Simple Opposed Twin Diesel using Owen Mate Components

[edholly]

I haven't posted here for a while as other things have been taking priority. But I have started down the path of my next diesel, a 4cc opposed twin based on the wonderful piston/cylinder design of David Owen's - Owen Mate. Just for fun calling it the HOLLY OWEN OPPOSED TWIN - or HOOT for short ...

This will be my 13th engine (all diesels) built from scratch and my 4th multi-cylinder. The 60 degree Vee twin and the inline twin both based again on David's cylinder/piston/conrod setup run really nicely, so a flat twin should round this off nicely.

As with all opposed twins, the double throw crankshaft presents some challenges, either you make a built up shaft or have caps on the conrods - I have chosen what might be a simpler way, taking a bit of a leaf out of the inline twin.

To keep it simple - I have made a interconnect shaft which will locate snugly into a short rear shaft and at the front into the driving shaft, the interconnect shaft being only supported by the front and rear shafts. I have run this through my mind many times and cannot see why it won't work, hence the commitments in time to see if it does in practicality.

If it does, it will be a very simple engine to make, not much harder than a single, but with a lot less vibration, well that's the theory.

I haven't done any detailed plans, just sketches for the bits as I go along, but if anyone wanted to put it on CAD that would be terrific, as I think it would interest other builders down the track if it works.

The secret to it functioning as intended is I think the interconnect shaft, I have made the disc from spring steel which is super tough with drill rod for the pins, a very tight press fit. The only disadvantage is the thickness of the interconnect disc to get stability into the pressed in pins, means that the cylinders will be a bit more staggered than normal.

I note Brian Rupnow has a similar engine on the go too, terrific stuff ...

Ed

 

[quinette7]

Great project! That truly is a HOOT!

I had fun making my Mate, and will be watching as this proceeds. Drawings or sketches would be most welcome.

13th diesel! I'm impressed!

Bob
Salt Lake City

 

[edholly]

Well after making the the rear disc and then the holes a beautiful snug fit for the pins in both the crankshaft and the rear disc and then assembling it, I found that it doesn't work.

You know how there is so little movement of a piston at TDC, well I think that is what conspires to work against this principle, the forces involved are very high and allow the interconnect shaft to move slightly and any movement no matter how small will mean that this arrangement is not feasible.

Oh well back to the drawing board.

Thanks to all who have taken their time to look at the thread.

A photo of the il fated shaft - and 11 engines made, the 12th is missing - it powers a Veron Cardinal ..

Ed

 

[quinette7]

Yeah, the forces will be pretty high, and I can see now how they would conspire against you. That is a clever concept, however, and might have been a problem solver. Congratulations to you for taking it this far along and testing it. I think part of the appeal of this hobby is the learning process and puzzle solving, but that does entail a certain degree of frustration along the way.

Nice line-up of diesel engines!

Bob

 

[Niels Abildgaard]

I am impressed by the courage of Edholley starting to make a press fitted two throw crankshaft.
I have tried many times and have not succeded yet.
Was the 60 degree v2 ever tried for rpms with one cylinder just not igniting?On each cylinder?

 

[Niels Abildgaard]

Hello Ed

Have reconsidered the crankshaft for your boxer Owen Mate.
Distance between main bearings shall be as short as possible
Journals are not hardened.
Two stroke conrods are always in compression.You wonderfull 60 degree thing has proven ,that bigger crancase volume is NOT detrimental.
Your engines up til now are not in Team Race country concerning journal surface speeds.

As far as I can see this means that cranskhaft shall better be solid and conrod bigends dividable.The present big end journals are 5 mm diameter and 4 mm long.
7 and 3 is miles more rigid and allow 3 mm wide cheeks.
When You are at it make a single throw shaft for two conrods side by side on a single 7 times 6 mm big end journal.
Where can I get a drawing of a normal Owen Mate?
Kind regards
Niels

 

[777engman]

Neils is right the fix for this engine is a 1 piece crank with split big ends, make the rods from 7075 t6 and it will run sweet. photo shows my flat four that uses this same setup.
cheers
Dean

 

[Niels Abildgaard]

Hello Dean
Very nice engine
I assume there is some kind of diverter integrated in crank to supply the two crankcases?
Two pistons igniting while two scavenges?
Do You have pictures please?

 

[edholly]

Dean,

I am jealous ....

Beautiful work, congratulations on it.

Like Neils would love to know how you split the bigends .... ?

Ed

 

[777engman]

hey guys here are some photos of the conrods I made a while ago for a project still under construction, the conrod thickness is 4,5mm and the big end is 5mm dia bearing. the fixture shown is to drill and tap the 0/80 threads of the big and bolts. I have a separate jig to fit the rods in to cut the cap. basically I make the whole rod complete, then cut the cap off with an 0.008" slitting saw, after drilling and tapping the bolt holes. Then clean up the faces and bolt back together then re-ream to the finished size. This method has worked flawlessly for all my engines. below is the link to my blown V12 2stroke engine build on model-engineer.

http://www.model-engineer.co.uk/forums/postings.asp?th=90605

it has more info in it about setting up the rods etc..... I don't have a photo of the crank set up but basically when you make the crankshaft you drill the intake hole in from the rear and right through to the front web without drilling the web. then you drill a slightly oversize hole to the font edge of the center main journal, leaving a lip for the valve to stop up against., next you set it up in the mill to crossdrill the 2 intake holes right through the bearing( in the right place timing wise of course). when this is done and cleaned up, deburred etc you machine up a small tube like valve, this is drilled in from each end but not right through. when this has been pressed into the crank and secured you just angle drill carefully through from the 2 opposite intake holes to each side of the crank and your all done. obviously you need to make sure the 2 cases are sealed from each other so don't drill in to close through the center portion, and of course you drill into the correct end of the crank for the intake timing. On this flat four the 2 front pistons go in together and the rear 2 pistons work the exact opposite, so 180 degs aprt from the front two. hope this helps, and actually its not that hard so give it a go mate. if you need any help feel free to ask me.
Cheers for now
Dean

 

[777engman]

Hey ed did you get my pm regarding david owen? please reply if you did.
Cheers
Dean

 

[777engman]

Hi again Ed, just wondering if you got my message regarding finishing this engine? be good to see it running after you started with so much work,
cheers
Dean

 

[edholly]

Dean,

Thanks for offering to help with split bigends, I can see that is the only real way to make this engine now. Unfortunately I am about to start on the restoration of a 1961 Lotus Elite which has to be finished by August next year, so building model engines will be a bit quiet for a while - but you never know. The 60th anniversary of Elites is at Eastern Creek then and I have been told it has to be there! I am already a bit down the track with it, but still a long way to go.

Really do want to design a flat twin using David's cylinder arrangement though.

 

[777engman]

Oh ok, good luck with the rebuild. I have been down that road myself being a mechanic by trade, also do panel and paint bla bla bla so hearing your pain mate. do you have drawings for the twin, i wouldn't mind building it over the Christmas break maybe.
cheers
Dean