EGT/CHT Inconsistant

Question for the group. PA-12 with 160hp and cruise prop. We just installed an engine analyzer on this airplane. The gauge shows that Cylinders 1 and 2 are significantly cooler (in 100 deg range) and the EGT is also significantly cooler for those Cylinders (in the 250 deg range). Leaning does not seem to change the disparity in the readings.

What is your experience? Is this something that needs to be addressed? Engine sounds fine and develops good power.

Partially cover the front cylinders with a piece of aluminum to keep some of the ram air off them.

I thought about that, but considering that the EGT is also low in these cylinders, I'm wondering about the fuel mix flow through the manifold. Do others see this disparaty?

Are all your EGT probes the same distance down from the flange?
When I installed mine I used calipers to to get the EGT probes at the same distance from the flange. What I have noticed is that when the CHT temps on #3 and #4 are substantially hotter so are the EGT's.

There are several threads on this subject with some good ideals on what to do. Usually leaning will even out the EGT depending on RPM and altitude. To start with I would make sure you baffling is good with no leaks. Than use aluminized tape on the front cylinders just as Nimpocub said. Start with 11/2 wide strip then test flight add tape at about 1/4-1/2 inch each test flight until your temps get closer. You need to fly this setup for about a year because things will change some from winter to summer. Once you have the right setup you can change to metal. My CHTs are usually within 5-20 degrees for all cylinders. 5-10 degrees per side. I am going to put ramps on the front next, think it will help some.
Egt temps tend to be more of a air/fuel mix issue so make sure you don't have any intake air leaks. You should be able to get at least 100 degree change in EGT when leaning to peak EGT or you are jetted to lean. Cub Crafters had issues with the 0340 I believe and have the pepperbox jet for sale on there site. Do a search on pepperbox jet and one pice venturi. Reports are that this will also even out some of the CHT/EGT issues but it is a lot of work to get it right. This will give you about a weeks worth of good reading.
DENNY

When measured with MK-I Mod-1 eyeballs, they do look the same distance. The fact that the EGT and CHT are both low on these two cylinders, I'm convinced that it is not a gauge/sensor error. Just wondering if it is normal.

If I remember correctly on of the MN boys had a post on insulating the front intake runner in winter to help keep it warm and fix a EGT issue. Start with the CHT issue with tape it is a easy fix to protect the rear jugs than work on the entire package.
DENNY

You might be on to something with an intake manifold leak. What's the easiest way to test for a leak?

Frodo
I think what you are seeing is common for this motor. Especially the wide CHT spread. That is why I am not a fan of single CHT/EGT gauges. The only way people know it there is a problem is if the have a 4 cylinder gauge. So I would suspect there are many cub type aircraft with this issue. Thirty years ago when people broke in a new motor the common thought was you could just go by oil temp because that was the hottest that the motor got. With people putting on accurate gauges we see there are a lot of issues nobody knew about. BUT, there is not a blanket fix for this because each cowling is different. I think all the information you need to fix the issue is already been covered just do some reading and you will find it. Some info may not pertain to your situation but it is good knowledge in general.
DENNY

Pressure test the motor at 1-2psi and spray soapy water on stuff. Do it carefully so you don't blow out front seal with too much pressure. Caution!! I am not an A&P so you might want some more expert advice on this subject.
DENNY

I will get with my co-owner and check for leaks. Thanks.

I believe an intake leak, allowing excess air to the cylinder would lead to leaner mixtures & hotter EGT. Which doesn't seem to be your issue. I have a 160 hp O-320 in a Supercub with very tight baffle seals. I lean to around 1350F which usually is #2 cyl but #4 & #3 are close, within 20 to 30F. The #1 cyl EGT always is much cooler, usually around 1280F. All 4 cyl head temps are closely grouped together in the 320-350F range. I do have #2 (left front) cyl intake pipe wrapped with insulation to protect it from cold intake air - it is the only cyl that doesn't have an exhaust pipe in front of it. I'm not sure but I think that the the cold #2 intake pipe makes it hard for the mixture to stay atomized. Just installed carb temp gauge & plan to run the carb at a minimum 39F also to promote atomization.

I've noticed my egt's have gone up with the Sutton exhaust. They are within 80 degree of each other. Cht's have dropped 20 deg, and are within 19 degree of each other.