A Taplin Twin type engine of 4cc

[edholly]

In a way this is a continuation of a previous thread called the

60 degree Vee Twin 1.6cc and the remnants of that thread at time of starting this one can be found at http://www.homemodelenginemachinist.com/f31/60-degree-vee-twin-1-6cc-22760/index6.html where mention is made of this new design.

Just a bit of what has happened in the past - wanted to build a twin and experimented with a 60 degree Vee design by building 2 engines. End result is they run - but with inefficiencies inherent in any 2 stroke naturally aspirated 60degVee design they do not produce any more power than the single cylinder version on which they were based.

So back to square one - enter this engine - an inline twin along the lines of a Taplin Twin - but something I believe will be fairly easy to build, based on the proven Owen Mate formula - but redesigned as a sideport with some novel features such as bolt on rear crankdisc, ball bearings, less transfer and exhaust porting.

As usual my draftsmanship is rudimentary, but good enough to get me to the next step. I am taking a lot of photos along the way, so will be able to do a .pdf file which will show the build, and if the engine is a success then maybe someone could do a cad drawing of it.

Anyway - here is a photo of about 8 hours work to get the crankcase done, alongside the Owen Mate and the V-HOT which is the 60 degree Vee Twin based on the OM.

Haven't decided on a name yet - but inclined to go with I-HOT for Inline-Holly Owen Twin.

Next steps are bolt holes for front and rear housings, then bore cylinder and hold down threaded holes and remove metal for the plenum chamber housing between the cylinders, along with inlet holes from the chamber itself. A rough drawing of the engine is attached. Just a working drawing no detail much so far. Obviously the venturi at the front won't be there.

Here we go again !

Ed

 

[edholly]

Here is the completed crankcase - documented on a .pdf

Will also photograph and describe other facets of the build as we go along.

Hopefully if the engine is successful then might serve to inspire some budding machinists to build one.

Ed

View attachment Making IHOT crankcase.pdf

 

[edholly]

Have now completed the cylinders and the crucial interconnect shaft which has a bolt on rear crankdisc. Using 2mm caphead bolts the crankdisc can be removed and this allows the shaft to be supported by ball-bearings internally.

Drilling 4 x 12 mm holes then tapping was done very carefully, a broken drill or tap and you start again from scratch. thankfully all went ok.

Have done a .pdf as it makes it easier to tell the story that way. One thing I left out is the crankpins will be pressed in.

The cylinders were done as per David Owen's - Owen Mate instructions on the MEN website but of course being a sideport the porting has been redesigned big time.

Anyway its all here on the attached file - so far.

A pic though to whet your appetite !

Ed

View attachment Making cylinders and interconnect crankshaft.pdf

 

[GailInNM]

It's looking good Ed.
Your interconnect spool looks like it is going to work very well. A good solution to a difficult problem on inline twins.
Gail in NM

 

[Niels Abildgaard]

My solution even if I liked the V2 better.

I do not know that Ed Holley will use pressed in crankpins.
I should remove this whole letter and picture,but I love the drawing just as superfluouse kittens.
Am not cruel enough.

It is nice that one can edit former errors.

 

[edholly]

A bit more progress ....

Interconnect shaft housing made and installed with countersunk screws from beneath. Was going to hide them under the plenum chamber but realised that the rotating masses will be pushing against the screws and against the thou or so clearance, better to position them at the bottom where they will assist stabilse the housing against the bottom of the arc.

Next is to install the crankpin on the rear bolt on disc and a to-size hole for the nose shaft to fit into. Thought about putting the bolt on disc to the front, but if the caphead 2mm bolts ever sheared, then it would get ugly, whereas in the rear half the shaft should just rotate without too much damage, well that's the theory. Having the bolt on at the front would have been good though as it lessons the impulse torque from the rear by having a bit more mass, albeit it is close to the centre.

The NTG bearings have a shield on them, these will be removed before final assemby. I have some high clearance bearings coming and will pick up tomorrow night - David Owen prefers these to standard bearings and believe it or not they are 1/3rd the price of these NTG ones.

Have to own up to 2 stuff-ups ... first was the original interconnect shaft was 5mm short. Without a component drawing I measured off the length but erred by missing out on the bit inside the bearing - then when drilling the stabilizing holes for the housing in the crankcase bottom, made it too wide and hit the bearing itself. no damage done except to the ego, that's why that extra hole is adjacent to the contersunk one - damn.

