25 cc Horizontal Engine

[Roger B]

As I had fitted the four jaw independent chuck to make another fuel pump body I decided to make an adaptor to try another carb on this engine. It came from the sell off tray at the local model shop so I'm not sure what engine it was designed for. The bore is around 6mm and it has a slide throttle together with an idling needle and jet. The adaptor is a piece of 14mm diameter brass turned eccentrically to give a couple more threads for the grub screw. It is soldered onto the original exhaust stub from the engine.

[fumopuc]

Hi Roger, I am curious about the result of your experiment with this carb. My estimation is, that you will get a good idle of the engine by the special needle adjustment. But I am affraid that by opening the throttle the vaccum will brake down and the engine will stall. 6 mm is a very big diameter for this small engines. I have heared that 3mm should more than enough for this low revving engines. I have a simillar set up at my Webster, the bore is still to big.
So I am waiting for your first test of the carb.

[Roger B]

Quite a successful day I made a bracket for the water pump and connected it up. There doesn't seem to be any significant water leaks and the puffs of steam in the outlet pipe from the cylinder head have gone away. Next I need to make some brackets for the radiator.

I then fitted the new carb. I had to turn the adaptor down a  little to get clearance for the fixing nuts.

It ran far better than expected    Together with the new generator bracket I got up to 11V at 11A ~120W at an engine speed of 3000rpm with the throttle fully open. There is also a good throttle response. I need to make a control before I go any further. The slide does not stay in place on it's own    I also need a shorter screwdriver for the adjustments to keep my hand away from the flywheel and starting dog 

The carb I have been using on this engine has a barrel bore of 4.2mm and was obviously limiting the power. The previous best was 80W at 2500 rpm.

<a href="https://www.youtube.com/watch?v=f941X4lxYF8" target="_blank">http://www.youtube.com/watch?v=f941X4lxYF8</a>

<a href="https://www.youtube.com/watch?v=_t_d2roV8W8" target="_blank">http://www.youtube.com/watch?v=_t_d2roV8W8</a>

[fumopuc]

Hi Roger, good result, so my estimation was wrong.

[Kim]

Congratulations Roger!  It certainly looks and sounds successful to me! 
Kim

[Roger B]

Thank you Kim, I'm getting there 

The next hurdle is lubrication. The little commercial oiler I am using for the cylinder fell apart yesterday, probably a combination of temperature and vibration. As it was coming apart the needle came out of the seat resulting in too much oil flow and oil everywhere, up the wall, over my instruments, over me 

I need to make splash shield to go over the crank (one was in the original planning, but I haven't got round to it yet) and decide what to do about lubrication. I could make some better drip feed lubricators (I like the look of the four post ones over on the Pacific Vapour Engine thread) or I could make an oil pump, possibly like the ETW metering pump with the rotating plunger. In any case I think I will have to drill the crankshaft for lubricating the big end. I can't see a drip feed lubricator doing well at 3000 rpm 

Achim, I hunted down the origin of this carb. It's from a 2.5 cm3 two stroke for model cars rated 1.1kW and 30,000 rpm. My engine is 10 times the capacity running at 1/10 of the speed so the gas flows are similar, but my output is rather less. The spec sheet for the motor I am using as a generator give a maximum efficiency of 61%. If I am running in this area the engine output is around 200W. Taking a less optimistic figure and drive belt losses the engine may be reaching 300W.

[Roger B]

On with the splash shield (should have made it months ago  ) Its a piece of 0.8mm brass sheet fixed by the cylinder lubricator and a couple of M3 screws at the back. The curves are a nominal 55mm radius so bending round a piece of 90mm dia. bar gave enough allowance for the spring back.

[Don1966]

Looks like great results Roger and a well deserved great work mate............


Don

[Roger B]

Thank you Don 

As I had the 4 jaw chuck on the lathe again I made a throttle connector for the new carb. It was supplied with a very short arm with a ball on the end probably for connecting to the throttle servo in an RC car. This piece will fit over the end of the throttle slide and connect to my original lever and linkage although I will have to move the lever to the end of the base.

[Roger B]

I connected up the throttle linkage, fitted the radiator to the support for the cooling tank and gave it a try.

The throttle response was very good, but I need to make a much better linkage. I had underestimated the effect of the suction on the slide. It pumps in and out when the engine is idling and sucks itself back in if I let go of the control at larger openings.

As expected I also need to fit a fan, it started boiling after 10-15 minutes of running. I can either fit an electric fan (Pabst/Muffin type) or use a belt from the water pump shaft. It needs a bit more thought.

With the engine running at a suitable speed to give around 6V from the generator I connected the output to the coil and then disconnected the battery. It continued running steadily supplying it's own ignition system load.

<a href="https://www.youtube.com/watch?v=w18zhtuLBoc" target="_blank">http://www.youtube.com/watch?v=w18zhtuLBoc</a>

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

[fumopuc]

Hi Roger, very well done. So you have build a very economic "green" model engine, now we have to reduce the Co2.

[zeeprogrammer]

Just finished reading through your thread. It's amazing how much good work has been done on this forum during my hiatus.

Sounds excellent and as you say the throttle response is very good.

[Roger B]

Thank you both.

When I ran the last trials it felt as though the piston picked up a couple of times so I stripped the engine down to check. The big end was ok, the oil grooves (chatter marks from reaming) were still visible but the piston had two big scores and the second ring was jammed in the groove. I decided to increase the clearance from around 0.03mm to 0.05-0.06mm ( a bit approximate as I don't have an internal mike).
The second ring broke when I tried to take it out (could already have been broken  ) but I had a spare. I cleaned up the piston with very fine abrasive paper (called polishing cloth here) increasing the clearance a couple of hundredths. It all assembled ok with good compression so I now need to make a better control for the new carb.

[Roger B]

I decided to make a slotted sector to fit over the carb inlet to try and get better control. This cut from 4mm aluminium plate and held in place with a brass collar.
The slot is a bit rough (blunt cutter?) but is ok for a trial. If it is successful I will remake it (brass may be a better material as the action seems a bit sticky.

The R&D department was closed due to snow so testing will have to wait.

[Roger B]

I decided to use an electric fan for the radiator and bought a suitable 60mm x 60mm 12V one. The frame will be made from some aluminium sections I have from a previous plan to build a girder bridge for my LGB garden railway. I found a suitable dodgy set up to mill a radius in the two cross members to not block any air flow. Off traveling again this week so no more workshop time