Author Topic: Two Cylinder Engine  (Read 13590 times)

Offline Roger B

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Two Cylinder Engine
« on: February 11, 2018, 07:51:21 AM »
I decided to make an updated version of my vertical engine using the same design concept but increasing the capacity and making it as a twin. I did think about a 4 cylinder version but it would be too large for my machines. The original was 16mm bore and stroke, this will be 20mm bore and 19mm stroke. The crankcase will be the same 40mm square aluminium with the crank running in two ball bearings. The cylinder liner will be more conventionally fitted but I am still wavering between cast iron or brass.
I started with the crankshaft. This is a piece of 30mm diameter moderate carbon steel (ST50). The ends were faced and centre drilled using the fixed steady and then one end was rough turned to 16mm. This reduced end was held in the Keats and the two centres for the crank throws were drilled on the mill. The Keats was then mounted on the faceplate and the bar was centred. The V block part of the Keats was then moved across the required 9.5mm (towards the centre for better balance) and the centre was put in the appropriate centre hole.
I started cutting with a 1.5mm blade type parting tool at 500rpm and 0.1mm depth of cut. As expected there was significant chatter but not a problem as the finishing cuts will be made with conventional tools. A short way in I realised that it would be better to cut the throw furthest from the chuck first  ::) The shaft was loosened and turned 180, the alignment being checked with a square on the side of the Keats and a square across the centre holes.
Best regards

Roger

Online crueby

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Re: Two Cylinder Engine
« Reply #1 on: February 11, 2018, 02:26:24 PM »
Great start, will be following along...

Offline Roger B

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Re: Two Cylinder Engine
« Reply #2 on: February 11, 2018, 04:25:11 PM »
Thank you Chris  :ThumbsUp:

I gradually turned the journal to round but there were various clearance problems which resulted in an ever greater overhang. The crankwebs were finished with LH and RH 8mm shank tools. I them moved on to finishing the journal with 6mm tools but there was too much overhang with the Hobbymat toolpost. The QCTP gave more support to the tool. The ridge in the middle was removed with an 8mm straight tool. Back to the other journal.
Best regards

Roger

Offline Art K

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Re: Two Cylinder Engine
« Reply #3 on: February 11, 2018, 09:15:45 PM »
Roger,
Count me in, I'll be following along.
Art
"The beautiful thing about learning is that no one can take it away from you" B.B. King

Offline stevehuckss396

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Re: Two Cylinder Engine
« Reply #4 on: February 12, 2018, 12:05:25 AM »
Nice start. Looking forward to your updates.
Do not be like the cat who wanted a fish but was afraid to get his paws wet.

Offline gldavison

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Re: Two Cylinder Engine
« Reply #5 on: February 12, 2018, 12:48:15 AM »
Me  too

Offline fumopuc

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Re: Two Cylinder Engine
« Reply #6 on: February 12, 2018, 04:32:58 AM »
Hi Roger, great start with this crankshaft. Something I have to do for my OPT engine twice in the near future.
Any Idea how to block the already machined journal against bending during the machining of #2 ?
I have seen special made spacers, fixed with tape or ty-rapes. Mr. Kelley has recommended this fixation by soldering.
My prefered idea is some epoxy glue.
Kind Regards
Achim

Offline Roger B

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Re: Two Cylinder Engine
« Reply #7 on: February 12, 2018, 09:44:49 AM »
Thank you all for your interest  :ThumbsUp:

Achim, one of the benefits of using the Keats angle plate is that it takes most of the bending moment. The tailstock centre only really absorbs the out of balance forces. On a couple of other engines I fixed a bridge across the webs using the fixing holes for the balance weights as in the picture from my diesel build.
Best regards

Roger

Offline Roger B

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Re: Two Cylinder Engine
« Reply #8 on: February 14, 2018, 07:25:42 PM »
I turned the second journal with the same series of tools  and then mounted the 16mm end in a ER25 collet and started to turn down the  shaft. This was at 500rpm and 0.5mm depth of cut.

Best regards

Roger

Offline Roger B

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Re: Two Cylinder Engine
« Reply #9 on: February 17, 2018, 07:18:36 AM »
I then moved on to finishing the shafts. The reduced end was held in an appropriate ER25 collet (hence roughing out to 16mm) and the bearing seat and shaft were turned. It was then turned round and held in a 6mm collet for finishing the other end. With the centre removed there was very little run out so the distortion from two 180 crankpins seemed to balance  :)
Best regards

Roger

Offline Jo

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Re: Two Cylinder Engine
« Reply #10 on: February 17, 2018, 08:46:45 AM »
That was a lot of metal that needed to come off that crank Roger I bet your pleased with the progress  :).

Seeing your crankshaft has reminded me that there is the beginnings of a crankshaft for a twin sitting in that box of castings sitting on the dining room table that Surus was exploring. But I don't think it is as big as your new crankshaft ;)

Jo
Usus est optimum magister

Offline Roger B

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Re: Two Cylinder Engine
« Reply #11 on: February 18, 2018, 07:55:41 AM »
Thank you Jo, I am pleased with the way it went but still need to improve the way I turn the crankpins, maybe a slightly bigger parting tool  :headscratch: As both crankshafts are sitting on sheets of A4 paper I don't think there is much difference. What's the engine, it looks like a flat twin?

The next step was to prepare the blocks of Aluminium that make up the crankcase and cylinder block. This was made easier with the new bandsaw even though I can only use it on the floor  ::)

I made a quick check that my boring bar was in fact long enough and then started squaring and sizing the blocks with a flycutter. The two halves of the cam carrier need to be screwed together so I can flycut the face that joins to the cylinder block.
Best regards

Roger

Offline Roger B

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Re: Two Cylinder Engine
« Reply #12 on: February 18, 2018, 03:28:59 PM »
The cam carrier was drilled, counter bored and tapped M3. When assembled the mounting face could be flycut. The rest of the pieces were set vertical in the vice and flycut to length.

Back to lathe mode. The crankcase was centered in the independent chuck (the piece of 3mm rod is to give some clearance to protect the chuck when boring) and drilled 2.5mm using one of the long drills I bought for drilling the oilways in the diesel crankshaft. The hole was then opened out to 13.5mm (my largest MK1 drill) ready for boring.
Best regards

Roger

Offline Roger B

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Re: Two Cylinder Engine
« Reply #13 on: February 18, 2018, 03:35:52 PM »
I then set up the boring bar with a new APT aluminium tip and set a stop to protect the chuck at the end of the bore. Next I made sure there was enough clearance between the carriage and the tailstock (I can take the tailstock off but it's a pain :(  ).

Boring was OK so far at 500rpm and 0.08mm/rev. Initially it was difficult to clear the swarf but as the hole got bigger it was easier.
Best regards

Roger

Offline Roger B

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Re: Two Cylinder Engine
« Reply #14 on: February 22, 2018, 08:13:16 PM »
The next step was to bore out the big end clearance in the middle of the crankcase. This required the boring bar to be set at an angle and the crankcase to be turned round to finish the second end. The bearing surfaces were then clocked concentric and finished to size.
Best regards

Roger