Author Topic: GDB4 - Inline 4 Cylinder, 4 stroke IC engine, plans by George Britnell  (Read 2858 times)

Offline eccentric

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GDB4 - Inline 4 Cylinder, 4 stroke IC engine by George Britnell
I am kicking off another engine build and as my last was a twin, I thought I might move up to a 4 cylinder.  George Britnell has always been a hero of mine and has made available plans for an inline 4 cylinder that meets my criteria as a next build. George is a true craftsman and does incredible work.  I am very fortunate that he has taken the time create plans of his masterpieces so that I can continue to build my skills as a hobby machinist and fabricate one of his engines.  I know I will not be able to meet his exacting standard, but I hope to end my quest with a running engine.
First, several photos of George's engine to get motivated.
 


 
This will be the smallest engine I have ever built, so I will be challenged by the smaller scale.  My last engine used 6-32 screws to secure the oil pan to the crank case, this one uses 0-80.  Yipes.

I looked over the plans of the crankcase, as good a place to start as any, and established that the most critical aspects of the design is the relationship between the crankshaft and the camshaft.  They need to be perfectly co-linear and the proper distance apart since a set of timing gears reside between them.  I have decided to let the camshaft be my first major datum. 
Working from CAD models helps me visualize the engine and allows me to develop my machining strategy.
 

Lets make some chips!
My plan is to square up a block of aluminum for the crankcase oversize by .050" on all sides, then drill and reamed the .3125 hole for the camshaft.
First I squared up the block of aluminum on the mill, then moved to the lathe to drill the camshaft hole.  I did not have a drill long enough, so I drilled most of the way through with a standard drill bit, but then finished the job with a custom D-bit made from .3125 drill rod.  I had to cut a .0625 groove down the side of the D-bit as air would get trapped inside and I couldn't push the bit in to cut. If you look closely at the D-bit you can see the groove.

 
Once I punched all the way through with the D-bit, I followed up with a reamer.  Fortunately my reamer was long enough to make it all the way through.



Below is a picture of the crankcase with a .3125 drill rod installed in place of the camshaft.  This is now the my master datum and I will create other features from this.



 
I squared up the bottom and the left side of the crank case to the camshaft on the mill.  These two sides are now square to the camshaft and can be used a datum planes for future milling operations.  Next I plan to machine the crankshaft  referenced to the camshaft.


 
I took a strip of aluminum with the same cross section as the crankshaft main bearing caps and using a 1/4" ball end mill, mill a slot down the middle .125" deep.  My intention here is to create a matching groove down the bottom of the crank case where the crankshaft will be centered.  This will allow me to place the crankshaft exactly where I want it with respect to the camshaft.
 
Then I cut a matching groove down the crankcase perfectly positioned with respect to the cam shaft.
 
Finally I clamp the long bearing cap strip to the crankshaft using a 1/4" drill rod to align it to the crankcase and drill the crankshaft bearing cap mounting holes.

 
Once I screw the bearing cap strip down I will ream the crankshaft hole to size.
Hope this all makes sense.

« Last Edit: October 30, 2021, 01:05:04 AM by eccentric »

Offline Craig DeShong

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Re: GDB4 - Inline 4 Cylinder, 4 stroke IC engine, plans by George Britnell
« Reply #1 on: October 30, 2021, 12:56:23 AM »
Hoo boy, looks like fun. 

I'm in the gallery.  :popcorn: :popcorn: :popcorn:
Craig
The destination motivates us toward excellence, the journey entertains us, and along the way we meet so many interesting people.

Offline 90LX_Notch

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Re: GDB4 - Inline 4 Cylinder, 4 stroke IC engine, plans by George Britnell
« Reply #2 on: October 30, 2021, 01:41:08 AM »
Nice start eccentric.  You’ll probably finish your build before mine is finished.


-Bob
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Offline Admiral_dk

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Re: GDB4 - Inline 4 Cylinder, 4 stroke IC engine, plans by George Britnell
« Reply #3 on: October 30, 2021, 01:45:36 PM »
Another great build to follow  :popcorn:

I'm sure that George will enjoy seeing another one being build.

Best wishes

Per

Offline eccentric

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Re: GDB4 - Inline 4 Cylinder, 4 stroke IC engine, plans by George Britnell
« Reply #4 on: October 30, 2021, 10:55:29 PM »
Crankcase Bottom Machining
I  tap the bearing cap screw holes in the crankcase using a taper tap first, then a bottoming tap.  The bottoming tap only buys me three more threads so I am not sure this extra step is worth it. Especially since anytime I am tapping near the bottom of a hole, I taking a small chance the tap will break.



