45 Degree V8

[dvbydt]

I started contruction of this engine on the other group, but since a lot of people have migrated to here, I will keep you updated.
After having looked and learned, I thought I would try a V8 using Chuck Fellows ball and spring valve system.



 Well I don't know what special prayers and magic incantations he has in his skillset, but I could not get it to work on my single cylinder test engine. So I reverted to ball valves, see the cross section later.

To recap - I made the crankshaft first, not as big a problem as I thought. A 25 mm dia. mild steel bar was centered and 4 centres at 90 degrees on a 12 mm PCD drilled in one end on my mill. The setup on my 12 x 36 lathe fitted with the 4 jaw chuck and a rotating centre in the tailstock, was to use a rear toolpost  parting off tool to rough out the journals and the front to finnish to size. Conrods were made out of leaded bronze. So here is the completed crankshaft assembly.



This engine started out as a 90 degree V8 but as a compressed air engine it meant that it was a "two stroke" and therefore had two cylinders "firing" together every 90 degrees. So I decided to make it a 45 Degree V, giving 8 pulses per rev.



The blocks were milled and the bores reamed.



Ports were drlled and reamed.



More to come.
Ian

[ScroungerLee]

Nice, I am looking forward to watching the progress.

Lee

[dvbydt]

Lee thanks for looking in.

Next job was the two end plates, they are "Y" shaped but by first making them out of rectangles I could hold them in the vise and use my DRO scales to get all the hole centres accurate.



Then I could rough cut them on my bandsaw and finish to size on the vertical mill.



Using two M4 cap head screws, the blocks were bolted together and the ends milled to suit the end plates and the end plate fixing holes drilled and tapped M3.



Piston material is PEEK, a high temperature (260 C) , stable, easy to machine plastic but it is expensive, about 15 X the cost of acetal, but you can pick it up on Ebay. 16mm bar was pilot drilled for the slot and parted to 1mm up on length, then faced to size.  The clearance slot for con rod small end was then milled.
The jig for drilling and turning was made of brass and a tight fit in the slot.



Drilling and reaming  the gudgeon (wrist) pin hole.



The same jig (turned down a bit) was mounted in the 7X12 lathe.



 Using a loose centre and the rotating centre in the tailstock, the piston OD was turned to be a sliding fit in the block bores.




Ian

[dvbydt]

Pistons all completed.



This photo shows all the bits made so far. The gudgeon pins have small discs of PTFE  to  stop them scoring the bores.



Completed all the valve bits. The "O" ring is just to stop the stainless steel balls making a bid for freedom - not that it would do them any good, as they would probably be devoured by my shop spider ( I can never find small things that get dropped)



Ian

[zeeprogrammer]

Those are very nice looking parts and an interesting model.
I'll be watching.

[ProdEng]

Interesting project and some nice looking parts made so far, especially the tiny conrods.  Haven't used PEEK before, is there any particular reason you chose that material?

[dvbydt]

Carl, thanks for looking in.

Jan - I had some PEEK left over from another project and it turns very well and takes a good finish. It does not absorb water like nylon so it is stable when turned. It is a bit harder than nylon and about four times better than PTFE in tensile but is twice the price of PTFE.

Now for the first BIG TEST - will they all go together without anything fouling



 and the crankshaft rotates OK.

Camshaft is the next problem to solve. I will use my single cylinder test engine to establish the timing for the inlet valves. With eight air pulses per rev, the V8 will use a lot of air,  but  if I use the steam engine idea of cut off, then maybe, at say 50%, it won't be so bad. the exhaust will be 180 degrees for each cylinder. Then  the machining of the cam can be completed using my small rotary table.

The centre main should be fairly straightforward to make using a split leaded bronze bush.

But guess what, I'm busy again, so it may be a while till the next installment - but it will  get finished!

Ian

[dvbydt]

Dug out the little single cylinder engine, here, for those who havent seen it.
<a href="https://www.youtube.com/watch?v=04RBvolzaiA" target="_blank">http://www.youtube.com/watch?v=04RBvolzaiA</a>
This is how it works.
(Photobucket is playing up, had to use imageshack .)

This is the set up for measuring the RPM.

These are the results of gradually making the cam duration smaller but keeping it opening at TDC.


Having got to a 70 Degree cam

It looks smaller than 70 degrees but the pusher lifts the ball and admits air long before the full stroke of the cam. The cam has a hex (Allen key made) broached hole to connect to the hex on the end of the crankshaft and I was able to retard the air admission by 60 degrees for the final test.
So what did I learn from all this, bearing in mind that this is an odd type of single cylinder set up?
1. Cut-off works on air as well as steam and, in this engine configuration, can give higher RPM.
2. Torque goes down as cut-off increases - I did not have any way to measure this but in between altering the air pressure I stopped the fly wheel by hand, well, fingers, so got an impression of the torque.
3. Retarding the air admission in the last test reduced top speed but seemed to increase torque over the top dead centre air admission, presumably because the air pressure was acting at a better mechanical advantage on the piston. In this, the last of my tests, air consumption was much reduced, judged by how often the air compressor kicked in.
Conclusions - I will be able to run the V8 at 70 degree cut-off and retarded air entry for more economic use of air and that this little engine deserves to be made into a proper project of it's own with full drawings and a bit of bling!
Final cam timing will need more experiments on the V8 engine with only one piston installed, but I now have a few guidelines from the above.

Ian

[Arbalest]

Nice looking build, thanks for posting.

[dvbydt]

Hi Guys,

Long time no post but the V8 Works!!!

<a href="https://www.youtube.com/watch?v=U6rjMyT6g5o" target="_blank">http://www.youtube.com/watch?v=U6rjMyT6g5o</a>

Details will emerge as I tidy it up.

Ian

[BronxFigs]

Ian-

Congratulations!  Looks like a great little engine.  Looking forward to the final design and other details.  Hoping you will make the measured drawings available.

Frank

[Roger B]

A nice runner   

[dvbydt]

Thanks Guys, Frank I don't think it would make a very good project from plans. I would be a bit of a sadist to inflict this on anyone else  But I will make a set of drawings for the single cylinder available based on the final design of the V8.

The biggest problem has been valving. As you can see from the previous drawings, I tried a ball and spring system but could not get the engine to run. Trying out a positive tappet to push open the ball for both inlet and exhaust, did not work very well. The torque required to turn the cam was as much as the engine was producing! There was also an element of the pea in a referee's whistle effect, the ball being blown about rather than closing the valve. Yes, the engine did run but used a lot of air.

What finally worked for me was the system developed for the single cylinder engine. The exhaust is via a 1.00 mm hole always open, the inlet is a cam controlled slug of PEEK plastic. At the moment I am working on the centre main, the exhaust porting and speed control. NEARLY THERE!!!!!!!

Ian

[BronxFigs]

Thanks for the added information, videos and diagrams.  All interesting.  Good luck with the final detailing and tuning of your engine design.


Frank

[Brendon M]

Nice job!

I can't help but notice that this is the same engine configuration as the GM Electro-Motive Division V8 Locomotive engine that powers my train service in the morning (see V/Line P Class)