Author Topic: 15cc Seal Help  (Read 6918 times)

Offline gadabout

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Re: 15cc Seal Help
« Reply #90 on: April 26, 2020, 07:53:47 AM »
On my castings the core was fine , just the length of the casting too great, I lost all the end details when machining to length ,leaving some material to remill  the water bosses on
Mark

Offline Vixen

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Vixen's 15cc Seal
« Reply #91 on: April 26, 2020, 10:33:49 AM »
Well you asked for some photos.

On the left is the billet of 6082 T6 I bought as an insurance policy in case the Hemingway casting did not arrive.

With the billet I get 6 potential datum flat surfaces, 12 potential datum edges and 8 potential datum corners to choose from. With the castings, nice thought they are, there is nothing flat or square or dimensionally accurate to measure from. I guess I am going to relearn all the old school marking out tricks.






Not sure when I will make a start because I am are still heavily committed to supporting our National Health Service workers by making the stuff that makes their lives a little easier. Currently the nursing staff are crying out for comfort clips which are intended to take the pressure of a surgical mask’s elastic straps off the back of the wearer’s ears. They stop painful chafing.  Simple things can make such a difference.




My "cheap as chips" £70 3D printer has been running 10 hours a day for the last 6 weeks. The continuous motion is taking it's toll on the plastic, linear bearings for the x and Y axis, particularly the Y axis. As a result, printing accuracy fell off early on, and now the Y axis slides have a tendency to lock up resulting in lost prints. I am in the middle of another 'bodge fix' to drag a little more life out of the printer.  A laser cutter would be a more efficient way of producing these comfort clips, but I don't own one.

Stay strong, this storm cannot last forever

Mike
« Last Edit: April 26, 2020, 12:39:36 PM by Vixen »
It is the journey that matters, not the destination

Oh! sod the journey, lets hit the bar and pool instead.

Offline scc

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Re: Vixen's 15cc Seal
« Reply #92 on: April 26, 2020, 11:20:46 AM »
Lovely, but too technical for us :Doh:        My wife is currently supplying  a short length of ribbon with a button at each end. Nursing folk seem happy with them.  We have also donated many rolls of fabric for local sewers? to turn into scrubs and scrub bags.  There seems to be endless help from ordinary folk to assist the national effort.  Wonderful to see.        Best Wishes    Terry

Offline Vixen

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Re: Vixen's 15cc Seal
« Reply #93 on: May 01, 2020, 08:49:45 PM »
We've run out of materials again and awaiting resupply; so I took some time out to look at the Seal castings.

I measured up and created a three view drawing of the Hemingway casting, which I superimposed over my CAD model of the cylinder block. The casting external features were found to be generously oversize in most places. The internal cored feature, though difficult to measure, appear to be spot on for size.

I maneuvered the internal casting features to be a best fit on the CAD model. I find the upper water jacket area to need about 70 thou" removed from the top, side and end faces. The lower crankcase area needs something like  0.13" removed from both ends and approx 30 thou" from the sides. This will obviously machine off the raised flanges on both ends will disappear.  The bottom (Sump) face needs a massive 0.17" or so, to be removed. There are few parallel faces, even the four mounting lugs have a 5 degree draft angle.

There's a lot of material to remove. When I am finished almost every external surface will have been machined (I may as well have made it from the solid billet). I am considering leaving the lower crankcase oversize so as to have some cast features left.

I think my machining sequence will start with facing off the cylinder head top face slightly undersize and then to bring the water jacket ends and sides to the drawing dimensions. I then propose to finish bore the cylinders, valve pockets and all the stud holes, while everything is set up in this position. I can then use the machined  top and sides of the water jacket as datums for when I invert the casting to do the bottom face and mounting lugs. That should give me a nice square block to hold when I do the crankshaft and cam shaft bores on either end of the casting.







Well that's the plan. and as we all know, most plans will change after the first encounter with the enemy.

Stay strong, while we ride out this storm together.

Mike
« Last Edit: May 01, 2020, 09:39:25 PM by Vixen »
It is the journey that matters, not the destination

Oh! sod the journey, lets hit the bar and pool instead.

Offline Dave Otto

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Re: Vixen's 15cc Seal
« Reply #94 on: May 01, 2020, 10:46:18 PM »
Hi Mike

Would it be possible to to use your CNC mill to re-create the features on the ends of the block after it has been machined to length; at least somewhat?
Not sure if removing even more material is a possibility without causing other problems.

If the bottom just holds the pan is it necessary to remove that much material? Can't you leave it a little tall?

Dave

ChuckKey

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Re: Vixen's 15cc Seal
« Reply #95 on: May 02, 2020, 09:44:08 AM »
I think my machining sequence will start with facing off the cylinder head top face slightly undersize ...

