Author Topic: By Jupiter  (Read 75249 times)

Offline Admiral_dk

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Re: By Jupiter
« Reply #105 on: May 02, 2018, 08:32:38 PM »
Great work and a very informative post, thank you very much :praise2:

I immediately got a few questions though ; are the full size valve guides and seats really screwed into place - I would have thought pressed / crimped (heat) ?

Do you not have too much "leverage" on the seat grinder, with a stiff handle so long (sixth picture) ...?... it looks to me that you easily change the angle from a perfect zero to a few arc seconds and therefore need more grinding afterwards  :noidea:

Where did you buy the pump ?

Best wishes

Per

Offline Vixen

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Re: By Jupiter
« Reply #106 on: May 02, 2018, 09:16:57 PM »
Hello Per,

I am pleased you found these valve lapping experiments interesting. I try quantify my research and then hand on as much of my experiences to fellow members, as I can.

The full size valve seats were shrunk in place, using dry ice to shrink the seats and an oven to expand the cylinder head. Liquid nitrogen was not so readily available in the 1920's. The valve  guide would have been pressed in place. It is much more difficult to achieve the require interference fits at model size with model makers equipment, so making screw-in components is a very practical alternative solution. I have had a shrunk fit valve seat come loose in a full size race car engine and would not wish to have that happen again.

The seat cutter is piloted by a well fitting dowel inside the valve guide. The cutter also floats on two pins sticking out of the handle, it is not rigidly attached. Yes, you are correct, the clearance which allows the cutter to rotate around the dowel pin could, and probably does, lead to a few arc seconds of misalignment. Nothing is perfect. We can only do our best with the equipment at our disposal.

Everything in the world can be bought from E-bay in you know the correct description. Search for "Hand Held Vacuum Pump Brake Bleeder Tester Set" You will find many suppliers and they are amazingly inexpensive at about £12.

Mike

« Last Edit: May 02, 2018, 09:23:33 PM by Vixen »
It is the journey that matters, not the destination

Sometimes, it can be a long and winding road

Offline Admiral_dk

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Re: By Jupiter
« Reply #107 on: May 02, 2018, 10:17:04 PM »
Quote
Nothing is perfect. We can only do our best with the equipment at our disposal.

I'm very sorry if it sounded as a critique :embarassed: - I was thinking out loud - does this make it harder more work for you, than if you used a shorter distance from cutting edge to the handle .... besides I'm very impressed with your builds  :NotWorthy:
.... and I kind of figured that you had it made like the full size tool.

The only full size tool I have used had a very strong expanding "guide pin" (in order to ensure absolute alignment with the valve shaft), and the only difference to your seat cutter, was that the 3 cutting bits could be changed and that the handle was a bar directly on the backside of the cutting head. This made it virtually impossible to not achieve perfect alignment - this does not prevent user errors completely  :-[ .... (though I got it second try a few minutes later).

Offline Vixen

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Re: By Jupiter
« Reply #108 on: May 02, 2018, 11:53:37 PM »
I'm very sorry if it sounded as a critique :embarassed:

That's not a problem with me, Per. We can all learn from discussions, like this one, between informed engineers.

The actual seat cutters, both the 45* and 60*angle cutters, are only 12 mm long, the two pins protruding from the handle act like a universal joint, therefore should not adversely affect the alignment of any of the seat cutters with respect to the valve guide axis. By definition, there must be some minimum clearance between the the cutter and the dowel or "guide pin" to allow rotation. I will look to see if this can be improved as there are still an number of valves yet to be lapped in. It may be fun trying to make a "very strong expanding guide pin" from a pin which is only 3.1mm in diameter.

On reflection, it would have been better to machine the valve seat face and valve guides in one combined operation, while the cylinder head was still on the milling machine, Perfect concentricity would have been achieved.  Unfortunately that opportunity occurred some years ago, so it's damage limitation today.

I am trying to develop a reasonably quick method of valve lapping which overcomes any minute build imperfections.

Mike
« Last Edit: May 03, 2018, 12:01:53 AM by Vixen »
It is the journey that matters, not the destination

Sometimes, it can be a long and winding road

Offline b.lindsey

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Re: By Jupiter
« Reply #109 on: May 03, 2018, 12:46:04 AM »
Amazing work Mike. How difficult was it to get each set of concentric valve springs the same length, or is there some leeway in that?

Bill

Offline Vixen

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Re: By Jupiter
« Reply #110 on: May 03, 2018, 08:47:51 AM »
The triple valve spring arrangement is true to the original Bristol Jupiter design. In the model engine the outer spring does about 70% of the work, the inner two springs are very light and can easily be stretched to the required length. Did you notice the middle spring is wound in the opposite direction to the other two? This is to stop the springs becoming coil bound during compression.

The use of three springs per valve was more to do with avoiding harmful resonances than high closing forces. Roy Feddon, the chief designer at Bristol's, would only use Swedish steel for the valve springs.

