Correct use of overdrive on a Mk3 Spitfire

[Jonah]

I’ve been mulling over whether to fabricate a steel frame the width of the car to fit across the chassis that could be lifted by the crane using chains 

my problem is that my trolley jack will only just about get the wheels off the ground 

space is a premium also so I guess I could sell the crane and invest in a better hydraulic lifter of some sort 

[JohnD]

The chassis cross member at the front will lift both front wheels securely and at once.

The cross member at the back, behind the diff will do the same. but it is mounted at an angle to the horizontal, so you risk a trolley jack slipping off.     I made a wooden block to go betyween the jack and the member:

As the step at the back is critical, and takes some strain, I reinforce it with two long wood screws, vertically down into the body of the block.

 

A proper trolley jack should have a dense rubber pad on it's tip, but many don't - you can buy cheap 'jack pucks' that make them more secure.  https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2060353.m570.l1313&_nkw=Trolley+jack+puck&_sacat=131090   You can use wood blocks instead, that will alllow the jack to lift a little higher,

But if your jack won't lift high enough - get a new jack!     Or else make up some secure way to get the jack you have higher.     "Cribbing" is the building of strong wood supports by layers with the grain successively in opposite directions.    A thick plank, wide enough to take the jack securely, will lift it a little, but add shorter lengths across the grain, screwed to the first for security, and if necessary another long plank, and you can lift the jack as high as you need.    Get fancy and make interlocking cribs, so you can add and take away as required:

This is not just a DiY blodge, but one used in heavy industry.   Stacking cribbing blocks are available commerically:

 

[Jonah]

Thanks very much John, I’ll get a new jack and investigate making cribbbng

my trolley jack will reach 380mm and is ok for getting a wheel off, I’ll look for something with a higher reach

best Julian