Sunday, 11 November 2012

New Sprint engine (part 4)

It's been a while since I dropped of two Sprint heads for some old fashioned modifications. But last week I got a message on my mobile phone saying that the head was ready. Needless to say I couldn't wait to pick it up! Have to say that it certainly has been worth the wait!

But before the actual work on the ports started, first thing to do was decide which of the two heads would be used for the treatment. So to start with they were pressure tested to check for cracks and porosity, and they both passed this test. Next test was checking if they were warped. This showed a clear winner, the head that came from my spare Sprint engine turned out to be completely flat. The spare head I acquired many years ago turned out to be slightly warped (0.25 mm concave). This is certainly re-usable but no point in not using my best parts.

The chosen head after it had been removed from the engine ...

And when I entered the work shop last Saturday this clean and very shiny cylinder head greeted me ...

Work that has been done to the head includes opening up the ports slightly and polishing them, blending in the valve seats, re-cutting the seats and grinding in the valves.
Also the inlet manifold I acquired over a year ago (how time flies) was matched to the head and doweled for a smooth flow from the throttle bodies into the cylinders. And the manifold's ports received some extra attention.
And last but not least the head was skimmed to increase the compression ratio from 9.5:1 to about 10:1. Added bonus was that this skim got rid of all the pitting caused by corrosion.

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