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Compression diagnosis 1200 herald


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Hi All

having just collected my new herald 1200 I have worked my way round a poor starting problem. Amongst the usual adjustments (inc valve clearances that were all too tight)  a new hi torque starter motor as helped enormously. However compression test cold ( can't run up to temp until new thermostat cover arrives) revealed some interesting and low results as follows 

1= 110 psi

2= 70 psi

3= 55 psi

4=90 psi

other than a very tired engine, does this likely mean a gasket fail between 2 and 3? 

Before leaping into a full rebuild, would a head off visual inspection for scoring,  relap of valves, skim and new gasket be a logical first step .... or am I simply putting off the inevitable? 

Your thoughts greatly appreciated ?


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So this is a cold test ?

Was the  throttle held open ??

Whats the running problems ?  Mis fire   lumpy  , lethargic or what ?

Is this with a std solex carb ? 

And yes HG bridged would give low on  2 and 3

Pull a head nut off look at the state of the washer if its all deformed by a now lost torqure on the nut    then a gasket failure is very likely

In the cost of things I would give the head and valves a good appraisal before you jump into deep  pocket sydrome

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You need to do another compression test, preferably with the engine hot, but more importantly including a second round with a couple of spoonfuls of oil added to each cylinder as a wet test.

If the compressions are significantly higher on the wet test, this suggests rings/bores are an issue. Little change implies valve seating issues. The latter is quite likely given the tight tappet settings you report.


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Yes throttle open

poor start from cold... seems to run quite sweetly but some blue exhaust fumes when under load ( reported by guy following me back home on collection) feels a bit lacking in power (but it is a few years since I last drove one ) haven't driven above 55mph because a wheel wobble needs sorting... then I found corroded thermostat housing that leaked a bit so waiting for replacement before further investigation

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