Left slick mag with impulse coupling timing

Help, I'm confused.
I'm told that you should hear the impulse mag click at TDC. Mine occurs 5 ring gear teeth past TDC (approx 12.5 degrees on 142 tooth ring gear) should I ad just? I can move mag to click at that point but then the timing light buzzer indicates at about 37 degrees before TDC instead of 25. This is new factory engine from Van's and I've flown for 132 tach hours over the first year. Starting became problematic. I'm doing condition inspection now using E 50 mag timing buzz box. Plugs looked fine. Filter quite dirty. Plug gaps .022 (range .016-.021).
I'm hoping just cleaning the filter and plugs and adjusting gap will result in easier starting. Also mag sync was off some and I fixed that. Just wondering why that coupling clicks when it does and if I need to do something with it.
Thanks!!

Mag

Pull the mag and send it to a magneto shop. Something is very wrong with the impulse if your calculations are correct. I will look it up to verify but most impulse couplings have a lag angle around 25 degrees which means if the mag is timed to 25 degrees before TDC the mag will fire at TDC at low r/m for starting. The impulse is then disengaged at relatively low r/m after start. Impulse couplings do fail and it is very important to verify that yours is ok. Failed impulse parts can trash all or most of your engine. It is possible that the impulse is just sticking but this is unlikely with a new engine.

Check the red data plate on the mag - it should list the lag angle, which is the number of degrees after normal timing (probably 25* BTDC) that the impulse coupling will fire. Our IO540 came with mags that caused difficult starting even though the timing was on. Turned out that model of magneto had too large of a lag angle, and when we swapped to a 'correct' (better) one our starting woes disappeared.

==dave==

Sounds like your timing has drifted. Your numbers do not point to a bad impulse coupler. Assuming you have a 25* coupler, everything adds up. The only thing you'll notice in this state is hard starting. In fact, you were probably getting better performance at cruise due to the additional advance. However, you are at a much greater risk of detonation in High MP situations. You'll want to get this timed correctly right away and in the future occassionally check nuts on the hold downs. As the new gasket compresses, it may need a re-torque.

I thought the general consensus was .016-.018 on the plugs. Better to be at the smaller end, as they will wear .002 or more between the 100 hour gap checks. The mag coils aren't that strong and you add a lot of wear, via heat, by running the gaps too big.

Larry

Thanks for responding. I'm going to try to research a bit more before I remove and send in.. I may not understand fully but isn't the piston on the power stroke once past the top center? Because that would mean mine is getting that impulse 5-6 gear teeth past to on the power side or just firing late. My calculations are about 2.4 degrees per tooth on 149 tooth gear. That's about 14.5 degrees past it.
I'm also asked to check "lag" time on data plate. Question I have is what is the lag time ref from. I.e. Is it lag degrees from top center or is it from the normal timing marks of 25 degrees before TC?
If anyone who has the lycoming O-360 with 4300 series slick mags could check to see when their coupling impulse actually clicks unload. I'd be interested to know if this is common or not.
Thanks again

MAG

I agree to send it out and have it checked. Champion was having problems with internal timing a year or so back and never published anything about it! Sometimes the problems would not start till 50 hours or more.

Jesse

Kato's 8 said:

Thanks for responding. I'm going to try to research a bit more before I remove and send in.. I may not understand fully but isn't the piston on the power stroke once past the top center? Because that would mean mine is getting that impulse 5-6 gear teeth past to on the power side or just firing late. My calculations are about 2.4 degrees per tooth on 149 tooth gear. That's about 14.5 degrees past it.
I'm also asked to check "lag" time on data plate. Question I have is what is the lag time ref from. I.e. Is it lag degrees from top center or is it from the normal timing marks of 25 degrees before TC?
If anyone who has the lycoming O-360 with 4300 series slick mags could check to see when their coupling impulse actually clicks unload. I'd be interested to know if this is common or not.
Thanks again

