A different opposed piston engine---

[BaronJ]

Looking good.

I'm looking forward to seeing it running too.

 

[Brian Rupnow]

Well--------------------The engine is moved out to the main garage and bolted down to my test bench. The power box is all hooked up. The 12 volt battery has been on the charger all afternoon.--I bought a new fire extinguisher this evening. I have to do 2 hours engineering design work for a customer tomorrow morning. I think I'll put the furnace on in the main garage while I'm doing the design work.--And then--Maybe---Gee, I hope this thing runs!!!

 

[Brian Rupnow]

This morning we are on our way---

 

[Brian Rupnow]

Okay--Now I have to sort out what to do next. Engine runs, but rings are awfully tight. This means that engine fires and runs like crazy with " starter drill assist" but bogs down and quits shortly after drill is removed. I can pull it apart to cut the ring grooves a little deeper, or I can make a temporary extra flywheel, in hopes that the added mass will give that extra inertia to keep the engine turning over between "hits". The rings will wear in a bit as soon as I have consistent running, and a temporary add on flywheel is probably the easiest thing to do for now.

 

[Brian Rupnow]

The pulley is only lightweight aluminum, wouldn't do as a flywheel. If I oil all the pivots, bearings, etc. with a squirt oil can its good for 1/2 to 3/4 of an hour of running. These are low speed engines. I have tried the needle valve at many different settings to make the mixture leaner or richer. There is definitely an effect, but not enough effect. We aren't through yet. I'm going to make a 4" diameter x 1/2" thick steel second temporary flywheel. I may try my model airplane carb. I am right on the cusp of a running engine.

 

[BaronJ]

Ooh the suspense...

 

[johnmcc69]

Looking good Brian!!
From what I've seen (& read.) on similar designs like
the Atkinson Differential engine, they use a larger flywheel
& oilers.

John

 

[Brian Rupnow]

I'm going to give it up for today. The frustration level is getting too high. The second flywheel helped a great deal, and I have gotten a few sustained runs of 20 to 40 seconds, but then it dies. When an engine does that, if its a weak coil, it won't start up again right away. Mine will start up again right away, so I don't think there is anything wrong with the ignition. When engines start at all and give a sustained run of 20 to 40 seconds and then die, it is generally a carburation problem. Either it is running out of gas, or it is flooding itself, getting too much gas. I have played enough for today, and of course I have advanced the timing and retarded the timing many times trying to find the "sweet spot". I did cut one coil from the intake valve spring, as I wasn't seeing any movement in the valve while turning the engine over with the drill. Removing one coil seemed to do the job, as I could see the valve "dance" after that while it was turning over.--And of course, the engine has loosened up considerably after a number of short duration runs.Tomorrow I will try it with my model airplane carb and see what happens.

 

[Philjoe5]

When an engine does that, if its a weak coil

Brian,
I'm suspicious that I'm dealing with a weak coil too. Is there any way to check it other than looking at the quality of the spark?

My spark is hard to see and yellow, not blue. I thought I remember reading somewhere that you should be able to hear the spark, with the plug out of the engine. True?

Cheers
Phil

 

[Brian Rupnow]

Phil--I'll probably take flack for this, but I don't think you can tell by the colour nor by the sound of the spark. In a perfect world all sparks would fat, loud, and blue-white. That actually happens about 1/3 of the time. Lots of times the sparks are yellow, quiet, and not all that big.---and the engines run just the same!!! If your engine fires, starts, runs for a few seconds and then won't stay running it could be the coil. But if you immediately try to restart it and get the same results, its probably not the coil. If a coil goes out, it stays out for a while until it cools off. Its more apt to be a carburation issue. If it doesn't fire at all, then its either coil or points or sparkplug.

