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  #21  
Old 07-17-2016, 08:15 AM
lr172 lr172 is offline
 
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Originally Posted by scard View Post
She flew around on only the lightspeed for 10min and all temps were exactly in line with our normal expectations. Are we just making less power with the mag off, thereby cooler? I would think the lightspeed can support near complete combustion based on its very low mag drop during runup.
In simple terms, a plug ignites the mixture and the flame grow until it reaches a point where maximum pressure exists in the chamber. It takes a bit of time for the flame front to roll across the chamber, so the designer ignites the spark before the point he wants peak pressure (advance). The movement of this point impacts power, heat, detonation potential, etc.

In a dual plug engine, you have something I call relative timing. Each plug fires at opposite ends of the chamber and the fronts meet in the middle (flame front travels approx 1/2 the diameter of the chamber). If you stop igniting one plug, the remaining flame front must travel close to the full diameter to reach max pressure. This will cause the peak pressure to occur late and creates an effective reduction in ignition advance. retarded ignition reduces CHT's and increases EGTs.

This concept also applies to blended timing advance when using different ignitions with different timing. Your low mag drop on the LS ignition is due to it's earlier timing (it is doing a larger share of the work in reaching peak pressure). These advance changes do affect power, but it is often not significant and hard to notice. The movement of heat between the chamber and exhaust is much more noticeable. Optimum peak pressure keeps more heat in the chamber doing work moving the piston. late peaks produce less heat in the chamber, as they are letting more of that heat flow out the exhaust.

Knowing all of this should help you sort out if timing is a factor in your particular case. The fact that reduced timing brings your temps right back in line with expected would point me toward investigating your actual igintion advance. A mag can be tested with simple tools. The lightspeed is a computer and you will need a timing light to confirm what it is actually doing to your advance, either across the board or at any given RPM/MAP combination.

Larry
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Last edited by lr172 : 07-17-2016 at 08:36 AM.
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  #22  
Old 07-17-2016, 10:28 AM
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skylor skylor is offline
 
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Default RPM Drop

Quote:
Originally Posted by scard View Post
I would think the lightspeed can support near complete combustion based on its very low mag drop during runup.
This is a false assumption. The reason the Lightspeed (and most electronic ignitions) have very little drop during run-up is because they advance the timing at low manifold pressure whereas the mags remain fixed at less than optimal timing for run-up power. At high power settings, there is little to no difference in the "completeness" of combustion between a mag and an electronic ignition. Therefore, running on one ignition (Lightspeed) in flight still reduces the effective timing of the engine and will result in lower CHT's.

Skylor
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  #23  
Old 07-17-2016, 10:30 AM
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Ok, I think we have something. Thanks for the additional nudge to prove the Lightspeed. We got a timing light on it and it's base timing (without the MP connected) is stuck at about 43deg BTDC! It didn't change at all with or without the MP tube connected. Yikes. We dutifully stepped through the troubleshooting flowchart. This isn't going to be a fun conversation with Klaus I bet.

Now we're just on Logistics to find an ignition to get to OSH.
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  #24  
Old 07-17-2016, 10:50 AM
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Carl Froehlich Carl Froehlich is offline
 
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Quote:
Originally Posted by scard View Post
Ok, I think we have something. Thanks for the additional nudge to prove the Lightspeed. We got a timing light on it and it's base timing (without the MP connected) is stuck at about 43deg BTDC! It didn't change at all with or without the MP tube connected. Yikes. We dutifully stepped through the troubleshooting flowchart. This isn't going to be a fun conversation with Klaus I bet.

Now we're just on Logistics to find an ignition to get to OSH.
Assuming the Lightspeed is working correctly, I'd guess timing was set on it with the crank at 25deg BTDC instead of TDC as required. If timing was set at TDC, then look at the remote timing control (if one is connected), then the only thing left is to fix or replace the box. If you replace, recommend shifting to one or preferably two pMags.

Carl
Former Lightspeed owner - pulled and replaced with dual pMags.
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  #25  
Old 07-17-2016, 11:06 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by scard View Post
Ok, I think we have something. Thanks for the additional nudge to prove the Lightspeed. We got a timing light on it and it's base timing (without the MP connected) is stuck at about 43deg BTDC! It didn't change at all with or without the MP tube connected. Yikes. We dutifully stepped through the troubleshooting flowchart. This isn't going to be a fun conversation with Klaus I bet.

