Converting large nitros to gas ..... How to? - Page 2 - RCCanada - Canada Radio Controlled Hobby Forum
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Large Engines Discuss Engines Used on Giant Scale Aircraft. Gas/Glow, as long as they're big!

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Old 09-30-2016, 01:42 PM   #11
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Re: Converting large nitros to gas ..... How to?

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i have an rcs 140 just has bushing on wrist pin 80-1 optimal crank end is needle. works a 1
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Old 09-30-2016, 06:36 PM   #12
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Re: Converting large nitros to gas ..... How to?

Originally Posted by Bdegan View Post
Most glow engines use bronze bushings on the upper and lower con rod knuckles.
They require a very high oil content ratio in the fuel. Like 20%. Most glow fuel is around 20 % oil.
Gas engines run on a much much lower oil to gas ratio. A range of 1% to 3%. Not enough oil for bronze bushings. You can't add much more oil or you just end up fouling the spark plug very quickly. That and the engine just won't run right.

Gas engines have needle bearings in the upper and lower con rod knuckles.
First thing to check on any engine you are thinking of converting, is to see if that particular engine has bushings or needle bearings.
Converting the big Super Tigers to gas was very popular 20 or so years ago and yes they do have needle bearing rods. I can't imagine trying to buy glow fuel to keep those thirsty engines happy!
The new line of Saito gas engines do not have needle bearing rods and seem to be working out ok as far as I have heard. Anyone know what OS and others making small gassers are doing with their rods?

Originally Posted by Bdegan View Post
Some glow engine manufacturer's tried selling their engines as gas models several years ago. They slapped a gas carb and ignition on their current glow motor. All failed in short order.
I am not sure where this is coming from, it appears to me that this trend is happening right now and getting bigger all the time. With glow fuel getting harder and harder to find and more and more expensive when you do, I can see it becoming the norm.
I presently own 2 of Saito's factory conversions and am seriously considering converting some of my older engines.
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Old 10-01-2016, 05:13 PM   #13
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Re: Converting large nitros to gas ..... How to?

I converted two Super Tigre 3000s to ignition, one using a CH ignition and the other using an RCEXL ignition. However, I didn't convert to Gas. My motive for the conversions was to make them more reliable for inverted running. No glow 2-stroke engine likes to run upside down...especially true for big Super Tigres.

The conversion also permitted me to run a home brew of paint store methyl hydrate and Klotz oil at 10:1. The big displacement engines don't need 5:1 (20%) lubrication, even with bronze bushings on the con-rod. Remember, as displacement increases in cubes (to the power of 3) Surface area increased in square (to the power of 2). so as engine size increases, there's less surface area relative to the displacement, hence, less oil required proportionately.

If I was to use gas in my ST conversions, I'd probably shim the head to drop the compression as glow engines run much higher compression, which is not required for gas. This would also increase the combustion chamber volume. I'd probably run the 2-stroke gas-oil mix at 10:1 or 15:1, perhaps even 20:1 if using a very high quality synthetic oil.

Also, if running gas using the same glow carb, it would be difficult to maintain a fine adjustment. It would be far more reliable to use a walbro adapter and carb. Unfortunately the ST Walbro adapters are hard to find these days. CH used to have them, however, the last time I spoke with Adrian at CH he said the machine shop that made all his conversion hubs, carb adapters, etc. closed down and he still hadn't sourced a replacement shop to make the parts for him. He advised that for many of his conversion items he's down to one of each, which he won't sell. I don't know of anyone else who makes the walbro adapters for Super Tigres.

Anyway, that's my story. If you like to tinker, as I do, by all means do it, but there are more practical alternatives.

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