Click to expand...

sorry about that. I assumed when you said past TDC you meant advanced. I just assumed you used the wrong terminology because the numbers added up and it seemed too coincidental. If you are 37 advanced for normal timing and 12.5 degrees retarded on the impulse, something is wrong with your coupler. However, something doesn't add up here. It's possible that something bad is happening inside the mag. But that is a big timing drift (25-37).
If it were me, I would reset the mag timing to 25 (assuming that is the spec) and see what happens to your impulse timing. It's probably worth a bit of effort to insure you have a problem before you send the mag back and bear the time and expense.

The lag reference is the number of degrees late that the impulse will fire. If you set the timing to 25 BTDC and have a 25 lag, your mag will fire at TDC when below approx 300 RPM and at 25 BTDC when above 300 (impulse coupler stops working at a specific RPM). If your set the mag timing (via your box) at 37 BTDC and have a 25 lag, your mag will fire at 12 BTDC when below 300 RPM. You can see how I jumped to my conclusion and why I think you may have made a measurement error.

When turning the prop by hand you will hear the impulse coupler snap at the point you should expect mag firing when your RPM is below approximately 300 RPM.
Larry

Don't forget to check the spark plug resistance too. If it is over 5000 ohms, the plug is shot and will eventually burn out a mag coil. Ideally, < 1500 ohms is what you want, IMO.

All good points to consider. No pun intended!
I asked a fellow Rv 8 builder who hung his Van's supplied lycoming IO 360 with the same mags installed from lycoming to see when his impulse mag clicked. Guess what? 7 teeth past top center! That's from a new magneto on new engine that has not been run yet, other than test runs at factory. Now I realy don't get what's going on here. Is slick covering up a problem? Or is it realy not a problem at all?

Timing

The late firing with the impulse is probably the cause of your starting problems. My 0 320 with 10-1 pistons is set to 22 degrees so impulse fires 3 degrees past TDC. Cold starts consistent on first or second blade and almost as good for hot starts. Bendix mags.
You probably have an internal timing problem but you simply cannot afford the chance that the impulse is damaged.
Aircraft Magneto in Helena MT is a highly regarded shop. Just ask for a check of impulse and internal timing. $200 plus/minus against the cost of a new engine if the impulse comes apart.

Mag

I will try to explain this a little more. The impulse coupling is purely mechanical. At low r/m pawls on the impulse coupling engage fixed pins on the mag flange. The impulse coupling spring "winds up" and at a fixed point the pawls disengage and the impulse coupling momentarily rotates the mag at a much faster speed to improve the spark. If the engine starts the impulse pawls stay "retracted". The relationship between magneto drive gear and the impulse never changes. (A key maintains this relationship and there is no adjustment) The relationship between the impulse and the internal magneto timing CAN change. Dirty or damaged breaker point or worn breaker point "cam followers" are among the possible causes. The breaker point cam follower is some type of plastic which does wear causing the timing to change.
This MAY be what is happening to the OP. Whatever the cause, the "firing point" of the impulse has been compromised.
All of the above and much more is what led to the development of the shower of sparks system which eliminates the impulse. There is at least some history of failed impulses destroying engines. Failed impulse fragments fall into the accessory case and can make their way thru the entire engine rather quickly.
The Lightspeed ignition with the crank sensor eliminates this possibility IF you eliminate the impulse mag.

All good points to consider. No pun intended!
I asked a fellow Rv 8 builder who hung his Van's supplied lycoming IO 360 with the same mags installed from lycoming to see when his impulse mag clicked. Guess what? 7 teeth past top center! That's from a new magneto on new engine that has not been run yet, other than test runs at factory. Now I realy don't get what's going on here. Is slick covering up a problem? Or is it realy not a problem at all?

