Cht too low

[Browncbr1]

I've never really been able to get my CHTs very hot.  I have the original cowl with a top prop on my 67 F.  On climb, I can peak CHT right at about 300.  In cruise with cowl flaps closed, running at about 65% power by book, I'm always running about 255-285 CHT...   Yesterday, I flew for an hour at 7500ft and back at 8500ft...   2550rpm, peak-25LOP, ~21"map.   It wasn't wide open throttle, but I know everyone says fly them WOT...   Either my JPI830 isn't calibrated properly, or I have unusually effective cooling. Any advice?

thanks!

Edited October 16, 2015 by Browncbr1

[N601RX]

Most likely the Jpi is correct.  Does the cht's, egt's and oat all read the same or very close while in the hanger after stabilizing?  Also is the timing low or on 25deg?

[ArtVandelay]

Check them at room temperature, do they read correctly?

[Browncbr1]

The chts all read correctly at ambient air temp. I thought maybe my MAP is not correct and I am actually running easier than I should be.  I set MAP according to the instructions in the jpi handbook, and it reads a bit different from the original gauge.  Rpm is higher on the jpi too.    Gami spread is .9 and #1&2 peak last.  If I run #1&2 at peak at those power settings, jpi shows 7.8gph.  I haven't fine tuned K factor yet though.   

[Browncbr1]

A friend has a timing cone and we will check the mags again.   He said he recalls that the data plate calls for 20 BTDC.  Does that sound right for a io360-A1A?   Newly overhauled slick mags with new tempest massive plugs and new harness.  

[Shadrach]

An IO360 can be configured for 20° and 25° BTDC.  20° Will certainly lead to lower CHT's.

Edited October 16, 2015 by Shadrach

[Browncbr1]

I found a very old thread about the change in timing a number of years ago.  Two of you posted quite a lot in that thread.  It explains why there is 25 degrees stamped on the flywheel, but just a permanent marker approximately where 20degrees is.   

[Shadrach]

FWIW, my stock 67F is and always has been at 25°.

[MHemperly]

I keep mine at .25 per the data plate on the engine. IO-360 A1A

[Browncbr1]

My jpi cht leads are rings that are held on by the tanis heater probes.    Do you guys have this kind of cht lead?  I know some have the ones that go on the spark plug, but unsure if maybe this is causing lower cht readings?

[Browncbr1]

Just called tanis.  They said the cht rings that fit on their probes will usually read 20-30degrees cooler than actual cht probes.  

[Shadrach]

Even so, I'd see about resetting the timing back to 25°.  I think that you will find it kind of "wakes up" your airplane on takeoff and climb.  You'll likely see a few knots in cruise and be able to run deeper LOP.

Edited October 16, 2015 by Shadrach

[Browncbr1]

I looked at the data plate, and sure enough it says 20 degrees.  I live in TN, so not too concerned with extreme cold flying.   I spoke to my A&p and he agrees that it should be 25 like some people here.   What is involved with getting this done legally?

[N601RX]

 Lycoming has a service bulletin that shows what was changed to set it to 20. That will have to be undone. 

[Browncbr1]

I've been search how to undo an sb that was performed.   Can't seem to find a clear description of what is needed.   Anyone have experience doing this?

[jetdriven]

you undo Lycoming SI 1325C.  Read the document but basically u change the left magneto for a different part number which contains a different impulse coupler, and stamp a 5 on the data plate over the zero and reset the timing to 25 degrees.  Log entry of course.  

http://mooneyspace.com/topic/3877-io-360-a1a-what-mag-timing-20-or-25-deg-btdc/

 

[Browncbr1]

Thank you!

[Shadrach]

you undo Lycoming SI 1325C.  Read the document but basically u change the left magneto for a different part number which contains a different impulse coupler, and stamp a 5 on the data plate over the zero and reset the timing to 25 degrees.  Log entry of course. 

He's like running a Bendix SOS mag.

Edited October 19, 2015 by Shadrach

[Gary0747]

Many 67 F models have the fixed third cowl flap mod installed midway between the two variable cowl flaps. While this mod helps nicely to keep CHTs down in hot weather climbs it does provide too much cooling in cold weather and needs to be blocked off in the winter months to avoid the low CHT issue. 

Lycoming did reduce the BTC setting 3 degrees a few years ago to increase the percieved margin between detonation.  I asked the rep once if the engine was still rated at 200 hp and was told yes within the 5 pct rounding margin. In any case the CHT issue is nominally the same regardless of the btc change in timing. It is basically an air flow issue. 

Edited October 20, 2015 by Gary0747

[jetdriven]

The lycoming rep is repeating an oft-told lie that they invented.  The factory measures CFM on the dyno and says the horsepower is the same based on that. Yes I called them.  No mention why the airplane climbs 200-300 FPM better or is 3-5 knots faster. They deny this but I went out and spent 500$ to document it.    

And if it's such a good idea due to safety, reliability, etc why is the IO360-A3B6D not approved for 20 degrees timing?    

[Browncbr1]

I'm using slick mags, not bendix.   

4370 and 4347. (25 degree lag)

[Shadrach]

I'm using slick mags, not bendix.   

4370 and 4347. (25 degree lag)

I'm so sorry! 

[ArtVandelay]

I'm using slick mags, not bendix.   

4370 and 4347. (25 degree lag)

I have slick mags as well, when I do an in flight mag check I get this:

I've read when they peak differently it's because the mags are time differently, now much I don't know.