Author Topic: Two cycle Engine from Bar stock  (Read 11202 times)

Offline Brian Rupnow

  • Full Member
  • *****
  • Posts: 7573
  • Barrie, Ontario Canada
Two cycle Engine from Bar stock
« on: February 06, 2016, 08:45:02 PM »
I am going to attempt to design and build a 2 cycle engine from bar stock, which uses no castings. I have spent a couple of days searching the internet for a 2 cycle engine which has a relatively low compression ratio, spark ignition, and can be machined using a conventional lathe and mill. I have found what I have been looking for, thanks to a member in the U.K., and although it is made from castings, it is a proven design so I know that the port layout positions are correct. The engine which I will be using as my reference is the "Wombat", originally designed  by Edgar T. Westbury in the 1930's or 40's. My design is going to be a radical departure from the original designers, so I am not concerned about copyright infringement, however, I want to give credit where credit is due. This engine will have a 1" bore, X 3/4" stroke single cylinder configuration with ball bearings on the crankshaft. It will be machined from aluminum with a cast iron liner, and have (gasp) cast iron rings.  It will have rotary valve induction. I am in no rush at all to get back into my machine shop, as I need some recovery time from 4 months of building my twin opposed i.c. engine. Stay tuned--This could be fun!!!---Brian

Offline NickG

  • Global Moderator
  • Full Member
  • *****
  • Posts: 1430
Re: Two cycle Engine from Bar stock
« Reply #1 on: February 06, 2016, 09:38:49 PM »
I'll be watching as usual.

Offline Brian Rupnow

  • Full Member
  • *****
  • Posts: 7573
  • Barrie, Ontario Canada
Re: Two cycle Engine from Bar stock
« Reply #2 on: February 06, 2016, 09:59:14 PM »
Yes, I know--looks pretty strange doesn't it!! This is "more or less" what the original casting would have looked like without the fins on it. It is correct in terms of bore, crankcase i.d. and size and positioning of ports. Now, I wouldn't try to machine this shape from solid in a million years.  However, I have to model this main body, and then all the parts that fit into it as accurately as I can, just to determine to my own satisfaction how everything fits together and how all the parts interact with each other. After doing that, I will be able to determine how I can modify the body shown here to make it more "machineable friendly".


Offline Brian Rupnow

  • Full Member
  • *****
  • Posts: 7573
  • Barrie, Ontario Canada
Re: Two cycle Engine from Bar stock
« Reply #3 on: February 07, 2016, 01:56:34 AM »
There!!! That'll do me for today. All of the other parts which I am modelling, although they too have the same critical dimensions as the cast and machined parts, are being greatly simplified as I model them. This is to make them easy to machine from solid. I have to enter all the math data as I model the parts, so I will pull my detail drawings directly off the parts when I get ready to detail them. Some of the parts may get a bit of cosmetic  work if I think they look too "blocky" but I won't really have a good overview of that until everything is modeled.  I have found one error on the old original drawings. The dimension from the top of the cylinder down to the center of the exhaust port on the cylinder is 21/32:. The dimension on the liner is 11/16" but it is taken from the top of the liner, not the underside of the 1/16" thick liner "lip". This puts the exhaust ports in the liner offset from the cylinder port by 1/32". I have changed the hole position in the liner to match the port in the cylinder.

Offline Jasonb

  • Full Member
  • *****
  • Posts: 9463
  • Surrey, UK
Re: Two cycle Engine from Bar stock
« Reply #4 on: February 07, 2016, 07:39:34 AM »
Be very careful about moving ports, it will affect the timing of the engine so may be better to adjust the crancase once you have done a few calculations to see where and when the piston reaches the exhaust port.

Why not have a go at making the crankcase as it is you may enjoy the challenge, I'll let you leave off the cooling fins ;)

Offline Roger B

  • Global Moderator
  • Full Member
  • *****
  • Posts: 6133
  • Switzerland
Re: Two cycle Engine from Bar stock
« Reply #5 on: February 07, 2016, 09:54:26 AM »
Another interesting build to follow along with  :ThumbsUp:  :ThumbsUp:
Best regards

Roger

Offline NickG

  • Global Moderator
  • Full Member
  • *****
  • Posts: 1430
Re: Two cycle Engine from Bar stock
« Reply #6 on: February 07, 2016, 03:05:57 PM »
It's a complex shape but looks like it could be fabricated in a few steps?

