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Hi Richard,

Do you have a pic? I envision part of the ring held under a small screw with the remainder of the ring up off the head. If that is the case you basically have a "shorted" thermocouple. For a thermocouple to work as expected all of the region where the dissimilar metals are in contact has to be at the same temperature.

Wes

Area 51% wrote:Why couldn't you get the spark plug senders to work? I know there's a little step down to the plug seat on my heads that wanted to distort the sender, so I got some aluminum oil pan gasket washers to put between the plugs and head to eliminate that miss-match.

But doesn't that mean your plug doesn't reach as deeply into the head? That's not good for flame propagation and efficiency.

Has anyone ever tried adding some small naca scoops over the rear cylinders on the cowling? Hard for me to say if they would add air or end up being an exit for the high pressure air in the baffles.

If you still have your spark plug senders and want to compare that location with what you have now, I can send you a couple of these washers. I had to buy a bag of 25. I have a couple left.

GraemeSmith wrote:

Area 51% wrote:Why couldn't you get the spark plug senders to work? I know there's a little step down to the plug seat on my heads that wanted to distort the sender, so I got some aluminum oil pan gasket washers to put between the plugs and head to eliminate that miss-match.

But doesn't that mean your plug doesn't reach as deeply into the head? That's not good for flame propagation and efficiency.

If I were racing this engine, I would be putting washers under the plugs to get all the electrodes pointing in the same direction anyway. If you look at the different installations of the second spark plug, some are shrouded, and some have a thread or two exposed.

Seems to me there might be advantages to updraft cooling on these engines. If nothing else, the aerocarb would be getting "fresh" air.
Automatic anti-icing for the windscreen.
Also, you would know about that oil leak almost immediately.

Hi Wes,
The CHT sensors I purchased are simply a 1/4" female connector attached to the sensor wires. I was supplied copper washers to go under the plugs, the copper washers had the 1/4" male connector hanging off the side. In the end I cut the ring portion away and attached the remaining copper directly to the cylinder head. You've all got me thinking though. I'm going to make up a single washer and connector out of aluminium as there is still heaps in my shed and give it a go. On a previous balls up, my engine was not running on the front L/H cylinder, due to the heat soaking throughout the entire head there was not much difference between the front and rear cylinders even though one wasn't running. The give away was that the EGT was zero on the non worker. This is why I am suspicious that I'm not getting an accurate CHT. With a little luck by next weekend I can find out whether I'm eligible for the smart cookie or the dunce hat!

area 51%...Q.....If I were racing this engine, I would be putting washers under the plugs to get all the electrodes pointing in the same direction anyway. If you look at the different installations of the second spark plug, some are shrouded, and some have a thread or two exposed.
A....to do this via/ one work around ; is to buy a extra set of spark plugs, and before installing, mark on top white part of the spark plug where the electrode is. and put in the plugs and see where the marks line up . and return the plugs ,to the store , the one's that do not line up, in doing this you may have to some mix and matching, "ie heads / plugs" to get things to workout....
good day ../rick








soxs

So you're the one that purchases a tool, that you need to use once, and returns it? I think I've also seen your handy work in the nut and bolt isle. 4 screws in a 5 screw bag with a hole in it.

sonex1566 wrote:The way that I've got it at the moment has to measure a bit cooler, it's just how much cooler is what I'd like to know.

I once did the test. Ran with three CHT sensors; one under the center cylinder head retaining bolt, one under the spark plug sensor and one screwed into the head sensor. Been too long ago to remember the actual data, but roughly 15 degrees cooler for the screwed in sensor and 30 degrees for the one under the head bolt. I posted the data to the old Yahoo groups Sonex list but that is long gone I presume. Practically, it doesn't matter. CHT readings are somewhat relative. What is important is that you know what is normal for your engine and be alert to any significant changes that may occur. Obviously, when you first run an engine you don't know what normal is, but as you get hours on the engine the pattern will establish.