Wednesday, June 29, 2011

Compression depression

Bugger.  I have been having such fun with the van.  Suddenly she dropped power and was running rough.  Nothing obviously wrong.

A compression test revealed 0 psi in cylinders 2 and 3.  120is in 1 and 4.  Hmmm.  Head gasket?

If so, why?

Any ideas out there?


  1. Hi JB Vanman -

    To have #2 and #3 drop compression at the same time, to the same level (zilch) points to a head gasket blown between the two cylinders. The reading of 120psi in #1 and #4 is OK for an engine in good condition.

    A good trick is to squirt a teaspoon of oil into each cylinder one at a time and re-test the compression. Little change will indicate good compression rings, while a noticeable improvement indicates that the oil is providing a seal, and that the rings are worn.

    So buddy, looks like the head has to come off. Not a difficult job, and an opportunity to have a lookimat the valves at the same time.

    Do you run a lead-substitute additive to the unleaded fuel? A protective coating used to be provided by the lead in the fuel. As the exhaust valve seats are quite soft, they will burn quite quickly if no additive is used.

    My head had knackered valves and seats, so I stuck in a new set of exhaust valves and hardened valve seats. This way I don't have to use an additive, just straight unleaded.

    Hope this all helps mate! Cheers - Bugly

  2. When you get the head off check it for flatness, it could be distorted which may be why it blew. It may need to be planed to get it flat again.

  3. Thanks Guys, great advice. Hopefully I will get some time this weekend to take her head off and sort out what is going on. I suspect the gasket went - but why.... I replaced it and machined the head only 12 months ago. I will check the block with a metal rule when the head comes off.

    Thanks for the encouragement.