Slick Magneto Issues

There are actually quite a few published issues with Slick magnetos. I found Service Bulletin SB1-12 which described the advancing problem with a range of magnetos (between two serial numbers, which actually is between two dates in 2006 to 2008). There was a cam issue that caused the advancing timing and issues with starting and also high CHT's.

Further investigation on the 'net also allowed me to find a series of magnetos from about May 2011 through to early 2012 that had a similar issue. I had an April 2011 mag that gave me trouble hot starting and I've now swapped it out at 115 hours, for a replacement. The engine has only been started twice on this new mag, once cold and once heat soaked for 15 minutes, hot! Both times starting was great. More data to collect on this.

Pulled the mag apart, used the Slick Overhaul manual, and could find no issue with any of the components. The only thing that was a real give away was the really poor spark from the mag, but there was no "obvious" reason for that given the components were all in spec.

However I knew the mag was advancing, as it had advanced 4 degrees in 4 months. Previously it was 7 degrees advanced. I'll fly a few more hours then recheck the timing.

If you're having trouble with the left mag, check the service bulletin and see if yours is in the serial number range.

Mine was not the only one that has given trouble in our neck of the woods. An RV8 driver came over to me at a recent fly in to say he had the same issues, replaced the mag and never had the same problem again.

It was a frustrating exercise trying to track down why I had such problems hot starting, but finally think the issue is fixed.

Do check the spark plugs too. Mine were champion brand from Lycoming via Vans. Most were around 4400- 4600 ohms, with one at 6600 ohms. Weak spark from the mag and high resistance plugs = poor starting.

The impulse coupling on mine fires off at TDC as expected.

Hopefully the above may assist you or others with starting issues.

I'll be checking service bulletins as suggested. I think right now I'll see how starting and run checks go after the condition inspection is done. My impulse mag is firing 5 teeth past TC. But it most likely was from the beginning because a fellow builder indicates the same thing with brand new and prior to first start on airframe. I will see how it performs again and if engine starting becomes problematic again in 2016 I'll be pulling that mag ad sending out for inspection and adjustment.
Thank you to all for input.
Bill

Another issue

I have a rebuilt engine not yet started.
When I turn the prop I do not get a strong
Pop or sound from my impulse mag. More like just a click
Sound. Do I need to replace the impulse gear? Can it be rebuilt?

I have experienced in the past a much stronger sound from the
Mag. Maybe something is frozen? Been a while since it was run.

{I have a rebuilt engine not yet started. Been a while since it was run}


Might just be the assembly lube on the flyweights. I wouldn't do anything unless you have starting problems.

Don Broussard

RV 9 Rebuild in Progress
Canopy time
N14DB

Kato's 8 said:

Help, I'm confused.
I'm told that you should hear the impulse mag click at TDC. Mine occurs 5 ring gear teeth past TDC (approx 12.5 degrees on 142 tooth ring gear) should I ad just? I can move mag to click at that point but then the timing light buzzer indicates at about 37 degrees before TDC instead of 25. This is new factory engine from Van's and I've flown for 132 tach hours over the first year. Starting became problematic. I'm doing condition inspection now using E 50 mag timing buzz box. Plugs looked fine. Filter quite dirty. Plug gaps .022 (range .016-.021).
I'm hoping just cleaning the filter and plugs and adjusting gap will result in easier starting. Also mag sync was off some and I fixed that. Just wondering why that coupling clicks when it does and if I need to do something with it.
Thanks!!

Click to expand...

You must have checked your timing before you did anything, what was it? Assuming it started life at 25 BTDC how much did it change and in what direction? This is what I?m always watching/checking at every oil change. I have never actually checked lag angle on my mags, maybe I should. My mags are tagged 25 degrees lag, I time my engine to 20 degrees BTDC so mine should be firing at start up 5 degrees PTDC and it starts fine set like that. I do know that too great a plug gap will result in hard starting; you want .016? not .022? that will make a big difference assuming everything else is ok.

Late Impulse Coupling Snap?

