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Michaels Web Site
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Date:  11-16-2016
Number of Hours:  0.00
Manual Reference:  
Brief Description:  If You Have a Hot Engine (Part 1)

I had high CHT/EGT problems after my last engine build. #1 was very, very hot; #3 was hot but not quite as bad. #2 & #4 were reasonable, but warm. There are many potential issues that could cause this, so I'll just throw out what I did. Until I got it sorted out I could only climb at 150-200 fpm to have any hope of keeping the rear cylinder temps in check.

First, my cylinders ALWAYS have different mixtures. I've taken the heads off several times and the front of the heads (2 & 4 cylinders) are much blacker (richer) than the tan colored (leaner) rear cylinder heads. But my engine purrs like a kitten right now, regardless. Instead of the scientific method of changing only one thing at a time, I changed lots of things at once and solved my issues. I can send you pictures of my heads if you'd like.

1. I have a bottom mounted oil cooler. I closed off most of the intake in the cowl by adding a blank off plate over most of the opening. Even in the dead of summer the oil temps this past summer didn't go over 190 or so, and so I could blank off even more. I think the excess air coming into the cowl from that inlet, was helping to positively pressurize the cowl and not let it dump heat overboard.

2. I increased the lower exit air opening in my cowl by 20%. I think that was the single biggest factor in dropping my temps.

3. I retarded the secondary ignition. The only way to check the RPM and temperature spread is in flight. It is totally unreliable to do it on the ground. In the air I first noticed an RPM difference between primary and secondary, of over 100 rpm. I would get on the ground, retard the ignition and go fly again. RPMs would be better, but still 50 RPM or more difference, and high temps. After doing this a few times I finally got the difference in RPMs in flight to be nothing or in the single digits.

READ THE PART 2 ENTRY, NEXT (Kitlog will only allow so much text in one post).
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