 
Then I screw the bearing cap strip in place with some scrap 2-56 screws.



 
I drill and ream the final hole through the crankcase and bearing caps.  I reamed the inside diameter of the bearing caps to .374" as my Bronze crankshaft  bearings will have an OD of .375".


 
Below is a picture of the bearing cap strip removed.


 
And finally I complete the machining on the bottom of the crankcase.

 
You can see the pocket for the camshaft  at the top of the opening and I am pointing to one of the oil pan screw holes, these will be tapped 0-80.  I also spot drilled the oil holes that will feed the main bearings.
In hindsight I should have left the bearing cap strip in place and machined the bearing caps at the same time that I machined the internal cavities.   Duhhh.

Next I will machine out the cylinder water jacket from the top side. I machine the outside features very last as I like to have the outside square and flat as long as I can so I have something easy to clamp on to.
« Last Edit: October 31, 2021, 08:35:14 PM by eccentric »

Offline Roger B

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Re: GDB4 - Inline 4 Cylinder, 4 stroke IC engine, plans by George Britnell
« Reply #5 on: October 31, 2021, 09:37:00 AM »
Off to a good start there  :ThumbsUp:  :ThumbsUp:  :wine1:
Best regards

Roger

Offline eccentric

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Re: GDB4 - Inline 4 Cylinder, 4 stroke IC engine, plans by George Britnell
« Reply #6 on: October 31, 2021, 08:30:38 PM »
Cylinder Block Top Machining
Now to turn my attention to machining the top of the cylinder block.  But before I do I want to machine the tappet cavity in the side.  this is indicated below. 


 

Since I am still working with a large chunk of aluminum, I need to machine down a bit to get to the pocket.
Below you can see that there looks like there is a pocket inside a pocket.  I do this because my 1/4" end mill only has a 3/4" length cutting flute and the tappet pocket is deeper than this.  I don't want to rub the edge of the end mill on the upper pocket.  Also you can see that the upper pocket has only a roughing mill pass, while the deeper, actual tappet pocket also has a finishing milling operation.



 

I make a 3D model of cylinder block with only the water jacket area around the cylinders features present.  Note the extra material at the top that needs to be machined off because I originally squared off an over sized block for the work piece.  In the picture below this extra material is semi transparent and indicated by an arrow. Also you can see a ledge that has been incorporated to the model.  This machining operation requires a reach deeper than my .75" flute length end mill, so at .7" I step out a tad to prevent the side of the end mill from rubbing as i mill further down.  I know, you are thinking why don't I just buy a longer fluted end mill.  I could, but I am altering the design to accommodate what is in my tool drawer.





 

Then I likewise create a model for the holes on the top of the cylinder block.



 
My little CNC router does not have much Zed clearance, so I can't drill, so I essentially use a small end mill to spot drill, then go to the Mill to drill, ream and tap the holes as applicable.







 
And below is the final result of the cylinder block top and bottom machining.

 
« Last Edit: October 31, 2021, 08:35:33 PM by eccentric »

Offline 90LX_Notch

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Re: GDB4 - Inline 4 Cylinder, 4 stroke IC engine, plans by George Britnell
« Reply #7 on: October 31, 2021, 09:45:08 PM »
CNC made quick work of that.  You have to love it.

-Bob
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Offline eccentric

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Re: GDB4 - Inline 4 Cylinder, 4 stroke IC engine, plans by George Britnell
« Reply #8 on: October 31, 2021, 10:18:07 PM »
Hey Bob,

I am doing an inventory of the hardware I need and it is a bunch of small stuff I have never sourced before.  I need 0-80, 1-72, 1-64, 3-48,... at a quick glance.  Have you purchased any of this hardware yet?  Any suggestions of a good supplier?

I have always enjoyed the CAD and CAM part of machining, which is good because it takes a lot of time on the computer to create the program to CNC a part.  I built this little CNC router many years ago to machine wood for mandolins and guitairs, but it does an OK job on aluminum if you take it slow.  It is built out of MDF so does not have the rigidity of most CNC machines. 

It was watching your build that convinced me to give this inline 4 a go!

thanks
« Last Edit: October 31, 2021, 11:16:58 PM by eccentric »

Online Kim

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Re: GDB4 - Inline 4 Cylinder, 4 stroke IC engine, plans by George Britnell
« Reply #9 on: October 31, 2021, 10:43:05 PM »
There's a thread on where people have found small fasteners here:

https://www.modelenginemaker.com/index.php/topic,628.msg209928.html#msg209928

I've also found that just searching for "0-80 screws" (for example) on Amazon comes up with a good number of options too.  Sometimes the best prices, sometimes not.  You have to check around.