Offline Brian Rupnow

  • Full Member
  • *****
  • Posts: 7573
  • Barrie, Ontario Canada
Re: Two cycle Engine from Bar stock
« Reply #7 on: February 07, 2016, 06:03:36 PM »
At this point I am beginning to get a much better understanding of how this two cycle engine works. The rotary valve is a new concept (for me). I still haven't redesigned the main body to make it more "machining friendly", but I have redesigned all of the ancillary parts to something that can be carved from bar stock on my lathe and mill. I haven't looked too closely at the ignition cam or points yet. I have an idea of how I am going to modify the cylinder head to match the upswept contour of the piston top--I just haven't done it yet.

Offline Brian Rupnow

  • Full Member
  • *****
  • Posts: 7573
  • Barrie, Ontario Canada
Re: Two cycle Engine from Bar stock
« Reply #8 on: February 07, 2016, 06:07:30 PM »
Jason--Leaving off the cooling fins is very tempting. Also the possibility of making it water cooled. I am just about at the point where I can go back and revisit the shape of the main body. I couldn't really do that until I figured out where everything else went.

Offline Brian Rupnow

  • Full Member
  • *****
  • Posts: 7573
  • Barrie, Ontario Canada
Re: Two cycle Engine from Bar stock
« Reply #9 on: February 07, 2016, 07:36:40 PM »
So--My questions are answered. I can get my favorite Chrysler ignition points and adjusting block on there, and one of my store bought Traxxas Pro-15 carburetors. Now that I know that, I can start chopping and hacking at the main body.

Offline NickG

  • Global Moderator
  • Full Member
  • *****
  • Posts: 1430
Re: Two cycle Engine from Bar stock
« Reply #10 on: February 07, 2016, 09:42:03 PM »
Looks pretty neat to me that. Did you decide on air or water cooled yet?

Offline Brian Rupnow

  • Full Member
  • *****
  • Posts: 7573
  • Barrie, Ontario Canada
Re: Two cycle Engine from Bar stock
« Reply #11 on: February 07, 2016, 10:01:06 PM »
This is what it looks like with the cylinder in "super simplified" form. All of the ports, bores, and bolt holes and mating surfaces are the same as the original model, and I have managed to squeeze in a few cooling fins. I can't make it any simpler than this and still make it from one piece and still have a chance to cool it somewhat. I did take the mounts away from the sides of the cylinder and add a separate baseplate to the bottom.




Offline crueby

  • Full Member
  • *****
  • Posts: 18554
  • Rochester NY
Re: Two cycle Engine from Bar stock
« Reply #12 on: February 07, 2016, 10:39:01 PM »
Fascinating to watch the design develop like this - thanks for sharing!

Offline Brian Rupnow

  • Full Member
  • *****
  • Posts: 7573
  • Barrie, Ontario Canada
Re: Two cycle Engine from Bar stock
« Reply #13 on: February 07, 2016, 10:57:58 PM »
Fascinating to watch the design develop like this - thanks for sharing!

Crueby--You've been watching it develop in real time today. On a cold winter Sunday in February it's not like I had a whole lot else to do. I love doing this stuff!!! ---Brian

Offline Jasonb

  • Full Member
  • *****
  • Posts: 9463
  • Surrey, UK
Re: Two cycle Engine from Bar stock
« Reply #14 on: February 08, 2016, 07:43:39 AM »
Brian, I mentioned it earlier but strongly advise you to look at the port positions, it looks as though you now have the exhaust and transfer ports at the same height. Normal practice is to have the exhaust above the transfer. This can easily be seen on teh cross section at the start of teh articles. I've commented on the inlet elsewhere.

 

SimplePortal 2.3.5 © 2008-2012, SimplePortal