Monday, 26 November 2012

Hillman Imp, May 1963 and the very first engine batch

I wonder, as one engine I sourced had a July 1963 stamp on the bottom of the steel engine oil sump.

A standard 875cc bore piston and without the valve cut outs that the later Imp pistons all had. If you right click on the picture and enlarge it, you should see the small nick where the inlet valve has touched the piston?

The intention is to rebuild the motor to a standard Mk1 Hillman Imp specification in time for the celebrations in Coventy, England, next year.

Pistons are cast in LO-EX aluminium alloy and have two compression rings and one oil scraper ring. The piston runs in a nominal bore size of 2.6770 in. dia and the piston-to-bore clearance, measured at the skirt is, depending on tolerances, between 0.0017 in and 0.0010 in. These measurements are taken at right angles to the gudgeon pin hole.

On all except very, very early engines, of which only a few were built, the pistons have two cutouts machined in the top to provide clearance for the valves. Two compression ratios are available as far as the pistons are concerned. The one for use in the cars gives 10 : 1 cr, whilst the low compression for commercial vehicles such as the Imp van give 8 : 1 cr.

More info here.

In my case the fact that I have the pistons with no valve cut outs, plus a Mk1 oil sump panel with the date 5th July 1963 clearly says this is a rare piston set.

This early Mk1 sump had its box section removed to make a larger capacity sump for the sprint car built 2011/12, check the white date stamp to the right.

The date on this Imp sump is the only one I have ever seen.

There is a spot of rust on the 3 but it was clear enough when I got the Imp engine.

The early Imp piston and con rod set, they have been cleaned. The bearings are still good too, I also have new Rootes standard piston rings in stock.