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Where to align TC timing mark?

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PhatRV

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I am trying to find the alignment position of the TC mark on the flywheel to the starter motor. People in the field is saying the reference timing mark is at the black line shown in the picture. Other said the reference mark should be to line up the TC mark on the back of the flywheel to the middle engine case. So what should be the correct alignment to use? From the position in the photo, the mark in the back of the flywheel is off the centerline of the case

Thanks
 

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Forward markings should line up with small "hole" on starter housing.

Aft side markings should line up with crankcase split on top of engine.
They should correlate.

If your starter doesn't have the "hole", do not use the forward side markings.
 
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Mel said:
Forward markings should line up with small "hole" on starter housing.

Aft side markings should line up with crankcase split on top of engine.
They should correlate.

If your starter doesn't have the "hole", do not use the forward side markings.
Click to expand...

Dead on! And the black mark with the sharpie (on your picture) is absolutely incorrect….
 
Looking at the photo, it seems your crank is positioned at 10 deg BTC, like Paul says, not correct
 
Small hole...

You can see it in the attached -- and I marked it in your picture as well...
 

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Thanks everybody. The mark on the starter screw hole in the picture aligns with the case split TC mark on the back. It's hard to see the front mark now that the propeller is in the way. I will use the TC mark in the back
 
Timing......

PhatRV said:
Thanks everybody. The mark on the starter screw hole in the picture aligns with the case split TC mark on the back. It's hard to see the front mark now that the propeller is in the way. I will use the TC mark in the back
Click to expand...

And look at your engine data plate to see what the correct/recommended timing offset is. If you are using 25 degrees, make sure that is what is on the data plate.
 
PhatRV said:
Thanks everybody. The mark on the starter screw hole in the picture aligns with the case split TC mark on the back. It's hard to see the front mark now that the propeller is in the way. I will use the TC mark in the back
Click to expand...

Stick a drill bit in the hole.... easy to line up.
 
Another method

Or, if you want to be absolutely certain, you can use a piston stop and the digital level you have in your shop.
 

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Taltruda said:
Sure it is.. you locate zero with the piston stop. Then set the digital level to zero, then back it up 25 degrees!
Click to expand...

Actually, back it up PAST 25°, and then turn the prop forward to 25°. Mag timing is properly set with the forward movement of the prop.

This compensates for gear backlash.
 
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For that measurement to be accurate the propellor and the inclinometer both have to rotate in a plane parallel to gravity. At 25 degrees there could be significant cross axis error with it taped to the angled blade.
 
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I’m not sure what that means, Mike, but it is the same method that the Time Rite timing device uses but they have a much smaller digital level that attaches to the spinner with bungee cords. I have compared the two and they both work well and are accurate. Many of the Continental engines are without external timing marks
 
I think you might be confusing a Time Rite device with something else but attaching a protractor to the spinner allows you to align the it to the propellor and gravity.

The electronic level on the tilted propellor blade might be repeatable and good enough but by definition is always wrong.
 
Mel said:
Actually, back it up PAST 25°, and then turn the prop forward to 25°. Mag timing is properly set with the forward movement of the prop.

This compensates for gear backlash.
Click to expand...

Not to mention first going forward past TDC so that the impulse coupling snaps.

My suggestion: have someone who knows what they're doing show you how the first time. (ETA: NOT whoever "people in the field" are who told you this: " People in the field is saying the reference timing mark is at the black line shown in the picture.")

There's a safety concern, as well...the mags have to be hot during timing, and you're messing around with the end that bites.
 
The level vs protractor difference is largely semantics but the instruments have an accuracy over a given measurement range. Near level the cross axis error component is near zero and can be ignored. Lots of the cheaper instruments quote a similar accuracy but it often over a smaller measurement range. Maybe 5-10 degrees. I have a Leica instrument that is specified to be accurate to 0.1 degrees over 360 degrees. It has cross axis compensation for tilts of +/- 10 degrees and wouldn’t report an angle taped to my prop with a minimum pitch of 11 degrees. Probably all of them would be accurate enough to set a mag (+/- 1/2 deg?) with some effort to get everything lined up to gravity.
If I had to do it I would use a piston stop to find TDC and set s a pointer on the ring gear teeth which make a pretty good protractor. A 149 tooth ring gear has a tooth every 2.4 degrees. Move it 10 1/4 teeth and be within .6 degrees.
 
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My starter had no timing hole either. I drilled a small hole in the front baffling and stick a hinge pin through to act as a pointer at the marks on the ring gear.
 
The "stop"

PhatRV said:
I am trying to find the alignment position of the TC mark on the flywheel to the starter motor. People in the field is saying the reference timing mark is at the black line shown in the picture. Other said the reference mark should be to line up the TC mark on the back of the flywheel to the middle engine case. So what should be the correct alignment to use? From the position in the photo, the mark in the back of the flywheel is off the centerline of the case

Thanks
Click to expand...

The puzzle pieces are addressed but they (IMO) need to be linked. When first timing your engine, first locate the marks and how you will "read" the position. The piston stop will create a stopping position on both sides of TDC at a reliable literally solid point. TDC will be established as half way between the stop points on the flywheel. This is done initially to validate the reference points, whether the case split or some pin point, or with a tool that indicates the rotation angle. If your case split matches the TDC mark then it validates that measurement method and flywheel mark. With the measurement method validated you can the locate the 25 deg BTDC for timing. Mel points out the importance of rotation direction for ensuring the gear backlash is not adversely affecting the position.

For my engine, there is a hole in the starter. I insert a 1/16 drill bit and use a flashlight to cast a shadow on the flywheel to eliminate the parallax effects at odd viewing angles. It seems to eliminate 1 degree of interpretation variation. YMMV.
 
lr172 said:
Sorry but that doesn’t make sense. Can you please explain why you think this is required?
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If mag is not hot, it is grounded. Then you can’t detect the points opening/closing. So, have a set of plugs out while timing with the hot mags.
 
Pull ONE plug out of each cylinder, maybe the mag is ungrounded while you pull thru and do the timing check but not much of a chance its going to kick back and bite. Besides that makes the pull thru a LOT easier.
 
jemer said:
If mag is not hot, it is grounded. Then you can’t detect the points opening/closing. So, have a set of plugs out while timing with the hot mags.
Click to expand...

OK, thanks. I thought he meant hot like temperature and couldn't see any logical reason for it needing to be hot to time it.
 
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