Robart R780

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Peter Heining

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Hello, does anyone have construction plans or an explosion drawing of the Robart R780 radial engine ?
 
Hello, thank you for the notice, the radial was only produced between 1990s and early 2000s; not many have been sold; I have the manual and also pictures/ descriptions from the www; just thought that some member dealt with the engine from a construction point of view, and would have more detailed drawings; I had a friend revamping it for gas and spark ignition and he wanted to know more about the oil distribution within the engine; but apparently it runs well on gas.
 
I would be interested to learn more about the gasoline/spark conversion with regard to lubrication. I don't have a lot of experience with gasoline/spark ignition RC engines vs. methanol/glow ignition, but I think most gasoline engines still require a bit of oil pre-mix with the gasoline if they have no direct oil circulation? I hear numbers like 25:1 for break in & 40:1 running. But those figures are predominantly 2-stroke where either the induction vapor and/or exhaust blow by contacts the moving parts & self-lubricates. I would imagine that 4-strokes, especially radials, might have a bit more challenging lubrication requirements if run gasoline only (no oil) because some of the components are physically further away or affected by gravity. Seems like most home made gasoline engines either have 1) oil pre-mix 2) separate oil pump lubrication, or 3) less strenuous running conditions and where parts can lubricated separately.

Some of this was discussed in my recent post, but related to methanol/glow radials.
https://www.homemodelenginemachinist.com/threads/radial-lubrication.31739/

I'd be surprised if anyone 'constructed' a Robart 780 because like you say, it was already a commercial engine. A few people on the forum have 'modified' RC 4-S glow engines to spark, but lubrication is a separate issue. Be interesting to hear related discussion.
 
To my knowledge many methanol engines can be converted easily without major issues. There are commercial rebuild sets available from https://www.morrisminimotors.com/conversion-kits.html in UK or https://www.ch-ignitions.com/engine-conversions/saito-engines.html in Florida; the guy who rebuilds my engines is retired but had a model engine production http://www.l-jurisch.de/ he usually employs gasoline with 5% oil (1:20) which basically is no issue for radial engines (e.g. Seidel always pointed out that his engines should be run with maximum 6% oil) but according to Lothar also works for engines like Enya VT 240 or OS FT-300 or the Kavan FK 50 (the latter one is an exception as it has a separate oil reservoir and pump); I use the gasoline for chain saws or lawn mowers which is sold in Germany under the nam ASPEN (or Stihl) https://www.amazon.de/Aspen-ASPEN-T...t=&hvlocphy=9041748&hvtargid=pla-698387154659 and a synthetic oil like Motul micro https://www.motul.com/de/de/products/micro-2t
 
Robart R-780 was designed by Robert Walker one of the original founders of Robart for sale. There are no prints.

Oil ratio for gasoline converted glow engines are all over the place. Saito recommends 20:1 And this appear to be safe for plain bearing rod engines. A few are willing to try less, and some get away with it. One of the guys was running 5:1 in a ~.50 two stroke on spark and gas, he later moved to 10%. There really is no hard science to this and few will deviate from manufacturer specs. A four stroke crank case is not actively being evacuated like a two stroke. Premix oil in gasoline is the norm for many model engineering designs, I'm not even sure why it's a question. Ratio of oil is hard to say.

Even within the same engine make oil requirements can vary wildly. YS has a line of spark ignition four stroke engines which run methanol fuel. These depending on model want 20% to as little as 5%. In the model that allows 5% there was apparently an upgrade for previous versions to allow low oil fuels.
 
It looks like it was a nice engine.

I found this YouTube video. Not quite sure what the fellow was priming or lubing with the syringe but at about 1:35 he mentions 'built in oil pump in the crank case". Your parts schematic surely would be able to identify something like this if that was the case.

 
I don't know much about this engine. The manual certainly mentions and oil pump, but isn't specific about how it works.
 

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Most methanol model engines do not fair well with petrol oil mix unless the big end is converted to needle rollers.
Many examples of this all over the internet where mostly it is done on SuperTigre engines.
 
Robart R-780 was designed by Robert Walker one of the original founders of Robart

Thanks for pointing that out. From what little I've seen of the engine, it looks well engineered. Not really related to the engine question, but some interesting trivia about the man & the company. Everybody in RC knows about Robart hardware but I never knew they produced a radial.
https://www.modelaircraft.org/sites/default/files/files/WalkerRobertL.pdf
https://www.chicagotribune.com/news/ct-xpm-2000-03-07-0003070204-story.html
 
bluejets said:
Most methanol model engines do not fair well with petrol oil mix unless the big end is converted to needle rollers.
Many examples of this all over the internet where mostly it is done on SuperTigre engines.
Click to expand...

And yet countless people are actually doing it. You just have to do your homework.
 
I watched the video of the engine starting up in the RC model airplane. Can somebody explain the weird shapes of the propeller starting at about the 2 minute, 15 second time on the video? I would like some scientist explain to my what my eyes are seeing???
Grasshopper
 
The odd appearance of the prop is the result of the way the video is recorded. Each frame is generated by a scan of the image. During the time it takes to scan the image (approx 1/25 second) the prop moves, so when the scan gets halfway down the image, the prop is in a different position to where it was at the start of the scan.
 
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