Mike
« Last Edit: May 03, 2018, 09:52:15 AM by Vixen »
It is the journey that matters, not the destination

Sometimes, it can be a long and winding road

Offline petertha

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Re: By Jupiter
« Reply #111 on: May 04, 2018, 07:17:21 PM »
Beautiful work Mike. I knew you would find Terry's work beneficial.

Re your seat cutter, do you mean you cut the teeth profiles from annealed tool steel & did hardening & post dressing yourself? Or you managed to cut them from pre-hardened stock?
Reason I ask is I bought the 45-deg multi-flute tool Terry & others had good experience with, a muzzle seat... something-er-other (sorry I'm not a gun guy). It is very sharp & does an excellent job, but the trick I found is the slightest of applied pressure. I think someone mentioned the weight of the cutter body itself. Otherwise what happens is the cut develops kind of its own kind of non-linear cyclic wavy profile that feeds on itself & gets progressively worse as you hand turn the tool. Maybe this is a slow speed version of what's happening when harmonic chatter occurs with countersinks etc. Anyway, I always wondered if an odd or staggered tooth set might help?

I made up two sets of piloted valve seat cutters from hardened silver steel (drill rod). Two at 45 degrees for the working face and two 60 degree cutters with which to thin the sealing face from 1.5 mm to approx 0.7 mm


Offline Vixen

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Re: By Jupiter
« Reply #112 on: May 04, 2018, 08:59:52 PM »
I have moved further valve lapping discussions from the "By Jupiter" build log to the existing "Valve grinding and lapping" topic, so that everything is under one roof,
This move should make searching easier in the future.

http://www.modelenginemaker.com/index.php/topic,8006.msg173066/topicseen.html#new
« Last Edit: May 04, 2018, 09:15:44 PM by Vixen »
It is the journey that matters, not the destination

Sometimes, it can be a long and winding road

Offline Vixen

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Re: By Jupiter
« Reply #113 on: May 25, 2018, 03:02:30 PM »
Time for an update on the Jupiter build.

My recent work has been directed towards finishing the cylinder heads and getting them to a ready to run state. The cylinders were all removed from the engine core so that each task could be completed on each of the nine cylinders, before moving on to the next.  Below, you can see the naked engine core and the propeller speed reduction gearbox. The inlet and exhaust pushrods are standing vertical. The rocker box location rods have been folded forward for convenience.






There was a reasonable amount of work to do on each of the cylinder heads. The rear (inlet manifold) face required 4.5mm to be removed to correct the profile. The mounting holes for inlet manifold and exhaust stubs were drilled and tapped 8BA. The valve guides were screwed in place sealed with Loctite 572 pipe sealant. I will not use screw-in valve guides again, the thread clearance is enough to upset the concentricity of the valve seat and valve guide. A press fit valve guide would have been much better.

Each of the 36 valves was lapped in and tested with a vacuum leak tester. I started by using Autosolv metal polish, This proved to be excessively time consuming. I next tried 600 grit silicon carbide, which was much quicker but did not give the best leak test results. Finally, I obtained some 1200 grit green silicon carbide powder from a jem stone polisher. The ultra fine powder was made into a paste with mineral oil and a little white spirit. The ultra fine abrasive powder worked well, each of the valves was lapped reasonably quickly and all were able to pass a full 30 second leak down test.

Nine cylinders, 36 valves, 108 valve springs, 18 exhaust stubs and 9 inlet manifolds later, we see the completed cylinders having a 'Team Talk before the big Match'




The cylinders were returned to the engine core. The cylinder heads are starting to look fully dressed with the manifolds and exhaust stubs in place.





Stay tuned

Mike

« Last Edit: May 27, 2018, 10:44:35 PM by Vixen »
It is the journey that matters, not the destination

Sometimes, it can be a long and winding road

Offline Stuart

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Re: By Jupiter
« Reply #114 on: May 25, 2018, 03:08:26 PM »
Mike

One word. Wow that sure does look the bees knees

Great work
My aim is for a accurate part with a good finish

Offline zeeprogrammer

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Re: By Jupiter
« Reply #115 on: May 25, 2018, 03:26:12 PM »
I'll use the same word. Wow!
And again...wow!!

That is really impressive work.  :ThumbsUp:
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
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Online sco

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Re: By Jupiter
« Reply #116 on: May 25, 2018, 03:38:04 PM »
Damn that looks good!

Simon.
Ars longa, vita brevis.

Offline crueby

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Re: By Jupiter
« Reply #117 on: May 25, 2018, 05:43:59 PM »
Whatever is beyond Wow, thats the word!

Offline Craig DeShong

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Re: By Jupiter
« Reply #118 on: May 25, 2018, 07:08:27 PM »
I am at a loss for complimentary words.  :Love:
Craig
The destination motivates us toward excellence, the journey entertains us, and along the way we meet so many interesting people.

Offline Admiral_dk

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Re: By Jupiter
« Reply #119 on: May 25, 2018, 09:18:50 PM »
Quote
I am at a loss for complimentary words.  :Love:

Me too ....

 

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