Tempest plugs

Radar Contact said:
I’m no expert. Did some research and decided on 24 Tempest Massive’s for my bird. Been good for a couple hundred hours. Remind me in a few more years and I’ll give you a better longevity PIREP.
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Any updates on your plugs? Mine are still sparking nicely and look very good 5 years later
 
I have 12 Tempest UHB32E's in my new engine and have had two fail.
There is no visible damage to the electrodes or ceramic.
We are at 80 hours on them now.
I checked one for ohms on the center electrode and it's open (any time I test plugs they show 1-3 MΩ)
I'm not going to ask about warranty, can't imagine that would be useful.

One failed as I was entering the blackest mountain area at night. Thankfully no weather and running on one mag stopped all roughness - nearest airport was home base.
 
Have over 600 hours on a set of fine wire Tempest in a 0-200. One failure at the 550 hr point.. This year I put in 4 new ones in bottom holes at annual.
 
Lachlan said:
A lot of people run them on the bottom, massives on top. Some run them all the way around.
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That's what I do. I've found the top plugs do not foul, and massive electrodes are fine there.
 
LWGII said:
That's what I do. I've found the top plugs do not foul, and massive electrodes are fine there.
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Years ago I started leaning more aggressively and I have never fouled a plug since. All massive electrode, both top & bottom. By "aggressively" I should say "properly" because the leaning method is consistent with the airplane and engine POH guidance. Full rich only when you are using 70% or higher power at or near sea level (below 3000' DA or whatever the POH says). That means leaning to near the idle cutoff during ground operations, full rich for takeoff near sea level, and leaning the mixture right after you pull back the throttle - even if you are flying at low altitude near sea level you don't need full rich during cruise. If you continue an extended full throttle climb to altitude, lean as you climb through 3000 feet (or whatever the POH says).

Too many pilots (not necessarily you, just generally speaking) leave the mixture knob full forward all the time whenever they're below 5000 feet. That wastes fuel, fouls plugs, gunks up the engine, promotes carb icing, and causes unnecessary pollution.
 
I ground lean until the engine starts to run rough then enrichen just until it runs smooth. My lower plugs look much better since I began that procedure.
 
I've got about 300 hours on a set of tempest plugs in my o-520. center electrode is already getting football shaped. I am not sure they will make it to 500 hours.
 
Wagondriver said:
I've got about 300 hours on a set of tempest plugs in my o-520. center electrode is already getting football shaped. I am not sure they will make it to 500 hours.
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Are you rotating one cylinder over and top to bottom every 100 hours or annual? The erosion pattern is opposite between the top and bottom plugs. One erodes the center electrode; the other erodes the wire. If you swap, you theoretically get double the life.
 
robin ardoin said:
I ground lean until the engine starts to run rough then enrichen just until it runs smooth. My lower plugs look much better since I began that procedure.
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If you are talking about idle settings, you're doing absolutely nothing with that technique. If you're talking about at run-up power settings, then this has been the standard procedure at higher altitudes for as long as I've been flying.
 
Kiddo's Driver said:
Are you rotating one cylinder over and top to bottom every 100 hours or annual? The erosion pattern is opposite between the top and bottom plugs. One erodes the center electrode; the other erodes the wire. If you swap, you theoretically get double the life.
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The erosion has little to do with the top or bottom positions. It's all to do with the polarity of the spark. The erosion happens when the spark (ionized gas) arrives at the electrode. The magneto is an alternating-current machine that generates sparks of alternating polarity, so rotating the plugs puts them in a cylinder and position that gets the opposite polarity of what it has been getting since the last rotation.

The best way is to use a spark plug tray like this one:

1737478096097.png

As the plugs come out they go into the holes corresponding to the positions labelled. Some trays have the labelling just stamped into the top of the tray. The top plug from #1 cylinder goes into T1, for instance. Once the plugs are cleaned and gapped and tested, always staying in that tray except when being serviced one at a time, the tray is rotated so that the T's go into the bottom positions, and vice versa. This gets their polarity switched properly. But you have to number them from the end opposite to the labelling so they don't end up in the opposite port in the same cylinder. This would be easier:

1737478969986.png
 
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flyingron said:
If you are talking about idle settings, you're doing absolutely nothing with that technique. If you're talking about at run-up power settings, then this has been the standard procedure at higher altitudes for as long as I've been flying.
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Isn't running the engine as lean as possible during taxi an accepted technique to avoid plug fouling?
 
AvNavCom said:
Isn't running the engine as lean as possible during taxi an accepted technique to avoid plug fouling?
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Yes, but what he does has no effect on the idle mixture. The mixture control doesn't do squat at idle because there's a separate (non pilot controllable) idle loop mixture. The only thing you can do is start cutting off the fuel with idle cutoff. If you "enriched" it from there, you just put it back to the preset idle mixture. You need to leave it to the "verge of dying" if you want to effect a leaning.
 
Yes, most carbs have an idle mixture circuit separate from the main mixture circuit.
Fact: as you open the throttle from the idle stop, the air & fuel from the primary carb throat and main jet gradually overwhelm what's coming from the idle jet.
Question: at exactly what throttle position/RPM does the idle mixture determine the A/F ratio? As you gradually push the throttle forward from the idle stop, how far until the idle mixture doesn't matter anymore because the red knob / main circuit dominates?

Clearly, at idle the idle mixture dominates - throttle pulled back to the stop. Call that 600 RPM.
Nudge the throttle forward just off the stop - call it 700 RPM - is the idle mixture circuit still dominant?
At what point does its influence diminish - 800? 900? 1000?
I've messed around with this and my experience suggests the point is just above the idle stop. Even as low as 800 RPM the red knob affects the mixture. That's just my experience, YMMV.
 
ALL of the idle and main nozzle fuel goes through the mixture control. The "idle cutoff" is just the point where the mixture control valve closes right off, and it can be used to lean an idle mixture if you're very careful with it. A vernier mixture control helps.

Only the accelerator pump fuel is taken separately from the float bowl.

This is the typical MS carb used on most carbed airplanes.

1737502566133.png
Note the mixture metering stuff at the bottom of the bowl. The fuel leaves the bowl and goes through that valve to both the idle delivery ports and the main nozzle.

Fuel injection systems work similarly. The mixture control can be used to lean the mix at idle.
 
Dan Thomas said:
The erosion has little to do with the top or bottom positions. It's all to do with the polarity of the spark. The erosion happens when the spark (ionized gas) arrives at the electrode. The magneto is an alternating-current machine that generates sparks of alternating polarity, so rotating the plugs puts them in a cylinder and position that gets the opposite polarity of what it has been getting since the last rotation.

The best way is to use a spark plug tray like this one:

View attachment 137406

As the plugs come out they go into the holes corresponding to the positions labelled. Some trays have the labelling just stamped into the top of the tray. The top plug from #1 cylinder goes into T1, for instance. Once the plugs are cleaned and gapped and tested, always staying in that tray except when being serviced one at a time, the tray is rotated so that the T's go into the bottom positions, and vice versa. This gets their polarity switched properly. But you have to number them from the end opposite to the labelling so they don't end up in the opposite port in the same cylinder. This would be easier:

View attachment 137408
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Forgive me. I explained the what without spending ten minutes explaining the why.
Did the what change?
 
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