LCGB Forums

Can anyone tell me how to interpret the measurements on this dial gauge....

I'm trying to work out if I've got another wonky rear hub or a bent shaft...so I've run the engine with the gauge at various points on the shaft - at the very end, in the middle of the thread and at the end of the thread in the space before the start of the spigots.

I've found vibration from the engine affects the reading so I've turned it over gently by hand and the reading moves about 5 on the outer dial. How much 'movement' is that? am I right in thinking each digit on the outer dial is .0005" (five thou)?

Is that acceptable..?

thanks

Martin

The increments of the DTI (Dial Test Indicator) depicted are in units of 0.0005", often referred by us Old Codgers as 'half a thou'

So multiply that by the variance of five (difference between the highest & lowest readings) that you state.

5 x 0.0005 = 0.0025

That is 2-1/2 thou' (0.0025") TIR (Total Indicator Reading)

But remember, that TIR is the extreme of one side to the other. So imagine that the centre of the splined area where the measurement is being made is revolving 0.0025" 'out of true'

So, the surface being checked, whilst undoubtedly running eccentric only affects where the cone sits. The centre of the layshaft itself might run absolutely true.

Anyway, 0.0025" TIR means that RADIALLY the surface is only half of that TIR eccentric, which is just 0.00125" (0.003125 mm)

What does that all mean? A layshaft running out of true by so little as 1-1/4 thou' is less than a stunted nat's c*ck!

Absolutely nothing to worry about & there's crankshaft builders in this country that don't achieve that amount of accuracy in their lives.

Unfortunately, you need to delve a little deeper into whatever the issue is with hubs & your scooter, Sherlock

Well......what a brilliant reply. Thank you very much..

I'm convinced its a second problematic hub/cone.

Martin

You will have been picking up play in the bearing too dont forget

Ah yes I see

thank you

Well...it was a second wonky rear hub.

Ended up with a UNI replacement which is perfect.

Cheers

Martin