Author Topic: Two Cylinder Engine  (Read 31738 times)

Offline Art K

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Re: Two Cylinder Engine
« Reply #255 on: December 29, 2019, 04:11:00 AM »
Roger,
Your twin runs good, I couldn't read what the meter's read to determine what sort of load you had. When I last went to the "local" model engine club he had a pony break set up so that anyone who wanted could set up their engine & check how much power it made. My Val engine put out 1/3 horsepower at 6100 rpm. Then it promptly stalled multiple times.
Art
"The beautiful thing about learning is that no one can take it away from you" B.B. King

Offline Roger B

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Re: Two Cylinder Engine
« Reply #256 on: February 19, 2020, 08:07:03 PM »
Thank you Art  :)  I got to about 80W (9V at 9A) but the carb is not optimum. Depending on the efficiency of the generator that puts the actual output at a bit under 1/4 hp.

Finally back to some engine making. I put together an electrical system in the same style I used for the other petrol engines and then made a clamp for the silencer from a 5mm x 0.5mm strip of phosphor bronze. I put some cooking alcohol in the tank and started it briefly to make sure the wiring was correct (I have used a 7806 regulator to reduce the voltage for the 6V ignition coil and have had problems before).

I now need to look at a new carb design to improve the response to loading if the engine is going to power a tractor  :headscratch:
Best regards

Roger

Offline Roger B

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Re: Two Cylinder Engine
« Reply #257 on: July 15, 2020, 07:46:45 PM »
The plans for this engine require a fuel pump for the SU type carb trial and then a fuel injection pump with the 360░ crank. I have been thinking about how to install these for a while and have come up with several designs for eccentrics and cams that would work but could not be assembled  ::) I finally had the inspirational moment and realised that if I turned the gears round it would be easy to fit the pieces over the gear bosses. The ignition side was easy as both keyways were vertical, the camshaft side is a little advanced but probably not enough to cause a problem.
Best regards

Roger

Online Kim

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Re: Two Cylinder Engine
« Reply #258 on: July 16, 2020, 05:25:15 AM »
Seems like a pretty good inspiration!  :ThumbsUp: :popcorn:
Kim

Offline Roger B

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Re: Two Cylinder Engine
« Reply #259 on: August 31, 2020, 08:22:25 PM »
When I started the next trials with the SU type carb it did not run well and I could feel fuel blowing back out of the carb intake  :( This usually means cam timing problems. I printed out a degree wheel and stuck it onto a piece of 4mm plywood. A check with a DTI showed that the exhaust valve was closing around 15░ BTDC and the inlet valve was open at around the same point. Firstly obviously too advanced by around one tooth and secondly where has the overlap gone  :headscratch: I moved the timing back by one tooth of the 40T gear (18░) which was somewhat more sensible.
The ignition timing was 36░ BTDC which I reduced to 20░.
Best regards

Roger

Offline Admiral_dk

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Re: Two Cylinder Engine
« Reply #260 on: August 31, 2020, 09:52:30 PM »
While very annoying ... at least you now got an idea about where to look for the reason.

I must admit that I can't remember how you did your camshaft - is it one solid piece or are the cams "loose" units assembled onto it ?

Offline AlexS

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Re: Two Cylinder Engine
« Reply #261 on: August 31, 2020, 10:33:15 PM »
It looks pretty familiar to me. my engine block has similar values of valvelap vs timing. Theoretically you assume a valve overlap of about 20+ degrees and practically it is a number of degrees like your engine. Option was to reduce lobe separation, but affects opening of the outlet and closing of the inlet.

I see your camshaft is made in one piece. only thing i can think of is the geometry between the size of the cams (base circle) and the valve lobes could possibly be changed. For my one cylinder I used rollers and I think, maybe the diameter of these are to large in comparison to the size of the cams (especially the smaller exhaust one).

Offline Roger B

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Re: Two Cylinder Engine
« Reply #262 on: September 26, 2020, 03:30:28 PM »
After some thought I decided to check the valve clearances. They were 0.2-0.3mm instead of 0.1mm (the base circle undercut). There is subjective amount of overlap now but I haven't measured it yet. I assume a fairly major stripdown will be required to fix the water leak (carb thread) so I will recheck the timing afterwards.
Best regards

Roger

Offline Zephyrin

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Re: Two Cylinder Engine
« Reply #263 on: September 27, 2020, 11:50:19 AM »
I also spend a lot of time adjusting the timing of the cams according to my diagram, and clearances carefully set, just like you do...
It's a never-ending job for me with unhardened cams and pushrods, the hammering of the valves means that ultimately the clearance is such that the diagram is never respected, not to mention inertia on rockers with fast runner, but surprisingly, the engines run...

Offline Roger B

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Re: Two Cylinder Engine
« Reply #264 on: September 27, 2020, 05:52:47 PM »
Most of my components are hardened but I guess there must be some bedding in.

The water leak was due to a bit of a bodged connection with some PVC pipe and an oversize pipe clip. I originally planned an elbow at the water pump inlet which I need to do. It will also give a better pipe run. I made up a small filter PCB for the cooling fan with a 220uF electrolytic and a 0.1uF ceramic which seems to have resolve the fan stopping problem. Finally I made the proper pivot pins for the fuel pump to replace the bolts.
Best regards

Roger

Offline Roger B

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Re: Two Cylinder Engine
« Reply #265 on: October 04, 2020, 10:41:15 AM »
Whilst waiting for some 6mm elbows to arrive from Germany (Drop it Hide it Lose it have taken 4 days from Krefeld to Speyer. I think I could walk faster) I decided to start a new camshaft for the 360░ version.

Based on my last experience I tested a couple of pieces of 10mm bar to make sure they wouldn't harden. The first one shattered but the second was ok. It didn't give a good finish with a steel tip but was ok with an aluminium one. The lobes were cut with a 2.2m tipped parting tool.
Best regards

Roger

Offline Roger B

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Re: Two Cylinder Engine
« Reply #266 on: October 05, 2020, 08:02:16 PM »
Next I milled the keyways in the 360░ crankshaft and the new camshaft using the little Proxxon mill. Alex S had very kindly made some balance calculations/designs in a 3D CAD programme for the 360░ crankshaft so I had to work out how the make this with the equipment I have. Using my middle size drill vice and the degree wheel from my camshaft milling jig I came up with a solution. I was a little nervous about the vibration loosening the drill vice but it seems to work  :)
Best regards

Roger

Offline Roger B

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Re: Two Cylinder Engine
« Reply #267 on: October 05, 2020, 08:07:45 PM »
I worked my way around the 4 flats. The fine details will be easier with a file than trying to do a milling set up.

I also received the 6mm elbows. I have Loctited one onto the water pump inlet and think I may use them on the other water connections to get better hose runs.
Best regards

Roger

Offline Admiral_dk

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Re: Two Cylinder Engine
« Reply #268 on: October 05, 2020, 09:41:00 PM »
That ought to improve the running quite a bit - I hope it is the here case too  :cheers:

Balancing an engine can be done to very good results, but will always be a compromise. You have now done the first important step forward. Adding a counter rotating balance axle is the next level, adding yet another (sometimes at double the RPM) is yet a step - BUT it's kind of the Law of Diminishing Returns along that road, and that's most likely the reason I never saw an engine with three balancing axles.

Offline steamer

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Re: Two Cylinder Engine
« Reply #269 on: October 05, 2020, 09:47:26 PM »
I like it a lot Roger!

Dave
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Damned ijjit!