I just noticed the same behavior on my magneto as described here and I am trying to determine if it is normal. My magneto is timed to 28 BTDC and the magneto has 25 deg of lag, so you would expect the impulse coupling to snap at 3 deg BTDC. But, it snaps well past TDC. Is this normal or a problem?

The reason I think it might be normal is that someone else reported this for a new engine in this thread, and when I am checking where it snaps, I am just bumping it a degree at a time. That's not exactly what happens during starting.

Thanks!

Ron Springer said:

I just noticed the same behavior on my magneto as described here and I am trying to determine if it is normal. My magneto is timed to 28 BTDC and the magneto has 25 deg of lag, so you would expect the impulse coupling to snap at 3 deg BTDC. But, it snaps well past TDC. Is this normal or a problem?

The reason I think it might be normal is that someone else reported this for a new engine in this thread, and when I am checking where it snaps, I am just bumping it a degree at a time. That's not exactly what happens during starting.

Thanks!

Click to expand...

Are you certain the magneto is timed to 28 degrees BTDC? This is 3 degrees advanced timing, and from the forums over the years, doesn't seem to be a very common practice. Far more common is to retard the magneto timing 2-3 degrees, to 23 or 22 degrees BTDC, in an effort to reduce CHTs in our tightly-cowled RVs.

If timing is retarded 2-3 degrees, and the impulse has a 25 deg lag, then it will snap at 2-3 past TDC. As far as I understand and have experienced, a couple degrees one way or the other won't adversely affect starting (maybe even as much as +/- 5 degrees).

Mags

It would be very helpful if people would describe their components-in this case magneto manufacturer and engine model- in greater detail.
If you have Bendix mags you probably have a 100 hour inspection on the impulse coupling. Failure of the coupling will likely destroy the engine.
There are some who claim that the latest and greatest coupling does not require the inspection.
In any case wear on the coupling or the pins can cause the lag angle to increase.
I agree with the previous post that 28 degree TDC timing is not a good idea. I ran my 10-1 O 320 for about 75 hours at 22 degrees and then reset the timing to 25 degrees. All this got me was a slight increase in CHT. NO measurable increase in performance.
If you were racing-either Reno or SARL, there might be a slight benefit to the higher timing number, but that will be at the cost of lower TBO.
The angle valve 360's specs called for the timing to be reset to 22 degrees. This occurred many years ago.

krw5927 said:

Are you certain the magneto is timed to 28 degrees BTDC? This is 3 degrees advanced timing, and from the forums over the years, doesn't seem to be a very common practice.

Click to expand...

Well, I didn't say what engine I was talking about. This is for a Continental O-200 and the data plate is stamped for 28 deg BTDC. And the magneto is a Slick 4300 series.

Mags

The 0 200 is a relatively low compression engine and will tolerate far more timing advance than the high compression Lycomings. The 0 200 in the F1 Racers commonly run VERY high advance settings. However almost all of these aircraft are trailered and most only fly an hour or two a year.
I have no recent experience with the Slick mags but the 500 hour overhaul definitely applies. You need to check with a specialty shop about the impulse.

jrs14855 said:

.
Aircraft Magneto in Helena MT is a highly regarded shop. Just ask for a check of impulse and internal timing. $200 plus/minus against the cost of a new engine if the impulse comes apart.

Click to expand...

They're in Missoula, not Helena

Follow Up

Follow up ....

I repeated the same test of where the mag snaps on a different plane with a similar new, rebuilt Slick mag and it snapped very close to TDC where I expected. So, I don't think that there is anything normal about my result where it snapped well after TDC on my plane.

I also talked to the builder of the plane and was able to piece togther the history of the magneto. It was installed new on June 23, 1995 and that was 1091 hours ago. It has never been opened and serviced to his knowledge in all that time (no internal timing adjustment, no 500 hour inspection, etc). I think we got our money's worth out of this mag, so a new one is being ordered.