dial-indicating bell housing alignment?

[toofast306]

I may be tackling the job of dial-indicating the bellhousing to crank alignment over the winter.
Dumb question: how do you centre the dial-indicator?
I understand the practice of mounting the indicator base on the flywheel, but how can the fixed point align on the exact axes of the input shaft, especially considering tolerances of .005?
Looking at some online guides, perfect alignment is not critical for mounting the base to the flywheel. However, the tight tolerances suggest there needs to be a more exact and repeatable method than trial and error.

[bbriann]

Lots good photos on internet....easier than words to describe. Can see photo of magnetic based dial indicator set up on my 5.3l modular nitrous build thread.
Factory bell housing usually ok straight up install, using cobra ford bell housing on my TKO600 mine was within .002.
SFI aftermarket bell housings likely require dialing in.
Anyway pretty straight forward. With flywheel installed and bell housing properly torqued down you use the magnetic base through the input shaft hole in bell housing and place magnet near centre of flywheel and place indicator tip on inside of bell housing hole. Then zero dial and use the harmonic balancer bolt to slowly turn crank shaft and recording the dial indicator movement. If the high and low measurement are within .005 you are good to go!

[toofast306]

Lots good photos on internet....easier than words to describe. Can see photo of magnetic based dial indicator set up on my 5.3l modular nitrous build thread.
Factory bell housing usually ok straight up install, using cobra ford bell housing on my TKO600 mine was within .002.
SFI aftermarket bell housings likely require dialing in.
Anyway pretty straight forward. With flywheel installed and bell housing properly torqued down you use the magnetic base through the input shaft hole in bell housing and place magnet near centre of flywheel and place indicator tip on inside of bell housing hole. Then zero dial and use the harmonic balancer bolt to slowly turn crank shaft and recording the dial indicator movement. If the high and low measurement are within .005 you are good to go!

This is the part that confuses me - how can you ensure the accuracy of the magnetic base's placement for the initial and subsequent measurements?

[bbriann]

This is the part that confuses me - how can you ensure the accuracy of the magnetic base's placement for the initial and subsequent measurements?

After you set the indicator up with a sturdy magnetic on /near centre of flywheel and zero it you don't touch it and make a continuous measurement by turning crank 360 degrees while stopping every so often to look at measurement. In essence its one continuous measurement.
So just repeat all over again next time you want take measurement again. It bell housing out of alignment this will have to be repeated often after adjustment.