My advice is to machine it slightly oversize. :facepalm:

Offline Vixen

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Re: Vixen's 15cc Seal
« Reply #96 on: May 02, 2020, 10:55:39 AM »
Hello Dave and ChuckKey

Thanks for calling in and taking an interest.  :ThumbsUp:

Dave, other than the water jacket boss, the features on the end of the casting are purely cosmetic and will eventually be covered by the bearing housings. I will leave the end faces flat. Good idea to leave the bottom long and make a shallower oil pan (sump)

ChuckKey, Did I mean oversize or undersize? I meant to say, I would be leaving about 40 thou of excess material on the top face, to be machined off after the cylinders and valve guides have been fitted.

Stay strong

Mike
It is the journey that matters, not the destination

Oh! sod the journey, lets hit the bar and pool instead.

Offline gadabout

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Re: Vixen's 15cc Seal
« Reply #97 on: May 03, 2020, 10:02:31 PM »
Mike,
I have been having a think about what I would do if I was building another Seal. I would make the block taller so the pistons are flush at TDC this would also help the error with the cam followers. Do you have the other castings? the water jacket and the manifolds? I would only just clean up the face where the manifold mates. Locating the cylinder head bolts to the plan might not work if you are using the water jacket cover as mine didn't line up with the bosses cast into the water jacket cover exactly ,I juggled the hole spacing about so the studs where as central to the bosses as possible for looks!  :) but as close to spec as I could get them. I machined the end faces of the block to plan length leaving material around the water bosses so I could remachine them back in(on). I also left the sump face slightly over size.
Mark

Offline Art K

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Re: Vixen's 15cc Seal
« Reply #98 on: May 03, 2020, 11:08:27 PM »
Mike,
Just thought I'd say something so you know that I'm following along. Looks like a fun project.
Art
"The beautiful thing about learning is that no one can take it away from you" B.B. King

Offline Jasonb

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Re: Vixen's 15cc Seal
« Reply #99 on: May 04, 2020, 07:34:43 AM »
I suppose the other option is to stretch the crank etc to make all the internal bits longer and then you could keep the cast external features but in Mike's case as it's all going to be hidden and expected to work then little point in this case. The flat surface may even be an advantage as it frees up your plumbing options and you could even go for modern push fit plumbing which would be more practical in an RC model than threaded connections.

Offline Vixen

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Re: Vixen's 15cc Seal
« Reply #100 on: May 04, 2020, 11:39:11 AM »
Thanks to all of you for calling in. Good to hear you are all well.

I'm still awaiting reordered materials for my support work for our NHS workers, that cannot stop. Have you noticed how prices are being hiked up every time you reorder something? I have been able to find a little time to look at the Westbury Seal.

Redrawing the engine in CAD gives a lot more freedom to make slight changes before the build. I have tried to incorporate all the valuable ideas and suggestions so generously provided by our MEM members. I have also read and reread the various build logs and the words of Westbury himself and fed in as many lessons as possible.

I made two big design decisions. First; the pistons should not protrude above the top of the cylinder block. Second; I decided to increase the cylinder bore and crankshaft throw in line with Westbury's suggestions while keeping the conrod length as designed. The engines displacement will now be closer to 20cc instead of 15 cc. Both changes require a slightly taller cylinder block. I also incorporated ChuckKey's advice to increase the tappet diameter to 9/32.

I only ordered the cylinder block and cylinder head castings, I plan to make all the other parts from bar stock as that gives me a little more flexibility to position thinks like the water cooling in/out lets to suite the Bren Carrier's installation. It also avoids the need to reposition bolt holes to fit the poorly positioned bosses of the castings.

First up, was to machine the upper half of the crankcase around the water jacket. I found that the valve gear pocket on the side of the casting was the feature which decided where the engine was positioned within the oversize casting. I set up the raw casting in my new (Christmas present to myself) machine vice, with the mounting lugs sitting on two steel rods acting as parallels. I selected a suitable datum from the drawing of the raw casting superimposed on by CAD drawing. I them machined the top face 0.04" overlength and the four sides of the water jacket to finished size. I now have five square faces and four edges to provide datums for all subsequent machining. You will notice the cast flanges on the water jacket  have been machined completely away. As Jason points out, that will provide greater flexibility for the plumbing.

The Aluminium alloy used for the castings appears to be of good quality and machines easily. I can tell it is softer then the T6 heat treatment normal with billet materials. I hope this softer alloy will not adversely effect it's ability to hold screws and studs.




I think it is about time to start a new build thread of my engine, which is separate from the 'Seal Help' thread.

'
Stick with the lockdown and distancing rules and 'Stay Safe'

Mike
It is the journey that matters, not the destination

Oh! sod the journey, lets hit the bar and pool instead.