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Just got my rebuilt 0-320 running, did a quick taxi test and my RV6A wants to flight real bad. I noted that at idol the #3 EGT quickly climbs to 1205 F when the rest of the EGTs read about 900- 1000. CHTs all seem to be OK about 300 - 350. Any ideas ? Need to solve this before doing any more tests. On the way home I got thinking, could that cylinder be sucking air. I don?t know where but when I increase power the other 3 EGTs seem to catch up to the one hot one.

Thanks
 
[email protected] said:
Just got my rebuilt 0-320 running, did a quick taxi test and my RV6A wants to flight real bad. I noted that at idol the #3 EGT quickly climbs to 1205 F when the rest of the EGTs read about 900- 1000. CHTs all seem to be OK about 300 - 350. Any ideas ? Need to solve this before doing any more tests. On the way home I got thinking, could that cylinder be sucking air. I don?t know where but when I increase power the other 3 EGTs seem to catch up to the one hot one.

Thanks
Click to expand...
Check to make sure the thermocouples are all in the same relative position and if so, it could just be poor fuel distribution at idle. It is a carbed engine after all.
If the other EGTs catch up at higher power levels, there is probably nothing to worry about..

-mike
 
If the wire lengths permit, try swapping #1 and #3 probes and run up again. This will tell you quick if it is a bad probe, or more likely, a little difference in the installation. As long as they even out when power is added, I wouldn't worry about it.
 
I have spent a fair amount of time chasing EGT irregularities and have learned the following:

1) It is completely normal to have a (large) spread in temps and the spread can change at various RPM's!

2) The location of the sensor matters. For example, one sensor is farther down stream than the others it will likely read cooler.

3) It is possible to get a very high reading if combusiton has not completed before the exhause value opens...

4) Conventional wisdom has lead very knowlegable people to say things like 'the absolute value of the temp doesn't matter, you only care about the temperature relative to the EGT peak". (Search for Dan Checkoway, Mahlon Russel et all on this stuff).

#3 lead me to a whole bunch of confusion because when this happens I got scared really fast thinking my engine was going to die a quick death. (If you do some reading I think you'll find that you can't hurt a Lyc running LOP at <65% power). While I was doing LOP testing I watched the EGT go down after the EGT peak and then go up significantly, CHT's continued to fall. I've also noticed that behaviour when flying in the pattern at relativly low MP. I asked many local experts and got answers on these questions that ranged from 'rebuild your FI', to 'why are you looking at the panel in the pattern!' After much head scratching I surmised that my hi EGT 'problem' was infact combustion that was not complete before the valve opened thus allowing still burning charge to pass by the EGT sensor.

I think last week I proved this was the case with the following experiment while testing my new PMag. I flew in a LOP situation (at low fuel flow) with 1 mag on and my electronic ignition off. I leaned until the temps went up more than 150F (1500F!) and then switched on the the EI. Within a second or two the temps went down 150F to where they 'should' have been.

I certainly learned from all this that it is really easy to get data but not so easy to turn that data into usefull information.

Chuck
 
EGTs

Mr. Chuck is correct on all 4 points. Here are a few more.
1.These engines are air cooled, and due to prehistoric technology, have tolerances fit for a locomotive engine. They flex a lot when warming up.
2. Ignition timing is fixed, if you are using the tried , true and equally prehistoric magneto.
3. If using 100W oil, valve lifter take a while to unload and "settle down", It's viscosity is not conducive (and never has been) for hydraulic lifters. Multi grades can help.
4. On the subject of lifters, incorrect bleed dowm clearances also add.
In the end, even when all these items are addressed, there will still be uneven temperature climbs.
BTW, recently we had a problem with a JPI engine anylizer. The instrument was fine. After much ado and calls to JPI. they finally admitted that the probes them selves were the issue. We changed that according to their recommendation and voila, it worked.
T88
 
also check ignition

EGT will rise significantly if a plug falls off for what ever reason. Verify when it rises with a mag check that the cylinder runs on each plug. A loss of a plug will show this type of indication.

Best,
 
Swapping plugs

Thanks for all the good input. Had the FAA & a Dar out last Tuesday and my RV6A officially became an airplane, The FAA came along to audit the DAR but it so happened that he was also the the one who approved A&P cert. for amateur built,.... so got that too. I was going to start my trouble shooting buy swapping plugs from one jug to another. Hope for first flight some time in the next month. Need some dual practice.. Don?t get much flying in when your building.

Thanks Again
 
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