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> TDC?
dumbjim
post Sep 30 2020, 08:50 PM
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This may seem like a stupid question but when your distributor rotor is pointed at cylinder 1, would that be tdc on your fan pulley?
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Robarabian
post Sep 30 2020, 09:51 PM
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Yes, but, the marks are not far off... so you to verify the cylinder is TDC. Put a plastic straw in there. Additionally, it is best if you pop off a valve cover and make sure where it is in the stroke.. intake versus compression.

You do this by turning the motor and watching the intake valve and exhaust valve.
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jaredmcginness
post Oct 1 2020, 05:32 AM
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Ideally, yes. Your distributor should have a little dot to confirm the the rotor is pointed correctly.
Also verify with the fly wheel - my marks were a bit off, but really close.
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ClayPerrine
post Oct 1 2020, 12:33 PM
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QUOTE(Robarabian @ Sep 30 2020, 10:51 PM) *

Yes, but, the marks are not far off... so you to verify the cylinder is TDC. Put a plastic straw in there. Additionally, it is best if you pop off a valve cover and make sure where it is in the stroke.. intake versus compression.

You do this by turning the motor and watching the intake valve and exhaust valve.



With the plug angle on a 914 motor, I would not recommend putting anything in the spark plug hole. It is likely to get broken off.

And DEFINITELY don't use a chopstick. (IMG:style_emoticons/default/av-943.gif) http://www.914world.com/bbs2/index.php?showtopic=22782
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Mark Henry
post Oct 1 2020, 01:06 PM
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Clay beat me to chopsticks (IMG:style_emoticons/default/wink.gif)
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TheCabinetmaker
post Oct 2 2020, 07:45 AM
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CHOPSTICKS! Wonder what happened to him?
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Frankvw
post Oct 2 2020, 07:58 AM
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I do not want to hijack this topic, but I have to say I never came cross the chopstick story before. Sorry for the person who had the chopstick trapped, but some of the tips and comments were hilarious. It was an interesting read on many levels ! I know I will use a straw whenever I come into a chopstick situation ! ! (so that is a bit on topic again)
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rgalla9146
post Oct 2 2020, 09:04 AM
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The most accurate method to determine true TDC is to thread a stop into the #1
spark plug hole. Rotate the crank (slowly, by hand) until the piston contacts the stop.
Mark that spot. Now rotate the crank in the opposite direction until the piston
makes contact again. Mark that spot.
True TDC is the mid- point between those marks.
The ignition rotor is a little better than an approximation.
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dumbjim
post Oct 2 2020, 11:46 AM
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QUOTE(rgalla9146 @ Oct 2 2020, 07:04 AM) *

The most accurate method to determine true TDC is to thread a stop into the #1
spark plug hole. Rotate the crank (slowly, by hand) until the piston contacts the stop.
Mark that spot. Now rotate the crank in the opposite direction until the piston
makes contact again. Mark that spot.
True TDC is the mid- point between those marks.
The ignition rotor is a little better than an approximation.

Can you elaborate a little on this procedure? What do you mean by a stop? what kind of stop screws into the sparkplug hole? Where do I put my marks? on the fan pulley, on the flywheel? or the stop? I'm trying to learn as much as I can to work on my 914. There's just not a lot of mechanics in St. Louis that work on air-cooled engines.
Thanks
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VaccaRabite
post Oct 2 2020, 01:21 PM
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QUOTE(rgalla9146 @ Oct 2 2020, 11:04 AM) *

The most accurate method to determine true TDC is to thread a stop into the #1
spark plug hole. Rotate the crank (slowly, by hand) until the piston contacts the stop.
Mark that spot. Now rotate the crank in the opposite direction until the piston
makes contact again. Mark that spot.
True TDC is the mid- point between those marks.
The ignition rotor is a little better than an approximation.



While this would work, its overly complicated.

Just go to top of travel and take a visual inspection of the valves to make sure they are closed for that cylinder. That is TDC for that cylinder. Bonus points for marking this in paint in the timing notch in the doghouse, but not even that is required since you don't need to do this very often.

Zach
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barefoot
post Oct 2 2020, 04:51 PM
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QUOTE(dumbjim @ Oct 2 2020, 01:46 PM) *

QUOTE(rgalla9146 @ Oct 2 2020, 07:04 AM) *

The most accurate method to determine true TDC is to thread a stop into the #1
spark plug hole. Rotate the crank (slowly, by hand) until the piston contacts the stop.
Mark that spot. Now rotate the crank in the opposite direction until the piston
makes contact again. Mark that spot.
True TDC is the mid- point between those marks.
The ignition rotor is a little better than an approximation.

Can you elaborate a little on this procedure? What do you mean by a stop? what kind of stop screws into the sparkplug hole? Where do I put my marks? on the fan pulley, on the flywheel? or the stop? I'm trying to learn as much as I can to work on my 914. There's just not a lot of mechanics in St. Louis that work on air-cooled engines.
Thanks

I knocked the ceramic out of a spark plug & welded a steel rod to the threaded bit. stuck out a little over an inch. (IMG:style_emoticons/default/smile.gif)
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rgalla9146
post Oct 2 2020, 05:26 PM
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QUOTE(VaccaRabite @ Oct 2 2020, 03:21 PM) *

QUOTE(rgalla9146 @ Oct 2 2020, 11:04 AM) *

The most accurate method to determine true TDC is to thread a stop into the #1
spark plug hole. Rotate the crank (slowly, by hand) until the piston contacts the stop.
Mark that spot. Now rotate the crank in the opposite direction until the piston
makes contact again. Mark that spot.
True TDC is the mid- point between those marks.
The ignition rotor is a little better than an approximation.



While this would work, its overly complicated.

Just go to top of travel and take a visual inspection of the valves to make sure they are closed for that cylinder. That is TDC for that cylinder. Bonus points for marking this in paint in the timing notch in the doghouse, but not even that is required since you don't need to do this very often.

Zach


It is certainly not an everyday necessity, it is the most accurate way to determine
true TDC. If your fan or flywheel are not marked ( and even if they are ) this will provide an accurate location.
A stop can be a modified spark plug as described that has a probe
that can be threaded in or out to provide a stop in piston stroke.
Summit or Pegasus would probably offer some version.
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