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Long and Short Glow Plugs in Webra 120

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Old 12-24-2018, 08:24 AM
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thailazer
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Default Long and Short Glow Plugs in Webra 120

Getting ready to run a Webra 120 and I noticed the glow plug is a long version. Is there any down side to using a short glow plug in this engine?
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Old 12-24-2018, 09:37 AM
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GREG DOE
 
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Most large displacement glow engines were designed for a long plugs; from approximately .40's and up.You can run it on a short plug, but there might be a slight loss in performance. Because there isn't as much thread contact, be carefully not to strip the head. Also pressures are higher in larger engines, so long plugs are less likely to "blow out", although unlikely if the threads have never been abused. Try to stick with long plugs if you can, because that is what the engine was designed for, but in a pinch it shouldn't hurt to run a short. I wouldn't hesitate to do it in a pinch.
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Old 12-24-2018, 09:51 AM
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Greg... Good point about the extra threads helping the plug forces. I made a donation to the Strega P-51 team at the Reno Air Races years back and they gave me a spark plug from one of their qualifying runs. That thing had an incredibly long threaded base to handle the compression.

Just ran the engine with the original long plug on my Hangar 9 C-182. The Webra is an impressive motor with an incredibly low idle.
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Old 12-24-2018, 12:26 PM
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speedracerntrixie
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The 120 is a fantastic engine. I ran mine with an Enya 3 plug and 10% nitro with 16% oil. They really like the APC 16x8.
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Old 12-24-2018, 12:43 PM
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Originally Posted by speedracerntrixie View Post
The 120 is a fantastic engine. I ran mine with an Enya 3 plug and 10% nitro with 16% oil. They really like the APC 16x8.
Yes, I am very impressed so far! Fantastic idle and tons of thrust on a 15-7 3 blade. I notice that the compression when cold is quite low, but hot, it is higher. Is that a characteristic of the Dykes ring? No issue on power though.
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