Spitfire speedometer under-reading

[Andrew Palmer]

Hello everyone. The speedo on my Spitfire Mk IV is under-reading at higher speeds. It's accurate up to 50mph but when travelling at 70mph it reads about 60.

I have a feeling this is to do with a weak magnet. Is that right? And, is this something I could try to fix myself, or is that crazy talk?

Many thanks.

Andrew

[johny]

The movement of the needle is smooth is it, no kicking or sticking? About all you can do is remove the internals to clean and lubricate the needle drive bearings. If the magnet or return spring are wrong then a professional repair will probably be needed. Theres a good free manual (amongst many) here that explains everything:

Vitessesteve Other manuals

[Pete Lewis]

just dont remove the needle without knowing the turns of the hair spring 

and the drive plate 

some makes use a dob of silicon grease on the needle spindle to act as a damper 

this can go hard and upset readings ,  but   not generally used by smiths /jaeger 

Pete

Edited November 6 by Pete Lewis

[Andrew Palmer]

That's brilliant, thank you both. Johny, that manual is gold dust!

[johny]

yes some good stuff on there courtesy of Vitessesteve👍