Timing, Dial Gauge or Degree Disc

[hydra]

I don't know how to use quote tool, but this reply is from firekdp.
"As a dial gauge is measuring piston travel as long as the gauge is zeroed anywhere in the dwell period then 2mm back will equal 19 degrees BTDC".

This is whats confusing, obviously during the dwell period where the Dial Gauge would not be moving because there is no piston travel, the flywheel and so the Degree Disc would be moving (I don't know how many degree's, I haven't got a disc), so how can you set a dial gauge anywhere in the dwell period, it would differ from the degree disc which would be at 0 or 360 degree TDC. I think I've answered my own question, surely the dial gauge should be set in the middle of the dwell.

[sean brady scooters]

do yourself a favour........and throw away the dial gauge............its useless really.........
use the positive stop method to find a true TDC..........
then use degree disc for ignition timing /port timing etc..............

[hobospeed]

I don't know how to use quote tool, but this reply is from firekdp.
"As a dial gauge is measuring piston travel as long as the gauge is zeroed anywhere in the dwell period then 2mm back will equal 19 degrees BTDC".

This is whats confusing, obviously during the dwell period where the Dial Gauge would not be moving because there is no piston travel, the flywheel and so the Degree Disc would be moving (I don't know how many degree's, I haven't got a disc), so how can you set a dial gauge anywhere in the dwell period, it would differ from the degree disc which would be at 0 or 360 degree TDC. I think I've answered my own question, surely the dial gauge should be set in the middle of the dwell.

Think about it this way, if you are using the dial gauge and only the dial gauge to set your timing then yes the instructions are correct. Keep in mind that the 2mm you are shooting for will always be measured from exactly when the piston starts to move away from TDC by the dial so dwell has nothing to due with it. Dwell becomes an issue if you are using the dial gauge to find TDC and then use a degree wheel to set the timing. I hope what I said makes some sense, it does to me...but thats not always a good indicator.



Tim

[rossi46]

Only use the dial guage to find TDC, turn the crank until the piston is 1mm from the top of the barrel and set the guage to zero then cary on turning the carnk until the needle on the dial guage begin to go the backwards at the point when the needle begins to go backwards take the measurment on the dial guage and half it then turn the crank until the dial guage reads this measruement that will the the centre point of the piston dwell and absolute TDC, mark the mag casing for TDC and then measure back your 2mm form there for your timing. When the engine is running check with a timing light.

[jason frost]

Dial gauge have used one for the past 25 years and have always worked fine.

[firekdp]

If you are using a dial gauge there is no point whatsoever finding true TDC because at any time in the dwell period the gauge (when zeroed) will read 0mm. It will read 0mm at one extreme of the dwell right through to the other extreme because obviously the piston isn't moving, so finding the mid point is irrelevant.
When the gauge reads 2mm it WILL be 19 degrees for a standard crank.
Different rod/stroke cranks will need a different mm setting, there is a table in "sticky's" giving the relevant figures for crank permutations.

[shocky]

If you are using a dial gauge there is no point whatsoever finding true TDC because at any time in the dwell period the gauge (when zeroed) will read 0mm. It will read 0mm at one extreme of the dwell right through to the other extreme because obviously the piston isn't moving, so finding the mid point is irrelevant.
When the gauge reads 2mm it WILL be 19 degrees for a standard crank.
Different rod/stroke cranks will need a different mm setting, there is a table in "sticky's" giving the relevant figures for crank permutations.

so what your saying is at any point in the dwell is ok for you to measure back 2mm or 19deg

[firekdp]

so what your saying is at any point in the dwell is ok for you to measure back 2mm or 19deg

No, if you use degrees you MUST find TDC as you are measuring crank rotation. If you use a dial gauge you are measuring piston travel, as there is no movement of the piston in the dwell period the gauge will stay at 0mm so it doesn't matter where you you zero it (as long as it is in this non moving period). Obviously the needle on the gauge will only start to move when the piston does. On a standard crank 2mm piston travel will equate to 19 degrees of crank rotation from TDC.

[shocky]

ok im understand now

[Monty]

So hanging the crankcase from hook onto the conrod and marking TDC on the flywheel is not good enough?
Its always worked for me