Westerbeke 90A FOUR — Engine Compression Test
Testing & diagnosis · Engine Cylinders
For the Westerbeke 90A FOUR, from the Westerbeke operator's manual.
Procedure
- Warm up the engine, shut off the raw water through-hull, remove all fuel injectors and disconnect the fuel shut-off solenoid wire.
- Install a compression adapter in the injector hole.
- Connect a compression tester on the adapter and crank the engine with the starter until pressure reaches a maximum value.
- Repeat this process for each cylinder.
- Look for cylinders with dramatically (at least 20%) lower compression than the average of the others.
- If a weak cylinder is flanked by healthy cylinders, check the valve clearances for the weak cylinder, adjust as needed, and test again.
- Apply a small amount of oil into the cylinder to seal the rings and repeat the test; if compression comes up, the rings are faulty.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Compression pressure should not differ by more than 42.7 lb/in2 (3.0 kg/cm2) at 200 rpm
Source: Westerbeke operator's manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.