Now we're just on Logistics to find an ignition to get to OSH.
Glad you found the problem. That's pretty agressive timing for 30" and 2700 RPM. Given that this has been going on for a while, it wouldn't be a bad idea to pull the top plugs and look for any detonation damage on the piston crown.

Larry
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  #26  
Old 07-17-2016, 11:14 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by scard View Post
Ok, I think we have something. Thanks for the additional nudge to prove the Lightspeed. We got a timing light on it and it's base timing (without the MP connected) is stuck at about 43deg BTDC! It didn't change at all with or without the MP tube connected. Yikes. We dutifully stepped through the troubleshooting flowchart. This isn't going to be a fun conversation with Klaus I bet.

Now we're just on Logistics to find an ignition to get to OSH.
You could also throw a mag on in a pinch. I have spare mags (both impulse and non-impulse) and a spare harness you could borrow, including a gear and good plugs. Would be happy to drop it at Fedex tomorrow.

send me a PM if interested and I'll give you my number.

Larry
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Last edited by lr172 : 07-17-2016 at 11:16 AM.
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  #27  
Old 07-17-2016, 11:35 AM
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Originally Posted by lr172 View Post
Glad you found the problem. That's pretty agressive timing for 30" and 2700 RPM. Given that this has been going on for a while, it wouldn't be a bad idea to pull the top plugs and look for any detonation damage on the piston crown.

Larry
Yeah, I agree, pretty scary. I've been in each cylinder with a borescope very recently and will again armed with this new knowledge.

We've also been commiserating with Dr. Horton who had some good ideas for 'hacking' the lightspeed to fix it at 23deg in order to meet our immediate objective . "See ya' next weekend!"
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  #28  
Old 07-17-2016, 12:31 PM
lr172 lr172 is offline
 
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Originally Posted by scard View Post
Yeah, I agree, pretty scary. I've been in each cylinder with a borescope very recently and will again armed with this new knowledge.

We've also been commiserating with Dr. Horton who had some good ideas for 'hacking' the lightspeed to fix it at 23deg in order to meet our immediate objective . "See ya' next weekend!"
Good luck with that, but be careful. until you find cause of the failure, you're kind of flirting with disaster, as you don't know what it will do next. I am not sure that I would be confident that it will stay at 43*, if your thinking of adjusting the pickup or setting up an offset to move that back 18*

One could assume that it is just the MAP sensor failing. However, I don't think you would get 43* at any MAP setting in the lower RPMs (at least it shouldn't be set up that way). That would lead me to think it is more than just a MAP sensor.

Good luck.

Larry
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Last edited by lr172 : 07-17-2016 at 12:33 PM.
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  #29  
Old 07-17-2016, 12:39 PM
jrs14855 jrs14855 is offline
 
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Just a comment on magneto mounting slippage. If the mag and mounting surface are properly cleaned, a new gasket and lock washer used, and the proper torque of 204 inch pounds used, it is virtually impossible for the mag to rotate on the mounting pad. It is vitally important that the lock washers not be reused. Torque the mag fasteners and then need to move the mag: replace the lock washers. I have seen A&P's reuse lock washers on many occasions. NOT ACCEPTABLE.
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  #30  
Old 07-17-2016, 05:09 PM
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scard scard is offline
 
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This has been quite the adventure. Definitely a Lightspeed Plasma II+ failure stuck at approx 43deg timing any way you cut it. A new replacement is installed and behaves exactly as it should. We shot it with the timing light and, yeah, this is the way it should be. A test flight agrees that we have the airplane we know so well back, no matter if it is hot out. CHTs and oil temp are back where they should be.

Borescope: Yeah, there are some areas of some pistons that are a little cleaner than I would like. I can't discern any real pitting, but maybe that is just wishful thinking. Definitely no chunks missing. We had really backed off of run time while we worked through this. Hopefully listening to the machine helped some. It is what it is at this point and we're extremely glad that we found the real smoking gun. Thanks to all for the comments.

We'll fly it some more this week then we'll see ya' at OSH!

(That sure is one ugly failure mode of the Lightspeed!)
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