EGT Imbalance

[Oddball]

I posted this on the SAMicro email talk list, now I am trying to cover all bases... :

Can any of you bright sparks shed some light on a problem that I am encountering?

I get a difference of around 45 deg C between the two cylinders on my 582 when I am at full throttle (around 6400rpm). The hottest EGT indicates 644 deg and the cooler one is at 599 deg.

644 deg is too hot for the cylinder hence the concern. As soon as I bring the engine speed down to below 5400 rpm the temperatures become lower (and within limits) and almost equal (about 15 -25 degrees between cylinders).



Any ideas on what may be causing this?

Oddball

[MADDOG]

Check the main jet, float level and needle & seat on the cylinder running hot.

[John Young]

I get a difference of around 45 deg C between the two cylinders on my 582

Oddball – the thermo-couple probe settings [depth] into the manifold are critical. One millimetre variance between the two can cause a big difference in reading.

Suggest you start here. Regards

[Duck Rogers]

I had a similar problem once. After scratching around for a while and wasting loads of time, I swapped the probes around and suddenly I had a hot cylinder on the other side! Could have saved myself a lot of time had I checked the probes first

[Microwave]

Ditto, I think that oddball is not so odd. My experience is that temperature sensors are mainly and usually the problem, whether it be water, EGT or cylinder head.

[Oddball]

I found the problem... thanks for all the suggestions. Here is what happened:
I was suspicious of the mixture or perhaps the slide opening of the carburettor in question so I started here. I found that the one slide was indeed more closed than the other one so adjusted them to the same height and tested it. Not much difference.
I had not looked at the jets although that was my next thought and one of the mails also suggested this. When I took the jets out the problem was immediately apparant- one had green oxide on it and this had produced a layer of little nodules in the orifice of the jet.
These nodules are very small but this is what I think they do; at full throttle when there is a large suction pressure from the cylinder these imperfections cause turbulent flow in the fuel orifice which causes cavitation. This leads to less fuel coming through, but still enough to support combustion, but with a lean mixture.
This is why the temperature difference is only seen at full throttle when the flow is great enough for the nodules to disturb the flow sufficiently.
I tested all of this by swapping this particular jet with someone elses and the problem was no longer apparant.
If I can figure out how to post a picture I will upload one in a moment to show you the jet.
Something learned, or rather, confirmed once more: having an accurate set of instruments monitoring your engine temperatures is vital- it is very very useful in telling you that something is going wrong. I have a Stratomaster Ultra L and it has been fantastic. In a previous problem, caused by a manufacturing defect on my 582 (30 hours on the engine when it happened) I saw that the engine temps were climbing gradually over a couple of flights (water temp). On one particular flight these temps were climbing and peaking even higher and my EGT's also started climbing in one cylinder, very quickly. I climbed and headed back to the airfield and the engine, without any other warning, coughed once or twice and quit. Since I was on an early downwind leg I simply s-turned and landed downwind (almost no wind so not an issue) dead-stick. Without the temperature warnings I would still have been fooling about over swampy land at low level.
Know what your normal temps are and pay atttention when they deviate- something is wrong...

Oddball