Two Cylinder Engine

[Roger B]

Thank you both  Somewhere near balanced will be fine for me. I will finish up the rough edges and put a radius in the corner by the balance weights with a selection of files.

[AlexS]

Great work, that looks nice!

It would be fun to see an model engine with one or two primary balancing to compensate the forces of the accelerating piston. But indeed no need for light weight piston and connecting rods!
It is possible to test the balancing, mount the crank in  the lathe with fitting the connecting rod and bearings. And connected the rods with an elastic at a fixed place, for example a wall. And supports it with a counter center.

[Roger B]

Thank you Alex 

I added some more elbows to the cooling system and neatened up the pipework. The feed to the block now goes over the flywheel end to make space for an injection pump. The connections also are ready for when/if this gets installed in a tractor and the radiator moves to the front.

[Roger B]

Whilst thinking about the next steps with the diesel I continued with the 360° camshaft for this engine.

First step was to make a thrust washer for the fixture as I had found that the shaft would slide along on the deeper cuts unless the clamp bolt was very tight. The rest was much as before, spread over several evenings to reduce the chance of me losing concentration and having to start again.

The new cooling system is better but on the limit at full load.

<a href="https://www.youtube.com/watch?v=aLP3_FKovd4" target="_blank">http://www.youtube.com/watch?v=aLP3_FKovd4</a>

[Roger B]

As the intention is to compare the 360° and 180° versions I needed to take some reference measurements for the 180° Version. At 2500rpm it delivered 4.2V at 2.5A, about 10W. At 5500 rpm I got 8v at 8A, 64W and at 7000rpm 9.5V at 11A, 105W. The full speed figure was slightly better that with the barrel type carb I used initially.
I then tried some on and off load testing at around 90W and 50W which it took without a stutter. Finally I tried revving it into a load, again without problems. On with the rebuild 

Low speed run 2500rpm

<a href="https://www.youtube.com/watch?v=onotmaoX6W8" target="_blank">http://www.youtube.com/watch?v=onotmaoX6W8</a>

Load dump 90W

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

Load dump 50W

<a href="https://www.youtube.com/watch?v=kV_tjLb6o-g" target="_blank">http://www.youtube.com/watch?v=kV_tjLb6o-g</a>

Revving under load

<a href="https://www.youtube.com/watch?v=k3TUprVcAas" target="_blank">http://www.youtube.com/watch?v=k3TUprVcAas</a>

[Admiral_dk]

I've just finished a book about the Kawasaki Racing effort in the USA by Randy Hall.
In the end of the first book in the series, he mentions that the KR250/350 started out as a 180 degree (remember this was a two cylinder tandem engine). Since it was a mere question of how you assembled it if it was a 180 or 360 degree firing interval - they tried both.
Initially they got exactly the same power, but with the counter rotating cranks the 360 degree version had much fewer vibrations and this meant that they could increase the RPM's quite easily .... mind you - almost all motorcycle racing two-strokes have a top RPM around 12,000 RPM .... yes you could go higher but at no gain.

The modern Four-stroke period has also experimented quite a bit on the phasing of the crank throws and firing order. They never got any power increase, but it has a big impact on tyre life and how likely the bike is to throw the rider off the bike ...!... and how well it behaves round corners etc.

[Roger B]

Thank you Per    I am interested in seeing the effect on mixture distribution with the siamesed inlet port  If I have equal firing angles I can use a single fuel injector driven at crankshaft speed.

I case hardened the cam and luckily it didn't distort much (straightened by thumb pressure)  It was easier to remove the engine from the base for the rebuild. First I stripped down the distributor to check the cam dimensions so I could make 180° version (I wasn't sure that the drawing was correct). There was a lot of oily goo inside the cap but it didn't seem to affect the operation.

[Admiral_dk]

Oh yes - I forgot about your inlet arrangement - on racing engines it's usually individual mixers - but on your engine it should make some difference and I understand your desire to see about a single injector solution, as it potentially could reduce the requirements of the construction ....

[Roger B]

The contact breaker cam is made from an offcut of 20mm mild steel. The original doesn't seem to show much wear so I probably won't case harden it. The design is such that the centre of the flank curve is on the circumference of the cam making it very easy to set up with the Keats angle plate. After turning the first flank the blank was rotated 180° using the scribed line for alignment to turn the second flank. The blank was then parted off and faced to length on a tapered mandrel. Finally the rotor fixing screw hole was drilled 2mm and carefully relieved with a 4mm end mill to clear the head.

[Roger B]

The fixing grub screw was then drilled and tapped M2.

[Kim]

Hi Roger,
I continue to follow along, though I don't have any experience in IC, I find it fascinating and try to understand what's going on. And initially, I couldn't initially understand why you moved to the keats setup, but I figured it out eventually. That is a pretty neat setup

So, did you leave the transitions between the different radiuses sharp? Or did you round them off a bit?  Just curious.

Kim

[AlexS]

I thought I had seen a video on this forum with the engine running (360 deg version)? On high rpm

[Roger B]

Thank you Kim   

I find the Keats useful for all sorts of setups. The transitions were just smoothed off with a fine file. As there is just a light plastic follower I don't think it needs anything more.

Alex, There are quite a few videos on here with the engine running in 180° form. However there seems to be some form of security problem and a lots of people are unable to see them. There is just a blank space in the post.

https://www.modelenginemaker.com/index.php/topic,10150.0.html

[Roger B]

The videos seem to be fixed now 

The distributor cap was fixed to a 16mm mandrel to make the seating for the 180° position. This was made as before. Luckily I could unscrew the existing connection and reuse it. I had made a spare brass nipple but it wasn't needed. I then continued stripping the engine down. The pistons and rings look fine but there was a bit of fibrous debris in no. 1 combustion chamber. The existing crankshaft looks good but I guess it has had less than 10 hours total run time. The new cfank fitted nad turned easily but is about 1mm too long  I need to check the dimensions 

[AlexS]

Thank for letting me know about the security problems, but it seen that they are been fixed!

+- 10 hour total run time!  Did you measured the dimensions of the piston rings before and after?