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magneto timing pin?

airguy

airguy

Unrepentant fanboy
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I need to re-time my 4373 Slick, and I understand there is a timing pin that must be inserted into the mag while the unit is matched to the engine. Is this a specialty item or will any appropriately sized wire/rod serve the purpose?
 
Right sized allen key

I used an allen key that just fit in the hole. works perfectly
 
A timing pin is only needed if the mag was removed from the engine. A drill bit will also work. A piece of tape will keep the drill bit from falling into the mag. Move the mag, not the prop when the pin is in place. If the mag was not off the engine, an inexpensive timing light is needed to set timing and synchronize the mags. There are several threads on setting the timing.
 
This engine is 105TTSN with 0SMOH, was reassembled after overhaul but never started or flown. My flywheel has two sets of timing marks - one on the front side and one on the aft. The one on the front side is correct, the mag was installed on the engine during the last rebuild according to the incorrect marks on the aft side. It's off by about 80 degrees, apparently actual TDC versus the marking was never checked by the guy that reinstalled it. Perfectly timed, just timed to the wrong set of timing marks. Now I have to assume my EI is timed that way also, I'll get to check that as well. I obviously have a used ring gear on this flywheel with two sets of timing marks, that's what I get for buying a second-hand engine.

I was just covering my bases as I finish up FWF and get closer to first start, and thought I better check the timing. Good thing I did...
 
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Timing marks

You can use either set of marks. The marks on the forward and aft surfaces of the flywheel indicate exactly the same thing. If you put #1 cylinder at TDC and line up the front TDC mark with the spot on the starter you will find the back side TDC mark lined up with the crankcase seam. Some baffle installations make it hard to use one set or the other.

Don B

RV 9. Rebuild in Progress
 
Yep, as Don said, most flywheels are marked on both sides, using different references.

No one mentioned, but be sure to pull that pin out before turning the prop! More than one person has forgotten, and it's an expensive mistake.
 
Use a SOFT pin

I would encourage you to NOT use anything hard like an allen key or drill bit. Use an aluminum pop rivet and turn it over and insert the stem. That way when you forget the opin is still there and turn the prop you won't have any damage to the magneto.

Vic
 
Only use the pin to stab the mag onto the engine with the engine preset at 25 degrees. Then pull the pin before twisting the mag or moving the prop.
 
cajunwings said:
You can use either set of marks. The marks on the forward and aft surfaces of the flywheel indicate exactly the same thing. If you put #1 cylinder at TDC and line up the front TDC mark with the spot on the starter you will find the back side TDC mark lined up with the crankcase seam. Some baffle installations make it hard to use one set or the other.

Don B

RV 9. Rebuild in Progress
Click to expand...

Maybe so, but in that case the guy that put the mag on had the aft marks lined up with the front starter mark. With Mike Hilgers help I used the spark plug block tool to find the hard stop on #1 cylinder on both sides and determined for certain where my TDC physically exists, it agrees with the front marks on the flywheel. The buzz box says the mag is nowhere close. It's easy enough to retime them, it just hacks me off that it wasn't done correctly during assembly. Makes me wonder what other shortcuts the guy took during the rebuild. I already found one other problem, it had the wrong vacuum pump drive gear put on the engine, the yellow tag had the correct part number but it was most definitely the wrong part installed, it was the one for an O-540 instead of my O-360.
 
airguy said:
Maybe so, but in that case the guy that put the mag on had the aft marks lined up with the front starter mark. With Mike Hilgers help I used the spark plug block tool to find the hard stop on #1 cylinder on both sides and determined for certain where my TDC physically exists, it agrees with the front marks on the flywheel. The buzz box says the mag is nowhere close. It's easy enough to retime them, it just hacks me off that it wasn't done correctly during assembly. Makes me wonder what other shortcuts the guy took during the rebuild. I already found one other problem, it had the wrong vacuum pump drive gear put on the engine, the yellow tag had the correct part number but it was most definitely the wrong part installed, it was the one for an O-540 instead of my O-360.
Click to expand...

Just to be sure, the 4373 is an impulse mag, so you need to pull the prop well past TDC until the impulse releases(with the p lead grounded and mixture ICO) , then back it up past TDC far enough to take the back lash out of the gear train to get an accurate indication coming forward again at the desired 20-25 deg. advance. If the impulse has not released, the buzz box does indicate way off.
 
F1R said:
Just to be sure, the 4373 is an impulse mag, so you need to pull the prop well past TDC until the impulse releases(with the p lead grounded and mixture ICO) , then back it up past TDC far enough to take the back lash out of the gear train to get an accurate indication coming forward again at the desired 20-25 deg. advance. If the impulse has not released, the buzz box does indicate way off.
Click to expand...

Yeah, figured that out when I got the impulse coupling to snap at TDC but the buzzbox was showing about 43 degrees AFTER TDC. Once I got over the impulse snap, backed up and hit it again, now it's right where it should be.
 
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