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Rotax 914 CHT under spark plug probe

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pestar

Joined: 11 Apr 2007
Posts: 61
Location: Auckland, New Zealand

Posted: Fri Mar 12, 2010 12:21 pm Post subject: Rotax 914 CHT under spark plug probe

I have a 914 for which I am using MGL EFIS's.  As part of this I

purchased the MGL under the spark plug 4 x CHT probes.  http://www.mglavionics.co.za/



In trying to fit them I find there is no room because of the copper tab

with the attached K type wire prevents the ring aligning itself with the

spark plug hole.   Even if I were to get this alignment I then cannot get a

plug spanner over the spark plug to tighten it because this tab is in the way.



Has anyone fitted under spark plugs CHT probes to a Rotax 91X series, if

so what type and how did you go about it.  



Would appreciate any ideas as I would like to be able to monitor all CHT's

rather than using the standard 2 built into the engine.



Thanks in advance.



Peter



Peter Armstrong

Auckland, New Zealand

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flyadive(at)gmail.com
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Posted: Fri Mar 12, 2010 4:00 pm Post subject: Rotax 914 CHT under spark plug probe

Hello Peter:



I wish I had know you were considering under the spark plug

thermocouples, I would have tried to talk you out of them.



If you have the option for any other (in head) type of thermocouple

PLEASE do so.  The under the spark plug type tend to read VERY high

and do not respond well or quickly to temperature changes.  The reason

why is most of the heat being sensed if from the spark plug and not

the heat of the cylinder, it is the heat generated by the spark.

There have been reported problems with NOISE and ERRONEOUS readings

because the probe is located in contact with the spark plug.  Also the

probe is of the GROUNDED nature which carries more noise than

un-grounded probes... This may be a problem when routing the cables.



Does the engine have in-head locations for thermocouples?



BUT!  If you are forced to use them, and as you say are having

problems with fit... You must remove the crush washer that comes

attached to spark plugs. And if you are using the large copper

washer... do not use it ... Use JUST the thermocouple.



Barry



On Fri, Mar 12, 2010 at 3:21 PM, pestar <peter(at)reivernet.com> wrote:

 	  Quote: 	
		   



 I have a 914 for which I am using MGL EFIS's.  As part of this I

 purchased the MGL under the spark plug 4 x CHT probes.  http://www.mglavionics.co.za/



 In trying to fit them I find there is no room because of the copper tab

 with the attached K type wire prevents the ring aligning itself with the

 spark plug hole.   Even if I were to get this alignment I then cannot get a

 plug spanner over the spark plug to tighten it because this tab is in the way.



 Has anyone fitted under spark plugs CHT probes to a Rotax 91X series, if

 so what type and how did you go about it.



 Would appreciate any ideas as I would like to be able to monitor all CHT's

 rather than using the standard 2 built into the engine.



 Thanks in advance.



 Peter



 Peter Armstrong

 Auckland, New Zealand





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