VansAirForceForums  
Home > VansAirForceForums

-POSTING RULES
-Advertise in here!
- Today's Posts | Insert Pics

Keep VAF Going
Donate methods

Point your
camera app here
to donate fast.


Go Back   VAF Forums > Main > RV Ongoing Maintenance Issues
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 07-23-2021, 04:33 PM
edbundy edbundy is offline
 
Join Date: May 2005
Posts: 20
Default Is it possible for a magneto to fire earlier than it is set for?

I've been chasing a high CHT (on all cylinders) issue for a while now. I've replaced the baffling, replaced intake tube gaskets, verified engine to mag timing, verified sufficient fuel flow, and everything else I can think of.

During climb all 4 CHT's will rise at roughly 1 degree/second and unless I aggressively get the airspeed up they will easily pass 400F. They never used to go above 370 in a climb.

The other day I thought to try isolating the mags during a climb. At about 1000' agl with both mags operating the CHT's were climbing rapidly. Switching to just the right mag didn't change anything. Switching to just the left mag not only immediately stopped the CHT's from climbing, but they then started going down fairly quickly. I switched back and forth several times and each time the right mag would make the temps climb and the left mag would bring them down.

It sure seems to me that the right mag has figured out a way to advance itself, but is it possible for a mag to fire earlier than the 25 degrees it is set for? These mags are absolutely set at 25 degrees, run up and mag drops are normal, starting is normal and the engine runs great just like always.
__________________
Ed Bundy
Vintage RV6-A
Built and first flown Nov. 1996
Reply With Quote
  #2  
Old 07-23-2021, 04:50 PM
Freemasm Freemasm is offline
 
Join Date: Nov 2017
Location: Orlando
Posts: 483
Default

What type of fuel are you burning?
What CR pistons?
What kind of mags?
What are EGTs doing during this?
Etc.

The move info, the better.

Despite your last paragraph, it certainly sounds as if one mag is timed to the impulse/start/retard point coupling. Let us know.

Last edited by Freemasm : 07-23-2021 at 07:36 PM.
Reply With Quote
  #3  
Old 07-23-2021, 08:35 PM
edbundy edbundy is offline
 
Join Date: May 2005
Posts: 20
Default

100LL exclusively.
0320 with standard compression.
Slick mags, left has impulse coupling.
EGT's normal when operating both mags, shows expected rise on individual mags.
Other than CHT's engine is operating normally.

I've triple checked the timing, they are both 25 degrees. If one were operating at a massively retarded setting wouldn't that show up when switching to that mag? And wouldn't that cause CHT's to go down?
__________________
Ed Bundy
Vintage RV6-A
Built and first flown Nov. 1996
Reply With Quote
  #4  
Old 07-23-2021, 10:26 PM
blaplante blaplante is online now
 
Join Date: Jan 2010
Location: Southern California
Posts: 298
Default Airborne mag check

Suggest an airborne mag check. See https://resources.savvyaviation.com/...t-diagnostics/
Then upload your data to Savvy (which is free). Then screenshot the plot and provide it to us here.

If one mag is running more advance than the other I'd expect a substantial differential in RPM.

What's your RPM drops on a ground mag check?
__________________
RV6A in phase 2 as of April 2016
Donation made Oct 2021

Last edited by blaplante : 07-23-2021 at 10:28 PM.
Reply With Quote
  #5  
Old 07-24-2021, 07:45 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 6,548
Default

certainly sounds like right mag is too far advanced. Suggest re-timing it. If it continues to be advanced, put an auto timing light on the rt #1 plug and confirm.' About the only way that a mag can readjust it's timing is for the hold down nuts to be too loose or improper timing procedures, such as not letting the impulse snap first or various other errors.

Larry
__________________
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019

Last edited by lr172 : 07-24-2021 at 07:47 AM.
Reply With Quote
  #6  
Old 07-24-2021, 08:10 AM
Freemasm Freemasm is offline
 
Join Date: Nov 2017
Location: Orlando
Posts: 483
Default

@Larry. I’m not a mag guy. I can’t think of another scenario. I would assume the OP is at strong risk of a kick-back and starter damage if I’m picturing this correctly

Last edited by Freemasm : 07-24-2021 at 08:24 AM.
Reply With Quote
  #7  
Old 07-24-2021, 08:26 AM
Ralph Inkster Ralph Inkster is offline
 
Join Date: Feb 2008
Location: Calgary, Alberta
Posts: 1,536
Default

How many hours on the mags?
__________________
Ralph
built a few RVs, rebuilt a few more, hot rodded more, & maintained/updated a big bunch more
Reply With Quote
  #8  
Old 07-24-2021, 08:41 AM
DanBaier's Avatar
DanBaier DanBaier is offline
 
Join Date: Mar 2009
Location: Rochester NY
Posts: 703
Default

[QUOTE...I would assume the OP is at strong risk of a kick-back and starter damage ...[/quote]

+1 Be very careful with this. The in flight mag check is a good idea.

I don't think I saw here when the last mag inspections were done. If I was anywhere close to the time, I'd pull these off and do the 500 hr inspection.

Dan
__________________
RV7A (N7101) - Flying 10/2008
CFI- SE/ME/Inst
A&P
KC2ZEL
Reply With Quote
  #9  
Old 07-24-2021, 09:01 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 6,548
Default

Quote:
Originally Posted by Freemasm View Post
@Larry. I’m not a mag guy. I can’t think of another scenario. I would assume the OP is at strong risk of a kick-back and starter damage if I’m picturing this correctly
As the cam and points wear, the timing becomes more advanced. However, this takes a good amount of time, like 100's of hours in most cases, though slick has had QC problems with cams wearing out VERY early. OP implied this was new issue and still occurred after re-timing the mag. Re-timing the mag will adjust the ignition timing, regardless of point wear, but doesn't adjust for e gap timing, which only affects spark energy and not ignition timing. If I misunderstood that and the mag hasn't been touched in 100's of hours, wear could be the cause and in that case the e gap will need attention, as misfires will be in the OP's near future.

Kick back wouldn't apply if the OP starts on only the left mag, like many/most do.

Larry
__________________
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019

Last edited by lr172 : 07-24-2021 at 09:14 AM.
Reply With Quote
  #10  
Old 07-24-2021, 10:36 AM
OKAV8r OKAV8r is offline
 
Join Date: Feb 2007
Location: Seattle
Posts: 172
Default another step

One other step I would make is to verify the orientation of the P-leads.
Does the mag switch(es) actually turn off the Left mag, when the switch shows running on Right mag only? Or are they reversed? P-leads get reversed too often. It could be significant, if the Left mag is actually the problem, as a bad impulse coupling could cause timing drift.
And, has been mentioned already, if the mags have more than 500 hours, or there are a couple of outstanding SBs, then it is time to get them into the shop. One SB deals with bad rotors, which could be a factor....

Last edited by OKAV8r : 07-24-2021 at 10:39 AM.
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 08:55 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.