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Rocket-List Digest: 6 Msgs - 09/24/07Rocket-List Digest: 6

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pvans(at)pacifier.com
Guest

Posted: Wed Sep 26, 2007 8:23 am Post subject: Rocket-List Digest: 6 Msgs - 09/24/07Rocket-List Digest: 6

Gentlemen,



There have been many emails concerning the mags and ignition timing. The 

actual problem is high CHTs . Ignition issues  MIGHT be a possible cause of 

this. But there are many other reasons that CHTs are high, and before 

delving into ignition issues alone, some of the other possibilities should 

be investigated.



As I see it here is a summary of  the situation:

1. new engine

2, New engine installation, a new cowling, baffles, instrumentation



Here is what I would check first:



1. Baffle and seal condition and fitment

2. Are CHTs high even at reduced power?  Yes the engine can make a lot of 

HP and heat, but at say 20 inches and 2300 rpm the temps should be low, 

assuming the cowling and baffles are working properly. If it will not run 

cool at low power, then the cowling design air flow must be improved.

3. Is the opening at the bottom of the cowling big enough?  I have had 

airplanes where the lower opening was too small, adding a cowl flap made a 

huge difference in CHTs. I am not saying this is necessary, but compare the 

opening to other Rockets first. The person who cut the lower opening may 

not have used the right dimensions

4. Investigate the fins on the cylinders, especially those between the 

spark plugs. You can look down and see right through there, but on some 

cylinders I have bought, there was a great deal of flashing not removed 

from the casting which reduces airflow there and hence heat dissipation. 

Not to mention, that is right where the CHT probe lives.



These problems can be frustrating. I am only trying to help direct your 

efforts to the place where the solution might be found. Good luck.



Peter van Schoonhoven

RV3, C210, Bucker Jungmann,  all flying; Harmon Rocket abuilding

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jrstone(at)insightbb.com
Guest

Posted: Wed Sep 26, 2007 5:14 pm Post subject: Rocket-List Digest: 6 Msgs - 09/24/07Rocket-List Digest: 6

Good points and most have been considered.

1. Baffles are good.

2.  CHTs only high above 23 inches MAP

3.  Don't know how to measure such an irregular shape such as the cowl 

opening.  I did little to no trimming on John's stock cowl.

4.  Will have a look at the cylinder fins for flashing.

 Thanks,

Jim Stone

Louisville

UPDATE  CHTs are now staying below 390 deg except for cyl #6 when above 23" 

MAP.  BTW, My oil cooler is aft of #6.  Oil temps are 200 ish and lately a 

bit less.  All indications are that the initial break in has occurred but I 

will continue to run it hard.  Did you know that Lycoming recommends running 

at 24"MAP and 2300rpm and every five minutes advance rpm to max and slowly 

retard to 2200 then back to 2300 and continue this routine for 20 minutes. 

After that, they don't really say.  Check out there videos on the Lycoming 

website under support.

---

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