How to check your head pressure

Why checking the compression is an essential fault-finder

1It’s all about the squeeze…

Checking an engine’s compression is an essential part of fault diagnosis. The test measures the efficiency of the piston and rings and bore and valves as they compress the air-fuel mixture, and a low reading would indicate wear or damage to these parts. Check your bike’s workshop manual for the ideal compression values.

2Warm up before you strip down

Once you have checked the manual, warm the bike up to the normal operating temperature. This is necessary because the piston and rings along with the wall of the cylinder will all expand with the heat and give their correct working clearances. Once up to temperature turn the bike off and start to remove the parts needed to gain access to the spark plugs.

3Tank off, ‘box off

Many bikes will require the tank and airbox to be removed to get to the spark plugs. Doing this will also involve unclipping fuel and breather pipes, as well as any sensors. Make sure you diligently follow the procedure for your specific bike. For example, this 1999 Honda FireBlade only requires the middle fairing to be removed to gain access to the spark plugs.

4Pull off the plug caps

Some bikes will be fitted with plug cap coils and others with traditional plug caps. Remove each one from the spark plug and make a note of which cap went where. Often there are numbered tags on the HT leads that reference each cylinder with a number. Typically, a four-cylinder bike will number the cylinders 1, 2, 3 and 4 from left to right as viewed by the rider.