Thread: CJ's Build
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Old 21st December 2019, 07:57
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I'd have the head off and check for:

Incorrect, dished pistons fitted reducing the compression ratio (already low at 8.5:1 on a 13/60).

New valves fitted 'out of the box' at some stage and never lapped in.

Thicker than standard head gasket.

A bit more work needed but if there's still nothing obvious:

Check the cam timing is correct - I managed to get my six-pot to start and run (very badly) with the cam 180 degrees out, and a very small error can leave the inlet valve open for too long during the compression stroke.

Check if all the piston rings are present - the SCCA Spitfire Competition Preparation Manual recommends not fitting the lower oil rings on a racing engine for more power at the expense of engine longevity.

You could also try a different compression tester or try yours on a known 'good' engine to see if it reads low.

Good luck!

Last edited by Mister Towed; 21st December 2019 at 07:59..
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