yeah – actually very easy (my shop managed to do it twice accidentally) ;-)
if you lift the rubber lip that normally blocks the airflow downward, so that it partly protects the visible part of the cylinder cooling fins of No 2, CHTs go up by about 30-40F.
Makes No2 the hottest cylinder, but only marginal above No 4 (my hothead :-) )
Suprisingly little influence on the other temps, both in climb and cruise.
Never thought of this as an improvement – have corrected it on each occasion…
I think a little plate like this would do it
Ed Kollin posted the following on a US site:
It seems a well supported concept. Occassionally, new information does appear in GA 
Doesn‘t apply unversally though.
1500hrs, IO-550, always run LOP, always relatively low power, CHTs in cruise always 300-320. Never had any problem.
Well, sure, it doesn’t happen immediately.
My reading of his assertion that this is becoming more common on Contis is that as “LOP” is becoming better known (via pilot education over the past 20 years gradually getting the message home that 150F ROP is dumb) and the proportion of pilots flying with low CHTs is going up.
For sure 300F is not going to make your valves stick immediately. I got just one sticky valve in 2500hrs / 18 years and I have done tons of long low power descents, and that is a Lyco which runs cooler than Conti.
But as the Cirrus community gradually moves to LOP, whatever issues are “close” will start popping up above the horizon.
Also it states that occassional high power operation clears the deposits off. So pilots flying IFR, naturally doing longer max-power climbs, are going to see less of this. That would be quite a lot on EuroGA but a tiny % of GA overall.
This lead-oxy-bromide thing is a red herring;
The well known CMI Continental problem has everything to do with manufacturing tolerances. My previous set of IO520 Cylinders were run 1100 hours before replacement due to AD, they were in perfect condition. The AD forced replacement after 17 years.
Here is a link to the Whyalla accident report where ‘leadoxybromide’ was improperly blamed: the-whyalla-report-junk-science
In over 7000 hours of engine operation, I have burnt exhaust valve and that was before LOP was the norm.
The well known CMI Continental problem has everything to do with manufacturing tolerances
Can you explain further, @dirkj?
Up until somewhere in the late 1980s, TCM exhaust valve guides were hand reamed and fitted by experienced craftsmen, each cylinder was different but it seemed to work. At one time there was a strike of the labour force and the engineers took over the cylinder construction, at the same time looking to automate the painfully manual valveguide centering.
This is when the well known TCM cylinder problems started (early 1990s). It is hard to find a set of those cylinders running more than about 600hr without a top overhaul unless the new cylinder was manually reamed by an experienced craftsman (not at TCM/CMI).
My first engine (new 1973) ran to TBO, only one burnt exhaust valve found and fixed during annual.
My second engine (new 1980) ran to TBO, I started flying LOP since about 1997 as early adopter and tester.
This same engine was then blueprinted and overhauled by a top US shop in 1999, using Superior cylinders. No problems whatsoever until the Superior AD (requested by TCM) required removal of all cylinders at 17 years calendar time. The same guy who did this overhaul supplied new Superior cylinders with his own reaming/adjusting.
After three years all is fine, good compressions, very low vibration, cool CHTs around 300°F in LOP cruise.
I think the TCM520/550 series is one of the best piston engines available if it has been properly assembled and set-up.
Doing the machine work for a valve job, including reaming new guides, is something any little rural automotive machine shop can do, and does, every day. It is not a manufacturing problem of measurable scale and if it’s being quoted as a long term problem with factory Continental cylinders, I’d guess something else is going on that is either not understood or being concealed.
Sticking valves explained. Also explains why Lycoming valves stick, where Continental valves usually don‘t:
It begs the question: why not run a couple of tanks full of UL91 on an aircraft that shows deposits on the valve seats?
