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High cylinder head temperatures during take off and climb.
By John Foy - foyboy6@hot.rr.com

Where do you start?

The aircraft: Van's RV 8 QB with a new Lycoming 0-360-A1A engine
The engine setup: Vision Microsystems VM 1000 display
Van's engine baffling modified to a plenum chamber.
Unison Lasar Magnetos.
Fuel system: Straight Van's with electric boost pump, engine driven fuel pump to Precision Airmotive MA 4-5 A-10-3878 Carburetor.

Since the carb came new with the new engine I ruled out the carb as a problem. Tweaking the plenum chamber during a series of flights showed no change.  Lasar magnetos were removed and reinstalled and timed to exact factory specs. No change after many flights in a lot of flight regimes Checked VM 1000 cylinder bayonet probes against boiling water and a multimeter that had a temperature probe. Well within limits.  Shipped VM 1000 "black box" back to Visionmicrosystems. Bench checked within tolerances. More flights and still no change. Many phone calls to Unison and Visionmicrosystems troubleshooting systems. More flights with no change.  Visionmicrosystems said they had heard from two other builders of high cylinder temps and they had finally traced it to MA 4-5 lean carb with the model # A10-3878. The conversion kit they used was #666-660.  

The conversion kit was installed and that solved the problem!

In the meantime Unison shipped me two brand new regular magnetos, two brand new Lasar magnetos and a wiring harness to hook up to a lap top computer for further troubleshooting. Thank goodness that I didn't have to use their equipment as replacing magnetos with all the wiring and plumbing in place is a chore!  A call to Lycoming early on came up with" Lycoming supplies Van's aircraft with exactly the engine and Carburetor they call for so they are not responsible for anything." Van's thought the plenum chamber modification might be the problem but couldn't say for sure unless they saw the setup.  Response from Microvisionsystems and Unison were all anyone could ask for and I sure thank them for all the support.  

As a side note, the conversion kit installation instructions said it was for the Mooney M20B and M20C aircraft with Lycoming 0-360-A1A and A1D engines, the service bulletin was dated 1962!

Hope this helps the rest

John Foy

1/21/03 Addition to this article from John:
"An addition to my note on the high cylinder temps:
The carb mod did NOT work out. After a few hours of test flights the cylinder temps were all in the 405 degree range so I reinstalled the regular mags and THAT solved the problem. Have over 80 hours on the RV 8 now. Have flown to Kansas City and back the same day to prove it all out. Then down to Hondo and back plus lots of local flights. I have installed the dual carb and outside air temp gage as per Jim Weir's article in Dec. Kitplanes. So far it seems to be working. In flight carb temp seems to hold steady at + 10 degrees Centigrade. There is a noticeable rise in Carb temp at first engine start up and Carb heat is applied so I guess the carb heater works!"