Kim

Offline Hugh Currin

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Re: GDB4 - Inline 4 Cylinder, 4 stroke IC engine, plans by George Britnell
« Reply #10 on: October 31, 2021, 11:06:09 PM »
eccentric:

Moving at hyper speed. Looks very nice.

I've used Micro Fasteners for very small stuff. I tend to get one of their assortment packs if one has what I need. Otherwise I end up with a bunch of one size when I only needed 4 (or 6) due to minimum order quantity. But It's nice to know a place that at least has small fasteners.

Thanks.

I am doing an inventory of the hardware I need and it is a bunch of small stuff I have never sourced before.  I need 0-80, 1-72, 1-64, 3-48,... at a quick glance.  Have you purchased any of this hardware yet?  Any suggestions of a good supplier?
Hugh

Offline eccentric

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Re: GDB4 - Inline 4 Cylinder, 4 stroke IC engine, plans by George Britnell
« Reply #11 on: October 31, 2021, 11:16:17 PM »
Great! thanks guys, lots of good sources for unusual hardware.

Offline 90LX_Notch

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Re: GDB4 - Inline 4 Cylinder, 4 stroke IC engine, plans by George Britnell
« Reply #12 on: October 31, 2021, 11:32:32 PM »
eccentric-

I make most of my hardware. 

-Bob
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Offline eccentric

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Re: GDB4 - Inline 4 Cylinder, 4 stroke IC engine, plans by George Britnell
« Reply #13 on: November 03, 2021, 10:39:11 PM »
Machining the Front of the Cylinder Block and the Oil Pan

My next area of focus is the front of the cylinder block, but I want to machine the front of the oil pan at the same time to get a nice blend between them.
So, to the oil pan.  First the inside. I square up a block of aluminum to the total outside dimensions on the mill, load it into the CNC router vise and let-r rip.  I run three programs, one to rough out most of the aluminum, one to finish the flat bottom surfaces, and one to finish the curved surfaces.  Finally I use a 1/16" end mill to drill the .070" clearance holes for the 0-80 hardware to secure the oil pan to the cylinder block. There is a 5 degree draft on the sides of the oil pan, but I did not run a finishing pass on these as they will be inside and not seen.  You can see the roughing steps in the long inside wall of the oil pan.

 
I need access the complete outside during the machining operations for the bottom and sides, so traditional clamping does not lend itself well.  I clamp an old 2X4 into the vise and using a wood router bit, flatten the top and cut a small ledge near one edge (see red arrow).  By pushing the oil pan down flat against the smooth routed surface and up against the little ledge, I have squared the part with both the Y and Z axis of the CNC router.  I use 5 minute epoxy to secure the work piece to the block and wait an hour before machining.  I run three programs, a roughing pass to remove most of the material, a horizontal pass to give me a nice finish on the top and the flats where the screws mount.  Finally I use a ball end mill on the rounded corners and the sides, which have the 5 degree draft.  I use a .004" step-over on the sides, but 5 degrees is really too steep to get a nice finish on my machine.  It would have been better if I had finished the two sides separately from the bottom, but it would have meant two more set ups and the alignment of the side to the bottom is problematic.  This way I have nice corners, but the sides will require more finishing work by hand.

 
I need to secure the oil pan to the cylinder block, so start with tapping the 0-80 screw holes in the cylinder block.
In my quest to find small hardware I tried some screws I had in a glasses repair kit, but the threads were wrong.  I lucked out and my hardware store stocks #0, #1, #2, #3, #4 and #5 hardware.  But just like Henry Ford's Model T, they come in any color you want, as long as its black.  Fine for now.

 
In the photo below I have highlighted a few features on the front of the engine that need special attention, particularly the fillets, or absence of them.  Where the timing gear case rises from the front of the engine, there is a 1/16" radius fillet all the around, except where the water pump mounts.  Also, inside the timing gear case there are no fillets to clear the gears.

 
Below are a couple of examples of models to get the CAM program to give me the tool paths that I want.   For example, the top photo cuts the clearance for the water pump.


 

 

Above is a photo on the machine as the final finishing passes are run with the 1/8" ball end mill.

The photos below are right off the machine.



 
I will machine the back in the same manner.  It is starting to look like a cylinder block.


« Last Edit: November 03, 2021, 10:43:15 PM by eccentric »

Offline Admiral_dk

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Re: GDB4 - Inline 4 Cylinder, 4 stroke IC engine, plans by George Britnell
« Reply #14 on: November 04, 2021, 01:43:01 PM »
Nice progress - you are really moving forward  :ThumbsUp:

 :popcorn:   :cheers: