design with a steel little end and shaft is probably a sensible option but needs some design checks. The likely failure mode is Euler buckling which is fairly easy to calculate and is proportional to the 4th power of the radius and the Youngs modulus.

Piston load at 80 bar combustion pressure ~2 500N

Based on a length of 60mm to allow for the big end block I calculated the following examples:

6mm diameter aluminium failure load 12 000N

5mm diameter aluminium failure load   5 800N

5mm diameter steel failure load         17 400N

5mm steel with a safety factor of 6 looks ok, 5mm aluminium with a safety factor just over 2 is not sufficient especially when the inertia forces due to rotation are taken into account.

Some designing to be done, especially around the joint between the steel shaft and the aluminium big end block  :headscratch:

Best regards

Roger

Offline pirmin

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Re: Junkers CLM
« Reply #302 on: January 06, 2025, 05:44:42 PM »
hey roger, dont give up ! this is a realy challenging project ! shit happens, now you have to make something out of it

Offline Roger B

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Re: Junkers CLM
« Reply #303 on: January 12, 2025, 12:10:17 PM »
Don't worry, I don't tend to give up. I've probably been working on the diesel fuel injection for more than 10 years  ::)

The original conrod was centred in the 4 jaw independent chuck and the rod was parted off. This was then drilled 4.5mm, the first part was reamed 5mm and the second part was tapped M5 x 0.5. The new rod is made from an offcut of 10 x 12mm moderate carbon steel (ST50). This was held in the 4 jaw self centring chuck with a couple of 1mm shims. It didn't turn nicely with a steel insert so I finished with an aluminium insert which worked much better.

<a href="https://www.youtube.com/watch?v=r_GqFLZRupU" target="_blank">http://www.youtube.com/watch?v=r_GqFLZRupU</a>
Best regards

Roger

Offline Roger B

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Re: Junkers CLM
« Reply #304 on: January 12, 2025, 12:17:38 PM »
The transition to the little end was radiused with a carbide form tool and the end of the rod was tapped M5 x 0.5. I am not sure if it would be better to cut a small stress relief groove at the start of the thread?

I turned up a 7.2mm diameter bronze bearing bush for the little end and pressed it in place, reaming the bore again to compensate for the compression. The little end was then rounded using the RT and a quick check showed clearance  :)
Best regards

Roger

Offline Roger B

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Re: Junkers CLM
« Reply #305 on: January 12, 2025, 12:19:22 PM »
Finally the two pieces were fixed with Loctite 648 and held in alignment until there is a good cure.
Best regards

Roger

Offline cnr6400

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Re: Junkers CLM
« Reply #306 on: January 12, 2025, 01:09:39 PM »
 :ThumbsUp: :ThumbsUp: :ThumbsUp: :popcorn: :popcorn: :popcorn:
"I've cut that stock three times, and it's still too short!"

Offline RReid

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Re: Junkers CLM
« Reply #307 on: January 12, 2025, 03:35:37 PM »
Quote
I am not sure if it would be better to cut a small stress relief groove at the start of the thread?
Hi Roger. I like to when possible and if the threaded joint will be subjected to stress. Little extra work.

As I'm sure you know, that point is a notorious stress riser. In my years ago career cutting tool joints in down-hole well drilling components, a stress relief groove, and bore-back for internal joints, was a common and recommended feature, especially for the larger joints (8 inch +)
« Last Edit: January 12, 2025, 03:47:08 PM by RReid »
Regards,
Ron

Offline Roger B

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Re: Junkers CLM
« Reply #308 on: January 26, 2025, 07:55:29 AM »
Thank you both  :ThumbsUp:

Ron, I cut stress relief grooves on the aluminium pull rods however I decided against on the steel conrod as the fatigue life of steel is generally better.

I radiused the pull rods to fit in the scavenge cylinder with a 4mm radius corner rounding end mill and then removed the crankshaft. This was set up in the Keats to allow me to polish the two top piston big end journals. I used a long strip of abrasive cloth to keep my fingers well away from the rotating parts.

When both rods moved freely I reassembled the pistons and rods to watch it all go round  :)

<a href="https://www.youtube.com/watch?v=ZnZf6Ripg00" target="_blank">http://www.youtube.com/watch?v=ZnZf6Ripg00</a>

I then checked the clearance between the two pistons at TDC to see how much I had gained/lost. It is meant to be 3mm however a 2mm drill shank just fits. Not a big problem, the pistons can be slightly shortened and I can shim the pullrods.
Best regards

Roger

Offline Admiral_dk

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Re: Junkers CLM
« Reply #309 on: January 26, 2025, 10:44:15 AM »
Great to see it Go Round 'n' Round, Roger  :whoohoo:

The increased Compression might make it easier to get the Pops  :noidea:   :thinking:

Can you feel the pressure if you put a finger across the hole in the middle ?

Per     :cheers:      :popcorn:

Offline cnr6400

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Re: Junkers CLM
« Reply #310 on: January 26, 2025, 12:38:31 PM »
 :ThumbsUp: :ThumbsUp: :ThumbsUp: :popcorn: :popcorn: :popcorn: Great video of the engine turning over Roger! Major milestone.  :cheers:
"I've cut that stock three times, and it's still too short!"

Offline Michael S.

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Re: Junkers CLM
« Reply #311 on: January 26, 2025, 04:06:57 PM »
Hello Roger, the movement sequences and the hood piston can be clearly seen. Later everything moves in a black box.

Michael

Offline Kim

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Re: Junkers CLM
« Reply #312 on: January 26, 2025, 04:16:43 PM »
Very cool video, Roger!  :ThumbsUp: :popcorn:
Kim

Offline Roger B

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Re: Junkers CLM
« Reply #313 on: January 27, 2025, 03:13:42 PM »
Thank you all  :ThumbsUp:

I made a temporary adaptor for the compression tester  and gave it a go. With no piston rings yet and no scavenge pump I could still reach almost 30 bar compression pressure and even at around 3000 rpm nothing bent or broke  :)

<a href="https://www.youtube.com/watch?v=sL9x0OvkPTY" target="_blank">http://www.youtube.com/watch?v=sL9x0OvkPTY</a>
Best regards

Roger

Offline cnr6400

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Re: Junkers CLM
« Reply #314 on: January 27, 2025, 05:40:36 PM »
 :ThumbsUp: :ThumbsUp: :ThumbsUp: :popcorn: :popcorn: :popcorn: Very good sign Roger! Nice work.  :cheers:
"I've cut that stock three times, and it's still too short!"

 

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