Secondary timing

[dreamweaver]

I just recently bought a used Sonex with Aerovee 2.1 turbo installed and over the past week I have noticed a slight hesitation during takeoff that had progressively gotten worse to the point I had to abort a takeoff yesterday.

Through much reading on the forum here and also looking through the manuals that came with the plane I'm heavily leaning towards it being a timing issue with the secondary.

When doing a runup at 1800RPM I lose about 100-150RPM when switching off the primary which based on the manual means the timing between primary and secondary ignition is off. I've also noticed that the number 3 and 4(especially 4) run much hotter than the other two cylinders CHT wise.

There is probably close to 100 hours on the engine/airframe and I'm wondering if somehow the bolt used to loosen and adjust the secondary ignition has come loose. I only think this because it has become progressively worse.

I did a runup with the tail tied down today for a very short run up to 3000rpm on primary and it had no hiccups or issues even though it ran a bit more rough than the electronic ignition(I haven't looked at the plugs yet). When I ran it up on the secondary ignition I made it to 2800rpm and it started running rough and losing power. I went back to only the primary and it ran fine again.

I plan on checking the timing on the secondary, being this is the turbo, the secondary is supposed to be set to 18 degrees BTDC from everything I have read. It looks like a really tight fit with the intake coming off the turbo looking like it is right in front of the spot where the secondary ignition gets adjusted. I'm new to working on this engine and if anyone has any tips or suggestions to how to make this easier it would be greatly appreciated.

[Bryan Cotton]

Welcome to the forum! Check out this helpful thread:
viewtopic.php?f=7&t=6527

Per this thread, there are 88 teeth on the flywheel:
viewtopic.php?f=7&t=7434&p=56196

That makes for about 4.09 degrees per tooth. So you will need a new mark on your case that is about 2.44 teeth retarded from the primary to time your secondary at 18 degrees BTDC with a timing light.

There are lots of things to look at - plugs, mixture, valve adjustment, and so on. But timing is one of those things. Mine has not moved in 270 hours.

[T41pilot]

I plan on checking the timing on the secondary, being this is the turbo, the secondary is supposed to be set to 18 degrees BTDC from everything I have read. It looks like a really tight fit with the intake coming off the turbo looking like it is right in front of the spot where the secondary ignition gets adjusted. I'm new to working on this engine and if anyone has any tips or suggestions to how to make this easier it would be greatly appreciated.

It is possible to adjust it without having to take anything apart. I just had to do mine recently. Get some light in there. Use a sharpie and mark a line horizontally on the edge of the magnet assm to establish a reference from your point of view. Use a small inspection mirror on a telescoping handle and view the present setting on the back side as noted in the picture in the service manual. Should be in the general neighborhood as shown in the picture. It will appear opposite in the mirror though since you are looking back to front. Use an allen wrench with a long tail to loosen the allen screw just enough so that it takes a little effort to move the magnet assm. Use the sharpie line as a reference and move it slightly in the desired direction. Maybe a 16th of an inch at a time. Tighten. Do a short ground run. If RPM drop test seems better, go fly and do the cht temp comparison test. In my experience, the rpm drops during runup don't have to be a specific number, they just have to match each other when secondary is set right. My drops vary from 75 to 100 range from one flight to the next but they both drop the same amount. If the process doesn't help, then there might be a different problem as Bryan suggested

[dreamweaver]

Thank you guys, really helpful information! I have one of those cheap harbor freight inspection cameras so I'll be using that to take a look. I plan on taking the cowling off this evening to dig into it.

[daleandee]

I just recently bought a used Sonex with Aerovee 2.1 turbo installed and over the past week I have noticed a slight hesitation during takeoff that had progressively gotten worse to the point I had to abort a takeoff yesterday.

I personally suspect your problem is with the fuel system. Here's a video with stumbles on take-off. Is this what you are experiencing?

https://www.youtube.com/watch?v=PWIFGfGhjOM

Dale
3.0 Corvair/Tailwheel

[dreamweaver]

I just recently bought a used Sonex with Aerovee 2.1 turbo installed and over the past week I have noticed a slight hesitation during takeoff that had progressively gotten worse to the point I had to abort a takeoff yesterday.

I personally suspect your problem is with the fuel system. Here's a video with stumbles on take-off. Is this what you are experiencing?

https://www.youtube.com/watch?v=PWIFGfGhjOM

Dale
3.0 Corvair/Tailwheel

It very well could be but, I am getting the difference between primary and secondary drop of about 100-150RPM on the primary and I noticed last night that while running on the secondary alone that 2800RPM is where a large power loss happens and extreme stuttering. I don't notice any such issues on the primary alone but, I'm not going to rule anything out at this point. I'm heading down to work on the plane this evening and should hopefully know for sure if it is a timing issue tonight.

[dreamweaver]

Well, I ran into some other issues that needed to be fixed so I went ahead and took care of them. Had a broken EGT clamp off the #3 cylinder so I replaced the sensor and connected it in the same spot as the original on the MGL board. I'm actually the third owner and it looks like red RTV gasket maker was used on the bottom mini oil sump but, they must not have had any of the copper washer/gaskets to put under the nuts so it was leaking very slowly but, causing a huge mess inside the cowling and under the airplane so I cleaned that all up and fortunately I was given a gasket set to go with the plane(now I know why, haha, not complaining just glad I had them), air filter was a dirty mess from oil and bits of exhaust wrap that was flapping in the wind(also took care of that) and then I got to the timing issue. At least what I thought was a timing issue. So I have it timed exactly like the turbo upgrade manual shows with the secondary being timed 18 degrees BTDC. I found the compression stroke on the 1st cylinder and then used my scope camera to watch the cylinder go all the way to the top and then backed the flywheel up 4.40 teeth(roughly 4 and half teeth) and set the trigger manet to 12 o'clock. After locking it in place with the 5/32 hex screw, I verified that when I have the primary magnet in line with the right side of the magneto just like in the picture in the manual that the line for the secondary trigger magnet looks just like the picture in the manual as well. I figured I was all good and buttoned everything up but, when I went to start it today it would not start. Starter is working fine of course but, like it is getting no fire.

Here is my question, when I originally looked at the secondary timing, the line was straight down in the 6 o'clock position as viewed if you were standing behind the engine but, now it is a little to the right of the 12 o'clock position. Did I set it wrong and it should actually be closer to the 6 o'clock position? I ran out of time to work on it today but, plan on going back first thing in the morning to set it back the way it was and see if it will start. Hopefully someone can set me straight.

[dreamweaver]

I went back out this morning and timed the secondary back to the way it was originally but, with the 18 degrees BTDC in mind for the turbo since based on how it was set before that would have been for the non turbo version since it was set to trigger at the same exact time as the primary before. Now it starts up with ease and I get no more than a 50 RPM drop and the engine sounds beautiful. I didn't have time to do a full run up to 3000 with the tail tied down but, I'm planning on doing that this evening after work. I'm thinking the whole stuttering issue didn't have much to do with the timing as it did with the completely filthy air filter on the aerocarb. That makes sense to me since it would have gotten progressively more dirty the more it was flown. I also think it being timed for the non turbo version could possibly be why the number 3 and 4 cylinders had hotter CGTs than the rest but, we will see. Have a couple more little issues to sort this weekend and then should be able to take it up for a test flight. Thanks for all the help and I'm looking forward to learning a lot more from you guys!

Dan