Engine guru Advice on CHT's and timing please

[gereed75]

I recently installed new cylinders and pistons on my IO 360 parallel valve with a left bendix mag and massives (bottom) and a right LSE Plazma II auto plugs (top). Replaced cylinders were "stock" chromed cylinders that were burning more oil than I liked.

I chose ECI nikasil and 9:1 pistons and Lycon porting. Since the installation I have been fighting high oil and CHT's on what used to be a very cool running set-up. I have a very well sealed Sam James plenum matched (and sealed) to stock Van's inlets with inter cylinder baffles and silicone fabric cylinder wraps.

After installation and careful break in (only 5 hours flight time), I was struggling to keep #3 & #4 below 400 degrees and oil temps below 200 at anything above 70% power.

I futzed for several days with timing and after several reductions in advance and test flights, I ended up with the following: Left mag at 23 degrees advance, right LSE with static timing 7 degrees retarded from TDC and dynamic timing with MAP disconnected showing 17 degrees advance at idle (right where Klaus said it should be for 9:1 CR). Both timings verified "dynamically" by an inductive timing light.

During run up the mag off drops 130 - 160 RPM and the LSE off drops 30 RPM

I still saw #4 above 400 degrees at full power even at full rich about 1 minute into the 120 KIAS climb.

Once leveled off at 6500' with reduced power (2220 RPM, 24.2 inches, 12.6 GPM) and 153 KIAS, the numbers were, 2220RPM, 24.2 MAP, 12.6 GPH, oil temps at 175, and 153KIAS yielded this:

With Both ignitions ON:
CHT's 342, 317, 360, 367 EGT's 1256, 1275, 1244, 1249

Securing the mag (running on LSE only):
CHT's 320, 296, 329, 331, EGT's 1322, 1331, 1301, 1313 (about 150 ROP)

HOORAY!! this is what I am used to seeing!!!

This was the first time during the post maintenance flying that I thought of troubleshooting by securing mags individually.

It would appear to me that the mag is still too far advanced at 23 degrees for the 9:1 ratios and only 5 hours fight time on the new cylinders. It also appears that the mag is inherently producing a much larger split between cylinders ( 50 degrees vs. 35 degrees).

What insight can the engine guru's give me (and others) from these numbers??

Should I retard the mag a few more degrees, wait for final break in and then possibly add a bit more advance back in (especially on the "better running" LSE)???

As has been posted here before - problematic high temp guys, look critically at your timing!!

[Bill.Peyton]

I can tell you that my cylinders took at least 30 hours to fully break in. My CHTs were high during full power takeoffs and even during cruise until they finally broke in.

[gereed75]

Thanks Bill, I have seen a variety of estimates for break in hours, but 15 - 20 seems to be the norm. I think I will keep my timing where it is and evaluate again after 20 hrs or so.