Ed
.

 

[edholly]

Next step was to insert the pins ..

I used drill rod 5mm diameter and pressed it into the rear disc by drilling the hole to about 4.9mm then machining down the drill rod to a thou over that isze the thickness of the disc, then a nice tight fit into the disc.

Next problem was the hole for the nose crankpin to fit into exactly 180 deg apart. So made a mount exact width of crankdisc diameter and drilled a 5mm hole for the rear's crankpin to fit into exactly in the middle - then put the interconnect shaft assembled onto the mount into the vice and the whole thing was then held as one. This then meant the hole to be drilled for the nose pin to fit into would be 180 degrees exactly from the rear one and drilled it. The nose pin will be integral with the nose shaft, and a sliding fit into the interconnect shaft as can be seen in the last photo.

That sort of completes the interconnect shaft, so next is the nose housing and associated shaft disc etc.

 

[edholly]

Nose piece, front crankshaft, propeller drive and spinner nut done.

The nose piece has a ball bearing on the internal end, but a bronze bush on the outer end. I am not sure why but I prefer this method of supporting the shaft, and it gives a better seal as well.

All the fits are very close, and the fit for the nose crankshaft into the interlink crankshaft is critical. The bronze bush is within a half thou of the shaft, so there is ot slop at all to work with, and there is is slightest binding of the shaft when mated into the rear interlink shaft, nothing to worry about but I know its there, I'm guessing but maybe the interlink hole is a thou or so out, I'm sure the first run it will be free.

Weight so far is 10.7 oz. conrod, pistons, cylinder muffs, tommy bars, rear cover, plenum chamber and needle valve to go, my guess is it will end up around 14 oz - my Owen Mate is 6.4 oz

One of our fellow HMEM members is doing the CAD drawings as I make each bit and supply him with my rudimentary drawings. So far like a doctor to chemist relationship Darren has been able to interpret them. David Owen has very kindly agreed to allow the Owen Mate componentry to be used in the design, so hopefully not long after the engine runs, a set of plans will be available for anyone that wants to make one.

Assuming it does run of course. .

 

[Niels Abildgaard]

How do You seal front crankcase from the rear one?

 

[edholly]

Hi Neils

The interconnect housing is about 15mm long and is a tight fit in the crankshaft tunnel, likewise the interconnect shaft is a very close it between the ball bearings - so although there would be a leakage of sorts - it for all intents and purposes negligible in my opinion. Certainly no worse than a normal crankcase to atmosphere ...

Although the bearings have seals here - they will be removed before final assembly.

Ed

 

[edholly]

Starting to look like a motor now !

Just honing bores, making pistons, conrods, contras and backplate to go. Oh and a couple of tommy bars to go back on the Vee Twin!

The plenum chamber worked out well, a nice snug fit between the uprights, so I don't think any sealant will be necessary. A bit complex an inlet hole for the venturi, meeting in the middle for the cross drilling - didn't leave much for the holding down bolts, decided in the end that just one would suffice. Morphy's law dictated I put it in the wrong side (why do we do that ?) easy enough to rectify, but whereas I had it perfect in the wrong side, it was out by about 1/4 mm doesn't matter - but it WAS perfect. The venturi is pretty standard, wanted it to look a bit chunky and think I achieved that, has a David Owen needle valve.

Darren is doing a great job with the CAD plans, will supply him some more rough drawings now. So good in fact I went to pick up one of the pieces on the desk and then I realized it was the rendering of it - not the real piece !

Maybe might finish it next week - started with the rough plans on Mon 9th June.

 

[edholly]

Darren Simpson, a fellow HMEM member has been keeping up with me very kindly doing the CAD drawings.

This rendering is fantastic, what an incredible tool CAD is. Darren says that it can even work out the weight of things when you put in what the various materials used are.

Compare this to the photo alongside....
.

 

[ausdier]

Just did a bit of polishing.

At least this is a little easier that another project I am working on so stay tuned...http://www.homemodelenginemachinist.com/f23/vimana-v-twin-22528/

 

[edholly]

3 weeks and 2 days later ....

[ame]https://www.youtube.com/watch?v=IsEZ9w8dW7I[/ame]

It runs quite nicely, but suspect there is a lot more power available with some tweaking. Video here with a 11 x 4 Turnigy wood prop.

One thing it has proven so far is that the bolt together interlink crankshaft appears to be working ok.