 

[Brian Rupnow]

I simply couldn't cope with an engine which had nothing out front to grab on to and turn by hand. Last night I pulled the starter hub off the front and bored out a piece of 2" diameter aluminum to press fit over the outer diameter. A bit of Loctite and a press fit, then let it set up overnight. This morning was able to knurl the o.d. of the aluminum. Now I can actually grab it and turn the engine over by hand. Compression on this engine is phenomenal, but I thought it would be after all those firing "pops' yesterday.---It bounces back when you try and spin it through the compression stroke by hand. I have a couple of hours of design work to do this morning, and then maybe we'll give it a go with the model airplane carb.

 

[Brian Rupnow]

I'm running out of tricks!! I changed carbs, and although perhaps it is marginally better with the model airplane carb, still no lasting joy. I have great compression. I have good gas. I have adjusted the timing both retarded and advanced to the point of ridiculous. Had a couple of 1 minute runs, just enough to get my heart beating real fast, but then it petered out. The only thing left to monkey with is valve timing. Now I have to pour a glass of red wine, go upstairs with my good wife, and consider things for a while!!

 

[Shopguy]

Brian,
Is something changing when it heats up?
Valves, pistons, fuel supply? Or cylinder pressure?
Possibly would increasing the mass of the flywheel help?
I mention this because the fuel air charge is going to start expanding once it hits the somewhat hotter intake ports and other internal parts, more so than in a cold engine. This would, theoretically require more force to overcome hence more flywheel inertia.
Keep at it you're getting closer.
Ernie

 

[canadianhorsepower]

Hi Brian,,
nice pieace of work if I can give my opinion
your intake track is way to long. The longer the higher your RPM has to
be for the pulse wave to work I would simply put a small 90 degree elbow
and put the carb right over the intake valve

good luck

 

[Brian Rupnow]

No, there is no thermal difference, because its not running long enough to develop that kind of heat. I have already doubled the mass of the flywheel so it now has two 1/2 " thick x 4" diameter steel flywheels, which should be lots. Luc's answer may carry part of the truth, and yet I see Chuck Fellows running his vertical engine with an intake track 5 or 6" long, so I doubt that's it.

 

[tonyr]

Brian,

I have had similar issues with a couple of engines I have made.
Try putting a tube on the air intake of the carb, then vary the size of hole in the end.
Start by covering the end with tape or card and put a small hole in it and try the engine.
Keep making the hole a bit bigger to see if it improves the running.
I think the extra depression in the carb inlet helps draw the fuel better.
It has worked for me a couple of times. If it improves the running you can make it permanent.

Tony


Sent from my iPad using Model Engines

 

[Brian Rupnow]

Tony--I may try that.---Brian

 

[dsage]

Tony:

You mean like a choke?

Brian:
Along this same line of thought. When you try to start it, and just before it dies, does it help to give it a quick finger over the carb - choke trick? This will tell you if it's getting fuel. The finger trick will cause it to suck raw fuel for an instant.

I'm sure you've thought of all the stupid things but I'll throw them out there anyway. For the benefit of others if nothing else.

You have a vented cap on the fuel tank - right?

You mentioned before that you have the fuel tank at the optimal height but you can prove this and also check for the ability of the engine to PULL fuel if you temporarily lower the fuel tank down a bit such that you have a tiny bit of air in the tube right where it enters the carb. When the engine is cranked over it should have enough suction on the fuel line to lift the fuel even though it is a tiny bit lower than the carb. If not, not enough vacuum on the intake stroke or too small a fuel needle opening or too big a venturi. Also related - in terms of an atmospheric intake valve but maybe too heavy/light of a spring.

How does the sparkplug look - wet/dry, fuel or oil soaked?

Good compression requires a good spark. Does the spark look like it has a bit of reserve.

Try running it in the dark. You might be able to see a spark leak somewhere.

Sage

 

[Niels Abildgaard]

Stupid remark removed.Excuse me

 

[Walltoddj]

Just a thought but could you have to much compression? I ran two stroke kart engines in the 70's and we had modified the cyl head for a better flow. When we ran it we had low power after a compression test we were over 300psi. Got it back to about 125psi and it worked fine. I know you've been trying all base just my idea.

Todd