Will give a longer report after some more running - so far has had about 35 minutes.

Ed

 

[GailInNM]

Sure looks good Ed.
Congratulations on a runner.
Even made me double check that I still had my set of Taplin drawings.
I really like your Plenum chamber arrangement.
Gail in NM

 

[ausdier]

Well done sounds like a great little screamer.woohoo1th_wavwoohoo1

 

[barnesrickw]

Sounds beefy. Very nice.


Sent from my iPad using Model Engines

 

[johnny1320]

Very nice! How do you find starting a twin diesel compared to a single?

 

[edholly]

Johnny, not much different really, in a single you get your fingers out of the way just a few degrees after top dead centre if you do it right - this is the same - except it fires 180 degrees earlier for the next impulse.

Well, I just ran it again this morning, trying to get a better feel for it.

Firstly No2 piston was way down on compression, so used that unique process and grew it by about a thou then judiciously brought it down to a tight fit - end result - perfect. Then immediately the No1 contra piston decided to go soft, so fixed him up with another growing session, a thou and he's a beaut fit now also.

Back to running and this made it beautifully consistent compared to previously. Would hang on to 5500 on my 10 x 6 wood test prop for minutes on end. Seemed pretty sensitive to compression, but not so much to needle valve.

The most annoying thing is - it will scream when first started, caught it with the rpm meter and it pulled 7000 - but it won't give that for more than a couple of seconds. I suspect the inlet tract is a bit convoluted and maybe a bit restricted, would welcome some ideas please.

I love its lack of vibration. and of course 5500 sounds like 11000 on a normal motor, unfortunately it annoys the hell out of the better half, so will wait till she goes to the shops to test next time, oh and I'm in trouble too for making the grass slippery with oil !

Now the interesting things are ... on my 10 x 6 wood test prop ...

1. The standard Owen Mate gave 5500
2. The 60 degree twin gave 6100 on a single cylinder with No2 blanked off
3. The 60 degree twin gave 6,000 on both cylinders
4. The Inline twin is now giving 5500 on both cylinders consistent, BUT with a promise of 7,000 if I can work out why it will go there on the first moments after starting.

No wonder these things keep you interested !

There is inside the engine the ability to change the inlet port timing .... I initially had it at a tad over 150 degrees, but thought that a bit ambititious to start with, so machined some inlets on the opposite side of the cylinder and put the cylinder in each other's holes for 119 degrees. Now if I want to try the 153 degree ports, all I have to do is put them back in the opposite to where they are now holes and try it. Will do that as the next phase of development. The unused holes are against the crankcase wall so have no eefect on the running.

So far so good with the bolt together rear of the crankshaft - the engine has had well over an hours running now and is startiing to feel as though it is getting close to that nice runned in feeling when turning over. Not that you get that happy back and forwards rotation, as immediately one piston is off comp the other is building it.

The various weights of these engines are
Owen Mate 6.03oz ... 171 grams
Inline twin 14.67oz ... 415 grams
60deg twin 11.21oz ... 318 grams


Ed

 

[edholly]

Today I transposed the cylinder/piston/muff/conrod assemblies from front to back and vice versa - by doing this I was able to ascertain what 150 degree inlet porting would do to the running of the engine, as I had erred originally by making the inlet holes at this spec, before making more conservative ones 180 degrees away on the opposite side of the cylinder walls.

Well, it didn't seem to make much difference to the starting, but the running was rock steady at 5550rpm with a best of 6150 when leaned out whilst still not quite up to operating temperature - so suspect the 5550 will improve a bit with more running. All this on a Turnigy 11 x 4 wood wide blade prop.

After the runs the engine now has about 40 minutes total.

Darren Simpson is working on the CAD drawings and has finished to the point where you can view the engine from any angle and remove components as well. Truly an amazing way of presenting an engine. Now that we have sorted the consistency problem and know that we can go with a bit more than 119 degree inlet timing, Darren can complete the plans. He has also allowed us to look at the bolt on rear disc, and although the 2mm cap-heads have done a sterling job so far, it would be better to make something a bit stronger. Problem is the pressed-in crankpin, but it looks like three 3mm cap-heads will do a stronger job and allow the crankpin enough meat to do its job, again CAD is a terrific tool to explore such modifications.

Meanwhile here's the start of the latest runs - 2nd flick and its away !

[ame]https://www.youtube.com/watch?v=HnG2qTlkoXs[/ame]

Ed
.